Chapter 15 Sapling – Flashcards
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How does the structure of DNA encode genetic info?
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The sequence of bases
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Describe the structure of DNA
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Adenine is paired with thymine and guanine is paired with cytosine
The five-carbon sugar of DNA is called deoxyribose
The two anti-parallel sugar-phosphate backbones twist to form a double helix
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What is the key feature of DNA that allows it to be copied?
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Complementary base pairing
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Choose the DNA sequence of the strand that is complementary to 5' CAGCTAAATC 3'.
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5' GATTTAGCTG 3'
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Since DNA is replicated semiconservatively, what does each new daughter cell receive from the parent cell after replication and mitosis?
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One of the original strands and one new strand
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The Meselson and Stahl experiment starts with E.coli containing 15N/15N labeled DNA grown in 14N media. Which result did Meselson and Stahl observe by sedimentation equilibrium centrifugation to provide strong evidence for the semiconservative model of DNA replication?
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The first generation has hybrid 15N/14N DNA, and the second generation has both hybrid 15N/14N DNA and 14N/14N DNA. No 15N/15N DNA was observed.
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Prokaryotic DNA structure
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Condensed only by DNA supercoiling
DNA is circular
Does not have a telomere region
Arranged in a single looped structure
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Eukaryotic DNA structure
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Condensed around histone proteins
DNA is linear
Has repeating telomere region
Arranged in multiple chromosomes
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Which enzyme joins fragments of DNA into a continuous strand?
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Ligase
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DNA replication steps
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1. Helicase unwinds the DNA double helix
2. Single-stranded DNA-binding proteins bind to each template strand
3. RNA primers are added
4. DNA polymerase synthesizes DNA
5. RNA primers are removed
6. DNA ligase joins DNA fragments togethers
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Which enzyme pairs corresponding nucleotides to a preexisting DNA chain in order to synthesize a new strand of DNA?
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DNA polymerase
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DNA replication involves various steps that require different enzymes. Which process does primase catalyze in DNA replication?
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Synthesis of a short RNA sequence that initiates DNA synthesis
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Two daughter strands of DNA are synthesized during DNA replication. Which term describes the new chain of DNA that begins at the origin of replication and is synthesized continuously in the direction of replication.
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Leading strand
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These discontinuous sequences of DNA nucleotides are synthesized by DNA polymerase and fused together by DNA ligase.
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Okazaki fragment
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What are telomeres?
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The DNA positioned at the ends of eukaryotic DNA strands
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What strategies do cells use to ensure that newly replicated DNA does not contain errors?
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Enzymes remove and resynthesize any misshapen sequences in the DNA prior to replication.
Enzymes proofread the DNA after the DNA has been replicated and replace any mismatched nucleotides.
As DNA polymerase synthesizes new DNA, the DNA polymerase finds and corrects misplaced nucleotides.
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Describe what happens during mismatch repair of DNA?
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Enzymes identify the newly synthesized DNA strand, remove a segment surrounding the mismatched nucleotides, and resynthesize the DNA segment correctly.
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DNA damage can occur as a result of exposure to chemicals or ultraviolet radiation. What happens during nucleotide excision repair of damaged DNA?
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Enzymes unwind the DNA, cut out a section on one stand that contains the DNA damage, and resynthesize the section with the correct DNA sequence.
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What generally causes thymine dimers to form in a strand of DNA, and why are thymine dimers a problem?
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Ultraviolet light can cause thymine dimers, potentially creating a mutation that could lead to cancer.
