19.01.06 Cell Cycle, Mitosis, Meiosis, Recombination

Question 1

quiescent/ senescent cells are in which cell cycle phase

Answer 1

G0. Resting phase after cell cycle where cell has stopped dividing

Question 2

Interphase is composed of which steps

Answer 2

G1, S and G2

Question 3

What happens in G1

Answer 3

Growth phase. Proteins and RNA synthesised. At G1 checkpoint cell is commited to division and moves into S phase. 9-12 hours.

Question 4

S phase

Answer 4

DNA synthesis replicates genetic material. Each chromosome consists of two sister chromatids. 6-8 hours

Question 5

G2

Answer 5

Cell continues to grow. G 2 check point ensures there is enough cytoplasmic material necessary for mitosis and cytokinesis. 2-5 hours

Question 6

Cell division

Answer 6

M phase. Cell stops growing. First mitosis (nuclear division) then cytokinesis (cell division). Metaphase check point ensures the cell is ready to complete cell division. 1 hour

Question 7

What is mitosis

Answer 7

Part of the cell cycle where chromosomes in the nucleus are separated into two identical sets of chromosomes contained within their own nucleus.

Question 8

Steps of mitosis

Answer 8

Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis.

Question 9

prophase

Answer 9

Chromosomes condense. Breakdown of nuclear membrane. Spindle fibres appear.

Question 10

Metaphase

Answer 10

Chromosomes align along metaphase plate

Question 11

Anaphase

Answer 11

Centromeres divide. Sister chromatids move to opposite poles

Question 12

Telophase

Answer 12

Nuclear membrane reforms. Chromsomes decondense, spindle fibres disappear.

Question 13

Cytokinesis

Answer 13

Cytoplasm divides. Parent cell becomes two daughter cells with identical genetic information.

Question 14

Cell cycle is regulated by

Answer 14

Heterodimeric protein kinases composed of Cyclins and cyclin-dependent kinases (CDKs)

Question 15

Cyclins

Answer 15

Regulatory subunit

Question 16

Cyclin- dependent kinases (CDKs)

Answer 16

catalytic subunit of the activated heterodimer which phosphorylates target proteins to orchestrate coordinated entry into the next phase of cell cycle.

Question 17

Which are constitutively active, cyclins or CDKs?

Answer 17

CDKs are constitutively active

Question 18

What phase is best for cytogenetic analysis

Answer 18

Metaphase. Cell cycle is stopped using colchicine. Stops spindle fibre apparatus formation.

Question 19

G1/ s checkpoint involves

Answer 19

Formation of CDK4/ 6-cyclin D. This phosphorylates retinoblastoma protein, relieving inhibition of E2F TF so cyclin E is expressed. Cyclin E then binds to CDK2

Question 20

g2/M checkpoint involves

Answer 20

p53. DNA damage leads to p53 activation which then inhibits progression through checkpoint. Also CDK1 activation by phosphorylation and dephosphorylation (by cyclin-activating kinase, CAKs) enables binding to cyclin B. This allows transition to M phase.

Question 21

Metaphase checkpoint

Answer 21

When chromosomes assemble on metaphase plate, anaphase-promoting complex (APC) is activated. This degrades cyclin B/CDK1 cmplex. Separase is then no longer inhibited and can cut spindles. Sister chromatids then separate and enter anaphase.

Question 22

Meiosis Prophase 1- leptotene step

Answer 22

Nuclear chromatin condense

Question 23

Meiosis Prophase 1- zygotene step

Answer 23

Maternal and paternal homologous pair to form bivalents, held together by synaptonemal complex.

Question 24

Meiosis Prophase 1- pachytene step

Answer 24

All homologues are now paired. Chromsomes thicken. Cross over and recombination of material occurs. 60-90 events per cell occur.

Question 25

Meiosis Prophase 1- diplotene step

Answer 25

Homologues separate (desynapsis) but held together by chiasmata.

Question 26

Meiosis Prophase 1- diakinesis step

Answer 26

Bivalents more contracted and nuclear envelope breaks down.

Question 27

Meiosis Prophase 1- detailed steps

Answer 27

leptotene, zygotene, pachytene, diplotene, diakinesis.

Question 28

Meiosis

Answer 28

specialised cell division that reduces the chromosome number by half. Interphase by two rounds of cell cycle to produce 4 daughter cells, which are not genetically identical to parent cells (unlike mitosis).

Question 29

Meiosis metphase 1

Answer 29

spindles formed, bivalents aligned

Question 30

Meiosis anaphase 1

Answer 30

homologous chromosomes drawn apart. Chromatids remain together

Question 31

Meiosis telophase 1

Answer 31

chromosomes at poles. Haploid daugther cells formed.

Question 32

Meiosis prophase/metaphase 2

Answer 32

cells pass directly from meiosis 1 to metaphase 2 with no prophase 2. Nuclear envelope breaks down, new spindle formed, chromsomes (consisting of 2 chromatids) align.

Question 33

Meiosis anaphase 2

Answer 33

separation of centromeres forming 2 haploid cells (4 in total).

Question 34

Gametogenesis

Answer 34

occurs by meiotic division of diploid gametocytes into various gametes. Oogenesis in females, spermatogenesis in males

Question 35

Difference between meiosis 1 and 2

Answer 35

1- leads to random independent assortment of chromosome pairs. Random crossover enables genetic recombination.
Meiosis 2- separation of chromatids to a haploid state

Question 36

Describe spermatogenesis

Answer 36

Spermatogonia differentiate into primary spermatocytes, which undergo meiotic division. After meiosis 2, there are 4 haploid spermatids which then mature into sperm cells.

Question 37

Describe oogenesis

Answer 37

Primordial germ cells migrate to the forming gonads to form oogonia. These cells proliferate my mitosis before differentiating into primary oocytes. Meiosis 1 begins, reaching meiotic prophase 1 at 8 months gestation. Stay in this state until onset of sexual maturity. SUrge in luteinising hormone (LH) leads to release of oocyte from follicle. After meiosis 2 there is asymtetrical cell division forming a smaller polar body and the ovum.

Question 38

Non-disjunction

Answer 38

when paired homologues (meiosis 1) or sister chromatids (meiosis 2) fail to separate.

Question 39

Non-conjugation

Answer 39

homologues fail to pair

Question 40

how can aneuploidy occur

Answer 40

when sister chromatids separate too early.

Question 41

When does recombination occur

Answer 41

during prophase 1 stage of meiosis. Homologous chromosomes line up in pairs and swap segments of DNA (crossing over)

Question 42

Describe process of recombination

Answer 42

1. Alignment of 2 homologous DNA strands.
2. Breakage of strands (double strand breaks)
3. Equal exchange of DNA segments between two strands. Single end invasions resulting in double Holliday junction formation.
4. Sealing of resultant DNA molecules with ligases

Question 43

Consequences of recombination

Answer 43

• NAHR (non allelic homologous recombination)
• Single gene disorder (deletion/dup of single gene), e.g. CF, Rubinstein-taybi (CREBBP, EP300 genes)
• Contiguous gene disorders (several genes deleted/duplicated). e.g. PAX6+WT1 genes in Wilms’ tumour aniridia genitourinary abnormalities.
• segmental aneuploidy syndromes (loss/gain large chromosome regions). Eg. Di George 22q11.2 deletion