Understanding the Cell Cycle and Its Phases

Cell Cycle

a repeated pattern of growth, DNA duplication and cell division that occurs in eukaryotic cells.

Purposes of Cell Cycle

GROWTH and REPAIR

Interphase

the growth phase of the cell cycle.

G1 phase

Gap 1 phase = cell grows and makes proteins

S phase

Synthesis phase = DNA replication occurs, doubling the number of chromosomes

G2 phase

Gap 2 phase = more cell growth and protein synthesis

Mitosis

the division phase of the cell cycle.

Cytokinesis

cytoplasm separation which begins at the end of mitosis

Prophase

Chromosomes condense & are visible as sister chromatids (in X's). Nuclear membrane disappears. Spindle fibers form out of centrioles.

Metaphase

Spindle fibers connect to the centromere of each sister chromatid. Chromosomes line up in middle of the cell.

Anaphase

Sister chromatids separate, pulling away from each other and becoming individual chromosomes. Chromatids move to opposite ends of the cell.

Telophase

Chromosomes decondense and start to look like chromatin again (threadlike instead of rodlike). Nuclear membrane re-forms around chromosomes at each pole. Spindle fibers break down.

Cytokinesis in Plant Cells

cell plate forms midway between divided nuclei and gradually develops into a membrane.

Cytokinesis in Animal Cells

forms a cleavage furrow that pinches the cell into 2 equal parts.

Cell Division Rate

Every cell divides at a different rate based on its need.

Internal lining of intestines

divides every 5 days

Skin cells

divide every 2 weeks

Red blood cells

divide every 4 months

Liver cells

divide every 1 year

Surface Area to Volume Ratio

Cells can't just get bigger to grow either - they have to stay small to maintain a high surface area to volume ratio.

Regulation of the Cell Cycle

Cell cycle is controlled by a chemical control system that starts & stops events in the cell cycle.

Checkpoints

critical point where "stop" & "go" signals can regulate the cycle.

Apoptosis

programmed cell death. Internal/external signals activate genes that produce self-destructive enzymes.