CHAPTER 10Cell Growth and Division

How big are cells?

Why don’t they grow larger?

10-1 Cell Growth

Limits to cell growth• 1. Not enough DNA

• 2. Not able to import and export materials for the cell fast enough.

Cell Membrane

• What is the purpose of the cell membrane?

Surface Area to Volume

• How do you calculate the surface area of a cube?

• If a cell has sides of 1cm, what is the surface area?

• 1 cm x 1 cm x 6 = 6cm2

• What if the sides are 2 cm, what is the surface area?

• What if the sides are 3 cm, what is the surface area?

How do you calculate the volume of a cube?

Length x width x height

If a cube has sides of 1 cm, what is the volume?

• 1 cm x 1 cm x 1 cm = 1 cm3

• If the sides are 2 cm, what is the volume?

• If the sides are 3 cm, what is the volume?

Surface Area to Volume

Side length Surface Area Volume Surface Area to Volume Ratio

1 cm 6 cm2 1 cm3 6/1 = 6:1

2 cm 24 cm2 8 cm3 24/8= 3:1

3 cm 54 cm2 27 cm3 54/27= 2:1

Cell division- the process by which a cell divides into two new daughter cells

Before the cell divides, it copies its DNA so that each daughter cell has a complete copy.

10-2 Cell Division

• Two type of cell division- Mitosis and Meiosis• Mitosis- makes two identical copies of a cell

• Asexual reproduction- daughter cells are genetically identical to the parent

• Used by single celled organisms to reproduce.

• Used by humans cells to grow and develop

Chromosomes• DNA is spread throughout the cell until it is ready

to divide. It then clumps together into chromosomes.

• Chromosomes- made of DNA and proteins• Each organism has a certain number of chromosomes

• Fruit flies- 8 chromosomes

• Humans- 46 chromosomes

• Carrots- 18 chromosomes

Chromosome structure

• Chromatid- each chromosome is composed of two sister chromatids. They are exact copies of each other.

• Centromere- portion of chromosome that holds the chromatids together.

Cell Cycle

• The cell cycle- grows, prepares for division, divides to form two daughter cells, the daughter cells begin the cycle again

• Interphase- growth and development phase• Mitosis- cell division phase

Interphase Mitosis

Cell Cycle

G1 Phase

S Phase

G2 Phase

Interphase Mitosis

Interphase:G1 Phase- Cell Growth PhaseS Phase- Synthesis Phase- DNA is copiedG2 Phase- Growth and preparation for mitosis, shortest of the three phases

S Phase

Prophase Metaphase Anaphase Telophase Cytokinesis

Interphase Mitosis

Prophase• First and longest

phase• Chromosomes first

become visible• Centrioles- separate

and move to opposite ends of the cell.

• Nuclear envelope breaks down

Prophase Metaphase Anaphase Telophase Cytokinesis

Metaphase• Chromosomes line up across

the center of the cell• Microtubules (spindle fibers)

connect the centrioles to the centromere of each chromosome.

G1 Phase S Phase G2 Phase Prophase Metaphase Anaphase Telophase Cytokinesis

Anaphase• Sister chromatids split and the

chromosomes moves towards the centriole along the spindle fiber at opposite ends of the cell

G1 Phase S Phase G2 Phase Prophase Metaphase Anaphase Telophase Cytokinesis

Telophase• Chromosomes begin to disperse• Nuclear envelope reforms• Spindle fibers break down

G1 Phase S Phase G2 Phase Prophase Metaphase Anaphase Telophase Cytokinesis

Cytokinesis• The cell membrane pinches

together and separates the cytoplasm

• In plants- a cell plate forms that becomes part of the cell wall

G1 Phase S Phase G2 Phase Prophase Metaphase Anaphase Telophase Cytokinesis

10-3 Regulating the Cell Cycle

• Not all cells more through the cell cycle at the same rate.

• Some do not divide- muscle and nerve cells• Some rapidly divide continuously- skin and

digestive tract cells

Controls on Cell Division

Cell Cycle Regulators

How does a cell know when to divide?

Cyclins- group of proteins that regulate the cell cycle in eukaryotic cells.

Cell Cycle Regulators

• Internal Regulators• Ensure that all the processes are completed before

moving onto the next phase

• Ex: protein that ensures that all chromosomes have been copied before moving to the mitosis phase

• Ex: protein that ensures that all chromosomes are attached to mitotic spindle fibers before moving to anaphase

Cell Cycle Regulators

• External Regulators• Tells the cell to speed up or slow down the cell cycle

• Ex: growth factors stimulate growth. When the skin is cut, the cells grown until the wound is healed. When it is healed, the cells stop growing.

Uncontrolled Cell Growth

• Cancer- cells lose their ability to control their growth

• Divide uncontrollably and form tumors• Cells from tumors can move to other parts of the

body and begin growing.

Uncontrolled Cell Growth

• Causes of cell cycle break down• Smoking

• Radiation

• Viruses

Damaged DNA can cause the cell to lose the ability to communicate with other cells or regulate its cell cycle

p53 “guardian angel of DNA”

• DNA damage activates p53• Stops the cell from dividing• Activates protiens for reparing DNA• If damage is too severe, p53 turns on suicide genes

(apoptosis- cell programed death)• 50% of all tumors show a missing or malfunctioning

p53

Stem Cells

• Zygote- forms from sperm and egg• 1 cell→2→4→8→16→32→…→trillions

• Differentiation-

cells specializing

Stem cells can become any other type of cell