$$G_1 + S$$ + $$G_2 + M$$ = \text{Cell Cycle}$$

Question 1

Which experimental technique did Alma Howard and Stephen Pelc use to visualize newly synthesized DNA in cells?

Accepted Answer

Autoradiography

Question 2

What was the main finding of Howard and Pelc’s experiment using radioactive phosphorus?

Accepted Answer

DNA synthesis occurs during a specific period in interphase

Question 3

Why was radioactive thymidine used in later experiments to study DNA synthesis?

Accepted Answer

It is incorporated into DNA but not RNA

Question 4

Which phase of the cell cycle is characterized by active DNA synthesis?

Accepted Answer

S phase

Question 5

What is the main purpose of the S phase in the cell cycle?

Accepted Answer

Copying the genetic material

Question 6

Which of the following best describes the cell cycle as defined by Howard and Pelc?

Accepted Answer

The orderly sequence of events leading from chromosome duplication to cell division

Question 7

If a scientist observes black dots in interphase cells but not in M-phase cells after autoradiography, what can be concluded?

Accepted Answer

DNA synthesis occurs during interphase

Question 8

Which of the following is NOT a correct statement about the S phase?

Accepted Answer

It is when chromosomes are partitioned

Question 9

A researcher uses radioactive thymidine to label cells. Which macromolecule will be labeled?

Accepted Answer

DNA

Question 10

Which of the following best explains why the process of DNA replication is separated in time from chromosome partitioning?

Accepted Answer

To ensure accurate duplication and distribution of genetic material

Question 11

Suppose a mutation causes DNA synthesis to occur during M phase instead of S phase. Which of the following is a likely consequence?

Accepted Answer

Chromosomes may not be properly duplicated before division

Question 12

Which of the following equations best represents the relationship between the phases of the cell cycle?

Accepted Answer

$$G_1 + S$$ + $$G_2 + M$$ = 	ext{Cell Cycle}$$

Question 13

In a real-world scenario, why might a cancer biologist be interested in the timing of S phase?

Accepted Answer

To determine when cells are most susceptible to DNA-damaging chemotherapy

Question 14

Which of the following would NOT be detected by autoradiography using radioactive thymidine?

Accepted Answer

Newly synthesized RNA

Question 15

If a cell is exposed to radioactive phosphorus and then visualized using X-ray film, what does the appearance of black dots indicate?

Accepted Answer

Active DNA synthesis

The Discovery of S Phase and the Cell Cycle

Study Guide - Practice Questions