BSC-2010 Lecture Notes - Lecture 4: Genetic Code, Tata Box, Transfer Rna

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6 Dec 2016
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Transcription
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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