Somatic Cell Division

Mitosis

Somatic Cells

All body cells except gametes (sex cells)

Somatic Cell Division

A cell divides into two identical cells

Replaces dead or injured cells

Adds new cells for tissue growth

DNA Replication (Duplication)

The DNA sequences that make up the chromosomes have to be copied so the same genetic material can be passed on to the new cells

Cell Cycle

The sequence of changes a cell undergoes from the time it forms until the time it duplicates its contents and divides into 2 cells

Two major time periods: Interphase – not dividing

Mitotic Phase - dividing

Interphase

The cell replicates DNA and manufactures additional cell organelles and cytosolic components

High metabolic activity

Most growth

DNA Replication

DNA nucleotides are synthesized in the cytosol and imported to the nucleusThe helical DNA uncoils and the 2 strands separate between the base pairsThe exposed base pair on each strand pairs with a newly synthesized complementary nucleotideThe new DNA strands take shape as chemical bonds form

DNA Replication - continued

The original DNA molecule has become 2 identical strands of DNA

Once a cell completes DNA replication, the mitotic phase can begin.

Mitotic Phase

Mitosis – division of the nucleus

Cytokinesis – division of the cytoplasm

Nuclear Division

The duplicated chromosomes become divided such that one set ends up in each nucleus

The process is divided into 4 stages:Prophase, Metaphase, Anaphase and Telophase

**Mitosis is a continuous process and one phase merges with the next**

Prophase

Chromatin fibers condense and shorten into chromosomesEach prophase chromosome consists of a pair of identical double stranded chromatidsMitotic Spindle is formed by the pericentriolar material and centrioles are pushed to opposite sides of the cellThe nucleolus and nuclear envelope break down

Metaphase

The centromeres of the chromatid pairs are aligned along the center of the mitotic spindle – this is called the metaphase plate

Anaphase

The centromeres split, separating the chromatid pair, which move to opposite ends of the cell.

Once separated the chromatids are called chomosomes.

Telophase

Final stage of mitosis

Begins when chromosome movement stops

The chromosomes start to uncoil, a new nuclear envelope forms, nucleoli appear and the mitotic spindle breaks up.

TWO nuclei are present and the cell starts to divide into 2

Cytoplasmic Division - cytokinesis

Division of the cell’s cytosol and organelles

Begins in late anaphase/early telophase with the formation of a cleavage furrow

Cleavage Furrow – slight indentation of the plasma membrane

Checkpoint

What is the difference between a chromatid and a chromosome?

In which stage of the cell cycle is the cell growing?

What are the mitotic phases in order?

What is a major event in each stage?