4A - The genetic code and nucleic acids Flashcards
What is the genetic code described as?
Non-overlapping, degenerate and universal.
What is the genetic code?
The sequence of base triplets (codons) in mRNA which code for specific amino acids.
In the genetic code, how is each base triplet read?
In sequence, separate from the triplet before and after it.
What does it mean that the genetic code is non-overlapping?
The base triplets don’t share their bases - they are read in sequence, separate from the triplet before and after it.
What does it mean that the genetic code is degenerate?
There are more possible combinations of triplets than there are amino acids (20 amino acids but 64 possible triplets) - this means that some amino acids are coded for by more than one base triplet, e.g. UAU and UAC.
What are some triplets used for?
To tell the cell when to start and stop production of the protein - these are called start and stop signals (or codons).
What are start or stop signals (codons)?
Triplets that tell the cell when to start and stop production of the protein.
Where are start and stop signals found?
At the beginning and end of the mRNA.
Give an example of a stop signal:
UAG
What does it mean that the genetic code is universal?
The same specific base triplets code for the same amino acids in all living things, e.g. UAU codes for tyrosine in all organisms.
How can you use data to give the DNA sequence for amino acids?
The mRNA codons for the amino acids are given in a table.
Because mRNA is a complementary of the DNA template, the DNA sequence for each amino acid is made up of bases that would pair with the mRNA sequence.
How can you use data to give the tRNA anticodons from mRNA codons?
tRNA anticodons are complementary copies of mRNA codons, so you can work out the tRNA anticodon from the mRNA codon.
How can you use data to write the amino acid sequence for a section of mRNA?
To work out the sequence of amino acids from some mRNA, you need to break the genetic code into codons and then use the info in the table given to work out what amino acid they code for.
What is meant by the term ‘degenerate code’?
Most amino acids are coded for by more than one triplet.
Why is DNA described as universal?
All organisms use same sequence to code for specific amino acid.
