Chromosomes and cytogenetics Flashcards
How is DNA compacted?
By forming complexes with histone proteins
What are the core histone proteins?
H2A, H2B, H3 and H4
How many times does DNA wrap around the histone proteins?
Twice
What is a nucleosome?
A section of DNA wrapped around histone proteins
What are histones packed into?
A 30nm fibre
What is the 30nm fibre wrapped around?
A protein scaffold
What is chromatin?
The DNA-histone subunit
What type of chromatin is most of the genome in?
Euchromatin
Difference of compaction between euchromatin and heterochromatin?
Heterochromatin is more permanently compacted
What is H1?
A linker histone
What is the effect of H1 dissociating?
The chromatin becomes less compact
What is the effect of chromatin becoming less compact?
Transcription factors and RNA polymerase can access the DNA more easily
What is the effect of chromatin becoming more compact?
Transcription factors and RNA polymerase can less easily access the DNA
What is the association and dissociation of chromatin used to do?
Regulate gene expression
What is the split in terms of how much of the genome is made up of euchromatin and heterochromatin?
More euchromatin
How does heterochromatin form?
Recruitment of condenser proteins
Example of a condenser protein?
HP1
What do condenser proteins do?
Indure permanent condensation of heterochromatin
What does heterochromatin have a tendency to do?
Spread
Why is heterochromatin spreading an issue?
It could cause genes to permanently shut off as it would condense them
What is position effect variegation?
Genes “turning off” due to them being condensed by heterochromatin
What is structural heterochromatin?
Heterochromatin that is found in structural elements
What structural elements is structural heterochromatin found in?
Centromeres and telomeres
Where are telomeres found?
At the end of each chromosome
What is one role of telomeres (cancer one)?
prevent chromosomal fusion
What is a problem with chromosomal fusion?
Chromosomes will separate incorrectly during mitosis, leads to cell abnormalities
What kind of repetitive DNA does structural heterochromatin contain?
Satellite DNA
What is small satellite DNA called?
Microsatellites
How long are telomeric DNA sequences?
10-15 kilobases
What are the two strands of the telomere called?
G rich strand and C rich strand
Why is the G rich strand called the G rich strand?
Has a high guanine content
Why is the C rich strand called the C rich strand?
Has a high cytosine content
Which telomere strand is longer?
G rich strand
How much longer is the G rich strand?
30 repeats longer
How is a T loop formed?
The g tail loops over and disrupts some of the upstream double stranded portion
What promotes and stabilises the formation of the T loop?
A telosome/shelterin complex
What is cytogenetics?
The study of chromosomes
What are cells treated with before making a karyogram?
Colcemid
What is the effect of colcemid?
It disrupts the mitotic spindle, and causes the cell cycle to arrest
When does the cell cycle arrest after the addition of colcemid?
metaphase
Why are the cells collected in metaphase?
They are highly condensed
What is done after treating the cells with colcemid (when making a karyogram)?
They are placed in a hypertonic solution
Why are cells placed in a hypertonic solution (when making a karyogram)?
To cause them to swell
What are the two arms of the chromosome?
P arm and Q arm
Short chromosome arm name?
P arm
Long chromosome arm name?
Q arm
How many levels is the p arm divided up into?
3–> the sub regions, the sub sub regions and the sub sub sub regions
How many levels is the q arm divided up into?
2–> the sub regions and the sub sub regions
