Describe the role of DNA polymerase in the semi-conservative replication of DNA.

Figure 5 shows the percentage of rat cells undergoing DNA replication. Some cells contained a protein called cyclin D and some cells did not contain cyclin D. All cells were in early interphase at time 0

It took less time for 25% of cells with cyclin D to be undergoing DNA replication than for 25% of cells without cyclin D.

Use Figure 5 to calculate this time difference as a percentage decrease.

Show your working.

Answer ______________ %

Cyclin D stimulates the phosphorylation of DNA polymerase, which activates the DNA polymerase.

Describe how an enzyme can be phosphorylated.

Some tumour cells contain higher than normal concentrations of cyclin D.

Use Figure 5 to suggest why higher than normal concentrations of cyclin D could result in a tumour.