A culture ofcells was studied and the following results were obtained: (1)5% oft
ID: 218011 • Letter: A
Question
A culture ofcells was studied and the following results were obtained: (1)5% ofthe cells were forming typical metaphases. (2) After a pulse chase experiment with [H] thymidine, 20% of the cells were labeled, as detected by autoradiography. (3) When metaphase cells were checked for radioactivity, the first labeled chromosomes appeared 6 hours after the short [H] thymidine pulse. (4) Given that the doubling time ofthese cells is 24 hours, how long the different cell cycle phases (Mitosis, S-phase,G and Gy will take in hours? Answer question 2 for 15% of[H]tymidinelabeled cells Question 2- Question 3-Explanation / Answer
The dynamic processes and different pathways in a cell can be analysed by pulse-chase experiments.
The process includes, analysis of a cellular process over a time period, observing by exposing cell or cellular components by labelling (referred to as pulse), followed by analysis of the same component in unlabelled form (referred to as chase).
Pulse-chase experiment, using radioactive thymidine, the phases of cell cycle, (M, G1, G2, S) ca be measured.
In this case, it is given:
1. Cells in metaphase = 5%
2. Cells labelled = 20%
3. Time for first labelled chromosome to appear = 6 hours.
4. Doubling time =24 hours
A) Metaphase is part of mitotic (M) phase.
Hence, M phase = 5 % 24 hours = 1.2 hours
B) During the experiment, radiolabelling by thymidine is done during S-phase, when DNA is synthesized.
Thus, the proportion of cells that are labelled during the pulse indicate the S phase.
S phase = 20 % of 24 hours = 4.8 hours.
C) The time for first labelled chromosome to appear indicates the G2 phase.
G2 phase = 6 hours.
D) M+ S+ G1+ G2 = 24 hours
(1.2 + 4.8 + 6) + G1 = 24 hours
G1 phase = 24 – 24-12 =12 hours
Answer:
1. Mitosis = 1.2 hours
2. S Phase = 6 hours
3. G1 phase = 12 hours
4. G2 phase = 6 hours
Total = 24 hours.