21: Translation Flashcards
What direction are proteins made?
N->C direction
What is a codon?
3 letter base code for each amino acid (3^4 bases = 64 codons total) 3 stop and 61 AA coding including Met for start
What are the key features of the genetic code?
- almost completely universal
- non-overlapping
- no gaps
- redundancy of some codons coding for same amino acid
Why is the genetic code non-overlapping?
significant restrictions on what amino acid residues could follow each other
Where is redundancy common?
3rd codon position
What are the allowed Wobble pairs at the 3rd codon position?
5’ anti codon base, 3’ codon base:
C, G
A, U
U, A/G
G, U/C
I, U/C/A
What is the I anticodon base?
example of modified tRNA; modified A by deamination; smaller = more leniency
AA found less frequently…
have fewer codons
Why is Tryptophan found less frequent?
large and bulky
What are the stop codons?
UAA
UAG
UGA
similar codons are…
functionally related with similar structure (same charge) bc then a change in mutation will have a lesser effect = increase chance of functional protein in the case of a single base mutation
1st or 3rd base change
How was genetic code determined?
put same repeated code in a mixture and see translated amino acid
missense, silent, nonsense, mutation?
frameshift?
missense - change 1 base=new AA
silent - change 1 base = same AA
nonsense - change 1 base = stop codon
frameshift - insert or delete 1-2 bases affecting everything downstream
When are mutations problematic?
loss of function, gain of function
What are examples of loss of function?
missense mutation in important AA residue
nonsense or frameshift causing shortened or different protein
mutation leading to loss of structural integrity, stability, may degrade
What are examples of gain of function?
permanent ON of oncogene (loss of control)
new function that are toxic to cell
Current example of gain of function?
delta variant of covid have special jackknife function to help virus fuse with cell membrane more efficiently = more infectious
What are the important components of tRNA?
acceptor stem attaches to amino acid on 3’ end
anitcodon binds to mRNA
each tRNA has a specific amino acid that it binds to depending on anticodon
What are the structural characteristics of tRNA?
2ndary structure clover leaf, with double helical structure
highly modified and fairly stable
looks like an L in 3D structure
2 key single stranded region: 3’ acceptor site + anticodon
also has D loop and T loop
Why is there only 1 type of Phe tRNA?
GAA anticodon
bc can do wobble
What are the mechanics of wobble?
5’ end of anticodon (1st position) and 3’ end of mRNA (3rd position) are the wobble position
What Is the purpose of amino acyl tRNA synthetases? What is a characteristic?
enzyme that charges tRNA with an amino acid and some have proofreading function
there is at least one synthetase for each amino acid (highly specific)
couples the 3’ end of tRNA to its correct amino acid, recognizing anticodon
What does the structure of tRNA + amino acid look like?
adenine of tRNA covalent bond ligation to carboxyl group of amino acid
What are the steps of the Aminoacytl-tRNA synthetase reaction to put an amino acid onto a tRNA?
- amino acid reacts with ATP to form an aminoacyl-adenylate (aminoacyl-AMP) - energy translation
- activated AA reacts with tRNA to make aminoacyl-tRNA (high energy) inside the aminoacyl tRNA synthetase active site AMP released