DNA replication Flashcards
What happens when a cell prepares to divide?
The 2 strands of DNA double helix separate, each strand serves as a template for a new double stranded DNA molecule
What is semi conservative replication?
-DNA helicase separates the 2 DNA strands.
-Free nucleotides that have been activated are attracted to their complimentary bases
-Once activated the DNA nucleotides line up and are joined together by DNA polymerase
- 2 new identical DNA molecules formed, 1 original strand one new strand in each
What are the 2 main enzymes in DNA replication and what are their functions?
-DNA helicase, travels along backbone catalysing reactions that break H+ bonds between complimentary base pairs as it reaches them (unzipping)
-DNA polymerase, catalyses the formation of phosphodiester bonds between nucleotides.
What is continuous replication?
-Because DNA polymerase can only move along the template in the 3’ to 5’ direction(as it can only bind to 3’ OH)
-DNA polymerase has to replicate each template strand in the opposite direction
-The strand that is unzipped from the 3’ end can be continuously replicated as it unzips, this is called the leading strand.
What is discontinuous replication?
-When the other strand is unzipped from the 5’ end, so DNA polymerase has to wait until a section has unzipped then work back along the strand
-This results in DNA being produced in sections(Okazaki fragments).
-These fragments then have to be joined, this strand is called the lagging strand.
What are replication errors?
Mutations, these are a change in the sequence of bases due to random errors occurring in the newly copied strand.
What is the genetic code?
DNA codes for a specific sequence of amino acids, this is called the genetic code.
Its universal, same code but sequences of bases coding for each individual proteins will be different in each organism.
What is a triplet code?
A sequence of 3 bases, called a codon. Each codon codes for an amino acid.
A section of DNA contains a complete set of bases(codons) which code for an entire protein called a gene.
What is the degenerate code?
Where multiple codons can code for one amino acid.
Provides a buffer against mutation, as a change in one base might not alter the resulting amino acid sequence.
