Topic 3.4 DNA Replication Assessment Statements Answers
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Topic 3.4 DNA Replication Assessment Statements Answers

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Topic 3.4 DNA Replication Assessment Statements Answers

Topic 3.4 DNA Replication Assessment Statements Answers

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  • 1. I-Shou International School IB Biology 3.4 DNA Replication Assessment Statements (SL) 3.4.1 Explain DNA replication in terms of unwinding the double helix and separation of the strands by helicase, followed by formation of the new complementary strands by DNA polymerase. State the phase of the cell cycle that DNA replication occurs in. S Phase (synthesis). State the purpose of DNA replication. So each daughter cell will have a copy of the DNA. Identify the end product of DNA replication in a human somatic cell. A. 23 chromosomes B. 46 chromosomes C. 23 pairs of chromosomes D. 23 pairs of sister chromatids Outline the role of the following enzymes in DNA replication. Enzyme Helicase DNA Polymerase Role Unwinds DNA by breaking the hydrogen bonds between the complementary base pairs. This creates the replication fork. DNA polymerase joins together the nucleotides together with strong covalent phosphodiester bonds To form a new complementary polynucleotide strand. State the kind of bonds formed between nucleotides as they are added to the DNA molecule in replication. Covalent phosphodiester bonds There are approximately 3.0 x 109 (3 billion) base pairs in the human genome. During replication, new nucleotides are added to the DNA molecule at a rate of about 3000 bases per second. At that rate, it would take about 11 days to make a copy of the DNA in a human cell. However, laboratory observations of mitosis show that it only takes a few hours. State how this is possible. Because there are many origins of replication in eukaryote DNA, which means that many parts of the DNA molecule are replicated simultaneously (at the same time).
  • 2. I-Shou International School IB Biology Outline the process of DNA replication making reference to helicase and DNA polymerase. 1) Helicase unwinds the DNA molecule by breaking the hydrogen bonds between complementary base pairs. This creates the replication fork. 2) Plentiful, free (unattached) nucleotides in the nucleus are available for the formation of polynucleotides. 3) DNA polymerase joins the free nucleotides to the growing polynucleotide chain by creating strong covalent phosphodiester bonds. 4) The new nucleotide is complementary to the base in the template strand. The two bases form hydrogen bonds between them. 5) The newly formed DNA molecule (with one “old” strand and one “new” strand) rewinds into a double helix. There are now two copies of the DNA behind the replication fork, whereas before replication there was just one. 3.4.2 Explain the significance of complementary base pairing in the conservation of the base sequence of DNA. Label the bases in the following DNA molecule with A, C, G, or T. State how the complementary strands are held together. C T G G C C A G G C (adapted from http://www.colorado.edu/Outreach/BSI/k12activities/dnastructureteacher.html)
  • 3. I-Shou International School IB Biology Explain how complimentary base pairing provides a mechanism for replication. The DNA sequence is preserved from one generation to the next. T only pairs with A, C only pairs with G. This means that the bases in the template strand will pair with its complement only, and thus providing a mechanism for replication. 3.4.3 State that DNA replication is semi-conservative. Define the following types of replication and identify which one happens inside of cells. Conservative Semi-conservative Dispersive the original molecule is completely retained an a new molecule (two new polynucleotide chains are combined). each of the new double helices contains one of the original polynucleotide chains. fragment of the original double helix serve as templates for the new DNA . The fragments are randomly arranged. State the name of the experiment that showed this. The Meselson-Stahl Experiment In 1958 Matthew Meselson and Frank Stahl (California Institute of technology) carried out the experiment which convinced everyone that the actual mechanism was semi-conservative as originally proposed by Watson & Crick.