Chromosomes and Cell Division

Question 1

describe function of a telomere on a chromosome

Answer 1

protects the ends of the chromosomes to make sure they aren’t eroded

Question 2

where is the centromere found?

Answer 2

typically in the centre of the chromosome (holds two chromatids together)

Question 3

what is heterochromatin?

Answer 3

non-functional units

Question 4

what is euchromatin?

Answer 4

functional units

Question 5

why is DNA replication not symmetrical?

Answer 5

DNA polymerase can only synthesise from 5’ to 3’ direction, adding free nucleotides to the 3’ end of the strand

Question 6

what happens over many generations to chromosomes?

Answer 6

they will get shorter

Question 7

what can telomerase do?

Answer 7

enzyme which can add a DNA sequence using an RNA template to a DNA which has been eroded

Question 8

what repeats does telomerase add to the ends of existing elongated chromosomes?

Answer 8

5’-TTAGGG-3’ repeats (hundreds of copies)

Question 9

Most cells in humans don’t express telomerase, but which cells do?

Answer 9

• fetal tissues
• adult germ cells
• tumour cells

Question 10

what occurs at G1 phase of cell cycle?

Answer 10

cellular components are duplicated, prepared for cell division

Question 11

what occurs at S phase of the cell cycle?

Answer 11

DNA synthesis

Question 12

what occurs at G2 phase of the cell cycle?

Answer 12

cell double checks chromosomes for error and makes any repairs

Question 13

what occurs at prophase?

Answer 13

• chromosomes condense and become visible/compact
• nuclear membrane disappears
• spindle fibres form from the centriole

Question 14

what occurs at metaphase?

Answer 14

• chromosomes align at the equator of the cell
• chromosomes attached by fibre by each centriole
• max. condensation of chromosome

Question 15

what occurs at anaphase?

Answer 15

• sister chromatids separate at centromere by spindle fibres
• separate longitudinally
• move to opposite poles of the cell

Question 16

what occurs at telophase?

Answer 16

• new nuclear membrane forms

- each cell now contains 46 chromosomes (diploid)

Question 17

what occurs at cytokinesis?

Answer 17

• cytoplasm separates

- two new daughter cells formed

Question 18

what do centromeres do?

Answer 18

hold two sister chromatids together

Question 19

what can happen if centromere doesn’t work properly?

Answer 19

Irregular separation occurs leading to cellular problems

Question 20

what forms centromeres?

Answer 20

satellite DNA (non-coding) forms heterochromatin

Question 21

what is a kinetochore?

Answer 21

protein complex assembled on the centromere which binds to spindle fibres (microtubules)

Question 22

how many genes does the human body approx. have?

Answer 22

20-30,000

Question 23

in what two places is satellite DNA found?

Answer 23

• cenromeres

- telomeres

Question 24

what 2 components are DNA sequences in our genome made of?

Answer 24

1. SINEs ( short interspread nuclear elements)

2. LINEs (long interspread nuclear elements)

Question 25

is majority of DNAm SINEs or LINEs?

Answer 25

LINEs

Question 26

what structures make up chromatin?

Answer 26

histones

Question 27

histone +DNA =

Answer 27

nucleosome

Question 28

what charge is DNA and histone?

Answer 28

DNA: -ve histone: +ve

Question 29

how many nucleosomes per turn are there in wrapping?

Answer 29

6 nucleosomes

Question 30

what structure is formed by compact DNA by a factor of 40?

Answer 30

solenoid structure

Question 31

what are the 4 levels of packaging DNA to form a chromosome?

Answer 31

1. nucleosome 2. chromatin fibre 3. fibre-scaffold complex (lots of heterochromatin) 4. chromosome

Question 32

what is the purpose of packaging DNA?

Answer 32

- negative DNA neutralised by positive histones - DNA takes up less space - inactive DNA can be folded into inaccessible locations until required

Question 33

what is the short arm of the chromosome called?

Answer 33

p arm

Question 34

what is the long arm of the chromosome called?

Answer 34

q arm

Question 35

what is a submetacentric chromosome?

Answer 35

centromere is not quite at the centre of the chromosome

Question 36

what is a metacentric chromosome?

Answer 36

centremere is at the centre of a chromosome

Question 37

what does chromosome analysis by karyotyping require beforehand?

Answer 37

blood sample

Question 38

what is a colchicine?

Answer 38

microtubule inhibitor, no mitosis occurs but chromosomes align (become visible)

Question 39

what does karyotyping allow us to do?

Answer 39

look at individual chromosomes

Question 40

what does FISH allow us to do?

Answer 40

used to look at sequence content of chromosomes (as karyotyping doesn't let us do it)

Question 41

how does FISH work?

Answer 41

- fragment of desired DNA sequence is isolated - DNA sequence is labelled with fluorescent dye - cytogenic technique that uses fluorescent probes bind only to the part of the chromosome with a high degree of sequence complementarity - specific regions on the chromosomes can be looked at

Question 42

what are the 4 different FISH probes?

Answer 42

1. unique sequence probes 2. centromeric probes - for determining chromosome number 3. telomeric probes - present in children with retardation diagnosis - detect subtelometic rearrangements 4. whole chromosome probes - detects translocations and rearrangements

Question 43

what is meiosis?

Answer 43

- cell division in germ cells - diploid cells divide to to form haploid cells - recombination or rearrangment of genes creates diversity - 4 haploid cells formed

Question 44

what is oogenesis?

Answer 44

process of egg formation

Question 45

what is speratogenesis?

Answer 45

process of sperm formation

Question 46

do sperm go through more cell divisions than eggs?

Answer 46

Yes- therefore higher chance of mutations

Question 47

what is fertilisation?

Answer 47

two haploid cells (sperm and egg) fuse to form a diploid cell (zygote)

Question 48

who does the embryo get their mitochondria (and its DNA) from?

Answer 48

the mother (maternal inheritance)

Question 49

why is X inactivation necessary in females?

Answer 49

- so only characteristics of one X chromosome are expressed (no double characteristics) - deactivation is RANDOM

Question 50

when does X deactivation happen?

Answer 50

in embryonic stage