Bi107-Study Guide 4

Study Guide 4

Dr. Barbara Gilson Hoberman

Bi 107

Chapter 16

1. Describe the Watson and Crick model of DNA and incorporate the work of Franklin and Chargaff.

• DNA is double stranded and is a helix.

• Sugars and phosphates are the backbone.

• The bases project into the interior of the model.

• One turn of the helix is 3.4nm & contains 10 base pairs.

• The base pairs are stacked .34nm apart.

• The helix is 2.0nm in width

• One purine is paired with one pyrimidine.

o Two purines is greater than 2.0nm.

o Two pyrimidines are less than 2.0nm.

• The base pairs are specific (A=T; G=C)

• The strands are complementary and antiparallel.

2. What is meant by semiconservative replication of DNA. Describe the

experiments of Meselson and Stahl using isotopes of nitrogen to prove that

replication is semiconservative rather than conservative or dispersive.

Semiconservative replication- A double helix of DNA unwinds and the two parental strands separate. Each parental strand serves as a template for the synthesis of a New complimentary stand. Each new “daughter” DNA molecule consists of one old parental strand and one brand of the new strand.

Meselson and Stahl concluded that replication of that replication of DNA duplex involves building new molecules by separating parent strands and then adding new nucleotides to form the complementary strand on each of these templates.

3. Regarding eukaryotic DNA replication, define each of the following and tell its role in replication:

a) origin of replication: a particular sequence in a genome at which replication is initiated

b) bidirectional replication: a type of DNA replication where replication is moving along in both directions from the starting point. This creates two replication forks, moving in opposite directions.

c) replication fork: a Y-shaped...