Chapter 9: Microbial Genetics- Part II
Chapter 9: Microbial Genetics- Part II 2420
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This 3 page Class Notes was uploaded by Siân L'Roy on Monday August 22, 2016. The Class Notes belongs to 2420 at Tarrant County College District taught by Mark Pulse in Summer 2016. Since its upload, it has received 6 views. For similar materials see Microbiology in Biology at Tarrant County College District.
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Date Created: 08/22/16
Microbial Genetics Part II DNA Gene Transcription: Starting/ Ending point mRNATranscript Translation: Determines phenotype of (proteins) Protein Phenotype of Cell Bacteria protein production is quicker than human protein production Important characteristics of prokaryotic RNA (ribonucleic acid): o 3 distinctive types: messenger (m)RNA, ribosomal (r)RNA, transfer (t)RNA o RNA is single stranded; Thymine (T) is replaced by another nucleotide Uracil (U) o Transcription of a DNA sequence to mRNA results in same base pairing; carries codon sequence (3 adjacent bases) o Anticodon sequence associated with tRNA and is used for protein synthesis 5’AGATCGTATGCTTACG3’ 3’UCUAGCAUACGAAUGC5’ st nd Gene expression includes 1 transcription and 2 translation Transcription is carried out by RNA polymerase and does not require ‘priming’ Microbial Genetics Part II mRNA can carry open reading frames for one gene (monocistronic) or multiple genes (polycistronic); pathogens o Transcription is initiated at a promoter sequence recognized by sigma factors (subunit of RNA polymerase); orients transcription o ‘Core’ portion of RNA polymerase continues to synthesize mRNA from the () strand of DNA; elongation occurs 5’ to 3’ o Multiple mRNAs can be generated from the same sequence by numerous RNA polymerases o Transcription is terminated by a specific sequence generating a ‘hairpin’ loop in the mRNA; RNA polymerase falls off Translation is more complex than transcription; proteins are generated by decoding the sequence of mRNA mRNA sequence is deciphered into deciphered into series of three adjacent nucleotides known as a codon Each codon encodes for a specific amino acid; there are 64 possible combinations that exist (meaning there are 23 amino acids and 9 essential); 61 are used for amino acids and 3 are used as stop codons (UAA,UAG,UGA) o Translation is initiated at the ribosome binding site; 30S subunit of ribosome binds to this sequence o Ribosome fully assembles at the start codon (AUG); fMet(starting point) (methionine) is carried to the site on a tRNA (UAC) o 50S subunit joins the initiation complex, forming the final 70S ribosome unit o During elongation, the codon sequence following the start codon is recognized by a tRNA carrying an amino acid and binds to the Asite of ribosome o fMet is covalently linked to amino acid carried on tRNA in Asite ribosome o Ribosome translocates or advances the distance of one codon (5’ to 3’ on mRNA) o fMet tRNA exits ribosome by the Esite, leaving fMet bound to the adjacent amino acid Microbial Genetics Part II o Codon sequence recognized by new tRNA carrying an amino acid and binds to A site of ribosome o Elongation continues until stop codon is reached (UAA,UAG,UGA) o Release factors free the newly synthesized polypeptide and the ribosome falls off
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