Chromosomes Flashcards
How many chromosomes do you have?
46 chromosomes - 22 pairs of autosomes and 1 pair of sex chromosomes
How many different types of chromosomes does a human male and female have?
Males have 44 autosomes and XY
Females have 44 autosomes and XX
How many chromosomes did you inherit from your father? From your mother?
From father - one sex chromosome and one full set of autosomes
From mother - one sex chromosome and one full set of autosomes
What are the major landmarks on a chromosome and what do they do?
Centromere - control separation
Telomeres - two at the ends
How does the packaging of a chromosome change at different stages of the cell cycle?
There are several stages of the cell cycle: G1, S, G2 and M
G1 and G2 are the growth stages
S involves synthesis of DNA
M is the mitosis stage
There is also a G0 phase which is an exit phase (some cells re-enter the cell cycle after G0 if damage has occurred)
Is DNA in the cell generally underwound or overwound? What does this mean? What is a DNA supercoil?
DNA is generally underwound in the cell and it is easier for the DNA to be open. Supercoiling relieves tension and there can be different amounts of supercoiling
How does supercoiling effect the running of a circular DNA on an agarose gel?
When you have linear pieces of DNA, they move based on size but when you have a loop this is difference.Since the DNA is supercoiled on the gel, it will move very fast.
What does a topoisomerase enzyme do to the structure of DNA? To the shape? To the size?
Relieves the tension
Makes the DNA linear
What is the general mechanism by which Type II topoisomerase acts?
The multisubunit enzyme binds a segment of a DNA molecule
A second segment of the same DNA molecule is bound at the N gate
The second segment of DNA is trapped - the light blue segment is cleaved on both strands to form two 5’ phosphotyrosyl linkages to the enzyme
The second DNA segment is passed through the break
The broken DNA is religated and the second DNA segment is released through the C gate
Operates as a dimer
Passed from the N gate to the C gate
What is a nucleosome? What is chromatin?
Nucleosome - DNA wrapped twice around histones
These proteins are called histones and 8 of them bound to DNA form a nucleosome - are the basic unit of chromatin
Chromatin- DNA and protein
What are 5 types of histones found in chromatin? What is the overall structure of a nucleosome? What is important about the histone N terminal tails?
H1, H2A, H2B, H3 and H4
Nucleosome - DNA wrapped twice around histones
These proteins are called histones and 8 of them bound to DNA form a nucleosome
The amino tails of the histones are highly disordered
They protrude from the nucleosome
This is where histones can be modified
Some of the amino acid tails can interact with the tails of the neighbouring nucleosome
Amino terminal tails (disordered, loose and highly modified)
Name three types of histone modification that can be used to regulate chromatin packing
- methylation
- acetylation
- phosphorylation
These changes alter the structure and packing of the chromatin - alters the access of the DNA to DNA binding proteins
What is meant by the histone code?
Recognised by proteins and mark the DNA for specific biological purposes
What is a 30nm fibre?
Nucleosome wrapping - 7 fold compaction
Plus one histone H1 between the nucleosome = 30 nm - not accessible to DNA binding proteins (must be opened up more)
What are the three things that can change to regulate access to DNA binding proteins?
- the positioning of the nucleosomes
- the presence of histone variants
- the covalent modification of nucleosomes
