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4 translation requirements:
- amino acids
- messenger RNA
- transfer RNA
translation of mRNA
the biological polymerization of amino acids into polypeptide chains
ribosomes are made of...
- ribosomal proteins (form surface)
- ribosomal RNA (rRNA) (form core)
- 2 sub units; small matches tRNA to codons; large forms peptide bonds
- mRNA binding site (on small sub unit),
- A, P, E (on large sub unit)
eukaryotic larger than prokaryotic
mRNAs with several ribosomes translating at once
tRNA is considered charged after its specified amino acid has been bonded to its 3’ end by aminoacyl tRNA synthase (one for each amino acid = 20)
eukaryotic pre-mRNA gets processed by...
- 5' cap w/ 7-methylguanosine
- 3' poly-A tail (polyadenylation)
- Splicing: introns excised
transcription begins with template binding by RNA pol at a _______.
Initiation begins when the ______ recognizes specific DNA sequences called the ______.
- transcription begins with template binding by RNA pol at a promoter. Initiation begins when the σ subunit recognizes specific DNA sequences called the promoter.--> found upstream (5') from initial transcription of gene
what is the direction of transcription determined by?
the orientation of the promoter
4 stages of transcription...
- 1. Binding of RNA pol (@ promoter) and local DNA unwinding
- 2. Initiation of RNA synthesis
- 3. Elongation of RNA
- 4. Termination of RNA synthesis
- In bacteria,
- a subunit of RNA pol, recognizes promoter
- σ factor detaches after transcription has initiated
-->what are their units called?
- in bacteria, mRNA that can encode more than one protein within the same transcript.
- units: operons
- (eukaryotes have monocistronic mRNA)
Transcription in eukaryotes...differences
- occurs in nucleus under the direction of three different forms of RNA polmRNA moves out of the nucleus into the cytoplasm for translation
- Euk. RNA pol rely on transcription factors to scan and bind to DNA
- In addition to promoters, other control units called enhancers and silencers also control transcription regulation
RNA pol II
determines where it should bind to DNA and where it begins copying DNA into RNA
core promoter element that binds TATA-binding protein of transcription factor TFIID and determines the start site of transcription
general flowchart of transcription factors and RNA pol II...
- D binds to TATA box → others bind →
- RNA pol II binds → phosphorylation → transcription begins
introns are spliced out of euk. pre-mRNA by the _______
- snRNPs, an important component of spliceosomes, are involved in excision
- (small nuclear ribonucleoproteins)
- Catalytic RNAs are called “ribozymes.”
- 1 kind of pre-mRNA → different version of mature mRNA
- Each mRNA transcript still gives rise to one polypepti
in bacteria the start codon codes for this modified amino acid
- UAA, UAG, UGA
- **if mutation one of these then nonsense mutation
modified bases on tRNA
- Inosinic acid (I)
- Pseudouridylic acid (ψ)
- -==- aid in wobble by being able to pair with more than one ribonucleotide
3 phases of translation
ribosome binding site of bacterial mRNA
- Shine-Delgarno sequence
- -where rRNA small subunit binds to mRNA
- --small subunit binds to initiation factors (IFs)
- --then tRNA fMet binds to P site and mRNA binds
- --then large subunit associates
elongation during translation flowchart
- initial P-site bonding of tRNAmet
- elongation continues w/ charged tRNA binding to A-site
- large subunit catalyzes bond b/t P-site tRNA and its amino acid (peptidyl transferase)
- peptide bond formed b/t hydrolyzed aa chain and incoming A-site tRNA aa
- discharged tRNA translocated to E-site and ejected
ribosome binding site of eukaryotic mRNA
- Kozak sequence
- increases efficiency of translation by interacting with initiator tRNA
base-pair substitutions/insertions or deletions create 4 types of mutations
- missense - different protein
- nonsense - stop
- silent - no change