The cell cycle

Question 1

Two things must happen for the cell cycle

Answer 1

1. Duplication of the cell contents e.g. DNA, organelles, cytoplasm…
2. Division into new progeny cells

Question 2

How many cycles does it take for unicellular organisms to replicate

Answer 2

Each cell cycle gives 2 new organisms

Question 3

How many cycles does it take for multicellular organisms to replicate

Answer 3

Zygote must undergo many rounds of the cell cycle to make a fully grown human

Question 4

Phases of the cell cycle

Answer 4

M, S, G0/G1/G2 phases

Question 5

Why and which cells are in the G0 phase

Answer 5

1. Cell cycle isnt possible e.g. nerve cells since they are fully differentiated
2. Maintained in G0 unless stimulated to divide e.g. hepatocytes
3. Constantly in the cell cycle e.g. epithelial cells of the gut or haematopoietic cells in the bone marrow

Question 6

How can you visually see the DNA content changing during the cell cycle

Answer 6

Fluorescence activated cell sorter (FACS) analysis

Question 7

Gap 1 phase function

Answer 7

Growth and preparation for s phase

Question 8

S phase function

Answer 8

Chromosome duplication

Question 9

Gap 2 phase function

Answer 9

Growth and preparation for M phase

Question 10

Prophase

Answer 10

Chromosomes condense, centrosomes move to opposite poles, mitotic spindles start to form

Question 11

Prometaphase

Answer 11

Nuclear envelope breaks down and chromosomes attach to mitotic spindle

Question 12

Metaphase

Answer 12

Centrosomes are at the opposite poles, chromosomes are at the most condensed state and line up at the equator of the spindle

Question 13

Anaphase

Answer 13

Sister chromatids separate, each new daughter chromatid moving to the opposite pole

Question 14

Telophase

Answer 14

Chromosomes arrive at the spindle poles, chromosomes de-condense and nuclear envelope reforms

Question 15

Cytokinesis

Answer 15

Cytoplasmic division at the position of the metaphase plane. Contractile ring of actin and myosin II constrict the cell into 2 new daughter cells

Question 16

What makes up the mitotic spindle

Answer 16

Bipolar array of microtubules

Question 17

How does the mitotic spindle connect to chromosomes and what is it

Answer 17

Via the kinetochore; A large protein structure assembled on the centrosome

Question 18

What are the different types of mitotic spindle

Answer 18

1. Astral
2. Kinetochore
3. Interpolar

Question 19

What occurs in meiosis I

Answer 19

Homologous chromosomes line up on the spindle fibre and separate to opposite spindle poles

Question 20

What occurs in meiosis II

Answer 20

Sister chromatids line up on the spindle and separate to opposite spindle poles

Question 21

What is non-disjunction

Answer 21

Failure of homologous chromosomes to separate from one another at either meiotic division I or II

Question 22

what are some non fatal autosome mutations

Answer 22

Edwards syndrome - trisomy 18
Patau syndrome - trisomy 13
Downs syndrome - Trisomy 21

Question 23

what are some sex chromosome mutations

Answer 23

Turners syndrome - XO
Triple X syndrome - XXX
Klinefelters - XXY

Question 24

summarise the G1 checkpoint

Answer 24

Extracellular environment?
Growth factors?
Mitogenic signals?
Check DNA for damage?

Question 25

summarise G2 checkpoint

Answer 25

DNA replicated properly? | Check DNA for damage?

Question 26

summarise M checkpoint

Answer 26

All chromosomes aligned on the mitotic spindle?

Question 27

what are cyclin dependant-kinases - CDKs

Answer 27

Enzymes that phosphorylate target proteins used in the regulation of the cell cycle Becomes active when bound to a corresponding cyclin

Question 28

What are cyclins

Answer 28

Regulators of CDKs, different cyclins are produced at each phase of the cycle

Question 29

What is involved in the cell cycle of yeast

Answer 29

S-cyclin binds with CDK to trigger S phase | M-cyclin binds with CDK to trigger M phase

Question 30

Cyclin D pathway

Answer 30

1. Binds to CDK4, activating it 2. CDK4 partially phosphorylates pRB 3. E2F is released from pRB 4. E2F regulated genes can be made allowing the cell to progress from the G1 to S phase

Question 31

How does the cell cycle arrest in the G1 phase so damaged DNA can be repaired

Answer 31

1. P53 will be phosphorylated and activated when the DNA is damaged 2. P53 will bind to the promoter region of the P21 gene, stimulating its expression 3. P21 will bind and inhibit G1 CDKs therefore the cell cycle is stopped

Question 32

Cyclin dependant kinase inhibitors

Answer 32

1. INK4 - inhibits cycle progression after G1 point as it inhibits CDK4 2. CIP/KIP - inhibits all other CDK-cyclin complexes

Question 33

Neoplasia

Answer 33

mutated P53 and pRB genes lead to uncontrolled progression through the cell cycle

Question 34

What regulates the early G1 phase

Answer 34

Cyclin D and CDK4

Question 35

What triggers the S phase

Answer 35

Cyclin E and CDK2

Question 36

What regulates the completion of the S phase

Answer 36

Cyclin A and CDK1 and 2

Question 37

What triggers the M phase

Answer 37

Cyclin B and CDK1