Question

CELLS alive! - Cell Cycle Worksheet Answer KEY

What's happening now?

Answer 1

1 G1 phase In this phase cell is metabolicaaly active but don't undergo DNA replication.

2 G0 phase Some cells leave cell cycle and enter into quiescent stage of cell cycle.Cells in this stage remain metabolicaaly active but no longer proliferate until required.

3 This represents first check point governed by RB Gene which is key negative regulator of cell cycle proliferation..It is also regulated by CDK/Cyclins.

4 After passing this checkpoint cell starts preparing for S(synthesis phase)

5 Synthesis phase,It represent second check point G2/M phase.In this synthesis phase amount of DNA per cell doubles.This is a important check point as cells don't undergo mitosis till the damage is complete recoverd.Governed by PLK1 Gene.

6 G2 phase In this stage proteins are synthesized for mitosis while cell growth continues.

7 It represents transition to M phase as the cells don't cross this check point,till damage is repaired.

8,9 It represent stages of mitosis Marked by prophae metaphase anaphase and ended by telophase where daughter cells are separated into two.It is the longest phase of cell cycle.

10 It is marked by cytokinesis,in which synthesis of cytoplasm takes place.

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Answer 2

1. Following the M phase or the mitotic phase, the cells enter the G1 phase where the newly formed daughter cells grow in size and synthesis of proteins and mRNA takes place.

2. The G0 phase is the stage in cell cycle where the cell does not undergo any more divisions and is said to be in a state of 'rest'. This could be due to environmental, nutritional or functional facors. Some cells, as in the case of neurons and heart, enters the G0 phase and doesnot undergo mitoosis again once they have been differentiated.

3. This part is termed as the Restriction point or the G1/S checkpoint. The cell will be restricted from moving in to the S phase if there is an undesirable factors like damaged DNA, insufficient growth of cell etc.

4. This stage is termed as the G1-pre S phase where the cell begins to enter the synthesis phase of the cell cycle.

5. The S phase or the Synthesis phase is characterized by the process of DNA replication, production of histon proteins and thereby nucleosomes.

6. The G2 phase or the Gap 2 phase where rapid cell growth along with the production of cytoplasm, organelles and protein synthesis.

7. Prophase stage (first stage of M phase or Mitosis phase) marks the beginning of the mitotic division of the cell.Chromatin condensation, formation of mitotic spindle, breakdown of nuclear envelope (nucleolus) and movement of centrosomes to the poles of the cell are the main events during this stage.

8. During Metaphase, the chromosomes are aligned at the centre of the cell, attached to the centrosomes at the two poles.

9. In the Anaphase stage, the mitotic spindle pulls the chromosomes from either sides and the chromatids gets separated.

10. The final stage of M phase is the Telophse where nuclear envelope forms around the chromosomes and the spindle fibres break down. Following this stage, cytokinesis occurs and the cells are separated.