Biology 9700 · AS & A Level · Structure of nucleic acids and replication of DNA

Structure of nucleic acids and replication of DNA — practice question

The mitotic cell cycle in dividing cells is tightly regulated.
(a)[3]

Complete Table 6.1 to display the correct sequence of stages in the mitotic cell cycle. Several stages are already done for you.

(b)[2]

Vincristine and 5-fluorouracil are chemical compounds that act as cell-cycle inhibitors and may cause apoptosis. • Vincristine attaches to spindle microtubules and stops the spindle from functioning. • 5-fluorouracil blocks the synthesis of thymine nucleotides. Complete Table 6.2 to show which event in the cell cycle will occur when Vincristine or 5-fluorouracil are added to healthy dividing cells at the beginning of interphase. Put a tick (✓) where the event will occur or a cross (✗) where it will not occur. Every box in the table must be filled in.

(c)[3]

Vincristine has been used to treat certain forms of leukaemia. Fig. 6.1 is a photomicrograph of a blood smear from a person with one type of leukaemia that affects lymphocytes. Describe how: • the blood smear in Fig. 6.1 is different from a healthy person's blood smear • the lymphocytes in a person with leukaemia, such as those in Fig. 6.1, are different from those in a healthy person.

Worked solution & mark scheme

This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: recognition of interphase ($G_1$, $S$, $G_2$)

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