Unit 15- Proteins Flashcards
1 gene, 1 enzyme hypothesis
- gene function by encoding enzymes, and each gene encodes a sep enzyme
- aka 1 gene, 1 polypep hypothesis
Beadle and Tatum exper
- isolated auxotrophic mutants in Neurospora
- iradiated spores and placed on complete medium
- moved to min medium where only auxotrophic survive
- moved nonauxo to other mins w/ 1 amino acid. arginine was mutant as only place they survived
structure and function of proteins
- proteins are polymers consisting of amino acids linked by peptide bonds
- AA seq is primary structure
- structure folds to create secondary and tertiary structures.
- 2+ polypeptide chains associate to form quaternary structure.
dehydration reaction
- removes H2O to form peptide bond between AA
codons
a triplet RNA code
- 64 possible codons
(3 stop and 61 sense codons)
degenerate code
AA may be specified by more than 1 codon
synonymous codons
codons that specify the same AA
isoaccepting tRNAs
diff tRNAs that accept the same AA but have diff anticodons
wobble hypothesis
base at 5’ end of tRNA anticodon can pair with several diff bases in a codon (only at 3rd base)
reading frame
way in which the seq can be read in groups of three. Each diff 3 part seq can encode a diff AA seq
nonoverlapping
a single nucleotide may not be included in more than 1 codon
translation of mRNA
- Location: ribosome
- N terminus: amino acid end at end of chain
- C terminus: carboxyl end in the robosome
binding of AA to tRNA
Aminoacyl-tRNA synthetase: loads AA onto tRNA (tRNA charging)
- determines specificity between an AA and its tRNA
- 20 diff types (like 20 AA)
CCA: AA acceptor stem at 3’ end
initiation
- initiation factor: IF-3 (and IF-2, and IF-1)
- TRNA loaded with N-formylmethionine attached = fmet-tRNA
- Energy molecule: GTP
initiation recognition seqs
The Shine-Dalgarno consensus seq in bacterial cells is recognized by the small unit of ribosome
steps of initiation
- If-3 binds to the small subunit
- small subunit binds to mRNA
- tRNA charged with N-forylmethionine forms a complex with F-2 and GTP
- bings to intiation codon and IF-1 joins small subunit
5, initiation factors dissociate and GTP hydrolized to GDP - large subunit binds
elongation
-Elongation factors: Tu, Ts, G (EF-Tu; EF-Ts; EF-G)
- exit site = E
- Peptidyl site = P
- Aminoacyl site = A
steps of elongation
- met tRNA in P site of ribosome
- EF-Tu, GTP, and charged tRNA form a complex and enter the A site
- GTP –> GDP and EF-Tu-GDP released (regenerates)
- peptide bond forms between AA and P site tRNA releases AA
- ribosome moves down mRNA and repeats
(tRNA in P site now in E site and removed. tRNA in A site now in P site)
Termination
release factors bind to termination codon, causing release of:
- peptide from last tRNA
- tRNA from ribosome
- mRNa from ribosome
steps of termination
- reach stop codon
- RF-1 attatches to A site and RF-3 with GTP binds to ribosome
- everything released and GTP hydrolized
polribosome
an mRNA with several ribosomes attached
quality control
- messenger RNA surveillance (detect and deal with errors in mRNA)
- posstrnaslational modifications (folding: molec chaperones)
- nonstandard AA synthesis
