Back to AI Flashcard MakerBiology /Biology IB HL - 7.1 DNA Structure Part 2
How many bonds are formed between A and T, G and C?
Adenine and thymine paired via two hydrogen bonds, whereas guanine and cytosine paired via three hydrogen bonds
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Key Terms
Term
Definition
How many bonds are formed between A and T, G and C?
Adenine and thymine paired via two hydrogen bonds, whereas guanine and cytosine paired via three hydrogen bonds
What does the DNA structure suggest about the 2 mechanisms for DNA replication?
Replication occurs via complementary base pairing (adenine pairs with thymine, guanine pairs with cytosine)
Replication is bi-directional (proceeds in...
What type of process is DNA replication?
DNA replication is a semi-conservative process that is carried out by a complex system of enzymes
What is helicase's role in DNA replication?
Helicase unwinds and separates the double-stranded DNA by breaking the hydrogen bonds between base pairs
Where does helicase unwind DNA?
This occurs at specific regions (origins of replication), creating a replication fork of two strands running in antiparallel directions
What is the role of DNA gyrase?
DNA gyrase reduces the torsional strain created by the unwinding of DNA by helicase
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| Term | Definition |
|---|---|
How many bonds are formed between A and T, G and C? | Adenine and thymine paired via two hydrogen bonds, whereas guanine and cytosine paired via three hydrogen bonds |
What does the DNA structure suggest about the 2 mechanisms for DNA replication? | Replication occurs via complementary base pairing (adenine pairs with thymine, guanine pairs with cytosine)
Replication is bi-directional (proceeds in opposite directions on the two strands) due to the antiparallel nature of the strands |
What type of process is DNA replication? | DNA replication is a semi-conservative process that is carried out by a complex system of enzymes |
What is helicase's role in DNA replication? | Helicase unwinds and separates the double-stranded DNA by breaking the hydrogen bonds between base pairs |
Where does helicase unwind DNA? | This occurs at specific regions (origins of replication), creating a replication fork of two strands running in antiparallel directions |
What is the role of DNA gyrase? | DNA gyrase reduces the torsional strain created by the unwinding of DNA by helicase |
How does DNA gyrase reduce the torsional strain? | It does this by relaxing positive supercoils (via negative supercoiling) that would otherwise form during the unwinding of DNA |
What 7 proteins are involved in DNA replication? | helicase; DNA gyrase; SSB Proteins (single-stranded binding proteins); DNA primase; DNA polymerase III; DNA polymerase I; DNA Ligase |
What is the role of SSB's in DNA replication? | SSB proteins bind to the DNA strands after they have been separated and prevent the strands from re-annealing |
Apart from separating the DNA strands, what is the role of SSB's? | These proteins also help to prevent the single stranded DNA from being digested by nucleases |
What happens to SSBs once DNA replication is finished? | SSB proteins will be dislodged from the strand when a new complementary strand is synthesised by DNA polymerase III |
What is the role of DNA primase? | DNA primase generates a short RNA primer (~10–15 nucleotides) on each of the template strands |
What is the role of RNA primer? | The RNA primer provides an initiation point for DNA polymerase III, which can extend a nucleotide chain but not start one |
How is the new DNA strand created? | Free nucleotides align opposite their complementary base partners (A = T ; G = C) |
What is the role of DNA Polymerase III? | DNA pol III attaches to the 3’-end of the primer and covalently joins the free nucleotides together in a 5’ → 3’ direction |
In what ways does DNA Polymerase III move? | As DNA strands are antiparallel, DNA pol III moves in opposite directions on the two strands |
How does DNA P III work on the leading strand 3' to 5'? | On the leading strand, DNA pol III is moving towards the replication fork and can synthesise continuously |
How does DNA P III work on the lagging strand 5' to 3'? | On the lagging strand, DNA pol III is moving away from the replication fork and synthesises in pieces (Okazaki fragments) |
What is the role of DNA polymerase I? | DNA pol I removes the RNA primers from the lagging strand and replaces them with DNA nucleotides |
Which strand has more RNA primers? | As the lagging strand is synthesised in a series of short fragments, it has multiple RNA primers along its length |
What is the role of DNA ligase? | DNA ligase joins the Okazaki fragments together to form a continuous strand |
How does DNA ligase join the Okazaki fragments? | It does this by covalently joining the sugar-phosphate backbones together with a phosphodiester bond |
Can DNA Polymerase simply initiate replication? | NO | DNA polymerase cannot initiate replication, it can only add new nucleotides to an existing strand |
What must first happen for DNA replication to occur? | For DNA replication to occur, an RNA primer must first be synthesised to provide an attachment point for DNA polymerase |
What does DNA polymerase do to initiate replication? | DNA polymerase adds nucleotides to the 3’ end of a primer, extending the new chain in a 5’ → 3’ direction |