DNA Structure

Question 1

Who discovered, in 1953, that DNA is a double helix?

Answer 1

Rosalind Franklin and Maurice Wilkins

Question 2

Who discovered, in 1949, the base-pairing proportions and DNA varies between species?

Answer 2

Erwin Chargaff

Question 3

In 1953, who discovered the organization of DNA + complimentary base-pairing?

Answer 3

James Watson and Francis Crick

Question 4

In 1958, who discovered DNA replication?

Answer 4

Matthew Meselson & Franklin Stahl

Question 5

Erwin Chargaff determined base pair proportions through what?

Answer 5

paper chromatography (he invented the technique)

Question 6

Ratio of A equals that of ___

Answer 6

T (adenine = thymine)

Question 7

Ratio of G equals that of ___

Answer 7

C (cytosine = guanine)

Question 8

In humans, cytosine and guanine are less or more present in the composition than adenine and thymine?

Answer 8

LESS C-G

MORE A-T

Question 9

DNA is a ___ acid.

Answer 9

nucleic

Question 10

The building blocks of DNA are____.

Answer 10

nucleotides

Question 11

What composes nucleotide?

Answer 11

5-carbon sugar (deoxyribose)
Phosphate group
Nitrogenous base

Question 12

What are purines bases ?

Answer 12

Adenine and Guanine (A & G)

Question 13

What are pyrimidines bases?

Answer 13

Cytosine, Thymine and Uracil (C & T & U)

Question 14

What does 2nd position of carbon molecule mean?

Answer 14

If nucleotide is RNA of DNA

Question 15

What happens in the 3rd position of carbon?

Answer 15

Incoming nucleotide binds during replication

Question 16

DNA chains are ___

Answer 16

antiparallel (5’to 3’ orientation)

Question 17

How did Rosalind Franklin and Maurice Wilkins discover that DNA is helical?

Answer 17

X-ray chrystallography (3D structure of DNA)

[X-ray diffraction of DNA double helix]

Question 18

Franklin had concluded that:
_____ and ____

However, organization of bases was unclear.

Answer 18

1. there were two antiparallel sugar-phosphate backbones

2. the nitrogenous bases paired in the molecule’s interior .

Question 19

Who in 1953
deduced the structure of DNA using evidence from:
Chargaff
Franklin/Wilkins
others?

Answer 19

James Watson and Francis Crick

Question 20

What did Watson and Crick show?

Answer 20

1. DNA composed of 2 chains of nucleotides, each in a helix
2. DNA chains run anti-parallel to each other
3. Purine-pyrimidine base pairs (keep distance between chain constant)

Question 21

What happened when they tried to match purine and purine?

Answer 21

too wide

Question 22

What happened when they tried to match pyrimidines and pyrimidines?

Answer 22

too narrow

Question 23

What happened when they tried to match purine + pyrimidine?

Answer 23

width consistent with X-ray data

Question 24

Two strands of DNA are _______.

Answer 24

Complementary

Question 25

What did Watson and Crick deduce from replication?

Answer 25

Each strand acts as template for building a new strand in replication

Parent molecule unwinds and 2 daughter strands are built based on complemetary base-pairing rules

Question 26

What are “daughter” DNA molecules?

Answer 26

each consisting of one parental strand and one new strand

Question 27

What is the dispersive model?

Answer 27

Each strand is a mix of old and new

Question 28

What is the semiconservative model?

Answer 28

Predicts each daughter molecule will have one old strand

Question 29

What is the conservative model?

Answer 29

Two parent strands rejoin

Question 30

Matthew Meselson & Franklin Stahl, 1958

Showed the process of DNA replication uses

Answer 30

semi-conservative replication

Question 31

Used gradient centrifugation, E.coli, and nitrogen isotopes

Answer 31

Matthew Meselson and Franlinn Stahl

Question 32

Meselson and Stahl concluded that the mechanism of DNA replication is the _____ model.

Answer 32

Semi-conservative model

OR
Each strand of DNA acts as a template for the synthesis of a new strand.