Unit 3

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Cell growth & mitosis

Cells reproduce because:

- To make more cells for replacing old, worn out or damaged cells; repair

- For growth & development of an organism

- Create a new organism

Mitosis/asexual:

- Produce genetically identical offspring

- Reproduction is quick & produces a large number of offspring

Meiosis/sexual:

- Produces genetically diverse offspring

Cell cycle - Series of events cells go through to divide & create more cells

Some cells divide constantly:

- Embryonic cells

- Skin cells (every 24 hours)

-Gut lining cells(2x/day)

Other cells rarely or never divide:

- Muscle cells

- nerve cells (never)

Cell division: cell divides into 2 new IDENTICAL “daughter cells”

Mitosis: division of nucleus during eukaryotic cell division

Cytokinesis: division of cytoplasm during eukaryotic cell division

Chromosome:

- located in nucleus

- Made of DNA

Chromatid:

- half of the chromosome that has been replicated

- “sister” chromatids are identical

Centromere:

- area where each pair of chromatids attach (in center)

2 chromatids = 1 chromosome

Interphase:

- portion of cell cycle between divisions

- 75 – 80% life of cell

- 3 phases:

- G1 - cells grow & develop

- S - chromosomes replicate

- G2 - organelles required for division reproduce

Mitosis

PMAT:

1) Prophase

2) Metaphase

3) Anaphase

4) Telophase

Mitosis: Division of chromosomes

M phase (Mitosis):

- sends a copy of all the genetic information & necessary organelles into the new cell

- occurs in most somatic cells (All cells of the body except the reproductive cells)

Prophase:

- 1st stage of mitosis.

1) The chromosomes condense.

2) The nuclear envelope disappears.

3) The centrioles move to opposite poles.

4) The spindle starts to form, growing out of the centrioles towards the chromosomes.

- Chromosomes are visible, the nucleolus disappears, & the nuclear envelope breaks down.

- Centrioles move toward the poles & spindles form

Metaphase:

- chromosomes line-up in the middle

- spindles from centrioles connect to each chromatid

- Spindles: Microtubules that help separate chromosomes

Anaphase:

- chromatids are pulled apart (Away) to separate ends

- membrane begins to pinch off in the middle

Telophase:

- Nucleus & nuclear envelope reform

- Chromosomes start to decondense & disappear

Cytokinesis:

- complete division of cytoplasm

- cells “pinch” off from one another

- 2 daughter cells formed

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Cancer & meiosis

Cyclins: Proteins that regulate cell cycle

Cancer: Uncontrolled cell growth

Causes: Heredity, chemicals & radiation

1) Cell beings to divide abnormally

2) Cancer cells produce a tumor, which begins to displace normal cells & tssues

Tumor: Mass of cells resulting from uncontrolled cell growth

- Benign: Cells stay together

- Malignant: Cells spread & grow elsewhere (metastasize)

- Invade healthy issues

Meiosis

- Production of gametes (sperm & egg)

- Nuclear division that reduces the number of chromosomes by half

- Ex: Human Chromosomes (46 23)

Human chromosomes:

You have 23 pairs of chromosomes (1 from each parent) in each of your cells except sex cells

Gametes: Sex cells (sperm & egg)

Body (somatic) cells: All cells except gametes

Diploid: 2 sets of chromosomes (2N)

- In humans, 2N = 46 chromosomes

- Body cells are diploid

Haploid: 1 set of chromosome (N)

- Gametes are haploid

- In humans, N = 23 chromosomes

Zygote: Fertilized egg

- Made by combination of sperm and egg.

- zygotes are diploid

Homologous chromosomes (homologs): Corresponding chromosomes

- 1 from each parent

- Each 1 contains same traits

Meiosis:

- 2 divisions

- 2n -> n

- results in 4 different haploid cells

- forms gametes

Prophase 1:

- Homologous chromosomes pair up, forming tetrads

- Crossing over occurs

Anaphase 1:

- Homologs are separated; sister chromatids stay together