4B Eukaryotic Cell Cycle

Question 1

Interphase (define + purpose as it is the first + longest stage of the cell cycle)

Answer 1

Define:
Cellular growth + duplication of chromosomes (that exist as chromatin threads rather than discrete chromosomes in the nucleus)

Purpose:
- Synthesis necessary DNA, proteins, and organelles for growth + replication

Question 2

Identify + outline the three sub-stages

Answer 2

1. Gap 1 (G1) Phase:

• Increasing the volume of its cytosol
• synthesising proteins for DNA replication
• Replicating its organelles

2. Gap 0 (G0) Phase:

Cells come here or proceed to the next stage (Synthesis)

Two types of cells here are not required to replicate and rest:

• Quiescent dormant cells which can re-enter the cell cycle
• Terminally differentiated cells
  that have fully specialised and no
  longer replicate

3. Synthesis (S) Phase:

The cell replicates its DNA turning one chromosome into two genetically identical sister chromatids

4. Gap 2 (G2) Phase

Cell continues to grow + develop by:

• increasing the volume of the cytosol
• synthesising proteins in preparation for mitosis.

Question 3

Mitosis (define + purpose)

Answer 3

Define:

Separation of sister chromatids + the formation of two new nuclei

Purpose:

Growth + replace unworn cells

Question 4

Identify + outline the stages of mitosis

Answer 4

Interphase:

Chromosomes duplicate

Early Prophase:

The nuclear membrane begins to dissolve + chromosomes start to condense + spindle fibers forming

Late prophase:

The nuclear membrane has almost completely dissolved + chromosomes are fully condensed

Metaphase:

Chromosomes line up along the equator of the cell + spindle fibres are fully formed and attached to the centromere of each chromosome

Anaphase:
Chromosomes move to opposite poles + spindle fibers contract and split the centromere

Telophase:

Nuclear membrane re-forms + spindle fibres disappear + chromosomes decondensed

Question 5

Cytokinesis (define + purpose)

Answer 5

Division of the cytoplasm + formation of two daughter cells

Question 6

Difference between cytokinesis in plant and animal

Answer 6

Forms structures for the cell wall of the plant cell whereas Animal cells do not have a cell wall

Division occurs by cell plate formation for plant cells whereas for animal cells it occurs by the cleavage furrow

Question 7

Identify the steps of cytokinesis for animal cells

Answer 7

1. Cleavage furrow forms
2. Cleavage furrow reaches the centre of the cell
3. Cells are pinched apart into two new cells

Question 8

Identify the steps of cytokinesis in plant cells

Answer 8

1. Vesicles start to accumulate in the center of the cell
2. A cell plate begins
   to form along the
   equator of the cell.
3. New cell walls are
   formed producing
   two new cells.

Question 9

Regulation of the cell (checkpoints) - Purpose/what happens if damage is detected

Answer 9

Purpose:

1. The cell inspects itself for errors before
   proceeding to the next stage

Damage detected:

• The cell can pause for repairs
• If the damage is irreparable, then the cell undergoes programmed cell death.

Question 10

Identify + outline the three checkpoints and their purpose

Answer 10

G1 checkpoint:

• Cell grown to the correct size
• Enough protein for DNA replication
• DNA damage during mitosis and cell growth
• Enough nutrients and oxygen

G2 Checkpoint:

• DNA properly replicated in S phase
• Enough resources for mitosis

Metaphase Checkpoint:

• Formation of spindle fibres
• Chromosomes lined up correctly to proceed to Anaphase