Lecture 1: DNA, Chromosomes, and Genomes 1

Question 1

What is on the 5’ end of DNA?

Answer 1

phosphoryl group

Question 2

What is on the 3’ end of DNA?

Answer 2

hydroxyl group

Question 3

What is the sugar in DNA?

Answer 3

deoxyribose

Question 4

What is a nucleotide?

Answer 4

5 carbon sugar and nitrogenous base linked via glycosidic bond

Question 5

What are the purines?

Answer 5

adenine and guanine

Question 6

What are the pyrimidines?

Answer 6

cytosine and thymine

Question 7

How many hydrogen bonds between A-T? G-C?

Answer 7

A-T: 2 H bonds

G-C: 3 H bonds

Question 8

What is a genome?

Answer 8

complete set of information in an organism’s DNA

Question 9

Where is DNA enclosed?

Answer 9

nucleus

Question 10

What is chromatin?

Answer 10

DNA + protein

Question 11

Where to chromosomal translocations frequently occur?

Answer 11

cancer cells

Question 12

When do translocations occur?

Answer 12

during an abnormal recombination event

Question 13

What information is found on chromosomes?

Answer 13

Genes and interspersed DNA that does not contain genes

Question 14

What is a gene?

Answer 14

encoding proteins and encoding RNA molecules

Question 15

What are chromosomes like in interphase?

Answer 15

they are replicated here, and they are decondensed and can’t be easily distinguished

Question 16

What happens in mitosis?

Answer 16

Chromosomes are highly condensed and separated into two daughter nuclei

Question 17

What are the requirements for a chromosome?

Answer 17

DNA replication origin
Centromere
Telomeres

Question 18

What is a nucleosome?

Answer 18

where most basic unit of chromosome packing occurs

“beads on a string”

Question 19

How many and what kind of histone proteins make up a nucleosome core?

Answer 19

8 histone proteins

2 molecules of each: H2A, H2B, H3, H4

Question 20

What is a histone?

Answer 20

small proteins with common structural motif called histone fold

Question 21

How many turns is DNA wrapped around nucleosome core?

Answer 21

1.7 turns

Question 22

What is the importance of the N terminal amino acid tail that extends out from the nucleosome core?

Answer 22

subject to covalent modification and important for chromatin regulation

Question 23

What are three interactions that occur between DNA and histone?

Answer 23

• 142 hydrogen bonds between DNA and histone core at each nucleosome
• hydrophobic interactions
• salt linkages

Question 24

What amino acids make up 1/5 of the histone residues?

Answer 24

arginine and lysine, neutralizes the negatively charge DNA backbone

Question 25

Are histone highly conserved?

Answer 25

yes (most changes would be lethal)

Question 26

What does it mean when saying nucleosomes are in a constant state of flux?

Answer 26

DNA is unwrapped in the nucleosome 4 times per second, and remains unwrapped 10-50 msec before tightening again

Question 27

What happens in nucleosome packing?

Answer 27

Formation of dense fibrous structure with diameter of 30 nm, unknown how fiber is formed

Question 28

What is the zig-zag model?

Answer 28

Theory that explains nucleosome packing

• stacking may be facilitated by histone tails
• Histone H1 “linker histone” is present in 1:1 ration with nucleosome cores

Question 29

How do histone tails help to condense chromatin?

Answer 29

tails are largely unstructured, suggests that they are highly flexible and helps with condensation of the packaging

Question 30

Describe histone H1

Answer 30

• linker histone
• larger than other histone proteins
• less conserved
• contacts both DNA and protein
• changes the path of DNA as it exits the nucleosome