Introduction to DNA

Question 1

What is heterochromatin and what does it look like under an electron microscope?

Answer 1

Densely packed form of chromatin

Looks darker

Question 2

What is euchromatin and what does it look like under an electron microscope?

Answer 2

Lightly packed form of chromatin

Looks lighter

Question 3

What is the shape of DNA?

Answer 3

Right handed double helix

Question 4

What is a gene?

Answer 4

A section of DNA that codes for a protein

Question 5

How do you fit 2 metres of DNA into a 6 micrometre cell nucleus?

Answer 5

DNA is wrapped around histones to form a nucleosome

30nm of nucleosomes is a solenoid

Question 6

What is the human genome?

Answer 6

The entire DNA sequence of a human

22 and 2 sex chromosomes

Question 7

What are the two nucleic acids?

Answer 7

DNA and RNA

Question 8

What is a polynucleotide?

Answer 8

Linear polymer of nucleotides

E.g. DNA and RNA

Question 9

What is a nucleoside?

Answer 9

Sugar and base

Question 10

What is a nucleotide?

Answer 10

Sugar, base and phosphate

Question 11

Which is the difference between ribose and deoxyribose?

Answer 11

Ribose has two OH on carbon 2 and 3

Deoxyribose has a H and OH on carbons 2 and 3

Question 12

What bond links together nucleotides?

Answer 12

Phosphodiester bonds

Question 13

What bases are purine?

Answer 13

Adenine and guanine

Question 14

What bases are pyrimidine?

Answer 14

Thymine, cytosine and uracil

Question 15

What is at the 5’ end of a DNA chain?

Answer 15

Phosphate

Question 16

What is at the 3’ end of DNA?

Answer 16

OH

Question 17

What are the complementary base pair rules and how many hydrogen bonds form between them?

Answer 17

Adenine and thymine or uracil- 2

Guanine and cytosine- 3

Question 18

How do DNA strands connect?

Answer 18

Complimentary and antiparallel

Question 19

Which way of a DNA strand is left to right?

Answer 19

5’ to 3’

By convention top strand is this direction

Question 20

Where are cell cycle checkpoints?

Answer 20

Between G1 and S

Between G2 and mitosis

Question 21

What is the name of DNA replication?

Answer 21

Semi-conservative

Question 22

What enzyme catalyses DNA replication?

Answer 22

DNA polymerase

Question 23

What happens in the initiation stage of DNA replication?

Answer 23

recognise origin of replication

primase kicks starts process as DNA polymerase can only extend the 3’ end and shows where to start

Question 24

What happens in the elongation stage of DNA replication?

Answer 24

Moving replication fork
Helicase unwinds double helix
DNA polymerase extends 3' end only
lagging strand uses fragments of DNA called ozkazaki fragments- use primers 
RNA Primers are replaced with DNA 
DNA ligaments joins the fragments

Question 25

What happens in the termination stage of DNA replication?

Answer 25

When two facing replication forks meet DNA ligase joins final fragments

Question 26

What is a chromatid?

Answer 26

When chromosomes are connected by the centromere, they are the two arms If not connected by centromere a chromatid is a chromosome