mol.gen.outline - Chapter 2-transcription and translation...

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Chapter 2-transcription and translation, protein folding o Transcription involves a strand of RNA being built in the 5’-3’ direction, the template strand, is then read in the 3’-5’ direction o Transcription does NOT require a primer for initiation like dna replication does o RNA polymerase moves along DNA until it hits a terminator o Initiation of transcription occurs at a promoter upstream (5’ of the coding strand, 3’ of template strand)) 35 base pairs away o RNA polymerase contains 2 alpha complexes that assemble the Rnap and bind its regulartory proteins, 1 beta comples that catalyzes chain initiation and elongation, 1 beta prime complex that helps Rnap bind to the DNA template, one omega factor that restores denatured enzyme to its functional form , and the sigma factor, which binds to and recognizes promoters (AT rich regions) (leaves complex after it does this) o Transcription often pauses, often from hairpins in th RNA that interact with the flap of the beta subunit and cause cisplacement of 3’ OH from Rnap o Termination: Factor-independent: occurs at sites in DNA with a region of two fold symmetry followed by a stretch of A’s, this causes folding of the RNA transcript and breaks hydrogen bonding to the template strand, releasing rnap Factor-dependant: rho protein (a helicase) binds to rut sequences, chases the Rnap complex, and unwinds the dna/rna duplex. This requires ATP o Box 2.2: introns contain parasitic dna, they get spliced off between two exon sequence boxes o Base modifications: in mitochondria cytidine gets changed to uridine, also in mitochondria UGA encodes for tryptophan and in chloroplasts adenosine gets changed to inosine o Peptide bond formation: The carboxyl group of one amino acid forms a covalent link with the amino group of the next amino acid (a dehydration, water is released) o Genetic code is degenerate: several codons code for the same amino acid o Translation-the change from a sequence of nucleotides on the DNA to a sequence of amino acids in a protein, involves a 70S bacterial ribosome containing a 50S subunit, which is rigid (23S rRNA, 5S rRNA and 31 proteins) and a 30S subunit, which has domains that can rotate during translation (16S rRNA and 21 proteins) o Translation begins at an initiation codon (AUG), which occurs 5-10 basepairs downstreak from the Shine-Dalgarno sequence o The initiation tRNA is always always carries N-formyl methionine as it’s first amino acid. This tRNA binds to the Psite instead of the A site of the 30S ribosome. After the first tRNA is bound the 50S subunit attaches to the 30S subunit o IF-1,2 and 3 enzymes help fMet bind to 30s subunit o EF-Tu complexes with GTP to bind with tRNA’s before they enter 70S rna o 23S rRNA cleaves the carboxyl end of the peptide from the tRNA in the P site and forms a peptide bond with the amino acid to the tRNA in the end site o After the tRNA has given up it’s amino acid it leaves out the E site
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o Wobble: most of the time a 3 rd base change will not matter and will still
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