Lecture 12 Flashcards
1
Q
What are the key features of genetic code?
A
- 61 of a possible 64 codons specify an amino acid
- most amino acids have more than one codon
- 3 codons specify stop of translation (UAA, UAG, UGA)
- 1 codon specifies the start of translation (AUG)
2
Q
What is tRNA?
A
- transfer RNA
- adaptor molecule
- single strand of RNA
- at least one tRNA
- one region binds to amino acid and one with mRNA
3
Q
Why is an adaptor molecule needed for translation?
A
Because RNA and amino acids are too different from each other.
4
Q
A
5
Q
What are the key features of genetic code?
A
- 61 of a possible 64 codons specify an amino acid
- most amino acids have more than one codon
- 3 codons specify stop of translation (UAA, UAG, UGA)
- 1 codon specifies start of translation (AUG)
6
Q
Why is an adaptor molecule needed?
A
mRNA and amino acids are too different to be directly transcribed.
7
Q
What is tRNA?
A
- adaptor is small RNA molecule named transfer RNA
- single strand of RNA
- at least one tRNA for each amino acid
- each tRNA has a region which can bind an amino acid and a region which can interact with mRNA
8
Q
What are the key features of tRNA?
A
- 3’ prime end has amino acid attachment site
- anticodon, interacts with mRNA codons
- 3-D shape
9
Q
What does it mean for tRNA to be ‘charged’?
A
A tRNA which caries and amino acid
10
Q
How is tRNA charged?
A
- enzyme recognises both a specific amino acid and the correct tRNA for this amino acid
- joins them together
11
Q
What is translation?
A
The synthesis of proteins by ribosomes using mRNA as a set of instructions
12
Q
What are the parts of a ribosome?
A
- large subunit
- small subunit
- mRNA binding site
- E, P, and A sites
13
Q
How does initiation in translation work?
A
- charged tRNA binds to first starting codon AUG
- small ribosomal unit will recognise the mRNA with the 5’ cap, binding to it
- small ribosomal subunit will continue scanning across until it finds the tRNA with the AUG codon
- the large ribosomal subunit will bind on top of the small subunit, and the tRNA will be in the P site
14
Q
How does elongation in translation work?
A
- tRNA binds in A site with the correct enzymes for the next codon
- tRNA in P site will transfer amino acid to A site, forming a dipeptide linkage
- at the same time, the ribosome moves, the tRNA stays in the same spot, and the tRNA w/o an amino acid goes to the E site
- tRNA in E site pops off
15
Q
How does termination in translation work?
A
- long chain of amino acids is made
- ribosome aligns with stop codon (UAA, UAG or UGA)
- release factor protein is inserted in A site, releasing the polypeptide chain and tRNA
- polypeptide and tRNA split, allowing polypeptide to fold to fit function
- release protein is released
- large and small ribosomal subunits released
