THE CELL CYCLE

Chapter 6 Section 2

Grade 10 BiologyFall 2010

Bell Ringer

1. A typical eukaryotic cell spends 90% of its time in:

A. Mitosis B. AnaphaseC. InterphaseD. Cytokinesis

2. What do you think a cell spends its life cycle doing?

Objectives

Identify the major events that characterize each of the 5 phases of the cell cycle

Describe how the cell cycle is controlled in eukaryotic cells

Relate the role of the cell cycle to the onset of cancer

The Life of a Eukaryotic Cell

Cell division in eukaryotes is more complex than in prokaryotes

Involves cytoplasm, chromosomes inside nucleus, and internal organelles

The Cell Cycle

Cell cycle: repeating sequence of cellular growth and division during the life of an organism

A cell spends 90% of its time in the first three phases of the cycle Interphase

Only enters the last two phases of cycle if it’s about to divide

Cell Cycle

The Cell Cycle

Phase #1: First growth (G1) phase Cell grows rapidly and caries out routine functions Occupies major portion of cells life Cells that are not dividing remain in G1 phase Most muscles and nerve cells never divide

If these cells die the body cannot replace them

The Cell Cycle

Phase #2: Synthesis (S) phase Cell’s DNA is copied At the end of the phase, each chromosomes consists of

two chromatids attached at the centromere

The Cell Cycle

Phase #3: Second growth (G2) phase Preparations are made for the nucleus to divide Hollow protein fibers called microtubules are

rearranged during G2 in preparation for mitosis

The Cell Cycle

Phase #4: Mitosis Mitosis: nucleus of

a cell is divided into two nuclei

Each nucleus ends up with the same number and kinds of chromosomes as the original cell

The Cell Cycle

Phase #5: Cytokinesis Cytkinesis: the process during cell division in which

the cytoplasm divides

Cell Cycle

The Cell Cycle

Mitosis and cytokinesis produce new cells that are identical to the original cells

Allows organisms to grow, replace damaged tissues, and in some organisms reproduce asexually

Control of the Cell Cycle

How does a cell know when to divide?Cells have a system that controls the phases

of the cell cycle

Control of the Cell Cycle

Cell cycle as key checkpoints at which feedback signals from the cell can trigger the next phase of he cell cycle

Other feedbacks can delay the next phase Cell cycle in eukaryotes us controlled by

many proteins

Control of The Cell Cycle

Three Checkpoints

Checkpoint #1: Cell growth (G1) checkpoint Makes the decision of whether the cell will divide If conditions favorable and cell is healthy and large

enough, certain proteins will stimulate cell to begin synthesis (S) phase

S phase, cell copies DNA If conditions are not favorable, cells can stop at this

checkpoint Cells can also stop at this check point if cell needs to

go into resting period Nerve, muscle cells

Control of the Cell Cycle

Checkpoint #2: DNA synthesis (G2) checkpoint DNA replication is checked by DNA repair enzymes If checkpoint passed, proteins trigger mitosis

Control of the Cell Cycle

Checkpoint #3: Mitosis checkpoint Checkpoint triggers the exit of mitosis Signals the beginning of the G1 phase, the major

growth period of the cell

When Control is Lost

Cancer If gene that controls the proteins that regulate cell

growth and division is mutated, protein may not function and regulation of cell growth and division can be disrupted

Cancer: the uncontrolled growth of cells, may result Disorder of cell division Cancer cells do not respond normally to body’s control

mechanisms

When Control is Lost

Some mutations cause cancer Over producing

growth-promoting molecules

Inactivating the control proteins that normaly act to slow or stop the cell cycle

Review

1. Differentiate between the G1, G2, and S phases of the eukaryotic cell cycle

2. Relate what occurs at each of the three principal check points in the cell cycle

3. Why are individual chromosomes more difficult to se during interphase than during mitosis ?

4. In the cell cycle of typical cancer cells, mutations have caused:

A. Slower growth B. A failure in mitosisC. Uncontrolled growth

Answers

1. G1: growth and development; S: DNA is copied; G2: preparations made for nucleus to divide

2. Checkpoint 1: makes decision if cell will divide; Checkpoint 2: DNA replication is checked, triggers mitosis; Checkpoint 3: checkpoint triggers exit from mitosis

3. Individual chromosomes are more difficult o se during interphae than in during mitosis because they haven't condensed and divided

4. C) uncontrolled growth