Lecture 15 Nature of the Genetic Code Flashcards
How many amino acids are there
20
What is meant by the degeneracy of the genetic code.
The code is described as degenerate because there are more triplet codons than there are amino acids. In other words, for every amino acid, there are multiple codons.
- Eg glutamic acid is encoded by both GAA and GAG.
How many codons are possible
4 bases^3 = 64 possible triplet codes.
Why is the genetic code described as degenerate (model answer)
- Because there are 61 codons for just 20 amino acids
- This means every amino acid has multiple different codons
Of the 64 mRNA codons, how many specify amino acids
61
How many mRNA codons specify stop codons
3
The following statement is true or false
’ There are more than 1 transfer RNA species for certain amino acids’
True, due to the redundancy of the genetic code.
The genetic code is non overlapping… True or False
True. Each base is part of one codon at most.
How was the genetic code broken/ cracked?
- Through a series of experiments
- By using synthetic messenger molecules.
Define a stop codon and provide three examples
- Stop codons do not specify any amino acids
- Examples include UAA, UGA and UAG.
What does the Open Reading Frame refer to, in molecular genetics
An open reading frame (ORF) is the part of a reading frame that has the ability to be translated. An ORF is a continuous stretch of codons that begins with a start codon (AUG) and ends with a stop codon.
Explain the role of transfer RNA in translation
- Each transfer RNA serves as an adaptor that can bind an amino acid at one end and bind the mRNA codon
- The anticodon interacts with codons.
- The amino acid acceptor arm is where the amino acid binds.
Some transfer tRNA molecules can recognize more than one mRNA codon. Explain how such phenomenon occurs.
-Leucine is encoded by AUG, AUC, AUU. To get around this, each transfer RNA molecule can recognize different codons due to its ability to form wobble base pairs.
Explain the concept of Wobble base pairing
The first two bases of a codon must correctly pair with the anti-codon but the last base of the codon can “wobble” from its normal position to form unusual base pairs with the codon.
- Here G can pair with U
G can base pair with U. Discuss.
G U wobble base pairing can occur.
Why does wobble base pairing exist
This is the ability of transfer RNA to cope with the degeneracy of the genetic code. Eg, the fact that an amino acid has mutiple codons. So how does a transfer RNA charged with an amino acid bind to these slightly different codons. Well, it has flexibility, as long as the first 2 bases are the same, the third base can be different.
Define wobble base pair
A wobble base pair occurs in an RNA molecule and is the formation of a base pairing that does not follow Watson-Crick base pairing rules (AT CG).
Give an example of wobble base pairs
Guanine - Uracil pairing
List the 4 predominant wobble base pairs
- GU
- I U
- I A
- I C
where I is hypoxanthanine.
What is meant by the Wobble position
This is the 3rd nucleotide base in an mRNA codon.
Some transfer RNA molecules (charged with a specific amino acid) can recognize more than one mRNA codon. What is the name given to the theory that accounts for such phenomeon
The Wobble Hypothesis
What is the wobble phenomeonon
There is a relaxed set of base pairing rules at the third codon position, allowing a small number of transfer RNA molecueles to recognize multiple codons.
What is the most common start codon
AUG, which codes for methionine
Finish this sentance. Almost every protein chain begins with ….
AUG. The start codon Methionine.
