Organisation of DNA

Question 1

Is extranuclear/extrachromosomal DNA inherited from the mother or father?

Answer 1

Mother as it remains in the ovum, while only the nucleus from the spermatozoid is used.

Question 2

Are prokaryotic cells diploid or haploid?

Answer 2

Haploid.

Question 3

Why must DNA interact with proteins for packaging?

Answer 3

Neutralise the -ve charges of DNA with +vely charged proteins and allow compaction.

Question 4

What is the basic structure of chromatin?

Answer 4

Nucleosome

Question 5

Describe the structure of each nucleosome.

Answer 5

Flower arrangement made of each of two H2A, H2B, H3 and H4. Around each nucleosome DNA wraps around twice with a total of 150 bp around one nucleosome. 50 bp join nucleosomes with H1 stabilising them.

Question 6

Describe the difference between euchromatin and heterochromatin.

Answer 6

Euchromatin is less densely packed chromatin and appears light. It is present through interphase.
Heterochromatic is highly dense chromatin and appears dark. Cannot be transcribed and is present during mitosis and meiosis.

Question 7

What is the purpose of a centromere in a chromosome?

Answer 7

• Contains site at which sister chromosomes are paired before segregation
• Section that pull chromosomes to either pole
• Interacts with proteins and microtubules

Question 8

What is the structure if a centromere?

Answer 8

Highly repetitive sequences (satellite DNA)

• In humans short 170 bp repeats
• Repeated 2000-30000 times.
• Allows specific protein binding

Question 9

What is the purpose of telomeres?

Answer 9

Required for stability of the linear molecules during replication.

Question 10

How are telomeres synthesised?

Answer 10

Synthesised onto the end of chromosomes from an RNA template by telomerase. Results in the formation of a 5-10 kbp loop.