More Biological Molecules - DNA Replication

Question 1

DNA replicates by s___-c_________ r_________

Answer 1

DNA replicates by semi-conservative replication.

Question 2

What does semi-conservative replication ensure?

Answer 2

There’s genetic continuity between generations of cells.

I.e. the cells produced by cell division inherit their genes from their parent cells.

Question 3

What is the process of semi-conservative replication?

Answer 3

• The enzyme DNA HELICASE
  BREAKS the HYDROGEN BONDS
  between bases on the two polynucleotide DNA strands.
  This makes the helix UNWIND to form two single strands.
• Each original single strand acts as a TEMPLATE for a new strand.
  COMPLEMENTARY BASE PAIRING means that free-floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand – A with T, C with G.
• CONDENSATION REACTIONS join the nucleotides of the new strands together – catalysed by the enzyme DNA POLYMERASE.
  HYDROGEN BONDS FORM between the bases on the original and new strands.
• Each new DNA molecule contains ONE strand from the ORIGINAL DNA molecule and ONE NEW strand.

Question 4

DNA Polymerase moves __ ________ ____ along antiparallel strands.

Answer 4

DNA Polymerase moves IN OPPOSITE WAYS along antiparallel strands.

Question 5

What direction does DNA polymerase move in?

Answer 5

The active site of DNA polymerase is only complementary to the 3’ end of the newly forming DNA strand –
– so the enzyme can only add nucleotides to the new strand at the 3’ end.

This means that the new strand is made in a 3’ and 5’ direction and that DNA polymerase moves down the template strand in a 3’ to 5’ direction.

Because the strands in the double-helix are antiparallel, the DNA polymerase working on one of the template strands moves in the opposite direction to the DNA polymerase working on the other template strand.