Unit 10 part 1

Question 1

Cells can repair

Answer 1

their DNA

Question 2

who introduced the double helix

Answer 2

james watson and francis crick 1953
- prior identifying molecules of inheritance wasa. major problem.

Question 3

molecules of inheritance

Answer 3

dna

Question 4

Series of famous experiments showing the DNA is the genetic material

Answer 4

• Genetic Material: DNA or Protein?
• Frederick Griffith in 1928
• Alfred Hershey and Martha Chase in 1952
• Erwin Chargaff in 1950

Question 5

Griffith’s Experiment:

Answer 5

• Two strains of bacteria, one pathogenic and
  one harmless
• Transformation: change due to the introduction of foreign DNA
• People still thought protein was genetic material – a lot of heterogeneity and specificity of function

Question 6

Hershey and Chase’s Experiment

Answer 6

• More evidence for DNA as genetic material
• Studied viruses that infect bacteria, known as bacteriophage (phage)
• A virus is DNA or RNA enclosed by a protective capsid, often protein
• Experiment shows only one of the two components of phage (DNA or protein) enters an E. coli cell during infection
• They concluded that the injected DNA of the phage provides the genetic information

Question 6

• DNA is a polymer of nucleotides:
• Consisting of:

Answer 6

• Nitrogenous base * Sugar
• Phosphate group
• The nitrogenous bases can be adenine (A), thymine (T), guanine (G), or cytosine (C)

Question 7

Chargaff’s Rules

Answer 7

• In 1950, Erwin Chargaff reported that DNA composition varies from one species to the next
• Two findings became known as Chargaff’s rules:
• The base composition of DNA varies between species
• In any species, the number of A = T, and the number of G = C

Question 8

• Maurice Wilkins and Rosalind Franklin

Answer 8

• Using X-ray crystallography to study
  molecular structure
• Franklin produced a picture of the DNA molecule using this technique
• Franklin’s X-ray crystallographic images of DNA allowed Watson to deduce that DNA was helical

Question 9

Watson used the X-ray images to deduce:

Answer 9

• Helical structure
• Width of the helix
• Spacing of the nitrogenous bases
• The pattern in the photo suggested:
• DNA molecule was made up of two strands, forming a double helix

Question 10

Watson built a model in which

Answer 10

the backbone were antiparallel
Pairing a purine (AorG) with a pyrimidine (CorT) resultedin a uniform width consistent with the X-ray data

Question 10

The Watson-Crick model explains Chargaff’s rules:

Answer 10

in any organism the amount of A = T, and the amount of G = C

Question 11

DNA Double Helix

Answer 11

• Right-Handed Helix
• Antiparallel Sugar Phosphate backbone * Nitrogenous bases
• Major / minor groove
• Hydrogen bonds

Question 12

DNA replication and Repair
* The relationship between structure and function is evident in the double helix

Answer 12

• Watson and Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material

Question 13

The Basic Principle: Base Pairing to a Template Strand

Answer 13

• The two strands of DNA are complementary
• Each strand acts as a template for a new strand in replication
• In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules

Question 14

Competing Models of DNA Replication

Answer 14

• conservative model
• dispersive model
• semiconservative model (watson and crick)

Question 15

• Conservative model -

Answer 15

the two parent strands rejoin
( one brand new one original ) first replication
(3 brand new 1 new) second replication

Question 16

dispersive model

Answer 16

each strand is a mix of old and new
- first replication is 50/50 new old for both
- second replication is 25/25 each
- splotchy

Question 17

semiconservative model watson and crick

Answer 17

When a double helix replicates, each daughter molecule will have one old strand (“conserved” from the parent molecule) and one newly made strand

• 1:1 (new to old ratio) first replication
• 2 1:1(new old ratio) then 2 brand new second replication

Question 18

Determining model of DNA replication

Answer 18

Experiments by Matthew Meselson and Franklin Stahl supported the semiconservative model

• bacteria cultured in medium,
• bacteria transfered to medium with a lighter isotop, - dna was centrifuged,
• centrufuged again where the less dense and more dense portions separated

Question 19

Prokaryotic DNA Replication

Answer 19

• The copying of DNA is rapid and accurate * Numerous proteins and enzymes
  contribute to DNA replication
• Replication begins at sites called origins of replication (ori)
• Where the two DNA strands are separated, opening up a replication “bubble”

Question 20

Eukaryotic DNA Replication

Answer 20

• A eukaryotic chromosome may have hundreds or even thousands of origins of replication
• Replication proceeds in both directions from each origin, until the entire molecule is copied

Question 21

Replication fork:

Answer 21

at the end of each replication bubble
* Y-shaped region where new DNA strands are elongating
* Paired (one on either side of replication bubble)

Question 22

Helicase:

Answer 22

enzyme that untwist the double helix at the replication forks

Question 23

• Single-strand binding proteins:

Answer 23

bind to and stabilize single- stranded DNA

Question 24

• Topoisomerase

Answer 24

relieves the strain of twisting of the double helix by breaking, swiveling, and rejoining DNA strands

cleaves the dna strand

Question 25

DNA Polymerases:

Answer 25

• Enzymes that catalyze synthesis
  of new DNA at replication fork
• Require a primer (so they can add nucleotides) and a DNA template strand