A study of biology includes the study of the chemical basis of living organisms, DNA.
Short half-life corresponds to high reactivity. The one nanosecond half-life of the hydroxyl radical indicates that it is so reactive that it reacts with the first molecule it bumps into. Ascorbate forms H2O2 on autoxidation direct combination with oxygen.
Lipid peroxidation of polyunsaturated fatty acids exposed to oxygen leads to rancidity in foods. In living animal cells peroxidized membranes lose their permeability, becoming rigid, reactive and nonfunctional.
Lipid peroxidation can produce singlet oxygen, hydroperoxides and lipid epoxides. MDA is a major metabolite of arachidonic acid Aldehyde-bridge formation leads to the protein-protein cross-linking associated with lipofuscin formation.
Polyunsaturated fatty acids are more vulnerable to free radical oxidation than any other macromolecules in the body — and the sensitivity to free radical damage increases exponentially with the number of double bonds.
Animal cells contain three important enzymes to deal with the superoxide and hydrogen peroxide: A dismutase is an enzyme that catalyzes the reaction of two identical molecules to produce molecules in different oxidative states.
In the absense of SOD, two superoxide ions can spontaneously dismutate to produce hydrogen peroxide and singlet oxygen. SOD catalyzes a reaction between two superoxide ions to produce hydrogen peroxide and triplet oxygen.
CAT is present in membrane-limited organelles known as peroxisomes. Glutathione is a tripeptide composed of the amino acids cysteine, glycine and glutamic acid.
Glutathione is the major antioxidant in the non-lipid portion of cells most of the cytoplasm. Reduced glutathione hydrogen donation can neutralize a hydroxyl radical: The elimination of hydrogen peroxide by glutathione can be written as the reaction: The liver, in particular, is very high in SOD.
Cellular concentration of SOD relative to metabolic activity is a very good lifespan predictor of animal species. Most mammals experience a lifetime energy expenditure ofcalories per gram, but humans have an amazingcalories per gram.
Humans have the highest levels of SOD — relative to metabolic rate — of all species studied.
Oxidative damage to DNA is ten times greater in rats than in humans. Superoxide dismutase without glutathione peroxidase or catalase CAT to remove hydrogen peroxide is of little value.
Insects lack glutathione peroxidase, but experiments have been performed on fruit flies made transgenic by having extra genes for SOD, CAT or both. Radiation produces the hydroxyl radical, but most of the oxygen free radicals are byproducts of cell metabolism — particularly in the mitochondria, the lysosomes and the peroxisomes.
One of the reasons these organelles are surrounded by membranes may be to protect the cell from the free-radicals they generate. DNA may be sequestered in the nucleus, in part, as additional protection against free radicals. Nonetheless, free radicals contribute to DNA damage and mutation.
In addition to enzymes, the animal cell uses many other chemicals to protect against oxygen free-radicals. Melatonina hormone produced by the pineal gland in decreasing quantities with aging, efficiently crosses membranes including the nucleus and is effective against hydroxyl radicals.
Uric acid also protects against free-radical catalysis by binding iron. Humans have higher levels of uric acid than monkeys and other mammals because humans lack the enzyme uricase. But birds typically have twice the plasma uric acid concentration as humans.
Anti-oxidants are most valuable for animals that are cancer-prone, or subjected to radiation or chemical toxins. There are evidently homeostatic mechanisms in cells that govern the amount of allowable anti-oxidant activity.
For more on anti-oxidants and anti-oxidant enzymes, see my essay General Anti-Oxidant Actions. Most animal cells contain between a few hundred and a few thousand mitochondria. The most mitochondria are found in the cells that are most metabolically active:Biology: Biology, study of living things and their vital processes that deals with all the physicochemical aspects of life.
Modern principles of other fields, such as chemistry, medicine, and physics, for example, are integrated with those of biology in areas such as biochemistry, biomedicine, and biophysics.
Essay on DNA Replication | Genetics. Article Shared by. ADVERTISEMENTS: In this essay we will discuss about: 1.
Essay, Biology, Genetics, Molecular Genetics, Nucleic Acid, DNA, Give one example. 0 Answers. What is a peptide bond? The vast range of maximum lifespan differences between species provides convincing evidence that longevity is genetically influenced.
An elephant lives about 10−20 times longer than a mouse, yet both animals have roughly the same number of lifetime heartbeats — the elephant at 30 per minute and the mouse at per minute.
Lewis Thomas was a physician, poet, etymologist, essayist, administrator, educator, policy advisor, and researcher. A graduate of Princeton University and Harvard Medical School, he was the dean of Yale Medical School and New York University School of Medicine, and the president of Memorial Sloan-Kettering Institute.
In biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa.A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats, the arms of primates, the front flippers of whales and the forelegs of dogs and horses are all derived from the same ancestral tetrapod structure.
In the last two decades, the widespread application of genetic and genomic approaches has revealed a bacterial world astonishing in its ubiquity and diversity. This review examines how a growing knowledge of the vast range of animal–bacterial interactions, whether in shared ecosystems or intimate symbioses, is fundamentally altering our understanding of animal biology.