Chromosomes and cytogenetics

Question 1

How is DNA compacted?

Answer 1

By forming complexes with histone proteins

Question 2

What are the core histone proteins?

Answer 2

H2A, H2B, H3 and H4

Question 3

How many times does DNA wrap around the histone proteins?

Answer 3

Twice

Question 4

What is a nucleosome?

Answer 4

A section of DNA wrapped around histone proteins

Question 5

What are histones packed into?

Answer 5

A 30nm fibre

Question 6

What is the 30nm fibre wrapped around?

Answer 6

A protein scaffold

Question 7

What is chromatin?

Answer 7

The DNA-histone subunit

Question 8

What type of chromatin is most of the genome in?

Answer 8

Euchromatin

Question 9

Difference of compaction between euchromatin and heterochromatin?

Answer 9

Heterochromatin is more permanently compacted

Question 10

What is H1?

Answer 10

A linker histone

Question 11

What is the effect of H1 dissociating?

Answer 11

The chromatin becomes less compact

Question 12

What is the effect of chromatin becoming less compact?

Answer 12

Transcription factors and RNA polymerase can access the DNA more easily

Question 13

What is the effect of chromatin becoming more compact?

Answer 13

Transcription factors and RNA polymerase can less easily access the DNA

Question 14

What is the association and dissociation of chromatin used to do?

Answer 14

Regulate gene expression

Question 15

What is the split in terms of how much of the genome is made up of euchromatin and heterochromatin?

Answer 15

More euchromatin

Question 16

How does heterochromatin form?

Answer 16

Recruitment of condenser proteins

Question 17

Example of a condenser protein?

Answer 17

HP1

Question 18

What do condenser proteins do?

Answer 18

Indure permanent condensation of heterochromatin

Question 19

What does heterochromatin have a tendency to do?

Answer 19

Spread

Question 20

Why is heterochromatin spreading an issue?

Answer 20

It could cause genes to permanently shut off as it would condense them

Question 21

What is position effect variegation?

Answer 21

Genes “turning off” due to them being condensed by heterochromatin

Question 22

What is structural heterochromatin?

Answer 22

Heterochromatin that is found in structural elements

Question 23

What structural elements is structural heterochromatin found in?

Answer 23

Centromeres and telomeres

Question 24

Where are telomeres found?

Answer 24

At the end of each chromosome

Question 25

What is one role of telomeres (cancer one)?

Answer 25

prevent chromosomal fusion

Question 26

What is a problem with chromosomal fusion?

Answer 26

Chromosomes will separate incorrectly during mitosis, leads to cell abnormalities

Question 27

What kind of repetitive DNA does structural heterochromatin contain?

Answer 27

Satellite DNA

Question 28

What is small satellite DNA called?

Answer 28

Microsatellites

Question 29

How long are telomeric DNA sequences?

Answer 29

10-15 kilobases

Question 30

What are the two strands of the telomere called?

Answer 30

G rich strand and C rich strand

Question 31

Why is the G rich strand called the G rich strand?

Answer 31

Has a high guanine content

Question 32

Why is the C rich strand called the C rich strand?

Answer 32

Has a high cytosine content

Question 33

Which telomere strand is longer?

Answer 33

G rich strand

Question 34

How much longer is the G rich strand?

Answer 34

30 repeats longer

Question 35

How is a T loop formed?

Answer 35

The g tail loops over and disrupts some of the upstream double stranded portion

Question 36

What promotes and stabilises the formation of the T loop?

Answer 36

A telosome/shelterin complex

Question 37

What is cytogenetics?

Answer 37

The study of chromosomes

Question 38

What are cells treated with before making a karyogram?

Answer 38

Colcemid

Question 39

What is the effect of colcemid?

Answer 39

It disrupts the mitotic spindle, and causes the cell cycle to arrest

Question 40

When does the cell cycle arrest after the addition of colcemid?

Answer 40

metaphase

Question 41

Why are the cells collected in metaphase?

Answer 41

They are highly condensed

Question 42

What is done after treating the cells with colcemid (when making a karyogram)?

Answer 42

They are placed in a hypertonic solution

Question 43

Why are cells placed in a hypertonic solution (when making a karyogram)?

Answer 43

To cause them to swell

Question 44

What are the two arms of the chromosome?

Answer 44

P arm and Q arm

Question 45

Short chromosome arm name?

Answer 45

P arm

Question 46

Long chromosome arm name?

Answer 46

Q arm

Question 47

How many levels is the p arm divided up into?

Answer 47

3--> the sub regions, the sub sub regions and the sub sub sub regions

Question 48

How many levels is the q arm divided up into?

Answer 48

2--> the sub regions and the sub sub regions