Intracellularly - Chromosomes

Question 1

What is an example of the variability in genome size?

Answer 1

Bacteriophage MS2 has four genes in 3369 NT’s

Question 2

C-Value Paradox

Answer 2

The amount of DNA in a haploid genome does not correspond strongly to organism complexity

Question 3

What species has genomes thirty times the size of humans?

Answer 3

Amphiuma Salamanders

Question 4

Mutational Load

Answer 4

This is the total genetic burden of a population

Question 5

What causes C-Value paradox?

Answer 5

Mutational load

Question 6

What is an exampele of how the genome is larger than the cell itself?

Answer 6

E.coli DNA is 1500 nanometres whilst the cell is 2 nanometres in diameter

Question 7

What allows E.COli genome to fit inside the cell?

Answer 7

Supercoiling

Question 8

What are the two functions of supercoiling?

Answer 8

Fit the genome in the cell whilst making it accessible for expression when needed.

Question 9

Negative Supercoiling

Answer 9

This is when the right handed coiling of DNA, thus occuring counter-clockwise.

Question 10

How are Eukaryotic genomes compacted sufficienitly?

Answer 10

Nucleosomes

Question 11

Chromatin

Answer 11

An organized complex of DNA and proteins being a prinicipal component of the cell nucleis.

Question 12

What are the proteins that make up the nucleosome?

Answer 12

H1, H2A, H2B, H3 and H4

Question 13

Histone

Answer 13

Nucleosome components being 100-200 AA long with lysine/arginine abundance with positive charges.

Question 14

Why is the positive charge-ness of histones important?

Answer 14

It allows them to interact with negative charge phosphate groups of DNA.

Question 15

How does DNA relate to the nucleosome?

Answer 15

It wraps it 1.7 times(140BP) with linker DNA in between

Question 16

H1 Histone

Answer 16

Functions to bind entry/exit sites of DNA on nucleosome surface for the linker regions in between them.

Question 17

How much of the histone is made of its modifiable tail?

Answer 17

25%

Question 18

Which histones are recombination hotspots?

Answer 18

H3 and H4

Question 19

Recombination Hotspots

Answer 19

Genomic regions experiencing high levels of recombination.

Question 20

What is the mechanism of H3-H4 acting as a recombination hotspot?

Answer 20

PRDM9 methyl transferase enzyme methylates a lysine on histone tail, rendering it susceptible to dsDNA break.

Question 21

What does histone aceylation do?

Answer 21

Makes them bind DNA more loosely for transcription accessibility.

Question 22

What does physiological salt concentrations do to the nucleosomes?

Answer 22

Compacts them into 30-nm cohromatin fibres

Question 23

Chromosome Scaffold

Answer 23

A proteinous structure functioning in formation and maintenace of structural integrity of the mitotic chromosome

Question 24

What is the general structure of the chromosome scaffold?A

Answer 24

A protein core with dimensions of metaphase chromosome, with DNA loops of 80-120kb projecting from it

Question 25

What three proteins are involved in chromosome condensation in mitosis?

Answer 25

Condensins
Cohesins
Topoisomerase IIA

Question 26

Condensin

Answer 26

These containt SMC2 and SMC4 as well as CAP proteins.

Question 27

Cohesins

Answer 27

These are MP complexes, containing SMC1 and SCM3 for structural mainteanace and additional proteins that form a loop to wrap around sister chromtids

Question 28

Topisomerase IIA

Answer 28

This alters DNA supercoiling by breaking both strands of one helix and passing another one through it.

Question 29

What are the steps of chromosome condensation?

Answer 29

Cohesins stabilise paired sister chromatids
Condesins binds DNA creating stacked loops
Chromosome axial compressiong by condensin 2 and TIIA
Condensin I stabilise chromosomes, reducing diamter