Extension 3.7 Control of Cell Cycle at Checkpoints
3
Extension 3.7 Control of the cell cycle at checkpoints Student Salters-Nuffield Advanced Biology, Pearson Education Ltd 2008. © University of York Science Education Group. This sheet may have been altered from the original. 1 of 3 X3.07S Enzymes control the cell cycle at checkpoints Progress through the cell cycle is controlled at checkpoints between the stages G1, S, G2 and M. At each checkpoint the formation of proteins called cyclins controls the passage to the next stage. The cyclins activate enzymes called cyclin-dependent kinases (CDKs). These enzymes initiate reactions that occur in the next phase of the cycle. Figure 1 shows the role of CDK1 in initiating prophase. Cyclins accumulate during G2 of interphase. They attach to the CDK and the complex formed catalyses phosphorylation of other proteins. Phosphate added to the proteins changes their shape and makes them active. For example, phosphorylation of proteins associated with our DNA can lead to condensation of the chromosomes. Figure 1 The interaction of cyclins and cyclin-dependent kinases controls the different stages of the cell cycle. Here CDK1 controls entry into prophase of mitosis. Complete the interactive tutorial that accompanies this activity before completing this sheet.
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Transcript of Extension 3.7 Control of Cell Cycle at Checkpoints
Extension 3.7 Control of the cell cycleat checkpoints
Student
Salters-Nuffield Advanced Biology, Pearson Education Ltd 2008. © University of York Science Education Group.This sheet may have been altered from the original. 1 of 3 - 1 -
X3.07S
Enzymes control the cell cycle at checkpointsProgress through the cell cycle is controlled at checkpoints between the stages G1, S, G2 and M. Ateach checkpoint the formation of proteins called cyclins controls the passage to the next stage. Thecyclins activate enzymes called cyclin-dependent kinases (CDKs). These enzymes initiate reactionsthat occur in the next phase of the cycle.
Figure 1 shows the role of CDK1 in initiating prophase. Cyclins accumulate during G2 ofinterphase. They attach to the CDK and the complex formed catalyses phosphorylation of otherproteins. Phosphate added to the proteins changes their shape and makes them active. For example,phosphorylation of proteins associated with our DNA can lead to condensation of the chromosomes.
Figure 1 The interaction of cyclins and cyclin-dependent kinases controls the different stages of the cell cycle. HereCDK1 controls entry into prophase of mitosis.
Complete the interactive tutorial that accompanies this activity before completing thissheet.
StudentExtension 3.7 Control of the cell cycle at checkpoints
Salters-Nuffield Advanced Biology, Pearson Education Ltd 2008. © University of York Science Education Group.This sheet may have been altered from the original. 2 of 3 - 2 -
X3.07S
QuestionsQ1 a Label the G1, S and G2 phases on the cell cycle diagram (Figure 1).
b Draw arrows from the phrases on the right to the correct position on the diagram toshow the events in the cell cycle that control entry into mitosis.
Q2 Using the graph in Figure 2 below:a During which phase of the cell cycle do the cyclins combine with CDKs to form active
complexes that initiate mitosis?
b Draw and label a vertical line on the graph at the point where CDKs start to combinewith cyclins.
c Mark the G2 checkpoint on the graph.d The cell cycle checkpoints are bypassed in cancer. What problems may this cause?
Q3 Mammalian cells can be induced to fuse, producing a single cell with two nuclei (Figure 3on the next page).When a cell in mitosis is fused with a cell in any other phase (e.g. G2), the nucleus from thenon-mitotic cell immediately begins mitosis. From your knowledge of the control of the cellcycle, suggest an explanation for this observation.
CDK activate an enzyme whichbreaks down the activecomplex.
Synthesis of cyclins.
Cyclins combine with CDKs tofrom active complex.
Levels of active complexinitiate mitosis.
MITOSIS
Figure 1 The cell cycle
Figure 2 Concentration of cyclin and active complex during the cell cycle.
cyclinactive complex
G1 S G2 M G1 S G2 M
Con
cent
ratio
n
StudentExtension 3.7 Control of the cell cycle at checkpoints
Salters-Nuffield Advanced Biology, Pearson Education Ltd 2008. © University of York Science Education Group.This sheet may have been altered from the original. 3 of 3 - 3 -
X3.07S
Figure 3 Cell fusion.
Mitosis G2 Both nuclei in mitosis
Fusion
