Amino acids in protein synthesis

Genetic code Sequence of nucleotides along the DNA and coded in triplets (codons) along the mRNA that determines the sequence of amino acids in protein synthesis. The DNA sequence of a gene can be used to predict the mRNA sequence, and subsequently to predict the amino acid sequence. 

This definition expands our earlier thoughts in two ways. First, we have included specification of RNA molecules as well as proteins. As noted above, many RNA molecules serve a role as message carrier from DNA to the protein-synthesizing machinery (mRNA) and are translated into protein structures. Other RNA molecules serve other functions as components of the ribosome, rRNA, or as an interface between mRNA and amino acids in protein synthesis, tRNA. Finally, we have the very small RNA molecules known as siRNA. These species of RNA are not translated into proteins and this requires that the definition of a gene include the specification of their structure. 

MISSENSE MUTATION A mutation that changes one codon into another, leading to incorporation of a different amino acid in protein synthesis and sometimes resulting in an inactive protein. (See also NONSENSE MUTATION)... 

NONSENSE CODON A codon that does not specify any amino acid in protein synthesis, but instead specifies termination of a polypeptide chain the nonsense codons are UAA, UAG, and UGA. 

The backbone of a nucleic acid is a polymer of ribofuranoside rings (five-membered rings of the sugar ribose) linked by phosphate ester groups. Each ribose unit carries a heterocyclic base that provides part of the information needed to specify a particular amino acid in protein synthesis. Figure 23-21 shows the ribose-phosphate backbone of RNA. 

Reflect and. / ply The first amino acid in protein synthesis in the chlo-roplast is A formyl methionine. What is the significance of this fact ... 

It is impossible for DNA to act as a direct template in the ordering of amino acids in protein synthesis, because almost all DNA is located in the nucleus and protein synthesis occurs in the cytoplasm. The genetic information in DNA is transcribed to the intermediate RNA molecule that moves to the cytoplasm, where it directs the synthesis of the gene product on the ribosomes. The RNA differs chemically from the DNA in that the sugar molecule is ribose and thymine in DNA is replaced by uracil in RNA. Structurally, RNA is predominantly a single-stranded molecule with short, double helical regions providing some three-dimensional structure. 

Translation Process for sequential ordering of amino acids, directed by RNA during protein synthesis Codon A three-base sequence on mRNA that codes a specific amino acid in protein synthesis... 

Loftfield, R.B., Harris, A. Participation of free amino acids in protein synthesis. J. biol. Chem. 219, 151-159 (1956)... 

The multibranched shikimic acid pathway provides the intermediates for the synthesis of the three amino acids phenylalanine, tyrosine and tryptophan in microorganisms and plants. In plants, these three amino acids are precursors for a variety of secondary metabolites such as alkaloids, coumarins, flavonoids, lignin precursors, indole derivatives and numerous phenolic compounds (Fig. 1). The role of the aromatic amino acids in protein synthesis is well known as is the role of indoleacetic acid in plant development however, the function of the various secondary products is much less clear. Various physiological roles have been proposed including pest resistance, chromagens in flowers and fruits, and precursors for the structural component, lignin. 

Cells contain more RNA than DNA, and the three types of RNA are ribo-somal (rRNA), transfer (tRNA), and messenger (mRNA). rRNA constitutes about 75% of all the RNA, whereas tRNA accounts for 10-15% of the total and functions to transport amino acids in protein synthesis. mRNA consists of only 5-10% of the total and functions to carry information for protein synthesis from the nucleus to the cytoplasm. 

FUNCTIONS. DNA is the component of the chromosomes that carries the blueprint for a species—the heritable characteristics of each cell in the body and its descendants. It functions in the egg and sperm cells to pass the blueprint along from parent to offspring. Messages are relayed from DNA in the nucleus of cells to the cytoplasm by RNA, where upon the sequences of amino acids in protein synthesis are dictated by the order of the purine and pyrimidine bases transcribed from the DNA. Each cell of the body contains a full genetic blueprint, but only small parts of the genetic message are normally transcribed by RNA for cells to fulfill their role in whatever tissue they are located. 

Start Codon The first codon in a molecule of mRNA which begins the sequence of amino acids in protein synthesis in bacteria it always codes for methionine. 

On the surface the above mentioned experiments, especially those of Schweet and co-workers on the synthesis of hemoglobin, and those of Webster on the synthesis of soluble pea protein (accompanied by a parallel increase in ATPase activity) seem to establish quite definitely the RNA-AA compounds as the source of amino acids in protein synthesis. A more... 

Not all proteins are nutritionally equivalent. Mote of some than of others is needed to maintain nittogen balance because different proteins contain different amounts of the various amino acids. The body s requirement is for specific amino acids in the correct proportions to replace the body proteins. The amino acids can be divided into two groups essential and nonessential. There are nine essential or indispensable amino acids, which cannot be synthesized in the body histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. If one of these is lacking or inadequate, then—regardless of the total intake of protein—it will not be possible to maintain nitrogen balance since there will not be enough of that amino acid for protein synthesis. 

As already mentioned, a continual inflow of energy is necessary to maintain the stationary state of a living system. It is mostly chemical energy which is injected into the system, for example by activated amino acids in protein biosynthesis (see Sect. 5.3) or by nucleoside triphosphates in nucleic acid synthesis. Energy flow is always accompanied by entropy production (dS/dt), which is composed of two contributions ... 

Enzymes dependent on folic acid as coenzyme include participants in the synthesis of thymine, an essential component of DNA, and methionine, a common amino acid in proteins, among other important metabolites. A deficiency of folic acid results in the disease megaloblastic anemia. 

Small methyl groups are important in the stractnre of some small compounds, nucleotides, some bases in DNA mole-cnles and in postranslational modification of amino acids in proteins. The transfer of a single carbon atom is important in the synthesis of purine nncleotides. The componnds involved in the whole process of methyl gronp transfer, and are carbon metolism, are methionine, homocysteine, serine and the vitamins, folic acid and B12. 

Degradation of muscle protein contributes to weight loss and wasting in patients. It supplies aU amino acids for protein synthesis in tumour cells and some specific amino acids that have the following key roles ... 

The general nature of the genetic code was suggested by the structure of DNA. Both DNA and proteins are linear polymers. Thus, it was logical to suppose that the sequence of the bases in DNA codes for the sequence of amino acids. There are only four bases in DNA but 20 different amino acids in proteins at the time of their synthesis. It is obvious that each amino acid must be specified by some combination of more than one base. While 16 pairs of bases are possible, this is still too few to specify 20 different amino acids. Therefore, it appeared that at least a triplet group of three nucleotides would be required to code for one amino acid.371 Sixty-four (43) such triplet codons exist, as is indicated in Tables 5-5 and 5-6. 

Another way in which the phosphorylation state of the adenylate system can regulate the cycle depends upon the need for GDP in step/of the cycle (Fig. 17-4). Within mitochondria, GTP is used largely to reconvert AMP to ADP. Consequently, formation of GDP is promoted by AMP, a compound that arises in mitochondria from the utilization of ATP for activation of fatty acids (Eq. 13-44) and activation of amino acids for protein synthesis (Eq. 17-36). 

Production of l.-( Fl Fluoro Amino Acids for Protein Synthesis Overview and Recent Developments in Nucleophilic Syntheses ... 

Schachtschabel, D. and Zillig, W. (1959) Investigations on the biosynthesis of proteins. I. Synthesis of radiocarbon labeled amino acids in proteins of cell-free nucleoprotein-enzyme-system of Escherichia coli. Hoppe-Seyler s Z. Physiol. Chem. 314, 262-275. 

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