Chromosome structure and chromatin Flashcards
Which part of the cell contains the chromosomes?
Nucleus
What is a chromatin?
DNA packaged with proteins called histones.
How many base pairs does the human genome contain?
3 billion base pairs.
Space between base pairs?
~3.4 A
Total length of all the DNA in nucleus?
2.2 metres.
Diameter of a nucleus?
5-10 micrometres
What happens too the chromosomes when cell division starts?
Chromosomes condense and compact.
Who first described chromosomes?
Walther Flemming
Describe what a chromatid is?
One of the two copies of a replicated chromosomes, joined too its identical sister chromatid.
What is a centromere?
The chromosomal region that holds sister chromatids together and where kinetochore forms.
What is a kinetochore?
A protein complex that forms on chromosome centromeres during m phase that binds microtubules and directs chromosome movement in mitosis.
What is a telomere?
The ends of chromosomes.
What are the chromosomes like in interphase?
Visible less distinct and exhibit variable levels of compaction depending on their activity.
Euchromatin?
Largely de-compacted and potentially active in gene expression.
Diffuse and light-staining; actively transcribed genes, tend to concentrated to the middle of the nucleus.
Heterochromatin?
Highly compacted and transcriptionally inactive.
Dark staining, genes not transcribed; repetitive sequences; tend to concentrate at the periphery.
Histones that DNA is coiled around. (H?)?
(H2A, H2B, H3 and H4) X 2
What fifth histone protein is involved in chromatin condensing?
H1
What would happen if gene expression wasn’t properly regulated?
The timing and location of protein production could be messed by.
What does remodelling the chromatin do?
Increases the accessibility for DNA.
Why are nucleosomes dynamic?
So transcription factors can bind to DNA in the nucleosomes.
What enzymes permit chromatin remodelling?
Histone modifying enzymes that covalently modify chromatin structure and ATP-dependent chromatin remodelling complexes.
Describe a histones “tail”?
Positively charged and found at the N-terminus.
What molecule can change a histones tail charge and how?
Histone acetyltransferases.
Can change charge by adding acetyl groups to lysine residues.
HDACs remove them.
What does changes to tails charge allow for?
Increased DNA accessibility.
Facilitates transcription factor binding and recruitment of chromatin re-modellers and activates transcriptions.
What are the 4 possible mechanisms for increased local access?
Nucleosome sliding
Nucleosome displacement
Partial histone displacement
Replacement of octamer subunits with histone variants.
What are the two types of chromatin visible during interphase?
Euchromatin
Heterochromatin
