Intro to DNA (MCBG 1)

Question 1

What chromosomes do normal humans have?

Answer 1

22 pairs of autosomes and 1 pair of allosomes

Question 2

What is heterochromatin?

Answer 2

DNA that is tightly packaged around the histone, so the genes are not expressed

Question 3

What is euchromatin?

Answer 3

Beads on a string model of DNA, so genes are expressed as the DNA is loosely packaged

Question 4

What is a nucleosome?

Answer 4

A section of DNA wrapped twice around a histone core

Question 5

What is the DNA between histones called?

Answer 5

Linker DNA

Question 6

How many proteins make up a histone?

Answer 6

8 (so it’s an octamer)

Question 7

What is a solenoid?

Answer 7

A section of heterochromatin

Question 8

Are genes expressed in chromosomes?

Answer 8

No

Question 9

What’s the difference between nucleotides and nucleosides?

Answer 9

Nucleotides are a base + sugar + phosphate, whereas a nucleoside is only a base + sugar

Question 10

What’s the difference between ribose and n-deoxyribose? What is n?

Answer 10

n=2, as the second carbon in ribose has an OH attached whereas in 2-deoxyribose it has a H

Question 11

What’s the difference between purines and pyrimidines?

Answer 11

Purines have two rings (adenine, guanine) (nucleoside ends in -sine) whereas pyrimidines have just one (cytosine, uracil, thymine) (nucleoside ends with -dine)

Question 12

Which nitrogenous bases are zwitterions?

Answer 12

Cytosine and guanine

Question 13

How are nucleotides joined?

Answer 13

Phosphodiester bonds between C5 and C3 of the pentose sugar

Question 14

Which way is the DNA chain usually written?

Answer 14

5’ (prime) to 3’

Only the top strand which runs 5’ to 3’ is written by convention

Question 15

What is at each end of a DNA chain?

Answer 15

At 5’ end - phosphate group

At 3’ end - OH group

Question 16

What is the name given to the way a DNA double helix twists?

Answer 16

Right handed helix

Question 17

How does the secondary structure of DNA affect gene expression?

Answer 17

In the major groove (bigger gap) genes are expressed, in the minor groove they aren’t

Question 18

Describe the cell cycle

Answer 18

1) Mitosis - cell division
2) G1 - cell content replication
3) S - DNA replication
4) G2 - double check and repair

Question 19

How does DNA polymerase catalyse the start of DNA replication?

Answer 19

It separates DNA strands (dNMP)n and catalyses the reaction of adding a deoxynucleoside triphosphate (dNTP) to the 3’ end of a DNA strand, extending the chain ((dNMP)n+1 and releasing a pyrophosphate (PPi) which is then hydrolysed by DNA polymerase to break it down into inorganic phosphate to release energy

Question 20

How did they first discover DNA replication?

Answer 20

Through circular DNA in prokaryotes

Question 21

What are the three steps of DNA replication in prokaryotes?

Answer 21

Initiation, elongation, termination

Question 22

What is initiation in terms of DNA replication in prokaryotes? What does it require?

Answer 22

Recognition of origin of replication
Requires recruitment of DNA polymerase plus other specific proteins
Requires a ‘kick-start’ by primase (as DNA polymerase can only extend a 3’ end)

Question 23

Which way does DNA polymerase read DNA?

Answer 23

3’ to 5’, as it has to add a dNTP on the 3’ end

Question 24

What breaks the bonds between base pairs, and what are those bonds called?

Answer 24

DNA Helicase

Hydrogen bonds

Question 25

What are the two strands which are formed from the antisense strand called during DNA replication?

Answer 25

Lagging strand and Leading strand (continuous)

Question 26

What are sections of replicated DNA strands called?

Answer 26

Okazaki fragments

Question 27

What joins Okazaki fragments?

Answer 27

DNA Ligase