Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

29. Fungi

Fungi

General Biology

29. Fungi

Fungi

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2:39 minutes

Problem 9

Textbook Question

A particular cell type spends 4 hours in G1 phase, 2 hours in S-phase, 2 hours in G2 phase, and 30 minutes in M-phase. If a pulse-chase experiment were performed with radioactive thymidine on an asynchronous culture of such cells, what percentage of mitotic cells would be radiolabeled 9 hours after the pulse?
a. 0 percent
b. 50 percent
c. 75 percent
d. 100 percent

Verified step by step guidance

Understand the problem: The question involves a pulse-chase experiment with radioactive thymidine, which labels DNA during the S phase. The goal is to determine the percentage of mitotic cells that would be radiolabeled 9 hours after the pulse. This requires understanding the cell cycle and the timing of each phase.

Calculate the total duration of the cell cycle: Add the durations of all phases (G1, S, G2, and M). The total cell cycle time is: \(4 \text{ hours (G1)} + 2 \text{ hours (S)} + 2 \text{ hours (G2)} + 0.5 \text{ hours (M)} = 8.5 \text{ hours}\).

Determine the time elapsed since the pulse relative to the cell cycle: After 9 hours, the cells have completed one full cycle (8.5 hours) and have entered the next cycle. Subtract the total cell cycle time from the elapsed time: \(9 \text{ hours} - 8.5 \text{ hours} = 0.5 \text{ hours}\). This means the cells are 0.5 hours into their second cycle.

Identify the phase of radiolabeled cells: Radiolabeled cells are those that were in the S phase during the pulse. These cells will progress through G2, M, and G1 before entering the next M phase. Calculate the time it takes for these cells to reach M phase: \(2 \text{ hours (G2)} + 0.5 \text{ hours (M)} + 4 \text{ hours (G1)} = 6.5 \text{ hours}\). Adding this to the 2 hours spent in S phase, radiolabeled cells will reach M phase \(2 + 6.5 = 8.5 \text{ hours}\) after the pulse.

Determine the percentage of mitotic cells that are radiolabeled: At 9 hours, the radiolabeled cells have already reached M phase, and the culture is asynchronous. Since the cell cycle is continuous and the timing aligns, all mitotic cells at this point will be radiolabeled. Thus, the percentage of radiolabeled mitotic cells is 100%.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cell Cycle Phases

The cell cycle consists of several phases: G1 (gap 1), S (synthesis), G2 (gap 2), and M (mitosis). Each phase has a specific duration and function, with G1 preparing the cell for DNA synthesis, S phase involving DNA replication, G2 preparing for mitosis, and M phase being the actual division of the cell. Understanding the timing of these phases is crucial for predicting how many cells will be in mitosis at a given time.

Pulse-Chase Experiment

A pulse-chase experiment involves exposing cells to a labeled compound (the pulse) for a short time, followed by a period without the label (the chase). This technique allows researchers to track the incorporation of the label into cellular components over time. In this context, radioactive thymidine is used to label cells in the S phase, and the timing of the chase helps determine how many cells have progressed to mitosis.

Asynchronous Cell Culture

An asynchronous cell culture contains cells at various stages of the cell cycle, rather than all being synchronized in the same phase. This diversity is important for understanding the overall behavior of a population of cells. In the context of the question, it means that at the time of the pulse-chase experiment, some cells will be in different phases, affecting the percentage of mitotic cells that become radiolabeled after a specific time.

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