The Cell Cycle15 October, 2003Text Chapter 12

Cell division functions in

reproduction, growth, and

repair

genome: all of a cell’s DNA

chromosome: individual DNA molecule

chromatin: chromosomal DNA and its protein scaffold

sister chromatids: the two identical copies of a duplicated chromosome

centromere: the point of attachment for two sister chromatids

somatic cells: (most cells) have two copies of each chromosome (diploid)

gametes: (reproductive cells; sperm and eggs) have one copy of each chromosome (haploid)

Important Terms (part one)

cell cycle: the process of cell division

mitosis (M phase) nuclear division

interphase: the main part of the cell cycle

G1 phase - cell prepares for DNA synthesis, usually grows in size

S phase - DNA is duplicated

G2 phase - cell checks fidelity of DNA replication, prepares for nuclear division

mitosis subphases - prophase, prometaphase, metaphase, anaphase, telophase

cytokinesis

More Important Terms

Mitosis (1)

Mitosis (2)

The mitotic spindle is composed of microtubules, and directs the alignment of chromosomes on the metaphase plate.

During anaphase, the microtubules attached to each centromere guide the movement of chromosomes toward spindle poles.

The Mitotic Spindle

Polar Depolymerization of Microtubules

Microfilaments contract to divide the cytoplasm. Plant cells are less flexible, because of the cell wall, and deposit cell wall material between the two daughter cells.

Cytoplasmic Division

Mitosis (differential staining)

Mitosis in Growing Tissue

Binary Fission in Bacteria

Evolution of Mitosis

The cell’s place in the cell cycle is signaled by the presence or absence of cell cycle kinases.

A growth signal leads to passage through the G0

restriction point into G1. (See Fig 11.11)

The cell then executes a programmed series of steps that culminate in mitosis and cytokinesis.

Cell Cycle Control

is an example of kinase control of the cell cycle. It is like a license that allows the cell to begin M phase of the cell cycle.

MPF is a two-subunit enzyme. One subunit is Cdk (present during the whole cell cycle). The other subunit is a cyclin protein that builds up as M phase approaches.

When the cyclin concentration is high enough, cyclin binds to Cdk, forming the MPF enzyme. MPF activity signals the start of mitosis.

MPF

Normal cells are transformed to tumor cells when cell division is not controlled.

Cancer cells are growth-factor independent.

Cancer cells have escaped density-dependent inhibition.

Most cancerous cells are destroyed by the immune system, but some cells progress from benign to malignant, and possibly to metastatic.

Cancer

Cell Culture and Growth Factors

Density-dependent inhibition is a property of normal cells.

Cancer cells lack this inhibition.

Density-dependent Inhibition

Metastatic cancer cells spread throughout the body.

Metastatic Cancer