DNA Replication Flashcards
DNA replication produces ___ complete double helices from the original DNA molecule, each new one being _______ to the parent molecule. Each of the new helices ends up with one strand from the original helix and one from the new one. This style of replication is said to be _____________.
DNA replication produces **two **complete double helices from the original DNA molecule, each new one being **identical **to the parent molecule. Each of the new helices ends up with one strand from the original helix and one from the new one. This style of replication is said to be semiconservative.
What enzyme breaks the hydrogen bonds between paired bases in DNA?
DNA Helicase
What is the position called where DNA is first opened to be replicated?
Replication origin
DNA molecules that are in the process of being replicated contain Y-shaped junctions called ________ _____.
Replication forks
What is the enzyme that synthesises new DNA using an old strand as a template?
DNA polymerase
In what direction is new DNA synthesised?
5’ to 3’ direction
What units are added to a growing DNA strand to make it longer?
deoxyribonucleoside triphosphates
As DNA replication goes in one direction and there are two strands involved that run in opposite directions, a problem arises at the replication fork. How is this resolved?
Backstitching the lagging strand:
The lagging strand in DNA cannot be synthesised smoothly. The 5’ end which has to grow needs to be synthesised in small pieces. What are these called?
Okazaki fragments
What are two special qualities of DNA polymerase?
- monitors the base pairing between each incoming nucleotide and the template strand
- when a wrong base is added it can be corrected through proofreading
In the lagging strand a starting point is needed for the okazaki fragments. What are these starting points?
A short RNA fragment around 10 nucleotides long, called a primer, that provides a 3’ end starting point for polymerase.
What enzyme forms primers?
Primase
Primers are made from RNA. The RNA is removed by _______ that recognise it and degrade it. The gap is filled by DNA repair _____________ and the backbone is joined by ___ _________.
Primers are made from RNA. The RNA is removed by nucleases that recognise it and degrade it. The gap is filled by DNA repair polymerases and the backbone is joined by DNA ligase.
As the movement of the replication fork exposes a new stretch of unpaired bases, a new ___ primer is made at intervals along the _______ strand. DNA _________ adds a _______________ to the 3’ end of this primer to start a DNA strand which elongates until it runs into the next ___ primer.
As the movement of the replication fork exposes a new stretch of unpaired bases, a new RNA primer is made at intervals along the lagging strand. DNA polymerase adds a deoxyribonucleotide to the 3’ end of this primer to start a DNA strand which elongates until it runs into the next RNA primer.
What proteins make up the replication machine?
- DNA helicases
- Single-stranded binding protein (SSBS)
- Sliding clamp
- Clamp loader
What does DNA helicase do?
Use the energy of ATP hydrolysis to pry apart the double helix
What does the single-stranded binding protein (SSBS) do?
It clings to the single-stranded DNA exposed by the helicase, preventing it from re-forming base pairs and to keep it in an elongated form ready for DNA polymerase.
What are the roles of the sliding clamp and the clamp loader?
Sliding clamp: keeps polymerase attached to the template
Clamp loader: assembles the clamp around DNA using energy from ATP hydrolysis
What is the role of DNA topoisomerase?
Releives strain in the parental DNA helix by reversibly nicking the backbone
What is done if DNA polymerase makes a mistake in the 5’ to 3’ direction?
It is corrected by 3’ to 5’ exonuclease activity
What process is responsible for creating genetic diversity during meiosis?
Homologous recombination
What is the heteroduples region?
The region where two homologous chromosomes have crossed over and have exchanged DNA sequences
Outline the process of homologous recombination.
- enzymes geneate a double-strand DNA break and nucleases digest the 3’ ends
- DNA strands find homologous DNA by DNA synapsis
- The heteroduplex region is synthesised by branch migration
- The DNA strands are cut
What kind of proteins enable a DNA single strand to pair with a homologous region of DNA double helix?
RecA proteins
During recombination a structure is formed called the _______ ________.
Holliday junction
