Chromosomes, the Cell Cycle and an Intro to its Regulation

Question 1

In eukaryotic cells, what is a chromatin?

Answer 1

chromosomal DNA in a complex wtih RNA and proteins

Question 2

Histones

Answer 2

highly alkaline proteins which package and order DNA into structural units called nucleosomes
chief protein of chromatin, acting as spools around which DNA winds, and playing a role in gene regulation.

Question 3

What makes up a nucleosome?

Answer 3

2 loops of DNA double helix wrapped around a cluster of 8 histones

Question 4

How are chromosomes formed?

Answer 4

supercoiling and condensation of chromatin

Question 5

What are genes in relation to chromosomes?

Answer 5

specialised functional sites arranged along the choromosomes

Question 6

Forms of chromatin

Answer 6

in interphase nuclei:
heterochromatin
euchromatin

Question 7

Heterochromatin

Answer 7

more condensely and densely staining
tends to be found near nuclear envelope
represents genes that are switched off
two types: constitutive and facultative

Question 8

Euchromatin

Answer 8

less condensed and lightly staining
more central location
represents genes that are switched on

Question 9

How are tissues of the body divided in relation to cell turnover?

Answer 9

1. continuously renewing: epidermis of skin, intestinal epithelium, blood-forming tissues
2. conditionally renewing: liver, kidney, endocrine glands
3. static/non-proliferative: cardiac, nerve cells

Question 10

Cell cycle

Answer 10

G1 phase - S phase - G2 - M phase - cytokinesis - G1/G0

G0 = doing function, no division

Question 11

Mitosis

Answer 11

prophase - prometaphase - metaphase - anaphase - telophase

Question 12

G1-S phase transition importance

Answer 12

control point to deermine whether cells enter S phase

Question 13

S phase

Answer 13

replication of DNA and RNA and protein

Question 14

G2 phase

Answer 14

final prep for mitosis

Question 15

M phase

Answer 15

division of 2 sister chromatids of each chromosome into separate nucleoli and division of the parent cell into 2 daughter cells

Question 16

Prophase

Answer 16

chromatin condenses to form visible chromosomes
each chromosome comprises 2 sister chromatids joined at the centromere
centrioles duplicate
centrioles move apart to form 2 poles and act as microtubule-organising centres
microtubules form the mitotic spindle apparatus between the centrioles

Question 17

Prometaphase

Answer 17

nucleoli regress and nuclear membranes disassemble
chromosomes move towards the equator and interact with microtubules
each pair of sister chromatids has an attachment site - kinetochore, which attaches to spindle

Question 18

Metaphase

Answer 18

central region of cell forms a metaphase plate
chromosomes arrange themselves on this plate, 2 sister chromatids joined at centromeres
spindle consists of microtubules running from pole to pole or pole to chromosome
latter microtubules run to centromeres of sister chromatids and attach at kinetochores

Question 19

Anaphase

Answer 19

sister chromatids of each pair move apart to opposite poles of the cell - elongation of polar microtubules, shortened kinetochore microtubule
these chromosomes are pulled along by the microtubules

Question 20

Telophase

Answer 20

chromosomes reach poles and start to become less condensed
nuclear membrane reassembles
a cleavage furrow begins around the equator
spindle disappears
nucleoli reappear

Question 21

Cytokinesis

Answer 21

actin-myosin belt

cells separate to form 2 daughter cells

Question 22

Interphase

Answer 22

G0, G1, S and G2

Question 23

How is the cell cycle regulated?

Answer 23

cyclins and cyclin-dependent kinases

Question 24

What are cyclins and CDK?

Answer 24

regulatory proteins
determine cell’s progress through the cell cycle
coordinate cell’s entry into the next phase of the ceel cycle

Question 25

How do cyclin and CDKs regulate the cell cycle?

Answer 25

CDKs activated when they bind to cyclin activated CDKs cause phosphorylation to activate or inactivate target proteins these proteins coordinate cell's entry into next phase

Question 26

Clinical relevance of cell cycle regulation

Answer 26

inhibitors of cyclin/CDK complexes: 2 families of genes prevent the progression of the cell cycle can be used as anticancer agents - tumour suppressors

Question 27

Difference in cell cycle of cells undergoing mitosis and meiosis

Answer 27

in S phase of meiosis, DNA is duplicated (4c), therefore there must be 2 separate reduction divisions to achieve 1c amount in gamete

Question 28

Meiosis I

Answer 28

prophase, metaphase, anaphase, telophase

Question 29

Prophase I

Answer 29

recombination and pairing Leptotene - chromatin condenses -> chromosomes, chromomeres visible Zygotene - homologous chromosomes pair to form bivalents, split into sister chromatids, synapsis develop between sister chromatids of homo pairs Pachytene - synapsis completed and chiasma formed, where genetic info is exchanged Diplotene - chromatids held together by chiasmata and centromeres Diakinesis - chiasmata appear to move towards the ends of chromatids

Question 30

Metaphase I

Answer 30

each bivalent has 2 centromeres and arrange themselves by chance on opposite sides of the metaphase plate independent assortment results in genetic variation

Question 31

Anaphase I

Answer 31

chromosomes move to opposite poles of cell | each pole mix of maternal and paternal chromosomes - source of genetiv variation

Question 32

Telophase I

Answer 32

each daughter cell has half diploid number of chromosomes | nuclear envelope may reassemble before prophase II of the 2nd meiotic division

Question 33

Meiosis II

Answer 33

similar to mitosis | centromeres split at kinetochores and sister chromatids move to opposite poles

Question 34

Gametogenesis and meiosis

Answer 34

4 daughter cells formed at end of meiosis II in spermatogenesis but not in oogenesis oogenesis: ovum and 3 polar bodies

Question 35

Genetic variation in meiosis

Answer 35

pachytene of prophase I: genetic info exchanged bewtween homo pairs of chromosomes at chiasmata anaphase I: each pole has mixture of maternal and paternal chromosomes fertilisation

Question 36

Monosomy

Answer 36

individual missing chromosome from a pair | eg. Turner's syndrome (XO)

Question 37

Trisomy

Answer 37

individual has more than 2 chromosomes of a pair | eg. Down's syndrome (trisomy 21), Patau's syndrome (trisomy 13), Edward's syndrome (trisomy 18), Kleinfelter's (XXY)

Question 38

How does aneuploidy occur?

Answer 38

homo chromosomes in meiosis I do not separate properly, one has 24, other has 22 = non-disjunction