Cell Cycle and Regulation Questions and Answers

Answer: A

One hundred hours contains five doubling periods, and 2 raised to the fifth power is 32. Growth of this kind is exponential rather than linear, which is why tumours enlarge slowly at first and then rapidly. The same doubling time produces very different absolute increases over time.

Answer: B

Binding a receptor at the surface starts a signalling cascade that raises cyclin D and pushes the cell through G1. A cell deprived of them arrests and may enter G0 instead. Dependence on external signals is one of the things cancer cells escape.

Answer: C

Normal cells stop after a limited number of divisions, the Hayflick limit, and also stop on contact with their neighbours. Indefinite division in culture is a property of transformed and cancer cells. The HeLa line has been dividing in laboratories since 1951.

Answer: D

A single layer forms and then growth ceases, whereas cancer cells continue and pile up. Loss of the response is one of the changes seen when cells are transformed. Cancer cells grow over one another and form disorganised heaps in culture.

Answer: A

Its discovery in frog eggs showed that a diffusible factor could push a cell into division, and it was later identified as a cyclin-CDK pair. The finding linked embryology to yeast genetics. Two quite separate research traditions turned out to be studying one system.

Answer: B

Temperature-sensitive mutants that arrest at particular points allowed the genes to be identified one by one. Many of those genes turned out to have close human counterparts. Work in yeast therefore illuminated human cancer directly.

Answer: C

Correct answer: True

The conservation is close enough that human cyclin-dependent kinase genes can rescue yeast mutants lacking their own. That is how the machinery was identified: the cdc mutants of budding and fission yeast defined the components, and the human counterparts were then found by complementation - work that earned the 2001 Nobel Prize and that underlies the cell cycle drugs now used in oncology.

Answer: D

Adding the three named phases gives 19 hours, leaving one hour for mitosis. The proportions are typical, with the visible part of the cycle being much the shortest. Interphase dominates the cycle in almost every cell type.

Answer: A

The G2 checkpoint tests whether replication finished and whether the DNA is intact before mitosis begins. Size is assessed at G1 and spindle attachment during mitosis itself. Each checkpoint guards the step immediately after it.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason names the mechanism. The G2 checkpoint monitors whether replication is complete and whether the DNA is damaged, and it holds the cyclin-dependent kinase driving mitotic entry inactive until both are satisfied. Entering mitosis with unreplicated DNA would tear the chromosomes apart at anaphase, so the block is essential rather than merely prudent.