Anatomy and Physiology

Cell ReproductionThe Cell Cycle: Mitosis

The Cell Cycle

•The series of changes that a cell undergoes from the time it forms until the time it divides.

Interphase

Period between cell divisions when a cell is carrying on its normal functions and is preparing for division.

•Stages of Interphase• G1 - Growth phase - cells grow and

develop, rapid growth and protein synthesis.

• S - Synthesis phase - DNA replication occurs.

• G2 - Growth phase - centrioles replicate, cell prepares for cell division.

Mitosis

• Division of a somatic cell to form two genetically identical nuclei or daughter cells.

•P.M.A.T• Prophase• Metaphase• Anaphase• Telophase

Mitosis

• Somatic Cells - body cells, chromosome number is constant.

• Chromosomes exist in pairs. – Ex. We have 23 pairs of chromosomes or 46

chromosomes.

• Called diploid or 2N (two homologous copies of a chromosome)

• Each pair of chromosomes carries the genetic information for the same trait - Homologous.

Chromosome Structure

• Sister Chromatids– Duplicated

chromosome made in S phase of interphase.

• Centromere– Holds sister

chromatids together.

Chromatin

Chromatid

Chromosomes

All the DNA/proteins in nucleus … condenses to form chromosomes during Mitosis

Nucleus

Condensed chromatin .. Either 2 sister chromatids or 1 chromatid

Sister chromatid Sister chromatid

4 Stages of Mitosis: Prophase

– Chromatin in the nucleus condenses to form visible chromosomes.

– Nuclear membrane breaks down.

– Nucleolus disappears.

– Centrioles move to opposite sides of the cell.

– Microtubules form spindle fibers attached to centrioles.

4 Stages of Mitosis: Metaphase

Chromosomes align in the center of the cells and attach to the spindle fibers by their centromeres.

4 Stages of Mitosis: Anaphase

• Centromeres separate- sister chromatids move to opposite ends (poles) of the cell.

• The individual sister chromatids are now call individual chromosomes.

4 Stages of Mitosis: Telophase

– Like prophase in reverse.

– Chromosomes uncoil.

– Nuclear membrane reforms around chromosome set.

– Nucleoli become visible inside nucleus again.

– Spindle fibers break down.

Cytokinesis: Cytoplasmic Division

• Considered a separate stage.

• Cell membrane pinches in on itself until 2 daughter cells are formed.

Cytokinesis

• Regulation

• Internal and external factors regulate cell division.

• Cancer is the uncontrolled growth and division of cells.

• Cancer cells can kill an organism by crowding out normal cells, resulting in the loss of tissue function.

Cancer

cancer cellbloodstreamnormal cell

Benign Malignant

metastasize

• Causes of Cancer

• Internal Factors– Inheritance– Mutations

• External Factors» Carcinogens are substances that are known

to produce and promote the development of cancer.

– Radiation– Chemical– Viruses

Skin Cancer

Mitosis

Review

Cell Differentiation

• The process by which cells develop different structures and specialized functions.

• Controlled by the activation of certain genes.

Stem Cells

A precursor cell that can be triggered by genes to become any type of cell.

Meiosis

Why does it take place?

•Forming of gametes which are haploid cells

Where does it take place?

•Reproductive organs – Male = testesFemale = ovaries

+

fertilization

haploid haploid

46

23

46

46

23

Meiosis - Formation of Gametes

• Meiosis only occurs during the production of gametes.

• After fertilization, the diploid zygote divides by mitosis producing a multicellular, diploid organism.

Meiosis

• Meiosis reduces the chromosome number from diploid to haploid.

• Occurs in two divisions, called meiosis I and meiosis II.

• Divisions result in 4 daughter cells, each with half the number of chromosomes as the parent. (Haploid = n)

• Meiosis 1 separates the homologous chromosomes (2 copies of each chromosome-1 from mom & 1 from dad) and Meiosis 2 separates sister chromatids.

Karyotype of a FemaleHomologous chromosomes

Two Meiotic Divisions

Meiosis I

Meiosis II

Comparing Mitosis and Meiosis

Formation of Sperm vs. Formation of Eggs

4 haploid gametes … 4 spermProcess = Spermatogenesis 4 haploid gametes …

1 Ovum (egg) & 3 Polar BodiesProcess = Oogenesis