cell division + development.

Question 1

cell cycle? (4)

Answer 1

1. cycle of cell growth + maturity + division.
2. highly ordered sequence of events.
3. process that all somatic cells in multicellular organisms use to grow + divide.
4. produces 2 genetically identical daughter cells.

Question 2

length of cell cycle for an embryo? (1)

Answer 2

1. 8-60 min.

Question 3

length of cell cycle for yeast cell? (1)

Answer 3

1. 1.5-3 h.

Question 4

length of cell cycle for intestinal cells? (1)

Answer 4

1. 12 h.

Question 5

length of cell cycle for bone marrow cells? (1)

Answer 5

1. 18 h.

Question 6

length of cell cycle for stomach epithelial cells? (1)

Answer 6

1. 24 h.

Question 7

length of cell cycle for liver cells? (1)

Answer 7

1. 1 year.

Question 8

Interphase - Growth 1? (4)

Answer 8

1. cells increase in size + mass.
2. all metabolic processes remain active - e.g., protein synthesis, hormone production, and respiratoon.
3. organelles replicated - except chloroplasts + mitochondria.
4. increases protein synthesis occurs.

Question 9

Interphase - Growth 1 checkpoint? (6)

Answer 9

1. Cells check:
   - chemicals needed for replication are present.
   - for damage in DNA before entering S-phase.
   - cell is suitable size.
   - cell has sufficient nutrients.
2. If conditions are not correct, the cell enters a resting state (G0) and no longer divides.

Question 10

Interphase - Synthesis (S)? - (2)

Answer 10

1. DNA is replicated.
2. using semi-conservative replication (SCR).

Question 11

Interphase - Growth 2 (G2)? (4)

Answer 11

1. chloroplasts + mitochondria increase in size + divide (increases in no.)
2. cells continue to increase in size + mass.
3. energy stores are increased.
4. spindle fibres start to form.

Question 12

Interphase - Growth 2 checkpoint? (4)

Answer 12

1. Cells check:
   - all DNA has been replicated without damage.
   - cell is of correct size.
2. if this is correct, cell passes into mitotic stage.

Question 13

How long does interphase take? (1)

Answer 13

1. 90% of cycle time.

Question 14

How long does mitosis take? (1)

Answer 14

1. 10% of cycle time.

Question 15

Mitosis? (6)

Answer 15

1. Nuclear division.
2. Sub divided into:
   - Prophase.
   - Metaphase.
   - Anaphase.
   - Telophase.

Question 16

Cytokinesis? (3)

Answer 16

1. Equal division of cytosol + organelles.
2. Equal division of cytoplasm.
3. Formation of 2 genetically identical daughter cells.

Question 17

Name 3 cells that lose the ability to divide altogether? (3)

Answer 17

1. neurons.
2. erythrocytes.
3. muscle cells.

Question 18

Give 2 reasons some cells either temporarily or permenantly leave the cell cycle? (2)

Answer 18

1. Differentiation - cells become specialised and can no longer divide - e.g., mature erythrocyte (has no nucleus).
2. Damaged DNA - cell is no longer viable + hence enters G0 (resting state). Most cells can only divide an finite no. of times - once this is passed they enter a period of senescence (old/ageing).

Question 19

cell cycle controls? (7)

Answer 19

1. Sequence + timing of cell cycle controlled by cyclins (specialised proteins).
2. cyclins activate enzymes called cyclin-dependent-kinases (CDKs).
3. CDKS catalyse the addition of a phosphate group onto a protein (phosphorylation).
4. Phosphorylation of protein changes its tertiary structure of cyclins.
5. Specific CDKs control specific steps in the cell cycle.
6. Cell cycle stopped if errors are detected - e.g.,
   - if DNA is damaged - p21 (a protein) binds to CDK.
   - This halts the cell cycle at G1 stage in interphase.
7. Mutations to cyclin genes or CDK genes can lead to the failure to repair DNA -> cancer.