http://www.articletrader.com/ Articles at ArticleTrader en-us http://www.articletrader.com/science/biology/dna-replication-and-cell-division.html http://www.articletrader.com/science/biology/dna-replication-and-cell-division.html Sun, 23 Oct 2005 00:00:00 -0500 DNA replication basically means creating two entire DNA strands for each daughter cell in place of the single parent cell. Prior to the cell division, its DNA within the nucleus is released by an enzyme to break the hydrogen bonds between the bases, resulting in two halves of the DNA. The uninhibited nucleotides within the nucleus bonds with the bases of both strands. Bonds with T alone while C with G, leading to exact matches for both strands.


There are four phases in cell division, or mitosis (normal cell division, meiosis forms sex cells).


Prophase: Pairing of chromosomes occurs and following replication, the parent cell has two complete sets. Two poles are formed as the nucleus disappears.


Metaphase: Alignment of the chromosomes is at the equator between the two poles.


Anaphase: The chromosomes split up towards each pole. Cell membrane division begins.


Telophase: Appearance of nuclei is at each pole and membrane divides. Two cells possess identical chromosomes.


DNA Replication


The DNA composition where two separate strands store all genetic information, replicate easily. A DNA molecule has a polymer opposite of the other, like a photonegative. One side enables the other to be recreated. This duality simplifies copying a DNA molecule remarkably.


Replication causes synthesization of DNA molecules. First a helicase enzyme unwinds the double helix, at any point on the strand, progressing to two replication forks by enzymes extending the helix release in both directions. With unwinding and straightening out of the DNA, DNA polymerase, another enzyme functions. It matches the exposed nitrogenous bases with new nucleotides from the surrounding nuclear fluid. The nucleotides and separated polymers fuse as per the regular Watson-Crick pairing rules. The completion of the separation and re-matching of the DNA molecule makes two perfect copies.


DNA replication remains partially unknown. Signals that start the process, the reason some cells don’t replicate and the cause of uncontrollable replication of cancerous cells remain unexplained.


Replication in Prokaryotes


Prokaryotes or bacteria store almost the entire genetic information of an organism in a single large circular DNA ring and not in multiple chromosomes of DNA strings with unconnected ends. This replication is almost identical to eukaryotic DNA except in the use of only two replication forks. Eukaryotes and prokaryotes differ, with multiple replication sites active simultaneously in the former and the speed of the latter requiring only two, one for each direction The rate of replicating bacterial DNA is almost one million base pairs per minute whereas the average is 500 to 5000 pairs for other organisms.


DNA Replication is Semi-Conservative


On completion of the replication process, two DNA molecules result, which are identical both to each other as well as to the original. There is not the slightest alteration in each strand of the original molecule due to its role as the template for the synthesis of a complementary strand. This replication method has been termed semi-conservative; as one half of each new DNA molecule is old while the other half is new.


Finally…


The need for DNA replication or cell genome duplication is created by each cell division. As with all cellular activities, specialized proteins are needed for the purpose of replication. DNA replication is surprising as a process in all organisms except in the case of humans where comprehension can prove very complex.


Learn more about


Cell Biology and DNA replecation , visit http://www.biology-online.org







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Dr.Richard Waller has been helping thousands of infetile couples and gave hope to childless women since 1999 through the process of in-vitro fertilization. He is based in England. http://www.biology-online.org

Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/the-fertilization-process-and-implications-of-test-tube-babies.html http://www.articletrader.com/science/biology/the-fertilization-process-and-implications-of-test-tube-babies.html Sun, 23 Oct 2005 00:00:00 -0500 Through the wonders of science, infertile couples who were previously unable to bear children, due to reasons such as blocked fallopian tubes, low sperm count, low egg quantities or advanced age of the mother, are now able to conceive through in-vitro fertilization. The results are babies known as test-tube babies which are technically conceived outside the womb.





In a natural scenario, the conception of a baby occurs when the ovum, travels from the ovaries, through the fallopian tube to be fertilized by the sperm of the father during sexual intercourse. From this point on, the fertilized egg will travel down towards the uterus and during the process division of cells will occur until it reaches its final destination at the wall of the uterus. However, in the cases of block fallopian tubes, the eggs are unable to travel from the ovaries to the uterus and conception cannot happen.





Developed in the United Kingdom by Dr. Patrick Steptoe and Dr. Robert Edwards, the process of in-vitro fertilization involves removing eggs from the ovaries of the mother and combining them with the sperm of the father in a lab environment. The fertilized egg is then placed back into the uterus of the mother after 3 to 5 days and will remain there to grow till birth. Because of the low success pregnancy rate of this procedure, a few eggs are placed in the uterus to increase the odds of success. With this process, statistics have shown that the rates of multiple births have increased where 24 percent of the in-vitro fertilization births have produced twins.





The first test-tube baby, Louise Brown, who was born on the 25th July 1978, marked hope for other infertile couples to have a baby through this procedure. However, many others were concerned about the ethical issues surround this. One major area of concern was the fact that as the egg is located outside the womb for a few days while the cells multiplied before being put back inside the uterus, the health issues affecting this baby is unknown. Indeed, research has been shown that test-tube babies have a higher chance of birth defects and low birth weight, and researchers still have not been able to determine the reason for this.





Other issue of concern is that through this procedure, some of the eggs fertilized in the lab are later discarded. Does this procedure mean that the researchers are actually killing potential people? How is the line drawn in this case?





Then there is also the issue of commercial opportunities for eggs and sperms to be bought and surrogate wombs to be rented with the purpose of creating babies. This process of embryo transfer to another mother, not necessarily the same woman who had provided the eggs, is known as placing the embryo in a gestational carrier. This procedure has been becoming increasingly common through technological advancement, which has made couples including women with uterus problems, have a chance in having their baby.





Test-tube babies have really brought changes to the way in which babies are conceived and have given much hope to many who have had problems having babies through the process of . However, the downside of this are the ethical issues behind the procedure, with which still poses a big question mark and with which is still opposed by many factions.For more details on cell,


molecular and human biology


please visit http://www.biology-online.org/tutorials/1_cell_biology.htm







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Author's bio Dr.Richard Waller has helped thousands of infetile couples and gave hope to childless women since 1989. He is an expert on in-vitro fertilization and has conducted numerous seminars on the subject.

Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/the-truth-about-the-growth-rate-of-elearning.html http://www.articletrader.com/science/biology/the-truth-about-the-growth-rate-of-elearning.html Sun, 23 Oct 2005 00:00:00 -0500 Does your child need help with math or biology? Do you want to learn more about starting a home business? In the past you would have contacted your local learning center to help your child with their studies. Then you would have stopped by the local book store or library to find books on starting a home business. While these methods are useful, they are beginning to become a thing of the past. Elearning has begun to overshadow traditional learning methods.

What is elearning? Elearning refers to any education that you receive electronically whether it is through the Internet or from a software program. Elearning is sweeping the nation because it has become affordable and is easy to access from the comfort of your own home. Plus, you can work on your own schedule. You don’t have to worry about hiring a babysitter while you head off to class. The class comes to you through your computer when you have an hour or even minutes to spare during your hectic day.

Elearning began through various software programs available for your computer. You just popped in a disk or CD-rom into your computer and you were set to go. You could practice your typing skills at home and your children could practice their math skills through computer drills and games. This type of learning provided extra practice for your child. The software programs increased in number, but you were still limited to interacting only with the disk or CD-rom. You didn’t have access to the software program’s creator or additional resources to peruse through at your leisure.

Internet based elearning programs stepped in to fill these needs. Elearning on the Internet allowed users to break the confines of their personal computer and interact with the global community. The options to connect with the course creator/teacher, fellow students, and have live class discussions were now available. Additional resources for exploration and study are endless with the use of the Internet as an educational tool. Therefore, the growth rate of elearning has skyrocketed since the Internet has become a daily resource for many users.

Elearning contains so many different levels of interest. More in depth courses are provided at a cost, while free courses are also available. Users should take advantage of the elearning opportunities available on the Internet. You can start by typing your topic of interest in an Internet search engine. You will most likely find a course that suits your needs.







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To Discover more about Elearning and Education please visit www.elearningmagic.com

Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/your-choice.html http://www.articletrader.com/science/biology/your-choice.html Wed, 16 Aug 2006 00:00:00 -0500
The scientific community estimate that between 40% and 70% of our personality is inherited. That is to say no matter what our perception of freedom of thought we are programmed to behave in certain ways. We are programmed to behave like human beings for that is what we are. We have also inherited elements of our parents and our grandparents personalities.

And what of the remaining 30% to 60% of our personality that is not inherited? We know that early life experience is highly influential for this is when we learn to behave within our cultural boundaries. We learn the very basics such as language and human interaction. We gain experience in our early lives that shapes our adult development. Although we are aware that we have all been through this process rarely do we feel that our early years are at some level guiding our adult lives.

Naturally we look out from our eyes with the thoughts of free men and women for this is how we have evolved. We do not feel the confines of being human or the mental influence of previous generations. We are not aware of the circumstances which shaped our personalities in our earliest years. Our unconscious selves have been proven to make decisions before our consciousness is let into the secret and still we have the illusion of free will.

So I am faced with something uncomfortable. I have never been one for believing in fate or destiny and yet through our biology and early experience it seems as though I have little real ability to consciously decide what I will do in life. Perhaps this is one to ponder late at night with a cup of coffee... .you decide?.


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The author has worked in academia and the biotech industry for over 20 years. He is a contributor to .Natural Insight.
writing articles on our natural history and the human condition.

Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/energy-and-metabolism.html http://www.articletrader.com/science/biology/energy-and-metabolism.html Wed, 18 Oct 2006 00:00:00 -0500 Energy releasing processes, ones that "generate" energy, are termed exergonic reactions. Reactions that require energy to initiate the reaction are known as endergonic reactions. All natural processes tend to proceed in such a direction that the disorder or randomness of the universe increases. The fact that energy expenditure is related to body weight and even more closely to fat-free mass is well recognized. Evidence also supports the independent contribution of fat mass to the variance in energy expenditure. Therefore, it is not surprising that changes in body weight and composition induce proportional changes in energy expenditure. Despite this, it is now becoming apparent that factors other than body composition can influence the changes in energy expenditure that occur in response to weight loss.
Skeletal muscle is important in the regulation of energy expenditure and constitutes an important site for the utilization of both carbohydrates and lipids. Because the synthesis and re-synthesis of ATP within skeletal muscle is the result of five energy-generating pathways, and because there are rate-limiting enzymes in each of these pathways, it could be speculated that these enzymes influence energy expenditure. Doucet et al. hypothesized that inter-individual differences in the decrease in key enzymes involved in energy expenditure might be partly responsible for the changes in energy metabolism that occur in response to weight loss. This current study performed by some Canadian researchers investigated the relation between skeletal muscle enzymes and 24-hour energy metabolism in obese persons before and after weight loss.
Potential energy is stored energy, whereas kinetic energy is energy of motion: laws of thermodynamics govern movement of energy; according to the first law of thermodynamics, energy cannot be created or destroyed, although it can be transferred or changed from one form to another; total energy in universe has remained constant, but it is continuously becoming more diffuse through the universe.
The second law of thermodynamics states that when energy is converted from one form to another, some usable energy, some is degraded into a less usable form, i.e. heat.
It should be mentioned that entropy is a measure of disorder or randomness, it is organized, usable energy has low entropy, whereas disorganized entropy such as heat has high entropy. All energy conversions have efficiencies <100%. Compare the efficiency of gas-powered internal combustion engines (20-30%) with aerobic respiration (67%).
Enthalpy is the total potential energy of a system include bond energy is amount of energy required to break a chemical bond and total bond energy is equivalent to the total potential energy of the system, a quantity known as enthalpy. Free energy is energy that is available to do cellular work. It means that free energy is the amount of energy available to do work under the conditions of a biochemical reaction. Entropy and free energy are related inversely. Usually free energy increases during an endergonic reaction. It must occur in such a way that energy can be supplied from the surroundings. In cells, exergonic reactions are often coupled to endergonic reactions in order to provide the energy to drive them.
Another type of reaction is ATP which means the energy currency of the cell. It includes the coupling of a phosphate group to a molecule which is called phosphorylation, and it links exergonic and endergonic reactions. In any chemicals reaction bonds are either formed or broken. Since bonds are a form of energy all reactions result in either the absorption or release of energy. Exergonic reactions are ones that release energy; these reactions will usually occur spontaneously since they do not require energy to occur. On the other hand, endergonic reactions absorb energy to form bonds, so they do not occur spontaneously. Instead, they occur only if energy is available to be used in the reaction.
Some exergonic reactions do not occur spontaneously. Instead, they require a small input of energy from some outside source to cause the reaction. This outside energy is called the activation energy of the reaction. Exergonic reactions also have an activation energy
which is considerably higher than the activation energy for most exergonic reactions. Many reactions in cells are endergonic, so cells require a method of storing energy until it is needed in a chemical reaction.
Enzymes allow many chemical reactions to occur within the homeostasis constraints of a living system. Enzymes function as organic catalysts. A catalyst is a chemical involved in, but not changed by, a chemical reaction. Many enzymes function by lowering the activation energy of reactions. By bringing the reactants closer together, chemical bonds may be weakened and reactions will proceed faster than without the catalyst.
Enzymes can act rapidly, as in the case of carbonic anhydrase (enzymes typically end in the -ase suffix), which causes the chemicals to react 107 times faster than without the enzyme present. Carbonic anhydrase speeds up the transfer of carbon dioxide from cells to the blood. There are over 2000 known enzymes, each of which is involved with one specific chemical reaction. Enzymes are substrate specific. The enzyme peptidase (which breaks peptide bonds in proteins) will not work on starch (which is broken down by human-produced amylase in the mouth).
The principal energy laws that govern every organization are derived from two famous laws of thermodynamics. The first law of thermodynamics is often called the Law of Conservation of Energy. It states that in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." This is also commonly referred to as entropy. The second law, known as Carnot's principle, is controlled by the concept of entropy. The third law of thermodynamics states that if all the thermal motion of moleculars could be removed, a state called absolute zero would occur.
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Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/cloning.html http://www.articletrader.com/science/biology/cloning.html Wed, 18 Oct 2006 00:00:00 -0500 It was only in the last 250 years that scientists began speaking about chromosomes and genes and the role they play in the way one generation passes its traits on to the next. Only 30 years ago scientists have been able to describe specific genes from one organism and put them in another. But, at the end of XX century the first successful cloning was made (Dolly the sheep).
Today, cloning considered as the most progressive science, as well as the most controversial one. The paper discusses the cloning research from two perspectives: scientific and ethical. Both side of the question is important because cloning is one of the promising scientific fields is still under attack and restrictions which prevent further investigations. The new technology and discoveries in this field allow to find unique and universal remedy for many incurable diseases such as spinal cord injuries, cancer, Parkinson's Disease, diabetes, etc. The main advantage of cloning is that it becomes possible to treat causes of the diseases before they progress, but still, cloning is prohibited in many countries.
There are three types of cloning: embryo (therapeutic), reproductive and biochemical cloning. Reproductive cloning is a technology used to generate an animal that has the same nuclear DNA as another currently or previously existing animal. In a process called "somatic cell nuclear transfer", scientists transfer genetic material from the nucleus of a donor adult cell to an egg whose nucleus, and thus its genetic material, has been removed.
Reproductive cloning is expensive and highly inefficient. More than 90% of cloning attempts fail to produce viable offspring. For instance, Japanese researchers examined that cloned mice live in poor health and die early. About a third of the cloned calves born alive have died young, and many of them were abnormally large. Many cloned animals have not lived long enough to generate good data about how clones age. Appearing healthy at a young age unfortunately is not a good indicator of long term survival (Wertz, 2002).
Therapeutic cloning, also called "embryo cloning," is the production of human embryos for use in research. The goal of this process is not to create cloned human beings, but rather to harvest stem cells that can be used to study human development and to treat disease. Stem cells are important to biomedical researchers because they can be used to generate virtually any type of specialized cell in the human body.
In November 2001, scientists from Advanced Cell Technologies, a biotechnology company in Massachusetts, announced that they had cloned the first human embryos for the purpose of advancing therapeutic research. The results were limited in success. Although this process was carried out with eight eggs, only three began dividing, and only one was able to divide into six cells before stopping” (Mahowald, 2003). This type of cloning gives a lot of perspectives to the science. Therapeutic cloning technology may some day be used in humans to produce whole organs from single cells or to produce healthy cells that can replace damaged cells in degenerative diseases such as Alzheimer's or Parkinson's.

The third type of cloning is a biomedical cloning. It means the transfer of a DNA fragment of interest from one organism to a self-replicating genetic element such as a bacterial plasmid. The DNA can then be propagated in a foreign host cell. This technology has been around since the 1970s, and it has become a common practice in molecular biology laboratories today (Wertz, 2002).
The ethical issues are so important because embryonic stem cells are also hard to control, and hard to grow in a reliable way. In 1997 group of scientists led by Dr. Ian Wilmut of the Roslin Institute (Scotland), cloned the first mammal, a sheep named Dolly. When the scientists cloned, the cloning technique somatic cell nuclear transfer was used. is a fully grown mammal, with her DNA coming from a single cell taken from her mother-egg, which is fused with the mammary cell.
The fused cell then develops into an embryo, which is implanted in a "surrogate" sheep. The embryo grows into a lamb, which is genetically identical to the donor sheep. The announcement of her birth in February 1997 started the current fascination in all things cloned. It was a success, this scientists say that cloning procedure was not perfect. It took more than 277 attempts before "Dolly" was created as a health viable lamb (Campbell, Kind, McWhir, Schnieke, Wilmut, Ian, 1997).
Human cloning is far more complicated, with greater risks and potentials for error. As a result, scientists fear that applying this technique to humans might lead to malformations or diseases in the human clone. There are differences in early development between species that might influence success rate. In sheep and humans, the “embryo divides to between the 8- and 16- cell stage before nuclear genes take control of development, but in mice this transition occurs at the 2 cell stage”. In 1998, a Korean group claimed that they had cloned a human embryo by nuclear transfer but their experiment was terminated at the 4-cell stage and so they had no evidence of successful reprogramming (Friedrich, 2000).
The ethical issues are so important because cells are also hard to control, and hard to grow in a reliable way. “They have "minds" of their own, and are often unstable, producing unexpected results as they divide, or even cancerous growths” (Lopez, 2001).
Still there are a lot of pros and cons concerning cloning. Scientists say that a "human clone" is a time-delayed identical twin of another person. A clone is not an exact replica of the original, but just a much younger identical twin. As with identical twins, the clone and the orignal person will have different fingerprints. Human cloning research would enable doctors to determine the cause of spontaneous abortions, give oncologists an understanding of the rapid cell growth of cancer, allow the use of stem cells to regenerate nerve tissues, and advance work on aging, genetics, and medicines.
Supposed it is unethical to harm or destroy some human beings in order to benefit others. International documents such as the Nuremburg Code, the World Medical Association's Declaration of Helsinki, and the United Nations Declaration of Human Rights reject the use of human beings in experimental research without their informed consent and permit research on incompetent subjects only if there is minimal risk, and therapeutic benefit for “the human subject” (Wertz, 2003).
Scientists are concerned about the medical risks and uncertainty associated with human cloning. One fear is that if a baby is cloned, its chromosomes could match the age of the donor -- meaning that a "5-year old would look like a 10-year old and a 10-year would look like a 20-year old, with potential for heart disease and cancer to develop" (Wertz, 2002). As it was stated in testimony against cloning “Human cloning should be banned because it shows grave disrespect for human beings in the very act of creating them. It reduces human procreation to an assembly line, where fellow humans are manufactured to preset specifications and exploited for the sake of traits deemed useful by others” (Doerflinger, 2005).
The legislation of the USA accepted laws aimed to control cloning. Nine states have laws pertaining to human cloning. Therapeutic cloning is more controversial type, which arises disputes and discussions. Conservatives see the perspectives of these types in the possibility: ”to create a new life without a father”. Their opponents, liberals, suppose that: "Therapeutic cloning will allow them to create organs that are a perfect match for those in need of a transplant” (Human Reproduction and therapeutic cloning, 2005).
So, two opposing sides hinder human embryonic stem cell research. One side's key argument is that such research is able to answer many questions doctors currently have about diseases. Due to the damage embryos endure as a result of the process, the opponents suggest that it is immoral and does not care how much the research could benefit society. Both opinion has the right to exist but scientists, government authorities and the public should find the golden middle between their ethical prejudices and possibility to live longer and be free from incurable and chronic diseases. Undoubtedly, the state and medical regulations must exist in order to prevent negative outcomes, but in this very field nobody is able to draw the line between negative and positive, because in many cases fears based on hypothetical theories. And, sometimes the most negative and unpredictable results can lead to epoch-making discovery.
It is possible to say that cloning, as a science, has a great future, but law and legislation should control this “dangerous” sphere of knowledge. Many ethical and moral concerns have arisen over the potential applications of the cloning technology. The technology is still not perfect. Most scientists agree that human cloning poses a serious risk of producing children who are stillborn, unhealthy, severely malformed or disabled. It is also impossible to predict all potential applications of a new technology. Most will be beneficial but all technology can be misused in one way or another. The solution is not to regulate the technology itself but how it is applied.
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Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/genetically-modified-maize-vaccine-can-aid-farmers-in-developing-nations.html http://www.articletrader.com/science/biology/genetically-modified-maize-vaccine-can-aid-farmers-in-developing-nations.html Tue, 28 Nov 2006 00:00:00 -0600
Researchers in Mexico have been able to genetically modify maize crops to create an edible vaccine for poultry against the Newcastle Disease Virus. The researchers, including Octavio Guerrero-Andrade of the Center for Research and Advanced Studies (CINVESTAV) in Guanajuato, inserted a gene from the Newcastle Disease Virus into the maize crops’ DNA. Chickens that ate the genetically modified (GM) maize produced antibodies against the virus. The maize also provided a level of protection against infection comparable to that of commercial vaccines.

The researchers’ findings were published online in Transgenic Research earlier this month. They hope these genetically modified maize crops can help small-scale poultry farmers protect their flocks from NDV.

“The disease is important and a big killer,” said Frands Dolberg of the Network for Smallholder Poultry Development, which works with partners in developing countries to promote poultry farming as a way of improving livelihoods.

According to the findings, vaccines against the disease that can be given to poultry through food already exist, but are not usually available in the small quantities that are often required by single families or villages.

“There is a big problem in delivering the vaccine to the many millions of poor poultry keepers around the world, and the genetically modified (GM) maize could be a possibility,” said Frands Dolberg.

Farmers in developing nations struggle every day to make a living against unfavorable conditions. They also struggle to access new technologies that can help better their lives, including getting vital vaccines that can save their poultry farms. With this genetically modified maize that the researchers in Mexico have developed, these needed vaccines will be easily accessible, less costly, and won’t require refrigeration like traditional vaccines do. It will ultimately help save and secure the farmers’ futures.




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Alisa Baumer is a life sciences grant researcher and has first-hand knowledge of the latest trends in genetically modified food. To read more about Alisa go to Gmo Food for Thought

Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/lion-behaviour-and-distribution.html http://www.articletrader.com/science/biology/lion-behaviour-and-distribution.html Fri, 03 Aug 2007 00:00:00 -0500 General information on lions

Distribution

Lions were once found the length of Africa and the middle east all the way to India, where a small population still remains in the Gir Forest. Currently the lion is found in savanna and plains habitat across the continent, although is now absent from north and the far south of Africa. The last large remaining populations are found in the Serengeti National Park and Selous Game Reserve, Tanzania, and Kruger National Park, South Africa. The main reason for the decline in the lions range since the nineteenth century is competion with man due to hunting and loss of habitat.

Life history

Lion gestation lasts 3 1/2 months, with typically four cubs being born blind and helpless, weighing only 1-2kg. The cubs will be born in a den, which is often situated in a kopje or dry river bed, to provide them protection for the first few months of their life when they are especially vulnerable to predation by hyenas, leopards and other lions. The cubs will stay with their mother in the den for the first 2-3 months before being introduced to the rest of the pride, which allows them some time to grow and toughen themselves up a bit before having to deal with the rough and tumble of pride life. A pride can range from two to 19 related adult females plus their offspring. During this period the mother will often leave her cubs for upto 24 hours in order to feed and socalise with the rest of the pride. When you first see a new litter of cubs they will be around three months old, but often by this stage there will only be 2 or 3 cubs surviving as there is an 85% mortality rate in the first year, with 25% of this being due to infantacide, the rest to starvation and abandonment. The risk of starvation only receeds when the cubs are able to hunt for themselves. Tlhe cubs will start to eat scraps of meat when they are first led to kills by their mothers at around 2 months, and will be fully weaned by around 8 months.

As the females in the pride tend to have a synchonous oestrous, and lots of cubs born at the same time, mums and cubs will often form large creche groups. The creche will provide protection for the cubs as they grow up as there is safety in numbers. Another advantage of having cubs of a similar age is that older cubs won't monopolise the milk when females suckle one anothers cubs. Generally mothers won't tolerate cubs other than their own suckling, but as lions spend upto 20 hours a day sleeping, cubs often take advantage of this to sneak an extra feed from a lactating female. Over the next two years the cubs are dependant on their mothers and they will learn how to hunt and form bonds with siblings and other pride members. By the time the cubs have joined the rest of the pride they will be able to observe prey movements, and will imitate hunting behaviour such as stalking and killing actions in their play. The adult females, unlike adult males, are very tolerant of cubs playing with their tails and jumping all over them, and will occassionally join them in play.

At two years old the cubs become sub-adults and the males and females take two different paths. Females tend to be recruited back into their natal pride, whereas the males are kicked out by theirparents. Males will have a nomadic existance for the next 2-3 years, roaming around in unoccupied/poor lion habitat, such as the short grass plains of the Serengeti. During this time they try to avoid trouble with resident males and will grow in size and strength and develope a full mane. This is an important period for develping strong bonds with their littermates, as the coalition they form now will decide their future sucess at having a pride of their own one day. Males unfortunate enough to be born into a cohort without any other males will often team up with other lone males to increase the size of their coalition. Coalition size can range from a single male to up to seven males, with typically three or four males in a coalition. If less than three males there is a chance they might not be related, but if more than three will be related. Sometimes young females will leave the pride with their brothers, particularly if there has been a pride takeover or the pride has become very large. These females may set up a new terrirory adjacent to their natal territory or could return to the natal pride when they reach sexual maturity at 4 years old. By the time an adult female is fully grown she will weigh 126kg and stand at 110cm.

Adult males become sexually mature at five years and will weigh 198 kg and stand at 120cm. and this is the time when a coalition of males attempts a pride takeover. This is a bloody and brutal affair, with males often fighting to the death. Incoming males will kill or chase away all the cubs and sub-adults sired by the previous coalition. Cubs less than 9 months are generally killed, and cubs older than that are able to run away and are expelled from the pride, but will often starve as they are unable to fend for themselves. Female lions will vigorously defend their cubs from incoming males and occasionally do succeed in chasing away single males. It has also been observed that females will leave the pride with their cubs to avoid the infanticide of their cubs by new males. Male tenure of a pride is fairly short, only 2-3 years, which is just enough time to rear one cohort of cubs before the next coalition will take over the pride. The reason for the males committing infanticide is that due to their short tenure of the pride they don't have time to spend raising another males cubs. When a female loses her cubs, she will come back into eostrus fairly within weeks. However it has been observed that after a takeover females will mate repeatedly with the new males without ovulating. This allows the females not only to bond to the new males, but also to delay reproduction until the strongest coalition in the area vieing for the pride has made a successful challenge.

When a female is in oestrus she will mate roughly every 15 minutes for four days. Before a female comes into oestrus she will be mate guarded by the male in the coalition who gets to her first. There is no agression between males at this time and there is a 'first come, first served' approach. Within the male coalition there will be a dominance hirarchy and the most dominant individual will generally get to the female first at the peak of her oestrus. The next dominant male will then mate with her afterwards, but still has a chance of sireing cubs. As there is often synchonous eostrus within a pride, less dominant males will have the opportunity to mate as several females will be in heat at the same time and females will have a degree of mate choice at this time.

Hunting

Lions are oportunistic hunters and will readily scavenge kills from other predators, such as hyenas and cheetahs, and will follow vultures to a carcass. Although lions do the majority of their hunting at night, they will hunt in the midday sun if an opportunity presents itself. Lions favourite prey is wildebeest and zebra, but in the dry season they will take warthog and buffalo. Females do the majority of the hunting due to being smaller, faster and more agile than the males. Also they don't have a big mane to give them away when stalking prey! However, males will often help to bring down larger prey such as buffalo and giraffe. A lion hunt will be more successful if several individuals cooperate to bring down an animal, but it has been found that a lion will get more food over time when hunting on their own even though the percentage of successful hunts is much lower. After a kill it is each lion for himself around the carcass, with smaller, weaker animals losing out. As there is no hierarchy in lions they often get into scrapes round the kill which results in injuries such as ripped ears, missing eyes and missing tail tufts. A lion can eat up to 1/4 of its body weight in one sitting, although they will normally consume between 5-7kg per day.

Territories

Lion territories range in size from 20km2 to 400km2 depending on habitat type. Territories generally larger in poor habitat, as the lions have to range wider to find food and water. In woodland habitat, which is good for lions, territory size is much smaller as there is a greater concentration of resources. Both males and females actively defend their territories from other lions and patrol territory boundaries regularly scent marking by either spraying urine against trees or bushes and scraping the ground, along with head rubbing on trees and rocks. Roaring also has a territorial advertisement function, with bouts of roaring often occurring at dawn or dusk. Roaring also helps pride members locate each other and reinforce social bonds. Whilst patrolling their territory if lions encounter non-pride members they will drive them away and often get into fights. They will also chase and kill other carnivores, such as cheetahs, leopard and hyenas they find in their territories.



Visit Wild Things Tanzania Safaris for more information on visiting the Lions in the Serengeti.

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Kirsten Skinner is a former research scientist who works with Wild Things Safaris Ltd Wild Things

Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/serengeti-migration.html http://www.articletrader.com/science/biology/serengeti-migration.html Fri, 03 Aug 2007 00:00:00 -0500 The Serengeti Migration

In 1996, I went on a safari to the Serenegti National Park, Tanzania, to see lions. We saw a big pride of lions, but what was most impressive was the 'migration.' We were on the Serenegti short-grass plains, and as far as the eye could see were wildebeest, with the odd zebra family mingling in the massing herds. The view was framed by the Ngorongoro Crater to the South, the Gol Mountains to the East, and the Moru Kopjes to the West. This was in late March, and the wildebeest herds were massing on the short grass plains for the long trek North to the Maasai Mara in Kenya. Since then, I have had the pleasure and privilege of working in Serengeti for three years from 2003 to 2006 - the annual migration is still the most impressive thing I have ever seen.

What is the Migration?
The 1.4 million wildebeest, plus a million other ungulates, in the Serengeti ecosystem represent the world's greatest remaining aggregation of large mammals (Estes, 1991). Every year, in search of fresh pastures, 1.4 million wildebeest and 250,000 zebra move creating the spectacle of the Serengeti migration. The system is driven by annual rainfall patterns. The Serengeti short-grass plains are rich in minerals necessary for lactation, but lack water for most of the year. The short rains may fall anytime between October to December. While the long rains generally fall between January to April (with the majority falling in March and April). The short rains are highly variable, there are years when they fail, but typically you get one or two weeks of rain. The variability of the rainfall, make predicting where the migration will be difficult. But typically, the migration is on the short grass plains in Southern Serengeti from December to April. Typically the wildebeest give birth to their calves in February or March on the short grass plains. In April, the herds start massing for the long trek north to their dry season refuges. From May to July, the herds are generally in the Serengeti Western Corridor along the Grumeti River. If the year is particularly dry, the herds may by-pass the Western Corridor and head directly toward Northern Serengeti and the Maasai Mara. From the Western Corridor, the migration moves north, and by September the herds are in Northern Serengeti/Maasai Mara. The Mara River and its tributaries provide the herds with water during this dry period. In November, the herds again start massing for the long trek South to the Serengeti short grass plains. And the cycle begins again. Over the year the Wildebeest will cover over 400km.


The Wildebeest and Zebra
The wildebeest population has changed with time. A rinderpest epidemic swept across Africa at the start of the 1900s, which led to a marked decrease in the Serengeti wildebeest population. For much of the 20th centuary the Serengeti wildebeest population hovered around the 300,000 mark. In the 1960s, the cattle around the Serengeti were vaccinated against rinderpest. This freed the wildebeest population of rinderpest, and within a decade the wildebeest population had reached the 1.3 million mark. The Zebra population on the other hand has remained largely static around the 250,000 mark - this remains one of the great scientific mysteries (why has the zebra population not varied over time?).

Other Animal Movements
Other Serengeti animals also commute long distances. The eland and thompson gazelle are also migratory. The eland moves from Eastern Serengeti to Northern Serengeti, while the thompson gazelle moves from Southern Serengeti to central Serengeti. However, other species are more sedentary. These are year round residents: impala, warthog, buffalo, topi, kongoni and Grant's gazelle.

Wildebeest Behaviour
Wildebeest females give birth around the same time; few tropical mammals have such a restricted birth season, with 80%-90% of calves dropped during a 3 week period (Estes, 1991). At this time of year, wildebeest herds are at their most structured, with groupings of pregnant cows and of cows that have calved, groups of yearlings, and bachelor herds. During the breeding season or rut, bulls defend territories and attempt to herd females in these territories and keep out intuding males. This is quite a difficult task as the cows are migrating, so the bulls have to constantly move and set up new territories. During the rut, the bulls are constantly calling, creating a distinctive humming sound. The timing of calving and rutting is geared to rainfall in such a way that both occur under favourable conditions. The rut occurs at the end of the rains when the animals are in peak condition. While, calving occurs at the begining of the period of most reliable rain - thus ensuring an abundance of fresh pastures for the lactating cows.

Zebra Behaviour
Zebra's in Serengeti have a harem system. A stallion herds and defends 2-5 mares and his offspring by them from against other malesand against predators. Though unrelated, harem females spend their adult lives together, and continue to associate together even if the herd stallion is replaced.

The Migration and Carnivores
Hyenas commute large distances on a weekly basis, covering up to 100km from their den sites to the migration. Lions on the other hand tend to defend their territories and not move as much. However, during the rainy season, lion prides from central Serengeti will move south to the short grass plains to feed on the abundant herds of wildebeest. Lions in Serengeti have a period of gluttony when the migration is in town, followed by a period of starvation when the herds leave their territories. Cheetahs feed on smaller prey (e.g. Thompson gazelle), but have a feeding frenzy during the calving period. Leopards are similar to lions in that they have territories. Other species that are reliant on the migration for survival include crocodiles and the various species of vulture. The crocodiles are adapted to surviving for long periods without food, and feeding when the migration passes their territories. Vultures on the other hand employ the same technique as hyenas and cover large distances in search of food .

For more information visit Wild Things



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Roy J Hinde M.Sc. is a former research scientist who now is a director of Wild Things Safaris Ltd Wild Things

Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/biology/are-we-livin-or-just-survivin.html http://www.articletrader.com/science/biology/are-we-livin-or-just-survivin.html Mon, 10 Sep 2007 00:00:00 -0500

The inhibitor of apoptosis (IAP) family protects cells from self-execution by blocking the relentless caspase death cascade. IAPs bind to and inhibit activated caspases through their BIR domains. Some IAPs such as Livin also contain a RING domain that has E3 ubiquitin ligase activity and promotes the degradation of Smac/DIABLO through ubiquitination. Since Smac/DIABLO promotes apoptosis by inhibiting IAP-caspase interactions, degradation of Smac/DIABLO allows IAPs to more effectively block caspase activity thereby promoting cell survival.

In general, members of the IAP family are highly expressed in several types of cancer. However, Survivin, an IAP that lacks a RING domain, definitely stands out among the family for its clear association with cancer. Abundantly expressed during development but scarce in normal adult tissues, Survivin is upregulated during tumorigenesis and associated with chemotherapy resistance and poor patient survival.

IAPs are fast emerging as targets for potential diagnostics and therapeutics. For example, patients suffering from diverse cancers develop antibodies against Livin suggesting that Livin may be a novel diagnostic or prognostic tumor marker. Additionally, preclinical studies indicate that down-regulation of Survivin can sensitize tumor cells to chemotherapy, thereby increasing apoptosis and overall treatment response


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IMGENEX India Pvt Ltd. the only biotech company in Orissa and one of its kinds in Eastern India. IMGENEX India started in Oct as an outsourcing branch of IMGENEX Corporation, San Diego, USA. Find out more information about Apoptosis.

Source: http://www.articletrader.com ]]>