STRUCTURE AND FUNCTION OF RNA Not double stranded
STRUCTURE AND FUNCTION OF RNA Not double stranded (except some viruses), deoxyribose thymine uracil
STRUCTURE AND FUNCTION OF RNA messenger RNA (m. RNA), Transfer RNA (t. RNA) ribosomal RNA (r. RNA) m. RNA is less stable than others and can be cleaved by cellular nuclease.
RNA Polymerase It transfers the genetic information from DNA to m. RNA. Catalysts the formation of phosphodiester bonds between ribonucleotides. The extension of the RNA chain occurs by the addition of nucleotides to the 3 ’OH end of the ribose as in DNA. RNA polymerase synthesizes in the 5 ‘ 3' direction like DNA polymerase but does not require a primer. Unlike DNA polymerase, the first base in m. RNA synthesized is usually a purine. RNA polymerase uses a single strand of double-stranded DNA as a template. Genes are found in both strands of DNA.
RNA Polymerase RNA Polymerases are complex enzymes. E. coli contains five subunits β, β ’, α (2 copies), ω (omega) and σ (sigma). All of these subunits combine to form the active form of the socalled holoenzyme. The sigma factor can be readily separated from this enzyme. The role of sigma is to recognize the appropriate site in DNA to initiate RNA synthesis.
The gene is a DNA region whose final product may be a polypeptide or an RNA molecule.
The genetic code contains the codon for 20 amino acids. Amino acids can be modified and incorporated into the protein structure by posttranslational modification. 21. The amino acid Selenocysteine has the same structure as cysteine, with selenium in the selenocysteine instead of just the sulfur atom. The UGA stop codes the codon.
Unlike lysine, pyrolysin also has an aromatic ring and The UAG is encoded by the stop codon. This unique amino acid, found in archaea and bacteria, was first identified in methanogenic archaea.
Reading frame (RF) The m. RNA has codons encoding various amino acids after the initiating AUG codon, followed by a stop codon. Such an array is called a reading frame.
Open Reading Frame (ORF) In genome sequence analysis, it is very important to locate the genes encoding protein. If an RNA can be transcribed, this part of the DNA must contain ORF. That is, a start codon, codons that encode amino acids, and a stop codon are found in DNA. The identification of such ORFs in DNA, whether it is a protein or not, is extremely important in genetic engineering studies.
Transfer RNA There are 60 different t. RNAs in bacteria and 100 -110 different types in mammals. The t. RNA is short (73 -93 nucleotides) and single stranded. Double strands are formed in the t. RNA by folding. The t. RNA contains three nucleotides called anticodons that recognize the codon in the m. RNA. The three nucleotides (acceptor ends) at the 3 ’end of all t. RNAs do not form pairs, but have a CCA sequence. The amino acid to be transported to the ribose of the most extreme adenine is covalently linked by ester bonds.
Protein synthesis; 1. Initiation, 2. Elongation, 3. Termination and 4. Folding of the polypeptide Start of protein synthesis: At the 5 ’end of the m. RNA is the Shine. Dalgarno sequence with 3 -9 nucleotides.
It can synthesize multiple ribosome proteins on an m. RNA. This group of ribosomes is called polysomes.
Termination of the Protein Synthesis If there is no stopper codon in the m. RNA, the ribosome cannot be separated from the m. RNA. The ribosome becomes trapped. A small tm. RNA molecule drives the standing ribosome. The tm. RNA contains the alanine amino acid and the m. RNA fragment carrying the stop codon. When the tm. RNA binds to the ribosome, the stop codon releasing factor binds and protein synthesis is terminated.
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