DNA replication

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21 Terms

1
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When does DNA replication occur?
During the synthesis phase of interphase
2
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Why does DNA replication occur?
To create more/new cells
3
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What is semi-conservative replication?
Each new DNA molecule is made of 1/2 the old strand and 1/2 the new strand.
4
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How accurate is DNA replication?
3 mistakes per 3 million bases
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What are the main steps of DNA replication

1. Unwinding
2. Polymerization
3. Quality Control
6
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Describe the unwinding stage.
DNA unwraps from nucleosomes, DNA gyrase unwinds DNA. DNA Helicase breaks H bonds between nucleotides. SSBP attaches to stabilize and to prevent reformation.
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Describe the polymerization and quality control stages.
RNA primer attaches to the strands, it is used as a starting point. DNA polymerase(III) builds new strand in a 5’-3’ direction. Polymerase(III) builds the new strands of DNA and adds nucleotides to template strands. DNA polymerase(I) removes RNA primer and adds DNA nucleotides. It also checks for mistakes. DNA ligase creates p-diester links between Okazaki fragments
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What is the leading strand?
5’-3’. Polymerase works continuously towards the replication fork.
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What is the lagging strand?
3’-5’. Polymerase builds discontinuously away from the replication fork. This creates Okazaki fragments.
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Describe DNA
Double stranded molecule with anti-parallel strands. 5’ end contains phosphate group and 3’ end contains OH group.
11
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What are p-diester links?
These links occur between the phosphate group on the 5’ carbon and the OH group on the 3’ carbon.
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What is a purine?
Adenine and Guanine, larger double ring structure
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What is a pyrimidine?
Thymine and Cytosine, smaller single ring structures
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Explain H-bonding
Occurs between nitrogenous bases. Adenine and Thymine have 2 bonds. Cytosine and Guanine have 3 bonds.
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Why is there a leading and lagging strand?
The strands are antiparallel and DNA polymerase only works in a 5’-3’ direction.
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How is the lagging strand replicated discontinuously?
Lagging strand is 3’-5’ so it cannot be replicated continuously because polymerase only moves 5’-3’. The lagging strand replicates in sections called Okazaki fragments as polymerase replicates away from the fork.
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How are mistakes fixed?
DNA polymerase(I) checks for mistakes. The mistakes are cut out and replaced with correct code.
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How do large polymers fit in tiny nucleus?
DNA coils around nucleosomes to fit.
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What happens if SSBP malfunctions?
Strands will reconnect with H-bonds
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What happens if primase is inactive?
DNA polymerase would not have a starting point to attach to and would not be able to replicate
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What happens if DNA polymerase(I) is inactive?
RNA primers would not get cut out and mistakes will not be checked