Protein Synthesis
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When and who provided evidence that DNA carries genetic information?
1994 Avery
What happened in 1966
Nirenberg, Ochoa, and Khorona elucidate the genetic code
Give the rules of the genetic code
1) Three bases encode one amino acid = codons 2) The code is non-overlapping 3) The code is degenerate ue some amino acids are specified by more than one codon
How many codons are there which code for amino acids?
61 codons for 21 amino acids The others are stop codons
How many possible reading frames are there for one peice of DNA?
3
What is the start codon and which amino acid does it code for?
AUG = methionine
What are the three stop codons?
UAA UAG UGA
What do the tRNAs bind to?
One end base pairs with the codon = the anticodon loop The other end (3’) end carries the amino acid
What gives tRNA its structure?
Intermolecular base pairing
Although tRNAs have a similar structure what varies?
The nucleotides vary, even with in the double stranded regions
Describe the structure of the tRNA molecules
Have a D loop, Anticodon loop and T loop
How are tRNAs modified?
Psuedouridine Dihydrouridine
There are over 50 modifictions of tRNAs. What are their roles?
They affect the accuracy with which the tRNA is attached to the correct amino acid They can facilitate the recognition of the appropriate mRNA codon by the tRNA molecule
True or false - there is a 1:1 ratio of tRNA per codon
FALSE
What allows the same tRNA anticodon to bind to more than one codon?
Wobble base pairing at position 3
Give one way that a wobble is made by modification
Deamination of A creates an inosine which can pair to U, C or A
How many tRNAs do bacteria have?
31
Coupling of the amino acid to tRNA is achieved by what?
Aminoacyl-tRNA synthetases
What are the steps of coupling amino acid to tRNA?
1) The amino acid is firstly activated by the linkage of AMP to the carboxyl group = adenylated amino acid 2) AMP linked carboxyl group is transferred to the hydroxyl group on the 3’ tRNA forming an ester linkage This forms aminoacyl-tRNA
Aminoacyl tRNA is also known as what and why?
Charged tRNA Because the energy of ATP hydrolysis is still contained in the ester linkage
Translation of mRNA to amino acids requires how many adapters?
2
What are the two adapters used?
1) Synthetase that pairs the correct amino acid to the correct RNA 2) tRNA that pairs the correct codon to the correct amino acid within the ribosome
Which terminus are new proteins added on to?
The C terminus
What are the two subunits of ribosomes?
The large subunit The small subunit