Chapters 10 and 11 - DNA: The Chemical Nature of the Gene and Chromosome Structure

Question 1

What are the functions of genetic material?

Answer 1

• Must replicate, control growth and development of organism, and allow organism to adapt to changes in environment

Question 2

What experiment proved that DNA is the genetic material? How?

Answer 2

• Griffith’s experiment
• A substance in the heat-killed virulent bacteria genetically transformed type IIR bacteria into live, virulent type IIIS bacteria
• Bacterial transformation (DNA sensitive process)

Question 3

Describe the Avery-MacLeod-McCarty experiment.

Answer 3

• Find chemical nature of transforming substance
• Treat samples of transformed bacteria with enzymes (RNase, protease, and DNase)
• Add treated samples to non-virulent bacteria
• Cultures treated with protease or RNase contained transformed bacteria, but the culture treated with DNase does not
• Only DNase destroyed transforming substance, it is DNA

Question 4

What substance - RNA or protein - carries the genetic material in tobacco mosiac virus?

Answer 4

• Degrade both types of TMV to yield RNA and coat proteins
• Mix 2 types of protein to create hybrid viruses (red coat and blue RNA, vice versa)
• Infect tobacco with hybrids
• Type of RNA in hybrid parent determines RNA and protein of progeny
• RNA is genetic material of TMV

Question 5

What are nucleic acids composed of?

Answer 5

Nucleotides

Question 6

What does every nucleotide have?

Answer 6

• Nitrogen-containing base (Adenine, Thymine, Guanine, Cytosine, Uracil)
• Pentose sugar (deoxyribose, ribose)
• Phosphate (phosphodiester bond)

Question 7

What is the difference between deoxyribose and ribose sugars?

Answer 7

• Ribose has -OH on 2’ carbon where Deoxyribose has -H

Question 8

What are the purines?

Answer 8

• Larger; double rings

- Adenine, Guanine

Question 9

What are the pyrimidines?

Answer 9

• Smaller, single rings

- Cytosine, Thymine, Uracil

Question 10

What type of bonds are nucleotides joined by?

Answer 10

• Phosphodiester
• Links C-3 of one sugar to C-5 of another
• Same bond in RNA

Question 11

How was the structure of DNA deciphered? By who?

Answer 11

• Erwin Chargaff
• Determined precise base composition of different types of DNA
• A + G = T + C
  OR
• Purines = pyrimidines

Question 12

What did William Astbury discover?

Answer 12

• X-ray diffraction analysis showed that DNA is a polymer of stacked bases

Question 13

What did Rosalind Franklin and Maurice Wilkins find?

Answer 13

• DNA is a helix

- Photograph 51

Question 14

What is the Watson-Crick Model?

Answer 14

Background:
- %A = %T
- %G = %C
- Helical structure
- Bases stack like coins over each other
Assumptions:
- DNA is double helix
- 2 strands were anti-parallel
- Sugars form phosphate backbone
- Bases held together by H bonds

Question 15

How many H bonds are between T and A?

Answer 15

2

Question 16

How many H bonds are between C and G?

Answer 16

3

Question 17

What is the width of a DNA molecule (phosphate to phosphate on other strand)?

Answer 17

2 nm

Question 18

How many base pairs are there per turn of the helix?

Answer 18

10

Question 19

What is the distance between base pairs in DNA?

Answer 19

0.34 nm

Question 20

What is the major groove of a DNA molecule?

Answer 20

Space farthest from tight turn

Question 21

What is the minor groove in DNA?

Answer 21

Tight turn

Question 22

How does DNA become super-coiled?

Answer 22

• Relaxed, nicked, circular DNA is rotated 360 degrees
• One 360 degree left-handed rotation
• Can return to circular if you cut one strand, and do a 360 degree right-handed rotation

Question 23

How many times must E. coli DNA be condensed? How big is E. coli DNA and cell?

Answer 23

• Condensed more than 1000 times and folded into a chromosome
• Monoploid
• DNA = 1.5 mm circle
• Cell = 2 micrometer x 1 micrometer

Question 24

How is bacterial chromosome formed? What are the sizes of each stage?

Answer 24

• DNA is folded and supercoiled with help of RNA and proteins
• Circular unfolded = 350 micrometers
• 40-50 loops = 30 micrometers
• Supercoiled/folded = 2 micrometers

Question 25

How many nucleotides are in haploid human DNA?

Answer 25

3.3 x 10^9 nucleotides

Question 26

How many chromosomes are in the haploid genome?

Answer 26

23

Question 27

What is the total length of the diploid human genome?

Answer 27

2 meters

Question 28

What is the diameter of a human nucleus?

Answer 28

5-10 micrometers

Question 29

What must be done to human DNA?

Answer 29

Must be tightly packed into multiple chromosomes

Question 30

What do eukaryotic chromosomes consist of?

Answer 30

• One large linear DNA molecule
• 5 histones
• A divergent group of non-histone proteins

Question 31

What is the first level of DNA packaging in chromatin?

Answer 31

Nucleosomes

• 146 bps of DNA wrapped as 1 3/4 turns around octamer of histones
• Linker DNA in between, varying in length from 8-114 nucleotide pairs

Question 32

What is the approximate width of a histone?

Answer 32

11 nm

Question 33

What does the nucleosome core consist of?

Answer 33

• 2 molecules of each of 4 histones

- Protruding histone tails

Question 34

What does a complete nucleosome contain?

Answer 34

• Octamer of histones
• Histone H1
• Wrapped in DNA

Question 35

What is the second level of chromatin packaging?

Answer 35

• 30 nm chromatin fiber

- Nucleosomes fold together

Question 36

What is the third level of chromatin packaging?

Answer 36

• Inter-phase chromosomes

- Attached to chromosome scaffold (approx. 300 nm)

Question 37

What does the metaphase chromosome look like?

Answer 37

• Another stage of DNA packaging
• Looks like standard chromosome X
• Segregated into domains by scaffolds composed of nonhistone chromosomal proteins