CELL DIVISION AND MITOSIS

Reasons for Cell Division

1. Cell growth (the larger a cell becomes, the more demands it places on its DNA and will have difficulties moving nutrients/waste across the cell membrane)

2. Repair & replacement for damaged cells

3. Reproduction of a species

Surface area to volume ratio

The bigger the cell, the larger its ratio decreases. Smaller cells have a higher ratio, allowing it to exchange products efficiently.

Cell Division

The process by which one mother cell divides to form two identical daughter cells

Chromosomes

Giant molecules made of protein & a long, tightly coiled DNA molecule. Each cell must make copies before cell division occurs. Consist of two identical chromatids connected at the centromere.

Mitosis

The division of the nucleus. Divided into four stages:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Cytokinesis

The division of the cytoplasm

The Cell Cycle

The series of events that cells go through as they grow and divide. The cell grows, prepares for division, and divides into two daughter cells.

Interphase

Consists of three stages where the cell forms duplicates of its chromosomes and produces a supply of organelles for the two daughter cells. The nucleus is well defined; centrioles organize microtubules into spindles outside the nucleus. The phase where the cell spends 90% of its life.

G1 stage

The first stage of interphase where the cell increases in size. Enzymes, organelles, and other matter double in number.

S stage

The second stage of interphase where replication of synthesis occurs.

G2 stage

The third stage of interphase where the cell assembles special structures for cell division.

Prophase

The stage of mitosis where the chromosomes thicken and become distinct from one another. The nucleolus disappears, the chromosomes separate and start moving to opposite ends of the cell.

Late Prophase

The nuclear membrane fragments and the microtubules invade the nuclear area. The fibers of spindles attach to each chromosome at its centromere.

Metaphase

The spindle fibers push and pull the chromosomes, lining them up at the center of the cell.

Anaphase

The centromeres divide, and the chromatids are pulled to opposite ends of the cell. By the end, both sides of the cell have equivalent and complete sets of chromosomes.

Telophase

The nuclear membrane begins to form, and the nucleolus becomes visible in each daughter cell. The cell begins to pinch in, forming a cleavage furrow.

Cell Cycle Regulators

Proteins found on the inside and outside of cells that initiate or halt phases of the cell cycle. These control points are found in G1, G2, and M phases.