How many strands are synthesized in DNA replication?
Two strands b/c of DNA's antiparallel nature (leading and lagging strand)
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What is the leading strand?
The strand that is continuously created by DNA polymerase III b/c it is following behind the replication fork (where helicase is located)
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What is the lagging strand?
\-The strand that requires constant "priming"
\-grows backward
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How does priming work in a lagging strand?
Every time DNA helicase unfolds a segment of DNA an RNA primer is placed onto the lagging strand where DNA polymerase III will add nucleotides until it runs into another primer
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What are the fragments temporarily created on the lagging strand called?
Okazaki fragments
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What is the role of DNA polymerase I?
Removes the RNA primer and replaces it with DNA
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What is the role of DNA ligase?
Seals the gap between Okazaki fragments (forms phosphodiester bonds)
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How many replication forks are there at the origin of replication?
2 replication forks
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What happens to the end of the strands if it is not long enough to synthesize (min. 5 nucleotides long)?
Telomeres are added to protect the ends
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What are telomeres?
Special nucleotide sequences at the end of eukaryotic chromosomes created by an enzyme
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What is telomerase?
Contains an RNA template to help synthesize the complementary DNA sequence. Human telomere composed of TTAGGG repeats
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What happens to telomeres with age?
Telomeres shorten (helps determine age)
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Do all adult cells continue extending their telomeres?
No, when some reach a critical length, they stop proliferating
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What might shorter telomeres do?
Protect cell from cancerous growth by limiting the number of cell divisions; cancer cells exploit this b/c elongating a telomere of a healthy cell can create cancer cells
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What is the error rate of DNA replication?
1 error per 100,000 bp ; Actual error rate: 1 error per 10,000,000,000 bp
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Why is the actual error rate of DNA replication so low?
Enzyme that cuts out and replaces damaged stretches of DNA
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Why must sequence changes be fixed?
Sequence changes may become permanent and can be passed onto the next generation; the mutation can potentially become a tumor
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Are all changes (mutations) bad?
No, many are the source of genetic variation upon which natural selection operates
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What will happen when DNA polymerase III places a mismatched base?
It will notice the mistake and correct it or the NER (nucleotide excision repair) pathway will notice and correct it; the mistake must be fixed before division (otherwise a mutation will occur)
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What are thymine dimers?
Two thymines next to each other connected w/ a double covalent bond when exposed to UV light making it unable to bind w/ Adenine in the other strands due to lack of available electrons
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What is the most common energy currency of the cell?
ATP
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What are the energy storing molecules needed for cellular respiration?
ATP, NADPH, NADH (NAD+), FADH (FAD+), FADH2
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What does ATP do?
Supplies most of the immediate energy that drives metabolism in living things