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ap bio


study guide


Unit 4

4.6 Cell Cycle






written by

Annika Tekumulla

annika tekumulla

published on march 31, 2020

Last updated on June 11, 2020

The cell cycle is the sequence of steps prior to cell division. In eukaryotic cells, the cell cycle is highly regulated through the growth and reproduction of cells. The cell cycle consists of 5 phases: interphase (G1, S, and G2), mitosis, and cytokinesis.

Image courtesy of Bio LibreTexts.

1️⃣ Interphase

Interphase contains the phases G1, S, and G2. Over 90% of the cell cycle is spent in interphase! During interphase, the chromatin of the cell is threadlike so when looking at a cell undergoing interphase, a centrosome can be spotted with 2 centrioles. During the S phase, the centrosome is duplicated. 

Now, let’s break down the phases. 1️⃣ G1 is a period of intense growth and activity. 2️⃣ S is used to stand for the synthesis of DNA. In 3️⃣ G2, the cell continues to grow in order to finish cell division.

Image courtesy of Doc Kaiser's Microbiology.

4️⃣ Mitosis

Mitosis is the part of the cell cycle when the nucleus of the cell is divided. Even though mitosis is one process, it is broken down into prophase, metaphase, anaphase, and telophase.

Prophase is the first phase of mitosis. In prophase, the nuclear membrane begins to disintegrate, chromosomes condense, and the spindle begins to form. 

During metaphase, chromosomes begin to line up in the middle of the cell. Also, the centrosomes move to the ends of the cell. 

Anaphase is when the centromeres finally separate. The spindle pulls apart the now sister chromosomes (identical copies). 

Telophase begins when the chromosomes move to opposite ends of the cell. The chromosomes begin to uncoil and return to their threadlike shape. 


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Mitosis is complete once the cell separates and 2 separate nucleoli form.

Image courtesy of BioNinja.

5️⃣ Cytokinesis 

The process of cytokinesis is different in plant and animal cells. After mitosis occurs, cytokinesis begins. Cytokinesis is when the cytoplasm is divided. 

The process of cytokinesis is different in plant and animal cells.

For plant cells, a cell plate made of stiff sugars is formed and surrounds the cell membrane. In plant cells, the daughter cells do not separate from each other. Instead, a new cell wall is created.

For animal cells, a cleavage furrow is formed. A cleavage furrow is a groove that is created in the middle of the cell surface. The cytoplasm then begins to separate.

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