Nucleic Acids 3 + 4

Question 1

Describe the prokaryote DNA sequence

Answer 1

They don’t have introns

Question 2

How many chromosomes do humans have ?

Answer 2

46 chromosomes- 23 pairs
A greater no of chromosomes does not make an organism more complex

Question 3

Describe the forms of chromatin

Answer 3

Heterochromatin- DNA is densely packed
Euchromatin- DNA is loosely packed

Question 4

What is the packing ratio ?

Answer 4

It is how tightly DNA is compacted inside the nucleus
Packing ratio= length of DNA/ length of structure DNA packed into

Question 5

What is the composition of a chromosome at mitosis ?

Answer 5

1. 1/3 DNA
2. 1/3 histone proteins
3. 1/3 non-histone proteins

Question 6

What are the 5 types of histone proteins in eukaryotes?

Answer 6

1. H1
2. H2A
3. H2B
4. H3
5. H4

Question 7

What does conserved mean ?

Answer 7

Hasn’t changed over time

Question 8

What are nucleosomes ?

Answer 8

Fundamental structural unit of chromatin
They are 146bp DNA wrapped around “ core particle” containing histones (2 molecules of histones)

Question 9

What does histone H1 do ?

Answer 9

H1 binds to DNA outside core particle, sealing the DNA to the nucleosome
Ensures no DNA is hanging loosely

Question 10

What does the scaffold of a chromosome contain ?

Answer 10

1. Condensin
2. Topisomerase II

Question 11

What is Condensin ?

Answer 11

A ring shaped protein that can anchor the ends of a loop of DNA

Question 12

What is topoisomerase II ?

Answer 12

An enzyme that can remove or add supercoils within DNA

Question 13

What do scaffolds in mitosis and meiosis do ?

Answer 13

Anchor long loops of nucleosomes

Question 14

How can eukaryotic genes be regulated by modification of histone proteins ?

Answer 14

Acetylation
Adding an Acetyl group adds a negative charge, causing repulsion, which makes the DNA less tightly associated with the nucleosome and so exposing it for transcription and DNA replication

Question 15

How would you describe DNA replication ?

Answer 15

Semi-conservative

Question 16

What does semi-conservative mean ?

Answer 16

Each daughter molecule has one new strand and one pre-existing strand of DNA
Consists of replication forks

Question 17

What does conservative mean ?

Answer 17

The part DNA molecule is conserved and an entirely new daughter molecule is synthesised

Question 18

What are DNA polymerases ?

Answer 18

The enzymes that synthesise DNA

Question 19

What does a DNA polymerase need in order to synthesise DNA ?

Answer 19

1. All 4 deoxynucleoside triphosphates
2. A template
3. A primer

Question 20

What other enzymatic activities does DNA polymerase I have ?

Answer 20

1. 5’ to 3’ exonuclease- nick translation
2. 3’ to 5’ exonuclease- allows DNA polymerase I to remove incorrect nucleotides from newly made DNA (proof read)

Question 21

What is DNA polymerase III responsible for ?

Answer 21

Making most of the new DNA during replication because of its speed and high processivity

Question 22

Describe the events of DNA replication

Answer 22

1. Partial unwinding by helicase (breaks hydrogen bonds)
2. Synthesis of primers by primase (primers in DNA replication are made of RNA)
3. Supercoils caused by unwinding are removed by DNA gyrase
4. DNA synthesis by DNA polymerase III. Leading strand is synthesised continuously, but the lagging strand DNA is made in short, discontinuous fragments called Okazaki fragments
5. Removal of RNA primers by nick translation by DNA polymerase I
6. The gaps between Okazaki fragements are sealed by DNA ligase

Question 23

What is DNA gyrase ?

Answer 23

A type II topoisomerase

Question 24

What does single stranded DNA binding protein do ?

Answer 24

Prevents the reannealing of single stranded DNA