Cell Cycle and Mitosis

The Cell Cycle is:

the series of events that cells go through as they grow and divide.

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During the Cell Cycle, a cell:

grows, prepares for division, and divides to form two daughter cells, each of which begins the cycle again.

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Interphase is:

the period of growth that occurs between cell division.

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Interphase is divided into three phases:

G1, S, G2​

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G1 Phase:

The G1 phase is a period of activity in which cells do most of their growing. Cells will grow larger and synthesize new proteins and organelles.

S Phase:

The S phase replicates chromosomes and synthesizes DNA molecules. When DNA replication is completed, the cell enters G2 phase.

G2 Phase:

During the G2 phase, many of the organelles and molecules required for cell division are produced. When G2 is completed, the cell is ready to enter the M phase.

G₀ Phase:

G₀ is a special resting phase. Cells in G₀ do not continue through the cell cycle, so they do not divide.​

Some cells, like neurons (brain cells) stay permanently in G₀.

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Mitosis is divided into four phases: ​

p___________,

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m___________,

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a___________,

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t____________.

​1. ____________ 5. Chromosome

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2.​____________ 6.____________

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3. Nucleolus ​ 7.____________

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4.____________​ 8. Centrosome

​Interphase

​Interphase is divided into three phases:

____, ____, ____.

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Interphase is the in between stages of cell division.​

​Prophase

- Chromatin condenses into chromosomes.

- ​Centrioles separate

- ​Spindle fibers form

- ​Nuclear envelope breaks down

​Metaphase

- The chromosomes line up across the MIDDLE of the cell.

- ​Each chromosome is connected to a spindle fiber at its centromere.

​Anaphase

- The sister chromatids separate into individual chromosomes and are pulled away by the spindle fibers.

​Telophase

- The chromosomes gather at opposite ends of the cell & uncoil back to chromatin.

​- Two new nuclear envelopes form.

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​Cytokinesis

- The cytoplasm pinches in half.

​- Each daughter cell has an identical set of chromosomes.

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​Vocabulary

​Chromatin - unraveled, thin form of the DNA

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​Chromosome - tightly coiled and condensed form of the DNA

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​Chromatid - 1 part of the pair of matching chromosomes. 1 chromatid comes from mom, 1 chromatid comes from dad, and makes the chromosome pair. These are called sister chromatids.

​Vocabulary (Continued)

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Somatic cell - your body cells, ex: skin cells, muscle cells, liver cells, etc . . .

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​Diploid cell - cell that has a complete set of chromosomes (2N because there are 2 of every chromosome). In humans this is 23 pairs, or 46 total.

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​Spindle fibers - forms during cell division in order to separate the sister chromatids.

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​Centrioles - organelles that form the spindles during cell division.

​You will need to remember the order of the phases:

Interphase, prophase, metaphase, anaphase, telophase, cytokinesis

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A good way to memorize this is to make a mnemonic device that you can remember.​

One mnemonic device is:

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​I p_______ m______ a___ t____ c____________.

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Now try making your own!

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​Continued . . .

​After G2 is a checkpoint - this is where the cell is checked over for any damage or mistakes prior to dividing. If there is damage. Then the cell will not go into the mitosis until it is fixed or the cell is destroyed. This prevents damaged or non functioning cells from making more damaged, non functioning cells.

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Not all cells divide at the same rate. Example, your skin cells divide rapidly due to being exposed to external environments, but your liver cells divide fairly slowly. If a cell does not need to divide to make more cells it will enter G₀. Whenever your body needs more of those cells a signal is sent and the cell will re-enter the cell cycle.

Match

Match each phase of interphase with what occurs in the cell.

• The cell grows and performs its normal cell functions.

• The cell produces a complete copy of its DNA.

• The cell prepares for mitosis (cell division).

• The cell is in a resting phase. It will not continue through the cell cycle and will not divide.

G₁

S

G₂

G₀

• G₁

• S

• G₂

• G₀

Multiple Choice

Before a cell divides, it checks for mistakes in its copied DNA.

If it finds a mistake, it tries to fix it.

If the mistake is too big to fix, what will the cell do instead?

• The cell will divide anyway

• The cell will self-destruct (apoptosis) to prevent the mistake from being passed on

• The cell will stop dividing and go into G0 phase (Gap 0)

• The cell will go haywire and begin attacking other cells

Open Ended

The three phases of interphase, in order, are:

Open Ended

Why is it so important for the cell to ensure that it has copied its DNA correctly during S phase? (Hint: what disease can occur if the DNA is mutated, or copied incorrectly)?

Open Ended

Why do you think it is so difficult to treat brain and spinal cord injuries?

(Hint: neurons, which are brain and spinal cells, stay permanently in G₀ phase).