3: DNA replication and the genetic code Flashcards
What needs to happen for DNA to replicate?
- Double helix has to unwind and then separate into two strands (catalysed by DNA helicase) so the hydrogen bonds holding the complementary bases together must be broken
- Free DNA nucleotides then pair with their complementary bases, which have been exposed as the strands separate
- Once the activated nucleotides are lined up, hydrogen bonds are formed between them
- The new nucleotides join to their adjacent nucleotides with phosphodiester bonds, catalysed by DNA polymerase
What is meant by ‘semi-conservative replication’?
When DNA replicates, two new molecules of DNA are produced. Each one consists of one old strand of DNA and one new strand
What is the function of DNA helicase?
Unwinds and separates the two strands of the DNA double helix by travelling along the DNA backbone, catalysing reactions that break the hydrogen bonds between complementary base pairs
What is the function of DNA polymerase?
Catalyses the formation of phosphodiester bonds between free nucleotides and newly exposed bases on the template strands
What is a mutation?
A random and spontaneous error that leads to a change in the sequence of bases
What is the genetic code?
DNA coding for a sequence of amino acids
What is a triplet code?
It is a sequence of three bases, called a codon. Each codon codes for an amino acid
What is a gene?
A section of DNA that contains the complete sequence of bases (codons) to code for an entire protein
How many different base triplets/codons are possible?
64 (4x4x4)
How is the genetic code non-overlapping?
There is a single codon that signals the start of a sequence which ensures the codons are read from base 1 (rather than base 2 or 3)
Why is the genetic code known as degenerate?
There are a lot more codons than amino acids (only 20 different amino acids that regularly occur in proteins) so many amino acids can be coded for by more than one codon
