Why do Cells Need to Grow?

• Replace old cells• Replace damaged cells

• Make new life

When do Cells Grow?• Cells grow, or more accurately, divide to stay

small• Cells need to be small to function properly– Cellular organelles need to be able to

communicate to each other and the outside world

• The surface area to volume ratio needs to be high– That means, the cell needs more membrane and

less cytoplasm

The Cell Cycle• The cycle of growing and dividing of eukaryotic cells• It is a continuous production of new cells• Controlled by a series of signals

Three Main Stages of the Cell Cycle:1. Interphase

2. Mitosis3. Cytokinesis

Interphase- The Longest Stage

Broken down into Three Sub-Stages

1. G1 Sub-Stage• Period of cell growth and maturing into a

functioning cell• Some cells, like muscle cells, stop here

2. S Sub-Stage• Duplicates its DNA • DNA is copied to put into new cell

3. G2 Sub-Stage• Prepares for Division• Cell gets ready to divide

Mitosis and Cytokinesis

• Mitosis– When the nucleus and

cellular material divides

• Cytokinesis– When the cell’s

cytoplasm divides

MitosisThe accurate separation of the cell’s DNA

1. Prophase2. Metaphase3. Anaphase4. Telophase

Prophase• Longest phase of Mitosis• The copied DNA condenses into

chromosomes– Chromosomes are shaped like an X– The center of the X is called the

centromere– The pair of chromosomes are

called sister chromatids• Nuclear membrane disintegrates • Spindle fibers (microtubules)

begin to form

Metaphase

• Chromosomes attach to spindles (microtubules)

• Chromosomes align along the equator of the cell

Anaphase

• The microtubules of the spindles begin to shorten

• The sister chromatids are pulled apart

• The chromatids are moved to the poles of the cell

Telophase

• Chromosomes reach end of cell

• Nuclear membrane reappears

• Chromosomes decondense

Cytokinesis

• Division of the cytoplasm

• Animal cells – furrow

• Plant cells – cell plate

Cell Cycle Checkpoints

• The cell cycle has “checkpoints”• “security” proteins at the “checkpoints”• If something goes wrong, cell cycle stops• Also regulation on when cell cycle starts and

stops• What is it called when the cell cycle continues

uncontrollably?