BSC-2010 Lecture Notes - Lecture 4: Genetic Code, Tata Box, Transfer Rna
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•transcription: synthesizing DNA into RNA
•only uses 1 strand of DNA
•initiation
•elongation — RNA polymerase separates 2 strands of DNA for a short distance, RNA
transcript moves “downstream” toward coding region
•termination — RNA polymerase reaches the end of coding region, completes the RNA
transcript and unbinds from DNA
•enzyme — RNA polymerase
•nucleic acid synthesis always occurs at the 3’ end
•5’ —> 3’
•** attachment site for RNA polymerase — promoter region of DNA
•eukaryotic promoter:
•A-T rich region (TATA box)
•A-T only have 2 H bonds, easier to break than C-G
•several transcription factors bind to DNA
•lipid-soluble proteins (?)
•transcription initiation complex forms
•prokaryotes — RNA synthesis transcription product can be transported right away
•pre-mRNA (immediate transcript)
•eukaryotes — nuclear envelop, processing steps, mRNA has to be chemically modified before
it can leave the nucleus
•eukaryotes modify pre-mRNA
•5’ cap — protects mRNA from being broken down too quickly by hydrolytic enzymes
•signals ribosomes to “attach here”
•Poly A (Adenine) tail — protects mRNA from degradation and may help ribosome
attachment; facilitates mRNA export from the nucleus
•UTR — untranslated region
•leader and trailer are non-coding regions
•introns cut out and exons spliced together
•coding regions = exons
•non-coding regions = introns
•spliceosome
•snRNPs — small nuclear ribonucleic proteins
Genetic Code and Translation (Protein Synthesis)
•DNA —> RNA —> Protein [central dogma]
•growing polypeptide attached to tRNA
•anticodon part of tRNA sequence
•codon is 3 bases within mRNA sequence
•3 possible reading frames
•tRNA match up codon sequence with a particular amino acid
•peptide bond formed, polypeptide chain grows
•5’ —> 3’ direction
•amino to carboxy direction
•codon = 3 bases
•each mRNA base = A, C, G, U
•possibilities:
•1 base = 4, 2 bases = 16, 3 bases = 64
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