3.9 DNA replication and the genetic code Flashcards
Explain what bonds are broken during semi conservative replication
Two strands must unwind so hydrogen bonds between bases break
Explain what bonds are reformed during semi-conservative replication
- Free nucleotides pair with newly exposed DNA strands so hydrogen bonds between bases reform, and phosphodiester bond between nucleotides reform
Explain what enzymes are used during semi conservative replication
- DNA helicase travels along DNA backbone catalysing reactions that break H bonds
- DNA polymerase catalyses formation of phosphodiester bonds as free + newly exposed DNA pair up
Explain continuous replication
- DNA polymerase can only bind to the 3’ (OH) so travels from 3’ to 5’
- DNA polymerase only travels in 1 direction
- strand unzipped from 3’ can continuously replicate as
- This strand is called the leading strand and is said to undergo continuous replication
Explain discontinuous replication
- DNA can only bind to 3’ (OH)
- DNA polymerase only in 1 direction
- The strand is unzipped from the 5’ end so DNA polymerase has to wait until a section of strand has unzipped then work back along the strand
- This results in DNA being produced in sections (called Okazaki fragments) which then have to be joined.
- This strand is called the lagging strand and is said to undergo discontinuous replication
Define a mutation
A change in the base sequence leading to a newly-copied strand
These changes occur randomly.
Define a genetic code?
DNA must code for a sequence of AAs - this is called a genetic code
Define a codon
The code in the base sequence is a simple triplet code.
It is a sequence of 3 bases called a codon
Define a gene
A section of DNA that contains the complete sequence of bases to code for a protein
Explain degenerate code
Multiple codons can code for the same amino acid
