DNA and DNA packaging

Question 1

What is the chemical structure of guanine?

Answer 1

Question 2

What is the chemical structure of cytosine?

Answer 2

Question 3

What is the chemical structure of adenine?

Answer 3

Question 4

What is the chemical structure of thymine?

Answer 4

Question 5

What are pyrimidines?

Answer 5

A type of base derived from a six-membered pyrimidine ring i.e. C, T and U

Question 6

What are purines?

Answer 6

Bases that have a second five-membered ring fused to the first six-membered ring, i.e. A and G

Question 7

How many hydrogen bonds are there between adenine and thymine/uracil?

Answer 7

2

Question 8

How many bonds are there between guanine and cytosine?

Answer 8

3

Question 9

What is nucleic acid?

Answer 9

Any of a group of long, linear macromolecules, either DNA or various types of RNA, that carry genetic information directing all cellular functions: composed of linked nucleotides

Question 10

What are the two main types of nucleic acid?

Answer 10

Ribonucleic acid and deoxyribonucleic acid

Question 11

What is a nucleoside?

Answer 11

A sugar (ribose/deoxyribose) covalently attached to a base

Question 12

What is the general chemical structure of a nucleotide?

Answer 12

Question 13

What do the 5’ and 3’ ends correspond to in DNA?

Answer 13

The 5’ indicates the end with a phosphate group and the 3’ the end with the hydroxyl group

Question 14

The two strands in DNA run _____ to one another

Answer 14

Antiparallel

Question 15

What type of bonds link the sugars together in the sugar-phosphate backbone?

Answer 15

Phosphodiester bonds

Question 16

What novel bases are involved in methylation and demethylation of DNA as a means of regulatory control?

Answer 16

5mC (5-Methylcytosine) and 5hmC (5-Hydroxymethylcytosine)

Question 17

Approximately how many nucleotides are there in the human genome?

Answer 17

6x10⁹in 46 chromosomes

Question 18

What proteins assist in chromosome packaging?

Answer 18

**Histones **and non-histone chromosomal proteins

Question 19

What is chromatin?

Answer 19

DNA that is wrapped around protein complexes

Question 20

What type of packaging are histones associated with?

Answer 20

The nucleosome, which has a ‘beads on a string’

Question 21

What is a nucleosome core particle?

Answer 21

One unit in the nucleosome, which consists of a histone octamer and DNA wrapped around it two times

Question 22

How many proteins make up a histone?

Answer 22

8, two lots of:

• H2A
• H2B
• H3
• H4

Question 23

What is the next stage of DNA packaging after the nucleosome?

Answer 23

Chromatin fiber

Question 24

What does the chromatin fiber form of packaging depend on?

Answer 24

A 5th histone protein called **H1 **which is thought to pull the nucleosome into a regular repeating array

Question 25

Chromatin fiber can be further condensed into _________ _________

Answer 25

Lampbrush chromosomes

Question 26

What is the structure of a lampbrush chromosome?

Answer 26

The 30nm chromatin fiber loops out and attaches to a central scaffold.

Question 27

During ________, lampbrush chromosomes condense even further into ________

Answer 27

During prometaphase, lampbrush chromosomes condense even further into chromatids

Question 28

Define heterochromatin

Answer 28

Highly condensed chromatin visible by light microscopy in interphase eukaryotes

Question 29

Define euchromatin

Answer 29

Less condensed chromatin that contains 30 nm fibers and loops.

Question 30

At what stage do chromosomes become visible in the eukaryotic cell?

Answer 30

Metaphase