DNA Structure

Question 1

What are the four bases found in DNA?

Answer 1

Adenine, Thymine, Cytosine and Guanine

Question 2

Which two bases are the purines?

Answer 2

Adenine and Guanine are the larger purines

Question 3

Which bases are the pyrimidines?

Answer 3

Cytosine and Thymine are the smaller pyrimidines (also Uracil in RNA)

Question 4

How many rings do purines have?

Answer 4

Two

Question 5

How many rings do pyrimidines have?

Answer 5

One

Question 6

How many hydrogen bonds are formed between Cytosine and Guanine?

Answer 6

Three

Question 7

How many hydrogen bonds are formed between Adenine and Thymine?

Answer 7

Two

Question 8

Which form of chromatin stains lightly?

Answer 8

Euchromatin

Question 9

Which form of chromatin stains dark?

Answer 9

Heterochromatin

Question 10

What is a nucleosome?

Answer 10

A nucleosome consists of a length of DNA wrapped around a histone core

Question 11

What is the ‘beads on a string’ structure?

Answer 11

This is where DNA is wrapped around 8 histones twice to form nucleosomes (euchromatin)

Question 12

What is the solenoid stucture?

Answer 12

This is where the DNA is packaged as a 30nm fibre of chromatin as a result of the helical winding of nucleosomes (heterochromatin)

Question 13

In which form of chromatin are genes expressed?

Answer 13

Euchromatin (beads on a string)

Question 14

In which form of chromatin are genes not expressed?

Answer 14

Heterochromatin (solenoid)

Question 15

How many chromosomes are in a human diploid cell?

Answer 15

46 chromosomes (23 pairs)

Question 16

How many chromosomes are in a human haploid cell (gamete)?

Answer 16

23 chromosomes

Question 17

What is a gene?

Answer 17

A gene is a sequence of nucleotides that carries the code for proteins. They have a specific chromosomal location.

Question 18

What is the human genome?

Answer 18

The entire DNA sequence of a human

Question 19

How many chromosomes in the human genome?

Answer 19

24 (22 autosomes plus X and Y)

Question 20

What is a nucleotide?

Answer 20

Base + Sugar + Phosphate

Question 21

What is a nucleoside?

Answer 21

Base + Sugar (no phosphate)

Question 22

What are the two types of pentose sugars?

Answer 22

Ribose (in RNA) and Deoxyribose (in DNA)

Question 23

For example, what is the nucleoside and nucleotide associated with Adenine in RNA and DNA?

Answer 23

Nucleoside in RNA = Adenosine
Nucleotide in RNA = Adenosine monophosphate (AMP)

Nucleoside in DNA = Deoxyadenosine
Nucleotide in DNA = Deoxyadenosine monophosphate (dAMP)

Question 24

By what bonds are adjacent nucleotides joined?

Answer 24

Phosphodiester bonds

Question 25

The DNA chain has polarity. What are the two ends called?

Answer 25

It goes from 5’ to 3’. 5’ is the phosphate end and 3’ is the end with the OH

Question 26

Name two features of the two strands of DNA

Answer 26

Complementary and anti-parallel

Question 27

How long is DNA vs what is the size of a cell nucleus?

Answer 27

2 metres of DNA into a 6 micrometre cell nucleus

Question 28

What is the width of DNA?

Answer 28

2 nanometres

Question 29

What is the total length of DNA per cell?

Answer 29

2 metres

Question 30

What is on the 5’ end?

Answer 30

Phosphate

Question 31

What is on the 3’ end?

Answer 31

OH

Question 32

What is the difference between the major and minor groove?

Answer 32

The major groove occurs where the backbones are far apart, the minor groove occurs where they are close together.

Question 33

Which groove of the DNA is easier for proteins to bind to?

Answer 33

Major groove because the backbones are not in the way.

Question 34

How many base pairs in one complete turn?

Answer 34

10

Question 35

What is the space between the base pairs?

Answer 35

0.34nm

Question 36

In which groove are bases exposed?

Answer 36

Major