Lecture 14 - The genetic code Flashcards
How many different combinations of codons are there in nucleotides?
64
How many different amino acids are there in nucleotides?
20
What is the Nirenberg-Matthaei experiment?
- Bacteria was blended, this created all the means to make a protein apart from a nucleotide sequence
- Added nucleotide sequence of UUUUUUUU
- Set up 20 tubes each with a different amino acid
- Only labelled phenylalanine gave a labelled polypeptide that let the sequences be decoded
- Found out 3 UUUs was enough to code for an amino acid, and it codes for phenylalanine
- 61 of 61 codons coded for amino acids
3 didn’t and were stop codons
What is the meaning of a degenerate code?
It means more than one codon will code for the same amino acid
What is a reading frame?
The sequence of codons between a specific start codon to a specific stop codon
What is the function of tRNA?
To link a specific amino acid and recognise a codon in mRNA
This ensures a match between the amino acid and the codon
What is the structure of tRNA?
Made up of
An anticodon that interacts with a codon
An amino acid acceptor arm where the amino acid binds
Modified nucleotides, especially in the anticodon loop
What are aminoacyl-tRNA synthases?
Each tRNA is recognised by one of the 20 amino-acyl-tRNA synthases
Each one is specific for amino acid and tRNA
This means some tRNAs recognise more than one codon
How does one tRNA recognise more than one codon?
G-U base pairing
Inosine base pairs with A C and U