Other Functions amino acids
Amino acids are precursors of a variety of complex nitrogen-containing molecules. Prominent among these are the nitrogenous base components of nucleotides and the nucleic acids (DNA and RNA). Furthermore, there are complex amino-acid derived cofactors such as heme and chlorophyll. Heme is the iron-containing organic group required for the biological activity of vitally important proteins such as the oxygen-carrying hemoglobin and the electron-transporting cytochrome c.
Several α-amino acids (or their derivatives) act as chemical messengers. For example, γ-aminobutyric acid (gamma-aminobutyric acid, or GABA; a derivative of glutamic acid), serotonin and melatonin (derivatives of tryptophan), and histamine (synthesized from histidine) are neurotransmitters. Thyroxine (a tyrosine derivative produced in the thyroid gland of animals) and indole acetic acid (a tryptophan derivative found in plants) are examples of hormones.
The most important posttranslational modification of amino acids in eukaryotic organisms (including humans) is the reversible addition of a phosphate molecule to the hydroxyl portion of the R groups of serine, threonine, and tyrosine. This event is known as phosphorylation and is used to regulate the activity of proteins in their minute-to-minute functioning in the cell. Serine is the most commonly phosphorylated residue in proteins, threonine is second, and tyrosine is third.
Amino acids are used therapeutically for nutritional and pharmaceutical purposes. For example, patients are often infused with amino acids to supply these nutrients before and after surgical procedures. Treatments with single amino acids are part of the medical approach to control certain disease states. Examples include L-dihydroxyphenylalanine (L-dopa) for Parkinson disease; glutamine and histidine to treat peptic ulcers; and arginine, citrulline, and ornithine to treat liver diseases.
Certain derivations of amino acids, especially of glutamate, are used as surfactants in mild soaps and shampoos. D-Phenylglycine and D-hydroxyphenylglycine are intermediates used for the chemical synthesis of β-lactam antibiotics (e.g., synthetic versions of penicillin). Aspartame is a sweetener prepared from the individual component amino acids aspartic acid and phenylalanine.
Cell structures explained LEVEL 1 – BIOLOGICAL CONCEPTS
|Eukaryotic cells contain membrane-bound organelles, such as the nucleus, while prokaryotic cells do not. Differences in the cellular structure of prokaryotes and eukaryotes include the presence of mitochondria and chloroplasts, the cell wall, and the structure of chromosomal DNA.
Prokaryotes were the only form of life on Earth for millions of years until more complicated eukaryotic cells came into being through the process of evolution. The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among groups of organisms.
The most fundamental difference is that eukaryotes do have “true” nuclei containing their DNA, whereas the genetic material in prokaryotes is not membrane-bound. In eukaryotes, the mitochondria and chloroplasts perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur across the cell membrane; endosymbionts are extremely rare.
The cell walls of prokaryotes are generally formed of a different molecule (peptidoglycan) to those of eukaryotes (many eukaryotes do not have a cell wall at all). Prokaryotes are usually much smaller than eukaryotic cells.
Prokaryotes also differ from eukaryotes in that they contain only a single loop of stable chromosomal DNA stored in an area named the nucleoid, while eukaryote DNA is found on tightly bound and organized chromosomes.
Although some eukaryotes have satellite DNA structures called plasmids, these are generally regarded as a prokaryote feature and many important genes in prokaryotes are stored on plasmids. Prokaryotes have a larger surface area to volume ratio giving them a higher metabolic rate, a higher growth rate and consequently a shorter generation time compared to Eukaryotes.
Prokaryotes also differ from eukaryotes in the structure, packing, density, and arrangement of their genes on the chromosome. Prokaryotes have incredibly compact genomes compared to eukaryotes, mostly because prokaryote genes lack introns and large non-coding regions between each gene. Whereas nearly 95% of the human genome does not code for proteins or RNA or includes a gene promoter, nearly all of the prokaryote genome codes control something.
Prokaryote genes are expressed in groups, known as operons, instead of individually, as in eukaryotes.
In a prokaryote cell, all genes in an operon are transcribed on the same piece of RNA and then made into separate proteins, whereas if these genes were native to eukaryotes, each would have their own promoter and be transcribed on their own strand of mRNA. This lesser degree of control over gene expression contributes to the simplicity of the prokaryotes as compared to the eukaryotes.
|Amino Acids And The Origin Of Life On Earth
The question of why organisms on Earth consist of L-amino acids instead of D-amino acids is still an unresolved riddle. Some scientists have long suggested that a substantial fraction of the organic compounds that were the precursors to amino acids—and perhaps some amino acids themselves—on early Earth may have been derived from comet and meteorite impacts. One such organic-rich meteorite impact occurred on September 28, 1969, over Murchison, Victoria, Australia. This meteorite is suspected to be of cometary origin because of its high water content of 12 percent. Dozens of different amino acids have been identified within the Murchison meteorite, some of which are found on Earth. Some compounds identified in the meteorite, however, have no apparent terrestrial source. Most intriguing are the reports that amino acids in the Murchison meteorite exhibit an excess of L-amino acids. An extraterrestrial source for an L-amino acid excess in the solar system could predate the origin of life on Earth and thus explain the presence of a similar excess of L-amino acids on the prelife Earth.
This vision supports the continuous life theory. Live did not start, it has been transferred.
DNA structure and amino acids
All aging theories are based on the chemistry of life. Most of these theories focus on details of the total. To understand the process, knowledge of details is needed to get a vision of the total.
The backbone of DNA is based on a repeated pattern of a sugar- and a phosphate group. The full name of DNA, deoxyribonucleic acid, shows the name of the sugar – deoxyribose. Deoxyribose is a modified form of ribose. Ribose is the sugar in the backbone of RNA, ribonucleic acid.
DNA is made of nucleotides. These are made of three parts: a phosphate group, a sugar group and one of four types of nitrogen bases. To form a strand of DNA, nucleotides are linked into chains, with the phosphate and sugar groups alternating.
The four types of nitrogen bases found in nucleotides are adenine (A), thymine (T), guanine (G) and cytosine (C). The order, or sequence, of these bases, determines what biological instructions are contained in a strand of DNA. For example, the sequence ATCGTT might instruct for blue eyes, while ATCGCT might instruct for brown.
The complete DNA instruction website, or genome, for a human, contains about 3 billion bases and about 20,000 genes on 23 pairs of chromosomes.