The cell cycle:

Process in which a eukaryotic cell divides

Creates two identical cells

Each cell has same number of chromosomes as the parent cell.

The cell cycle is an endless cycle of mitosis, cytokinesis, growth, and chromosomal replication.

Chromosome—

Made up of many genes.

These genes are made up of DNA which code for one or more polypeptides.

The DNA is wrapped around proteins. .

Chromatids—

DNA synthesis produces two strands of identical DNA helices

Two strands connected by centromere or kinetochore.

Two connected strands are called sister chromatids

DNA = Deoxyribonucleic Acid

- Deoxyribose sugar

Nitrogen Bases:

Adenine - A

Thymine - T

Cytosine - CGuanine - G

S---p---S---p---S---p---S---p---S---p

p---S---p---S---p---S---p---S---p---S

A C T G C

T G GA C

S---p---S---p---S---p---S---p---S---p

p---S---p---S

A C T G C

T G

G

A

Cp---S

p---S

p---S

S---p---S---p---S---p---S---p---S---p

p---S---p---S---p---S---p---S---p---S

A C T G C

T G GA C

chromatid centromere

DNA = Chromatin => Chromosome

There are four stages in the cell cycle:

1) G1 (Gap 1)

2) S (Synthesis)

3) G2 (Gap 2)

4) M (Mitosis)

Cell Cycle

G1 Growth 1 (Gap) - Cell grows up

Interphase – Cell is doing its job

S Synthesis – Time during which genetic material is duplicated

G2 Growth 2 (Gap) – Cell prepares for division

Period when the cell is NOT dividing. Cell grows and prepares for mitosis during this time

Made up of three phases:

G1 (First gap period):

1) Chromosomes decondense.

2) Cell synthesizes the enzymes and proteins needed for cell growth.

3) Cell carries on with life functions (growth and performance of biochemical activities.)

S (Synthesis):

1)DNA synthesis (chromosomes are replicated)

2)Chromosomes are now present as sister chromatids (2 copies of the same chromatid.)

G2 (Second gap period):

1)Cell grows and prepares for mitosis.

2)Mitotic spindle proteins are synthesized (used in movement of chromosomes.)

Mitosis:

Division of the nucleus.

Continues throughout an life as body grows and repairs or replaces worn-out cells.

Mitosis consists of 4 stages:

1) Prophase

2) Metaphase

3) Anaphase

4) Telophase

Chromosomes condense and become more compact and visible.

Nucleoli disappear.  

The chromosomes line up on metaphase plate in the middle of the spindle apparatus.

The centromere/kinetochore lines up on the plate (chromatids may lie in any direction.)

The chromatids will split apart at their centromeres, with each replicated chromosome giving rise to two daughter chromosomes.

Sister chromatids are separated at their centromere and pulled to opposite poles of the spindle.

There is a resulting complete set of chromosomes at each pole.

Chromosomes uncoil into chromatin.

New nuclear envelope forms around each group of chromosomes.

Spindle fibers become disorganized.

Cell pinches in middle to begin formation of two cells.

Cytokinesis: Division of the Cytoplasm

Cytokinesis divides structures within the cytoplasm (ribosmes, Golgi apparatus, mitochondria, etc.)

In animal cells cleavage furrow forms at the metaphase plate to pinch cytoplasm in two.

In plant cells, cell plate is formed during cytokinesis (cell plate eventually becomes cell wall.)

Single celled organisms:

1)Allows these organisms to reproduce asexually.

2)Single celled organisms are able to grow in population.

Multicellular organisms:

• Allows these organisms to grow in size and maintain surface are to volume ratio.

• Allow for specialization through cell differentiation.

• Cells that are dead and damaged can be replaced.

What controls the Cell Cycle?

1) Environmental Factors: pH, nutrients, temperature, etc.

2) Density of cells: density-dependent inhibition—cell will not divide if it is crowded, must also be attached to a surface to divide

Cancer--uncontrolled division of cells.

1)Cells do not respond to normal cell division controls.

2)Cells divide indefinitely without aging and dying.

Transformation—normal cell is converted to a cancer cell.

If the immune system does not destroy this cancer cell it divides to form a tumor

Tumor is benign if it remains in the same place. A malignant tumor has the ability to spread.

Metastasis—cancer cells enter the circulatory system and spread to all parts of the body.