A.
 
TREATMENT
G1
S
G2/M
Non treated cells
55
16
29
Substance X treatment
95
2
3
 It does not alter the cell cycle.
Wrong- examine the results more carefully.






























































B.

TREATMENT
G1
S
G2/M
Non treated cells
55
16
29
Substance X treatment
95
2
3

 It arrests cells before the restriction point.
Possible- find another possible answer (there are two such answers).
Thencontinue.
































































C.

TREATMENT
G1
S
G2/M
Non treated cells
55
16
29
Substance X treatment
95
2
3

 It arrests cells before the G1/S transition point.
Possible - find another possible answer (there are two such answers).
Thencontinue.






































































D.

TREATMENT
G1
S
G2/M
Non treated cells
55
16
29
Substance X treatment
95
2
3

 It arrests cells during S phase.
Wrong - only 2% of the cells are found in the S phase. Most cells are found in G1.






































































  E.

TREATMENT
G1
S
G2/M
Non treated cells
55
16
29
Substance X treatment
95
2
3

It arests cells before the G2/M transition point.
Wrong



































































F.

TREATMENT
G1
S
G2/M
Non treated cells
55
16
29
Substance X treatment
95
2
3

 It arrests cells during M phase.
Wrong - only 3% of the cells are found in the G2 and M phases. Most cells are found in G1.























































G.

TREATMENT
G1
S
G2/M
Non treated cells
55
16
29
Substance X treatment
95
2
3

 It accelerates the transition of the cells through G0 and induces arrest in G1.

Wrong - arrest in G1 is possible, but the rate of the process (acceleration) cannot be determined in this experiment.




















































































 

Is it Possible to distinguish between arrest before the R point (answer B) and arrest before the G1/S transition (answer C)? (Look at the illustration to the right to get a hint). 

First, think

Thancontinue.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 


 

The present FACS analysis reveals that the vast majority of the cells (95%) contain DNA quantity of 2n, characteristic of phase G1 before and after the R point, as opposed to DNA quantity of 4n, which characterizes the end of the S phase, phase G2 and the beginning of M. 
This implies that substance X may arrest cells before the restriction point or before the G1/S transition point. However, the present FACS analysis cannot distinguish between these two possibilities, since they are both characterized by a DNA quantity of 2n. Additional experiments should be performed to distinguish between the two suggested points of effect of substance X.

Continue

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

.