2.7

Question 1

Roslin Franklin’s Xray diffraction model suggested what key points about the three-dimensional
structure of DNA?

Question 2

Is DNA a left-handed or right-handed helix?

Question 3

What does it mean that the two strands of DNA are anti-parallel?

Question 4

What is the “backbone” that each strand of DNA made up of and what is in the middle?

Question 5

Describe the bonds that hold the nucleotides of the same strand together and contrast these with the
bonds that hold the two strands together:

Question 6

How does a 5’ end differ from a 3’ end?

Question 7

WHat is the starting place of replication called in prokaryotes?
What shape is the DNA in prokaryotes?
How many initiation points are there?
Does replication proceed in only one direction or in both directions from the origin?

Question 8

Where does replication begin in eukaryotes?
What shape is the DNA in eukaryotes?
How many initiation points are there in eukaryotes?
Does replication proceed in only one direction or in both directions from the origin?

Question 9

What is a replication fork?

Question 10

Helicase

Question 11

Single stranded binding proteins (SSBPs)

Question 12

Topoisomerase

Question 13

Primase

Question 14

The enzymes that replicate DNA cannot initiate a polynucleotide, they can only add to an existing
chain. This chain is not actually DNA, it is _______________ and called primer (5-10 nucleotides).

Question 15

The next nucleotide is always added to the _______________end of the primer and growing
polynucleotide chain.

Question 16

Building a DNA molecule requires energy. This energy is part of a set of reactions related to the last
two _________________ that are lost from each nucleotide before being incorporated

Question 17

Why are there “leading strands” and “lagging strands” during replication

Question 18

Does each Okazaki fragment have its own RNA primer?

Question 19

DNA pol I

Question 20

DNA ligase

Question 21

DNA sequencing

Question 22

DNA polymerase makes mistakes during replication. When it does happen, can mistakes be
repaired? If so, how?

Question 23

double helix

Answer 23

the form of native DNA, referring ot its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape

Question 24

antiparallel

Answer 24

referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5’ to 3’ directions)

Question 25

semiconservative model

Answer 25

type of DNA replication in which the replicated double helix consists of one old strand, derived form the parental molecule, and one newly made strand

Question 26

replication fork

Answer 26

a y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are being synthesized

Question 27

helicases

Answer 27

an enzyme that untwists the double helix of DNA at replication forks, separating the two strands and making them available as template strands

Question 28

single-strand binding proteins

Answer 28

a protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA

Question 29

topoisomerase

Answer 29

an enzyme that helps relieve strand of untwistng the double helix by breaking, swiveling, and rejoining DNA strands

Question 30

primer

Answer 30

short polynucleotide with a free 3’ end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication

Question 31

primase

Answer 31

an enzyme that joins RNA nucleotides to make a primer during DNA replication, using the parental DNA strand as a template

Question 32

DNA polymerase

Answer 32

an enzyme that catalyzes he elongation of new DNA by the addition of nucleotides to the 3’ end of an existing chain

Question 33

leading strand

Answer 33

the new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5’ to 3’ direction

Question 34

lagging strand

Answer 34

a discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5’ to 3’ direction away from the replication fork

Question 35

okazaki fragments

Answer 35

a short segment of DNA synthesized away from the replication fork on a template strand during DNA replication. Many such segments are joined together to make up the lagging strand of newly synthesized DNA

Question 36

DNA ligase

Answer 36

a linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3’ end of one DNA fragment tot eh 5’ end of another DNA fragment

Question 37

DNA sequencing

Answer 37

determining the order of nucleotide bases in a gene of DNA fragment