Cell cycle

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Cell cycle


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USMLE® Step 1 questions

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High Yield Notes

15 pages


Cell cycle

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USMLE® Step 1 style questions USMLE

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An investigator teaches the cell cycle to his student. Which of the following processes occurs during the longest phase of interphase in the cell cycle?  

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Alkylating agents p. 449

in cell cycle p. 446

Antimetabolites p. 446

in cell cycle p. 446


in cell cycle p. 448

Bleomycin p. 447

in cell cycle p. 446

Cancer drugs

cell cycle p. 446

Carmustine p. 449

in cell cycle p. 446

Cell cycle phases p. 44

Cisplatin p. 449

in cell cycle p. 446

Cladribine p. 446

in cell cycle p. 446

Cytarabine p. 446

in cell cycle p. 446


cell cycle phase p. 44

Etoposide p. 450

in cell cycle p. 446

5-fluorouracil p. 446

in cell cycle p. 446

Hydroxyurea p. 448

in cell cycle p. 446

Irinotecan p. 450

in cell cycle p. 446

Lomustine p. 449

in cell cycle p. 449

Methotrexate p. 446

in cell cycle p. 446

Microtubule inhibitors p. 449

in cell cycle p. 446

Paclitaxel p. 449

in cell cycle p. 446

6-mercaptopurine p. 448

in cell cycle p. 448

Teniposide p. 450

in cell cycle p. 446

Vinblastine p. 449

in cell cycle p. 446

Vincristine p. 449

in cell cycle p. 446


The cell cycle refers to the events that somatic cells - which includes all of the cells in our bodies except the reproductive cells - go through from the moment they’re formed until the moment they divide in two identical daughter cells.

This cycle varies in length depending on the type of cell - for rapidly dividing cells, like skin cells, it takes less than a day, whereas for other cells, like liver cells, the cell cycle can last years.

The cell cycle has two phases: interphase, and mitosis.

Interphase the longest part of the cell cycle, and it’s a state of preparation, during which the cell carries out its cell functions, grows and replicates its DNA to prepare for mitosis - or cellular division.

After a parent cell divides, each of the two daughter cells enter interphase again.

Now, interphase can further be broken down in three subphases: G1, S, and G2. G1 stands for “gap” or “growth” 1, and it’s the longest phase of the cell cycle.

During G1, the cell mostly grows and the organelles take care of regular cellular business - like the synthesizing proteins and producing energy.

Inside the cell nucleus, there’s our DNA, organized as chromosomes - and during G1, each chromosome is made up of a single, thin spaghetti of DNA, called a chromatid.

At the end of G1, there’s a cell cycle control point called the G1 checkpoint - where the cell checks to see if the DNA is not damaged, and it synthesized the right proteins in the correct amount.

If it turns out that there is any reason for the cell not to divide - such as DNA damage, things can go one of two ways: the cell can either enter a non-dividing state, called the G0 phase, where the DNA repair mechanisms try to fix the problem, or the cell can self-destruct in a process called apoptosis.

Now, if the cell does get the go-ahead at the G1 checkpoint, it enters the S phase. S stands for “synthesis”, because during this phase, DNA is replicated, so that each daughter cell receives identical copies of the genetic material.


The cell cycle is a process that somatic cells go through that involves the duplication of DNA, growth, and division of the cell. The cell cycle can be divided into four phases: G1, S, G2, and M. G1 is the growth phase, where the cell performs all of its functions, and S is the synthesis phase, where DNA replication occurs. G2 is the growth phase, where the cell grows in size and prepares for Mitotic division, and M is the mitotic cell division phase, dividing the cell into two identical daughter cells.


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