Cell Growth and Reproduction

Chapter 10

The Big Idea• You are constantly changing

• Worn out cells get replaced

• Cuts and bruises heal

• 2-3 billion red blood cells get replaced each second

• Muscles you exercise get larger

The Cell CycleCell

Division

Interphase

Growth and Development

Preparing for reproduction

10-1 Cell Growth

Q: When a living thing grows, what happens to its cells?

A: Cells increase in number

There are two main reasons why cells divide

1. The larger the cell becomes, the more demands there are on the DNA

2. The cell has trouble moving enough nutrients and wastes across the cell membrane

Division of a cell• Before it gets too large, a growing

cell divides forming two daughter cells

• The process by which a cell divides into two new daughter cells is called cell division

Daughter cells

This solves the two problems of a growing cell

1. The cell replicates all of its DNA

2. The actual division of the cell decreases its volume

10-2 Cell Division

In eukaryotes cell division occurs in two main stages

1. Mitosis

2. Cytokinesis

Chromosomes• In eukaryotic cells, the genetic

information that is passed on from one generation to the next is carried on ___________________________Chromosomes

• Chromosomes are made of DNA – which carries the cells coded information – and proteins

• The cells of every organism have a specific number of chromosomes

• You can’t see chromosomes except during cell division, when they condense and compact

• Before cell division, each chromosome is replicated, or copied

• Because of this, each chromosome consists of two identical _______________________________

• When the cell divides, the sister chromatids separate and one chromatid goes to each of the two new cells

• Each pair of chromatids are attached at an area called the centromere

“sister chromatids”

Interphase• “In-between” period of growth

between division

• During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again

• The cell cycle consists of 4 phases

1. M phase

2. G1 phase

3. S phase

4. G2 phase

• G1 – Cells do most of their growing. They increase in size and make new proteins and organelles

• S – Chromosomes are replicated

• G2 – Organelles and molecules required for cell division are produced

• M – cell divides

Prophase• The chromatin

condenses into chromosomes

• The centrioles separate

• A spindle begins to form

• The nuclear membrane breaks down

Metaphase• Chromosomes

line up down the middle of the cell

• Each chromosome is connected to a spindle fiber at its centromere

Anaphase• Centromeres

split, allowing sister chromatids to separate

• The chromosomes move to opposite ends of the cell

Telophase• Chromosomes

unwind

• A nuclear membrane reforms

• Nucleolus becomes visable

Cytokinesis (In animals…)

Cytokinesis (In plants)• A cell plate gradually develops

into a separating membrane

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

Golgi vesicles move toward equator

Early cell plate

Cell Plate

The Big Picture!• Mitosis is the division of a

___________

• Mitosis produces two nuclei that have the __________ number of chromosomes as the original

same

nucleus

46 46

46 (Before Mitosis)

(After Mitosis)

10-3 Regulating the Cell Cycle

Knowing When to Stop•Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new.

1.How do you think the body repairs an injury, such as a cut on a finger?

2.How long do you think this repair process continues?

3.What do you think causes the cells to stop the repair process?

Controls on Cell Division

Controls on Cell Division• When cells come into contact with

other cells, they respond by not growing

• When an injury such as a cut occurs, cells at the edges of the injury are stimulated to divide rapidly, the cell division stops when the healing process is complete

A sample of cytoplasm is removed from a cell in mitosis.

The sample is injected into a second cell in G2 of interphase.

As a result, the second cell enters mitosis.

Cyclins• Protein that regulates the cell

cycle

• There are 2 types of regulatory proteins; those that occur inside the cell and those that occur outside the cell.

Internal Regulators• Allow the cell cycle to proceed only

when certain processes have happened inside the cell

• Ex.) several regulatory proteins make sure that a cell does not go through mitosis until all chromosomes have been replicated

External Regulators• Direct cells to speed up or slow

down the cell cycle• Ex.) growth factors• Molecules found on the surface of

neighboring cells often have the opposite effect causing cells to slow down or stop their cell cycles

• These signals prevent excessive cell growth

Cancer• A disorder in which some of the body’s

own cells lose the ability to control growth

• When cells divide uncontrollably, masses of cells called tumors can damage the surrounding tissues

• Cancer cells may break loose from the tumors and spread throughout the body

*(DNA interactive DVD)*

Q: What causes the loss of growth control?

A: smoking tobacco, radiation and chemical exposure, viral infections

All cancers have one thing in common: The control over the cell cycle has been broken

• Some cancer cells will no longer respond to external growth regulators

• Others fail to produce the internal regulators

p53• An astonishing number of cancer cells

have a defect in a gene called p53• p53 normally halts the cell cycle until

all the chromosomes have been properly replicated

• if we could fix p53 we could cure many forms of cancer

Is a cure in sight?• Cancer is a serious disease

• As difficult as a cure would be, at least scientists know where to start

• Cancer is a disease of the cell cycle , and conquering cancer will require a much deeper understanding of the processes that control cell division