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Copyright Pearson Prentice Hall

Cell Division

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Cell Theory

Cells are the basic unit of structure for all living organisms, and all cells come from other cells.


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In eukaryotes, cell division occurs in two major stages.

The first stage, division of the cell nucleus, is called mitosis.

The second stage, division of the cell cytoplasm, is called cytokinesis.

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New cells are identical to old ones

1. Instructions for making new cells are found in the DNA

2. When DNA is replicated, the new cell gets the exact copy of the DNA.

3. We say that the “parent” cell produces 2 identical “daughter” cells.


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Chromosomes

Genetic information is passed from one generation to the next on chromosomes.

Before cell division, each chromosome is duplicated, or copied.

1.Called chromatin when not dividing

2.Duplicated chromosomes are called chromatids

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Chromosomes

Each chromosome consists of two identical “sister” chromatids.

Each pair of chromatids is attached at an area called the centromere.

Sister chromatids

Centromere

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Chromosomes

How many chromosomes are in the nucleus?

1.Humans have 23 pairs or 46 chromosomes.

2.Karyotype- a picture of chromosomes where they are arranged by size and pair.

a.First 22 pairs are called autosomes

b.Last pair is called sex cells

i. female= XX

ii. Male = XY


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Chromosomes

When the cell divides, the chromatids separate.

Each new cell gets one chromatid.

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Mitosis

Mitosis- the division of the nucleus

1.Is the process body cells reproducing asexually

2.Has 4 stages Prophase, metaphase, anaphase and telophase.


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The Cell Cycle

The Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide.

Interphase is the period of growth that occurs between cell divisions.

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The Cell Cycle

During the cell cycle:

• a cell grows

• prepares for division

• divides to form two daughter cells, each of which begins the cycle again

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The Cell Cycle

The cell cycle consists of four phases:

• G1 (First Gap Phase)

• S Phase

• G2 (Second Gap Phase)

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Events of the Cell Cycle


During G1, the cell

• increases in size or cell growth

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During the S phase,

• DNA synthesis

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The G2 Phase (Second Gap Phase)

Growth and centrioles are formed

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Cell Cycle


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Mitosis

What are the four phases of mitosis?

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Mitosis

Mitosis

Biologists divide the events of mitosis into four phases:

• Prophase

• Metaphase

• Anaphase

• Telophase

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Mitosis

Mitosis

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Section 10-2ProphaseSpindle

forming

Chromosomes (paired

chromatids)Centromere

Click to Continue

Mitosis

Prophase

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Mitosis

Prophase

1. Chromatin turns into chromosomes.

2.Nuclear membrane starts to disappear

3. Spindle starts to appear

Spindle forming

CentromereChromosomes(paired chromatids)

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Mitosis

Chromatin- uncoiled chromosomes. They are long strands of DNA

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Centriole

Centriole

Spindle

Mitosis

Click to Continue

Metaphase

Metaphase

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Mitosis

Metaphase.

The chromosomes line up on the equator or the middle of the cell

Centriole

Spindle

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Individual chromosomes

Anaphase

Mitosis

Anaphase

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Mitosis

Anaphase

The sister chromatids separate into individual chromosomes.

Individualchromosomes

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Nuclear envelope reforming

Telophase

Mitosis

Telophase

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Mitosis

Telophase

1. Chromosomes unwind

2. Spindle disappears

3. Nuclear membrane reappears

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Cytokinesis

Cytokinesis

Cytokinesis

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Cytokinesis

During cytokinesis, the cytoplasm pinches in half.

Each daughter cell has an identical set of duplicate chromosomes.

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Cytokinesis

In plants, a structure known as the cell plate forms midway between the divided nuclei.

Cell wallCell plate

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Cytokinesis

The cell plate gradually develops into a separating membrane.

A cell wall then begins to appear in the cell plate.

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The series of events that cells go through as they grow and divide is called

a. the cell cycle.

b. mitosis.

c. interphase.

d. cytokinesis.

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The phase of mitosis during which the chromosomes line up across the center of the cell is

a. prophase.

b. metaphase.

c. anaphase.

d. telophase.

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Cytokinesis usually occurs

a. at the same time as telophase.

b. after telophase.

c. during interphase.

d. during anaphase.

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DNA replication takes place during the

a. S phase of the cell cycle.

b. G1 phase of the cell cycle.

c. G2 phase of the cell cycle.

d. M phase of the cell cycle.

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During mitosis, “sister” chromatids separate from one another during

a. telophase.

b. interphase.

c. anaphase.

d. metaphase.

END OF SECTION

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