Biology  by Bradford
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6.2 DNA Replication: revision map

The subtopic in the middle and four tasks round it: label a diagram, complete a table, put a process in order and fill 10 gaps. Every box rests on a learning objective of the topic in the AP Biology course and exam description. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.

Unit 6 practice questionsThe whole Unit 6 map

Topic 6.2

DNA Replication

AP Biology ยท Unit 6 Gene Expression and RegulationName

6.2.AA replication fork

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  1. 1
  2. 2
  3. 3
  4. 4
  5. 5

6.2.ACopying a stretch of DNA

Number the steps in order.

  1. Helicase unwinds the helix at an origin, opening a replication fork.
  2. Primase lays down RNA primers on the template strands.
  3. Primers are replaced with DNA and ligase seals the fragments.
  4. DNA polymerase extends each primer, 5' to 3'.
  5. The leading strand is made in one piece; the lagging strand in short fragments.
Topic 6.2DNA Replication

6.2.AThe replication team

EnzymeJob
unwinds the double helix by breaking hydrogen bonds
makes the short RNA primer that gives polymerase a 3' end to extend
adds nucleotides to the 3' end of the new strand, reading the template 3' to 5'
joins the Okazaki fragments of the lagging strand
Topoisomeraserelieves the twisting ahead of the fork

6.2.ASemiconservative

Each new DNA molecule has one old strand and one new strand, so replication is . Meselson and Stahl showed this by growing bacteria in heavy nitrogen and then in light nitrogen: after one generation all the DNA was of intermediate density. DNA polymerase can only add nucleotides to a 3' end, so one strand is made continuously towards the fork and the other, the lagging strand, in fragments away from it. Eukaryotic chromosomes have many origins, so large genomes are copied in a reasonable time.

Word bank DNA polymerasehelicaseHelicaseleading strandLigaseOkazaki fragmentPrimaseRNA primersemiconservative

Answer key

Every box on the sheet with its gaps filled in, as the subtopic reads in full.

  1. LabelA replication fork

    1. helicase
    2. DNA polymerase
    3. leading strand
    4. Okazaki fragment
    5. RNA primer

  2. TableThe replication team

    EnzymeJob
    Helicaseunwinds the double helix by breaking hydrogen bonds
    Primasemakes the short RNA primer that gives polymerase a 3' end to extend
    DNA polymeraseadds nucleotides to the 3' end of the new strand, reading the template 3' to 5'
    Ligasejoins the Okazaki fragments of the lagging strand
    Topoisomeraserelieves the twisting ahead of the fork

  3. OrderCopying a stretch of DNA

    1. Helicase unwinds the helix at an origin, opening a replication fork.
    2. Primase lays down RNA primers on the template strands.
    3. DNA polymerase extends each primer, 5' to 3'.
    4. The leading strand is made in one piece; the lagging strand in short fragments.
    5. Primers are replaced with DNA and ligase seals the fragments.

  4. GapsSemiconservative

    Each new DNA molecule has one old strand and one new strand, so replication is semiconservative. Meselson and Stahl showed this by growing bacteria in heavy nitrogen and then in light nitrogen: after one generation all the DNA was of intermediate density. DNA polymerase can only add nucleotides to a 3' end, so one strand is made continuously towards the fork and the other, the lagging strand, in fragments away from it. Eukaryotic chromosomes have many origins, so large genomes are copied in a reasonable time.