DNA Replication

Replication is the mechanism by which living organisms copy their DNA. Although both strands of a DNA double helix are copied during replication, this animation shows the process that occurs for just one strand. This strand is called the template. An enzyme called a polymerase, which for simplicity is not shown, assembles a chain of nucleotides that pair with those of the existing DNA strand. During replication, adenine always pairs with thymine by two hydrogen bonds, shown as green dashed lines, and guanine always pairs with cytosine by three hydrogen bonds. Because of the specificity with which base pairing occurs, the old strand and the new strand are said to be complementary to one another. The new strand does not have the same sequence as the old strand, but a complementary sequence. However, it should be noted that the two DNA double helices that result from replication are exactly identical.

Question 1: The enzyme _________ is responsible for assembling a chain of nucleotides that pair with those of the existing DNA strand.
  1. sythase
  2. gyrase
  3. polymerase
  4. endonuclease


Answer 1

Answer - (c) Polymerase

Question 2: Adenine pairs with thymine by ________ hydrogen bonds and guanine pairs with cytosine by _________ hydrogen bonds.
  1. 1,2
  2. 2,1
  3. 3,2
  4. 2,3


Answer 2

Answer - (d) 2,3

Question 3: True or False? The new strand has the same sequence as the old strand while also being complimentary to the old strand.
  1. True
  2. False


Answer 3

Answer - (b) False

Question 4: True or False? The new strand does not have the same sequence as the old strand, but does have the complementary sequence.
  1. True
  2. False


Answer 4

Answer - (a) True