From RNA to protein Flashcards
What carries the code from the genome to the ribosome?
mRNA
What makes proteins?
Ribosomes in the cytoplasm
What translates mRNA into proteins in the ribosome?
tRNA
When the protein comes out of the ribosome, what helps to fold the protein into the correct shape?
Chaperones
Who provided evidence that DNA carries genetic information and when?
Avery in 1944
Who figured out the DNA structure and when?
Waston, Crick and Franklin 1953
Who explained the genetic code and when?
Nirenberg, Ochoa and Khorana in 1966
What are the 4 ‘rules’ of the genetic code?
1) Non-overlapping
2) Degenerate
- Some amino acids are specified by MORE than ONE codon
3) Triplet code
- 3 bases encode an amino acid
- Invariable
4) Read from a fixed point (Start codon AUG = Methionine)
If there was no start codon, how many reading frames would mRNA have?
3
What is the start codon and which amino acid is specified?
Aug
Methionine
What are the stop codons in mRNA?
UAA
UAG
UGA
What is the ORF?
Open reading frame
The space between the start and stop codons
What is the structure of tRNA?
Clover-leaf: 3 loops joined together by base pairing WITHIN the tRNA
At one end - the ANTICODON loop
At the other end - Carries an amino acid
In a tRNA, where is the amino acid attached to?
The 3’ end
Is the nucleotide sequence of each tRNA the same?
No, they vary - even between the base pairs, which maintain the structure
How are some of the nucleotides altered in tRNA and why?
Altered by enzymes to form:
PseudoURIDINE and DihydroURIDINE
To increase the complexity of the molecule and allow more SPECIFIC, different interactions (H bonding) with different molecules
How many possible modifications are there that can be made to tRNA to increase specificity binding?
Over 50
What is ‘wobble-base pairing’ and what does this allow?
Position 3 can have non-Waston-Crick binding as the RNA is distorted in this position
Allows each tRNA to have more than one codon which it binds to - efficiency
In wobble base pairing, what can G in the CODON bind to? (bacteria)
C or U in the ANTICODON
In wobble base pairing, what can I in the ANTICODON bind to? (bacteria)
U, C or A
How can the anticodon in tRNA be modified?
A can be DEAMINATED to I (inosine)
How many tRNAs are there in bacteria for how many codons?
31 tRNAs for 61 codons
What must happen to the tRNA molecule before it gets to the ribosome?
What enzyme does this? How?
The tRNA must become charged with the RIGHT amino acid
Done by aminoacyl-tRNA synthetase - forms a HIGH ENERGY bond
How are tRNAs charged with the correct amino acid?
1) Aminoacyl-tRNA synthetase PRIMES the amino acid by adding AMP to the C-terminus (forming and adenylated amino acid)
- Phosphate bond has a HIGH energy, from the ATP hydrolysis to form AMP
2) Aminoacyl-tRNA synthetase then brings this into close contact with the 3’ end of the tRNA (-OH)
- ESTER linkage ( R1 - C - O - R2)
3) AMP drops off
- Energy from ATP hydrolysis is contained within the ester linkage
How are different amino acids the same/different to each other
They have the same backbone structure, with and amino end and a carboxyl end
They have different side chains