Molecular Biology Week 6

Question 1

What are the two different specialised chromosomal structures?

Answer 1

The centromeres and the telomeres.

Question 2

What are centromeres?

Answer 2

These are the sites at which the spindle fibers attach during cell division.

Question 3

What are centromeres composed of?

Answer 3

Highly repeated satellite DNA.

Question 4

Where are telomeres located and what do they contain?

Answer 4

They are located at the ends of chromosomes and they contain multiple repeats of short DNA sequences.

Question 5

What are telomeres responsible for in the chromosome?

Answer 5

They are responsible for maintaining chromosomal integrity and by protecting the DNA against degradation or arrangement.

Question 6

What enzyme adds telomeres to the ends of the chromosomes?

Answer 6

Telomerase.

Question 7

If a person has a short number of repeats per telomers what does this tell us about the person?

Answer 7

That they are elderly as this is a molecular marker in the aging process. Shorter the older the person is.

Question 8

What is the factor that DNA must be condensed by in order to fit inside the chromosome?

Answer 8

10 to the power of 5.

Question 9

How is the condensing of DNA accomplished in the chromosome?

Answer 9

By neatly wrapping the DNA around protein spools called nucleosomes.

Question 10

What is nucleosome? What are the two different categories?

Answer 10

These are proteins of chromatin which are in two classes: histones and nonhistone proteins.

Question 11

What are histones? These are the nucleosomes with abundant copies in the chromosome.

Answer 11

Histones are small, positively charged due to arg or lys rich proteins that interact via ionic bonds with the neg charged phosphate backbone groups on the polynucleotide backbone.

Question 12

Name the 5 distinct histones?

Answer 12

H1, H2A, H2B, H3, and H4

Question 13

Which histones aggregate to form an octameric core structure?

Answer 13

H2A, H2B, H3, and H4.

Question 14

What is the core of the nucleosome?

Answer 14

This is the octameric core structure around which the DNA helix is wound.

Question 15

How many base pairs are associated with an octamer?

Answer 15

200bp.

Question 16

What are the 200bp in an octamer composed of DNA type wise and amount of bp per type?

Answer 16

146 bp of B

54 remaining made up of A and Z

Question 17

What direction is the conformation of the B-DNA around the octameric core structure and how many turns does it make around the histone?

Answer 17

Left-handed superhelical conformation, it makes 1.65 turns around the histone.

Question 18

What is the function of histone 1?

Answer 18

Its function is to seal the ends of the DNA turns to the nucleosome core and organize the additional 54 bp of the DNA that links the consecutive nucleosome like beads on a string.

Question 19

Nucleosomes are wound in a fashion of a solenoid what does this mean?

Answer 19

This is having six nucleosomes per turn.

Question 20

What are the dimensions of the filament resulting from having six nucleosomes per turn?

Answer 20

30nm. This contains 1200bp in each of its turns.

Question 21

What causes stabilization in the H1 (sealing) components?

Answer 21

Components of successive nucleosomes stabilize the 30nm filament.

Question 22

What is the average amount of base pairs on the 30nm filament that then form the DNA loops of variable length?

Answer 22

Between 60000 and 150000 bp.

Question 23

How many variable loops are arranged radially around the circumference of a single turn forming the miniband unit of the chromosome?

Answer 23

18 such loops after analysis of chromosome 4.

Question 24

10 to the power of 6 of the 18 loops (miniband) arranged along the central axis of the chromatids are formed when?

Answer 24

At mitosis.

Question 25

Which is the shorter arm?

Answer 25

P-arm. Long Q-arm.