The Cell Cycle and Mitosis

Why do cells divide

Organismal Growth

Development

Tissue Renewal & Repair

Reproduction

Due to hormonal signals

Asexual reproduction

No sperm or egg

unicellular (prokaryotic & eukaryotic) organisms

multicellular (eukaryotic) organisms

Sexual reproduction

Requires fertilization of egg

Unicellular and multicellular eukaryotes

Fungi, plants, animals, algae, others

Mitosis

Produces somatic cells - one 'parent' cell divides to become TWO genetically identical 'daughter' cells

Meiosis

Produces gametes - one parent cell divides and ultimately becomes FOUR genetically different daughter cells that each have half as much DNA as the parent cell

Basic steps in cell division

1. Copying the DNA

2. Separating the copies

3. Dividing the cytoplasm to create two complete cells

The Cell Cycle

1. A dividing phase called the M (mitotic) phase

•Chromosomes are condensed

2. A nondividing phase called interphase

• Chromosomes are uncoiled• Cells are growing and carrying out their specialized functions

The Cell Cycle: Interphase

- S (synthesis) phase -when DNA replication occurs

- two gap phases: G1 phase is the first gap

• Occurs between the M phase and the S phase

- G2 phase is the second gap

• Occurs between the S phase and mitosis

M phase consists of two distinct events

1. Mitosis- the division of replicated chromosomes

2. Cytokinesis- the division of the cytoplasm

During mitosis

-The two sister chromatids separate to form independent daughter chromosomes

- One copy of each chromosome goes to each daughter cell

Mitosis subphases

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase

Cell division in a prokaryote

Bacteria divide via binary fission

Cyclin

Rotwein that is present in different concentrations throughout the cell cycle

cyclin-dependent kinase

A protein kinase that catalyzes the transfer of a phosphate group from ATP to a target protein

G1 checkpoint (restriction point)

Pass check point if:

Cell size is adequate

Nutrients are sufficient

Social signals are present

DNA is undamaged

G0

Mature cells do not pass this checkpoint

G2

Pass checkpoint if:

Chromosomes have replicated successfully

DNA is undamaged

Activated MPF is present

2 M-phase checkpoints

Pass checkpoints if

1. Chromosomes have attached to spindle apparatus

2. Chromosomes have properly segregated and MPF is absent

If DNA is physically damaged at G1 checkpoint, the p53 protein...

Either activates proteins that pause the cell cycle until damage can be repaired

Initiates apoptosis - programmed cell death

p53 is an example of a tumor suppressor

Damage to the p53 gene can lead to uncontrolled cell division

Cancerous cells have two types of defects:

1. Defects that activate the proteins required for cell growth when they should not be active

2. Defects that prevent tumor suppressor genes from shutting down the cell cycle

Normal cells exhibit:

Anchorage-dependence

Density-dependent inhidbition

Benign tumors

Noncancerous and noninvasive

Malignant tumors

Are cancerous and invasive. Can spread via blood or lymph and initiate secondary tumors