IB biology: topic 2/7: DNA REPLICATION

what is the structure of DNA?

double helix made up of two polynucleotide strands

what is semi-conservative model?

semi conservative model - after replication, the new DNA strand will be made up of one original polynucleotide strand and a new complementary strand.

what is a key part of DNA strands that allow it to be replicated?

can be replicated as they are antiparallel - one runs in a 5’ to 3’ direction and the other in 3’ to 5’

where does DNA replication start?

at the origin of replication

what enzymes/proteins are used in DNA replication?

DNA polymerase I / III,

helicase,

single strand binding proteins,

topoisomerase,

DNA primase

what is the role of single strand binding proteins?

avoid re-binding of complementary pairs

what is the role of topoisomerase?

relives strain on the coil

what is the role of DNA primase?

starts adding RNA primer at the 5’ end

what is the role of DNA polymerase I?

removes the primer

what is the role of DNA primase?

leaves RNA primers on the lag strand

what is the role of RNA primers?

initiation sites for DNA polymerease III on the lagging strand

what is the role of DNA polymerase III?

adds nucleotides together to form a new strand, using pre-existing strand as a template

what is the role of helicase?

enzyme that unwinds the DNA by breaking the hydrogen bonds between nitrogenous bases

what is formed as the DNA strands are separated?

y-shaped structures called replication forks

what is the role of sliding clamp proteins?

hold DNA polymerase in place as it continues to add nucleotides.

when does DNA replication occur?

during mitosis

what is the process of DNA replication? (1)

DNA unwinds at the origin of replication,

helicase does so by breaking hydrogen bonds between base pairs which form replication forks,

two replication forks are formed and extend bidirectionally,

single strand binding proteins coat strands to prevent winding back into double helix.

what is the process of DNA replication? (2)

DNA polymerase III adds nucleotides in 5’ to 3’ direction.

RNA primase synthesises RNA primer.

leading and lagging strand form

what is the process of DNA replication? (3)

sliding clamp protein holds DNA polymerase in place as it continues to add nucleotides.

topoisomerase prevents supercoiling of DNA ahead of replication fork.

RNA primers replaced by DNA polymerase adding dNTPs.

DNA ligase seals nicks in chain.

what are dNTPs?

deoxynucleoside triphosphates - nucleotides used in the formation of new DNA strands.

what is the leading strand?

strand which is complementary to the 3’ to 5’ direction and so has an overall direction of 5’ to 3’. This means that it is continuously synthesised towards the replication fork.

what is the lagging strand?

strand which is complementary to the 5’ to 3’ direction and so has an overall direction of 3’ to 5’. This means that it extends away from the replication fork, creating small Okazaki fragments. Each fragment has its own primers which are eventually replcaed by DNA polymerase I

what is the key component of DNA's structure that Watson and Crick discovered?

DNA strands are antiparallel - one runs in a 5' to 3' direction, the other runs in a 3' to 5' direction.

what term do we use to describe DNA replication?

semi-conservative

what does semi-conservative mean?

one strand will be from the original template molecule, one strand will be newly synthesised

who investigated the Semi-Conservative Theory of DNA replication?

Meselson and Stahl

what was Meselson and Stahl's investigation?

DNA molecules were prepared using the heavier 15N and then induced to replicate in the presence of the lighter 14N. DNA molecules were found to contain a mix of 15N (heavier) and 14N(lighter)