Cell Cycle

Question 1

What does mitosis result in

Answer 1

2 genetically identical diploid daughter cells

Question 2

What does meiosis I result in? Meiosis II?

Answer 2

Meiosis I - two genetically different haploid cells

Meiosis II - 4 haploid cells - two identical pairs

Question 3

What does crossing over occur?

Answer 3

Prophase I

Re-assortment of genetic material between homologous or paired chromosomes

Question 4

What are the phases of cell cycle

Answer 4

G1 - gap after mitosis of cell from previous cycle and before DNA synethsis

S - DNA synthesis

G2 - gap between completion of DNA synthesis and start of cell division

M - mitosis - cell division

(G0) - non dividing cells such as corneal endothelium, neurones remain in resting noncycling state

Question 5

What controls progression through cell cycle?

Answer 5

Cyclins

Cyclin dependent kinases stimulate cell cycle progression by phosphoylating specific proteins in the cell required for transiion to the next stage

Question 6

What is the restriction point in G1

Answer 6

Once passed the cell is committed to completing its cell division

Question 7

What occurs at the G1-S checkpoint?

Answer 7

Ensures that previous cycle of division has been completed and any resultant damage repaired

Question 8

What gene acts at the G1-S checkpoint

Answer 8

p53 gene - tumour suppressor gene - restricts entry of cells with damaged DNA to the S phase - regulates passage of cell through the restriction point

Question 9

What happens at the G2-M chekpoint

Answer 9

Ensures that dNA synthesis and resultant damage are repaired before mitosis occurs

Question 10

What arethe phases of mitosis

Answer 10

Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 11

What happens in prophase?

Answer 11

Cells chromatin condenses
Chromosomes become visible as a pair of sister chromatids - joined at centromere

Centrioles duplicate and migrate towards opposite poles of cell

Spindle of microtubules is formed - nucleoli disperse

Question 12

Prometaphase in mitosis

Answer 12

Breakdown of nuclear envelope
Formation of kinetochores - attachment point between chromosomes and the spindle at the centromere

Question 13

Metaphase (mitosis)

Answer 13

Chromosomes attach to the spindle by the kinetochore and line up to form equatorial plate

Question 14

Anaphase (mitosis)

Answer 14

Centromeres separate and the chromatids and pulled to opposite poles by spindle

Clustering of complete set of chromosomes at each pole of the cell

Question 15

Telophase (mitosis)

Answer 15

Chromosomes begin to uncoil again
Nuclear membrane reforms
Nucleoli reappear

Question 16

Cytokinesis (mitosis)

Answer 16

Cleavage forms in middle of cell dividing in two

Question 17

Prophase 1 (meisois)

Answer 17

Homologous chromosomes come together and cross over, exchange segments in homologous recombination

Question 18

Process of prophase 1 (meiosis)

Answer 18

Leptopene - spindle forms

Zygotene - chromosomes shorten, thicken

Pachytene - chiasmata form - crossing over

Diplotene - exchange of genetic material between homologous chromosomes

Diakinesis - recombinant chromosome formed

Question 19

Metaphase 1 (meiosis)

Answer 19

Chromosomes attach to the spindle

Question 20

Anaphase 1 (meiosis)

Answer 20

Whole chromosomes migrate to opposite poles)

Question 21

Telophase 1 (meiosis)

Answer 21

2 genetically different haploid cells are formed

Question 22

What happens in meiosis 2

Answer 22

In anaphase II - sister chromatids separate rater than chormosomes - forming 2 identical pairs of haploid cells (4 cells altogether)

Question 23

What processes generate genetic diversity?

Answer 23

Chiasmata formation from corssoing over in prophase I - random exhage of genetic material between homologous chromosomes

Independent segregation of homologous chromosomes occurs during anaphase I

Question 24

How many combinations possible in gamaets

Answer 24

2^23 combinations

Question 25

What is formed in meiosis of oocytes?

Answer 25

One definitive oocyte One secondary oocyte One polar body

Question 26

What is apoptosis?

Answer 26

Cell death that is programmed After intra or extracellular physiological triggers during development/remodelling, defence, homeostasis, ageing Pyknosis - condensation of nucleus Karyorrhexis - nucles fragments) Cells shrink Organelles maintain structure Cell membrane forms irregular buds Cells break into smaller bodes Phagocytosed by macrophages

Question 27

What is pyknosis?

Answer 27

Condensation and fragmentation of chromatin Condenses into patches against the nuclear envelope as a result of endonuclease activity

Question 28

What is karyorrhexis?

Answer 28

Nuclear envelope becomes discontinuous and DNA fragments

Question 29

What induces p53? What does it do

Answer 29

Tumour suppressor gene Induced by DNA damage TRanscription factor results in arrest of cell cycle in G1 to allow DNA repair

Question 30

What does Hcl-2 do

Answer 30

Suppresses some apoptotic pathways rEduction in levels of Bcl-2 associated with apoptosis

Question 31

What are telomeres?

Answer 31

Repetitive DNA sequences found at the end of chromosomes Synthesised by telomerase - no replicated in the same way as other chromosomal DNA

Question 32

How is apoptosis initiated?

Answer 32

Direct result of TNF production by macrophage Fas ligand binds Fas receptor - formation of death inducing signalling complex (DISC) - contains FAS assocatied protein with Death Domain (FADD), caspase-8 and caspase-10 Sequence of events triggers apoptosis