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Chapter 6

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Why do cells divide?

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Cell Reproduction/Cell Cycle A process that your body uses to make new cells in order to grow and repair itself

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CELL CYCLE

• Interphase– A cell spends 90% of it’s life in

interphase.

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Stop! Look at your notes!

What are characteristics that you can see in each the Interphase cells?

What is happening in Interphase?

Sketch a “general” interphase cell in your notes?

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Examples of Cells inInterphase

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3 Phases of Interphase

G1- First growth phase

S phase- synthesis

G2- Second growth phase

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G1 Growth Phase

Cell grows rapidly

Carries out routine cell functions

This phase occupies the major portion of interphase

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Synthesis (S) Phase

centromere

chromatid

DNA is copied

Each chromosome is composed of two chromatids (sister chromatids) attached together by a centromere.

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G2 Second Growth Phase

Cell continues to grow and prepares to divide

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Cells in Mitosis

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1. We will be looking at 5 drawings of cells in mitosis.

2. Try to put them in order.

3. Think through what is a logical sequence.

Hint: Which one LOOKS like it must happen 1st? Why? Which one LOOKS like it must happen last? Why?

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1

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2

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3

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4

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5

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1

54

32

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Correct Order

1st = Slide 4

2nd = Slide 2

3rd = Slide 1

4th = Slide 3

5th = Slide 5

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Mitosis (M) Phase

A process by which the material in a cell’s nucleus

is divided during cell reproduction

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What Cell Parts Are Involved?

Cell Membrane

Nuclear Membrane

NucleusChromosomes

Cytoplasm

Centrioles

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ProphaseNuclear Membrane

Chromosomes

Centriole

Spindle Fibers

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ProphaseChromosomes become visible by thickening

Nuclear membrane begins to disappear

Spindle fibers form between centrioles

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Metaphase

Chromosomes

Centriole

Spindle Fibers

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Metaphase

Chromatids line up across equatorial plate (middle)

Spindle fibers are attached to each set of chromatids

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Anaphase

Chromosomes

Centriole

Spindle Fibers

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Anaphase

Centromeres divide

Chromatids are pulled toward opposite ends of the cell

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TelophaseNuclear Membrane

Chromosomes

Centriole

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Telophase

Nuclear membrane begins to form at each pole.

Chromosomes uncoil (becoming less visible)

Spindle dissolves

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Cytokinesis

• Cytoplasm divides and two daughter cells are produced

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End of Mitosis

• Each cell now has original number of chromosomes

• Each new cell grows until it is ready to divide

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Mitosis

• All body cells (somatic cells) in humans are made through mitosis

• Sex cells (egg & sperm) are NOT made through mitosis

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Put It All Together!!!Animal Cell Mitosis

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What Are The Benefits of Mitosis?

• Helps us grow by producing new cells

• Replaces cells that were lost due to cell death and injury

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Think…

• In which body organs do cells carry out mitosis the most often?

Stomach, Intestine, Skin

• In which body organs do cells carry out mitosis the least often?

Brain and Muscle

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All Cells are Different!!

• All cells live for different lengths of time

• Cells carry out mitosis at different rates in different organs to replace cells that are worn out

Brain cells 30-50 yrs

Red Blood Cells 120 days

Platelets 10 days

Stomach Lining 2 days

Cells

Liver Cells 200 days

Intestine Lining 3 days

Cells

Skin cells 20 days

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Is the process the same in plants?

• What is missing? – Centrioles– Furrowing

• At the end of cell division a cell wall forms

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Flaws in Mitosis

When cells are dividing out of control, tumors are produced

Cancer is one type of tumor that can result from out of control mitosis

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Mutations

• Mutations = random mistakes in mitosis when DNA is duplicating

• Can result from radiation and pollution in the environment

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Stop! Look at your notes!

• Write a summary that explains the cell cycle in your own words.