Ch. 22b Post-Translational Processing & Genetic Code (Final Exam) Flashcards
Why does post-translational processing occur?
The polypeptide coming from the ribosome is inactive
What are the 4 structures of protein folding?
Primary, secondary, tertiary, and quarternary
Protein folding is aided by molecular chaperons. Where do they bind?
Hydrophobic regions of proteins
Why is chaperon binding important?
They keep protein in open conformation until it is ready to fold
What are the 2 functions of proteolytic cleavage?
1) Trimming to remove pieces of the N and/or C terminal to provide a shortened active protein
2) Cutting polypeptides into active protein segments
What drug is a common result of proteolytic cleavage?
Insulin
Post-translational chemical modification involves the…
Addition of small chemical functional groups to animo acids
What is the most common mode of chemical modification in animal cells?
Protein phosphorylation
Chemical modification promotes…
Protein diversity
What 3 amino acids are subjected to phosphorylation?
Serine, tyrosine, and theonine
What is the premise of protein degradation/ubiquitination?
Adding ubiquitin to misfolded proteins
What does the proteasome do once a protein is tagged with ubiquitin?
The proteasome recognizes the need for degradation into peptide subunits
In sum, how do post-translational mods affect proteins?
They change the structure, dynamics, behavior, and characteristics of proteins to allow for full activity
What do you call codons that code for the same amino acids?
Synonomous
Out of the 64 possible codons, how many represent amino acids, and how many are stop codons?
61 - represent
3 - stop codons
The tendency for identical or chemically similar amino acids to be represented by related codons minimizes…
The likelihood that a single base pair change will result in mutation
Are codons with chemically similar amino acids similar or different in sequence?
Similar
What is third-base degeneracy?
The insignificance of the base in a codon’s 3rd position (3’ end)
Why is a codon’s 3rd base in a set of 4 codons insignificant?
Often, the 4 codons only differ in the 3rd base and represent the same amino acid
What is the principle behind the wobbling hypothesis?
Multiple codons encoding the same amino acid most often differ at the 3rd base position
Does each triplet codon require its own tRNA with a complementary anticodon, or can a single tRNA respond to related codons?
Often, 1 tRNA can recognize more than one codon
An mRNA codon’s 3rd base position is a tRNA anticodon’s { } base position.
1st
What explanation did Crick give for the wobble hypothesis?
The anticodon’s 5’ end doesn’t have strict base-pairing requirements, so it can form hydrogen bonds with several bases at the codon’s 3’ end
Which ribosomal site permits the increased flexibility at the anticodon’s 1st base?
A
What would happen if the genetic code was no degenerative (i.e. allow for wobbling)?
Only 20 codons would code amino acids, and 44 would be stop codons, resulting in mutation
Anticodon 1st position base U corresponds to this codon 3rd position base(s).
A or G
Anticodon 1st position base C corresponds to this codon 3rd position base.
G
Anticodon 1st position base A corresponds to this codon 3rd position base.
U
Anticodon 1st position base G corresponds to this codon 3rd position base(s).
C or U
