I. The Cell Cycle

Cell Cycle: the series of events that take place in a cell leading to its division and duplication *some cells, such as muscle and nerve cells, never divide

A. Parts of the Cell Cycle

1. Interphase: The longest-lasting phase of the cell cycle in which a cell performs the majority of it’s function, such as preparing for nuclear division and cytokinesis

a. First Growth Phase (G 1 ): i. cell grows rapidly ii. organelles are duplicated iii. cells that are not dividing remain in this phase

b. Synthesis (S): i.DNA is copied -Genetic material in the cell doubles -This forms loosely coiled chromosomes

c. Second Growth Phase (G 2 ): i. Preparations are made for the nucleus to divide ii. Microtubules are assembled into centrioles to move the chromosomes

2. Mitosis: a nuclear division resulting in the production of two somatic cells having the same genetic complement as the original cell a. Forms diploid cells i. Diploid: a cell that contains 2 sets of chromosomes (ex: human diploid # is 46) b. Forms somatic cells i. Somatic cells: body cells

c. The Steps of Mitosis

1. Prophase i. Chromosomes become visible ii. Nuclear membrane and nucleolus break down iii. Centrioles begin to move to opposite sides of the cell

2. Metaphase (middle) i.Centrioles produce spindles ii.Paired chromatids move to the equator (middle) of the cell iii.Spindle fibers attach to the centromeres on the sister chromatids

3. Anaphase (apart) i. Spindles shorten, pulling the sister chromatids apart. ii. An equal number of chromosomes move to each pole of the cell

4. Telophase i. Spindle fibers disappear ii. Nucleolus reappears iii. Nuclear membrane forms around the 2 sets of chromosomes iv. Chromosomes unwind

3. Cytokinesis a. This may begin during teolophase b. Cytoplasm is divided in half c. 2 separate cells are formed d. Each cell receives an identical copy of the original chromosomes and half of its cytoplasm

e. In animal cells, the cell is pinched in half by a belt of protein threads f. In plant cells, vesicles fuse at the midline and form a cell plate

END RESULT a. 2 new cells with the same genetic info as the original cell b. Process used for the growth and repair of body cells

II. Changes in Mitosis

A. Cancer: The uncontrolled growth of cells

1. Causes of Cancer a. Mutations i. Mutations that cause over-producing growth promoting molecules which speeds up the cell cycle ii. Mutations that Inactivate proteins that slow or stop the cycle

Continued… b. Environment i. Tobacco ii. UV radiation iii. Viruses iv. Chemicals

2. Types of Cancer a.Benign: cancer cells that remain at the original site b.Malignant: cancer spreads to neighboring tissues and other parts of the body

c. Examples i. Melanoma: skin cancer ii. Leukemia: blood cancer iii. Lymphoma: immune system cancer

III. Asexual Reproduction A single parent passes copies of all of its genes to each of its offspring A. Binary Fission: a form of asexual reproduction that produces identical offspring 1. Used by bacteria

B. Budding New individuals split off from existing ones 1. Used by yeast, hydra, and sponges

IV. Sexual Reproduction Two parents form haploid reproductive cells, which join to form offspring

A. Meiosis: a two-phase nuclear division that results in the eventual production of gametes with half the normal number of chromosomes

1. Gamete: a specialized cell (egg or sperm) used in sexual reproduction 2. Forms haploid cells a. Haploid: a cell that contains only 1 set of chromosomes (human egg or sperm haploid # is 23) 3. Meiosis involves 2 divisions of the nucleus

4. Steps of Meiosis a. Prophase I -chromosomes condense -nuclear envelope breaks down -homologous chromosomes pair *Homologous chromosomes: chromosomes that are similar in size, shape, and genetic content.

Prophase I cont… -Crossing-over: an exchange of genetic material between homologous chromosomes; contributes to the genetic variability in offspring

b. Metaphase I -pairs of homologous chromosomes move to the equator -Spindles attach to the centromeres of the sister chromatids

c. Anaphase I -Spindles shorten -homologous chromosomes separate, chromatids stay together

d. Telophase I -individual chromosomes gather at each pole -cytoplasm divides, forming 2 new cells

e. Prophase II -a new spindle forms around the chromosomes

f. Metaphase II -chromosomes line up at the equator and spindle fibers attach to their centromeres

g. Anaphase II -spindles shorten -centromeres divide -chromatids are pulled to opposite poles

h. Telophase II -nuclear envelope forms around each set of chromosomes -cytokinesis occurs END RESULT: 4 haploid cells

5. Meiosis in Males a. Spermatogenesis: process by which sperm are produced in male animals

6. Meiosis in Females a. Oogenesis: process by which eggs are produced in female animals

Mitosis versus Meiosis

-1 cell division -results in 2 cells -chromosomes # stays the same -results in growth and repair Mitosis -used in body cells -chromosomes line up at the center of the cell -centromeres divide -centrioles are in pairs -PMAT Meiosis -2 cell divisions -results in 4 cells -chromosome # is divided in half -produces gametes (egg and sperm) -crossing-over occurs -Forms diploid cells -Forms haploid cells