Chapter 14

Question 1

Frederick Griffith

Answer 1

Studied streptococcus pneumoniae in rats
S virulent - causes disease. Polysaccharide coating
R - non virulent does not cause damage. No coating
Heat killed S and living R killed mouse through Transformation

Question 2

Avery, Macleod and McCarthy

Answer 2

Repeated Griffith’s experiment by removing protein, RNA, and DNA to see what R cells received coating. DNA supported as genetic material

Question 3

Hershey and Chase

Answer 3

Bacteriophages composed of only DNA and Protein. Used radioactive phosphorus in DNA and radioactive sulfur in protein. Protein became supernatant (liquid). DNA pellet in centrifuge spin. DNA is genetic material

Question 4

DNA composed of

Answer 4

Nucleic acid composed of 5-carbon sugar (deoxyribose) phosphate group, Nitrogenous base (A,T,C,G) attached to 5-carbon sugar, free hydroxyl group attached at 3- carbon sugar

Question 5

Purines and Pyrimidines

Answer 5

Purines - Adenine, Guanine. Double Ring
Pyrimidines - Cytosine, Thymine (DNA), Uracil (RNA). Single ring

Question 6

Bonds between nucleotides or helix

Answer 6

Nucleotide Phosphodiester
Helix Hydrogen bonds
Antiparallel 5’ to 3’ and the other 3’ to 5’

Question 7

Erwin Chargaff
Chargaff’s rule

Answer 7

Adenine = Thymine
Cytosine = Guanine
Always equal proportion of purines and pyrimidines

Question 8

Rosalind Franklin

Answer 8

Performed x-ray diffraction. Discovered DNA as double helix (helical).
Diameter of 2 nm and makes a complete turn every 3.4 nm

Question 9

James Watson and Francis Crick

Answer 9

Deduced with others work the structure of DNA as double helix with two polynucleotide chains running in opposite directions with hydrogen bonds between nitrogenous base.

Question 10

Number of H bonds

Answer 10

A and T have 2 H bonds
C and G have 3 H bonds

Question 11

Conservative model
Semiconservative model
Dispersive model

Answer 11

Conservative - Old with old strand. New strands together, two separate strands.
Semiconservative - Each double helix created gets one new strand and one old strand
Dispersive - Old and new strands mix parts, no fully new or fully old strands

Question 12

Meselson and Stahl

Answer 12

Bacteria grown in heavy isotope of nitrogen N15 and then put in N14. Supported semiconservative model, rejected other 2

Question 13

DNA Replication 3 steps

Answer 13

Initiation - replication begins
Elongation - new strands of DNA synthesized by DNA polymerase
Termination - replication is terminated
Zipping up coat

Question 14

DNA polymerase

Answer 14

Matches existing DNA bases with complementary nucleotides and links them. Add new bases to 3’ end of existing strands. Synthesizes in 5’ to 3’ direction

Question 15

RNA primer

Answer 15

Small sequence of RNA required to start replication
DNA primase makes RNA polymerase that makes RNA primer

Question 16

Replicon

Answer 16

DNA controlled by an origin

Question 17

DNA Polymerase 1 (pol 1)

Answer 17

Acts on lagging strand to remove RNA primers and replace with DNA
Has 5’ to 3’ exonuclease activity
Has 3’ to 5’ exonuclease activity (Proof reading)

Question 18

DNA polymerase II (pol II)

Answer 18

Involved in DNA repair processes
Has 3’ to 5’ exonuclease activity (Proof reading)

Question 19

DNA polymerase III (pol III)

Answer 19

Main replication enzyme.
Has 3’ to 5’ exonuclease activity (Proof reading)

Question 20

DNA helicases

Answer 20

uses ATP energy to unwind DNA and break H bonds for replication

Question 21

Single-strand-binding proteins (SBBs)

Answer 21

Coat strand to keep apart
Wedge strands apart, otherwise strands would go back together

Question 22

Topoisomerase (DNA gyrase)

Answer 22

Prevent supercoiling due to pressure. Binds and relieves torsion strain ahead of replication fork

Question 23

Lagging vs Leading strand

Answer 23

DNA polymerase can synthesize in only 1 direction
Leading strand synthesized continuously from initial RNA primer.
Lagging strand synthesized discontinuously with multiple RNA primers causing Okazaki fragments

Question 24

Replication fork

Answer 24

Partial opening of DNA strands as replication occurs

Question 25

Processivity

Answer 25

Beta subunit forms a sliding clamp to keep DNA pol III attached

Question 26

DNA ligase

Answer 26

Seals backbone. Gaps between Okazaki fragments on lagging strand.

Question 27

DNA Gyrase (Topoisomerase II)

Answer 27

unlinks 2 copies of DNA at termination site

Question 28

Telomeres

Answer 28

Specialized structures found on ends of eukaryotic chromosomes. Protects ends of chromosomes from nucleases (degrade DNA) and maintain integrity of linear chromosomes. Gradual shortening of chromosomes with each round of cell division

Question 29

Telomerase

Answer 29

Enzyme makes telomere section of lagging strand using an internal RNA template
Cancer cells generally show activation of telomerase

Question 30

DNA Repair

Answer 30

Specific - Targets a single kind of lesion in DNA and repairs only that damage
Nonspecific - Use a single mechanism to repair multiple kinds of lesions in DNA

Question 31

Mutagens

Answer 31

Any agent that increases the number of mutations above background levels (Radiation, chem, UV)

Question 32

Photorepair

Answer 32

Specific repair mechanism for UV light
Thymine dimers get to close and have extra bonds of T to T
Photolyase cleaves thymine dimer and absorbs light in visible range

Question 33

Excision Repair

Answer 33

Nonspecific. Damaged region removed and replaced by DNA synthesis
1 Recognition of damage
2 Removal of damaged region
3 Resynthesize using the information on undamaged strand as template