Aging Theories Essays - Molecular Biology, Senescence, Mutation

Aging Theories This report outlines the main theories of how the process of aging works. Since researchers have not discovered a universally-accepted theory of aging, the theories discussed are potential explanations of how we age. The likelihood of each hypothesis is considered roughly equal. The different theories discussed focus on the workings of different parts of the body, from the molecular level of DNA mutations and replication, to the organism level of becoming "worn out." Aging is a very complex and gradual process, and its ongoing operation is present to some degree in all individuals. It is a journey to the maturity, as well as to the degeneration of the body. Because aging affects every part of the body, many different steps are involved and various types of reactions occur. Changes in DNA take place, which can and often do affect the way the body functions; harmful genes are sometimes activated, and necessary ones deactivated. A decrease in important body proteins like hormones and certain types of body cells is almost inevitable. These, among many, are characteristic changes that take place in our bodies as time moves on and aging continues. At present, a universal explanation for how we age or why we age does not exist, but there are many theories to explain this puzzle, and they are supported by continuous research. In this report, some of the how theories of aging will be examined. Among them are theories concerning spontaneous mutations, damage from free radicals, the clock gene, cellular aging, a weakened immune system, wear and tear, and hormonal and neuroendocrinous changes. Spontaneous Mutations The spontaneous mutations theory, also known as the somatic mutation hypothesis, states that the crucial events that cause aging are mutations. These are changes in a cell=s DNA, which are passed on to daughter cells during mitosis. Since genes on DNA code for specific proteins, mutated genes may produce defective proteins, which do not work properly. Many proteins can be affected, such as enzymes, proteins comprising muscle tissue, and a recently discovered type of protein called transcription factors, which bind to DNA and regulate the individual activities of genes themselves. Physical mutagens are substances that increase the chance of mutation and include such physical phenomena as x-rays and radioactivity from radium. The atomic bombs dropped on Hiroshima and Nagasaki in Japan are examples of physical mutagens that caused an increase in the number of cases of leukemia. Certain chemicals and radiation cause mutations to occur in DNA by giving off high energy particles. These particles collide with the DNA and knock off atoms of the DNA randomly, damaging it. DNA consists of sequences of four possible nitrogenous bases: adenine, guanine, cytosine, and thymine, paired so that adenine always pairs with thymine, and guanine always pairs with cytosine. As cells repair the damaged DNA, a different DNA base is often substituted. This base-substitution is known as a point mutation and can cause the production of a defective or damaged protein. Apart from being caused by radiation or chemicals, mutations also occur spontaneously but at lower rates. Physicist Leo Szilard and biochemist Denham Harmon proposed that because most mutations are harmful, the more spontaneous mutations that arise, the more abnormalities that arise as defective proteins are produced. These could ultimately kill an individual (Ricklefs and Finch, 1995, 20). Although it has been proven that many proteins undergo alterations during aging, the spontaneous mutations theory is not the cause (Ricklefs and Finch, 1995, 21). It has, however, been proven that DNA is chemically altered during aging. Modifications in DNA bases, called I-spots, have been found to increase in number during aging. Besides I-spots, another modified base known as 8-hydroxyguanine, the DNA base guanine with an added OH group, has also been found to increase during aging. It is unclear how changes such as these arise, but similar changes seem to be caused be exposure to mutation-causing chemicals, some of which are found in tobacco smoke (Ricklefs and Finch, 1995, 21). Another factor supporting the spontaneous mutations theory may lie in the temporal occurrence of genetic mutations. Certain cancers and abnormal growths seem to appear more frequently as the process of aging continues. Two tumour suppressor genes called p16 and p53 are responsible for slowing cell proliferation, and therefore keep certain cells from becoming cancerous. However, if they become mutated, they do not carry out their function properly so cells with these mutations begin to grow and divide quickly, causing cancer and other growths (Ricklefs and Finch, 1995, 22). Werner's syndrome is a disorder that significantly accelerates the aging process starting at

Stegoceras - Facts and Figures

Stegoceras - Facts and Figures Name: Stegoceras (Greek for roof horn); pronounced STEG-oh-SEH-rass Habitat: Forests of western North America Historical Period: Late Cretaceous (75 million years ago) Size and Weight: Up to six feet long and 100 pounds Diet: Plants Distinguishing Characteristics: Light build; bipedal posture; extremely thick skull in males About Stegoceras Stegoceras was the prime example of a pachycephalosaur (thick-headed lizard)a family of ornithischian, plant-eating, two-legged dinosaurs of the late Cretaceous period, characterized by their extremely thick skulls. This otherwise sleekly built herbivore had a noticeable dome on its head made of almost-solid bone; paleontologists speculate that Stegoceras males held their heads and necks parallel to the ground, build up a head of speed, and rammed each other on the noggins as hard as they could. (They may also, secondarily, have used their heads to butt away the flanks of encroaching tyrannosaurs, though we have no objective proof of this behavior.) The sensible question is: What was the point of this Three Stooges routine? Extrapolating from the behavior of present-day animals, its likely that Stegoceras males head-butted each other for the right to mate with females. This theory is supported by the fact that researchers have discovered two distinct varieties of Stegoceras skulls, one of which is thicker than the other and presumably belonged to the males of the species. (However, some paleontologists dispute this theory, noting that such high-speed collisions would tend to be disadvantageous from an evolutionary perspectivefor example, a dizzy, concussed Stegoceras could easily be picked off by a hungry raptor!) The type specimen of Stegoceras was named by the famous Canadian paleontologist Lawrence Lambe in 1902, following its discovery in the Dinosaur Provincial Park formation of Alberta, Canada. For a few decades, this unusual dinosaur was believed to be a close relative of Troodon (which was actually a saurischian rather than an ornithischian dinosaur, and thus resided on an entirely different branch of the dinosaur family tree), until the discovery of further pachycephalosaur genera made its provenance clear. For better or for worse, Stegoceras is the standard by which all subsequent pachycephalosaurs have been judgedwhich is not necessarily a good thing, considering how much confusion still exists about the behavior and growth stages of these dinosaurs. For example, the presumed pachycephalosaurs Dracorex and Stygimoloch may have been either juvenile, or unusually aged adults, of the well-known genus Pachycephalosaurus and at least two fossil specimens that were initially assigned to Stegoceras have since been promoted to their own genera, Colepiocephale (Greek for knucklehead) and Hanssuesia (named after the Austrian scientist Hans Suess).

Bill Clinton and Racial Reconciliation Essay Example | Topics and Well Written Essays - 750 words - 1

Bill Clinton and Racial Reconciliation - Essay Example For the first time in history, America put in office the first African American as their 44th president. This was a great milestone and a step in the right direction towards the issues that Bill Clinton had mentioned. It now seemed that Americans were ready to give opportunities to other races that had been dominantly occupied by one race; the world was in surprised and the celebrations unceasing as President Barack Obama was sworn into office. It was finally a new dawn in the land of America and the struggle for equality had been achieved? Had it really? Many argue that it is not possible for one man to change the perspectives of a population, and I agree with them. Racial reconciliation has not really taken place in America yet, it is still a work in progress, but headed in the positive direction. President Obama’s win was a revelation, that people do want change. He garnered majority of the votes to defeat his opponent Mitt Romney. Despite his landslide win, the Americans d id not vote for him in the same overwhelming numbers across the different races that are represented. From the African American population, 93 percent voted for President Obama as compared to 41 percent from the whites. The other 59 percent favored Mitt Romney, this goes to show that, people were voting mainly, for their own and that is why the votes of the black population was able to swing the vote towards their chosen one. It is clear from this that difference in racial backgrounds is still an issue that the Americans have to deal with. While it was thought that the election of President Barack Obama meant that, the black community had been fully accepted in America, statistics prove otherwise. A research carried out recently by a Stanford University professor, Jon Krosnick, showed that fifty one percent of the Americans still exhibited anti-black attitude explicitly. This is in comparison to forty-eight percent in 2008, the same research revealed that fifty six percent of the Am erican population harbor anti-black attitude implicitly as compared to forty-nine percent in 2008. This brings to light that the different races in America have not fully accepted each other and to make matters worse, it seems like the divide is getting worse. The Declaration of Independence states that all American citizens are equal but the reality on the ground shows that a good number of the population does not agree with that just yet (Lawson and Franklin, 295). However, a population of the Americans especially, the blacks seems to think that President Obama is not addressing the issue of race as people thought he would. He has been openly criticized by some African Americans due to what seems as his effort to stay away from the talk of racial divide and the issues that need to be addressed. It is crucial for the issues that are brought about by different races to be addressed to avoid a repeat of history. The worst crimes against humanity were because of indifference towards o thers. With the deep feelings of negativity still rooted in most Americans it might only be a matter of time before another injustice against a race occur (Wiesel). On the contrary, others might say that, racial reconciliation has already taken place. This is because a couple of years ago, the election of a black president would have been unheard of. It seems that the different