Rudolf Virchow- “Omnis cellula e cellula”, all cells come from pre-existing cells

Functions of cell division:

1. Growth and development

2. Repair of damaged tissues and organs

3. Binary fission- asexual reproduction in unicellular organisms

4. Formation of sex cells- gametogenesis

Mitotic cell division

• produces somatic (body) cells

• No recombination

• Produces 2 genetically identical diploid daughter cells

Meiotic cell division

• Produces sex cells (gametes)

• Genetic recombination occurs

• Produces 4 genetically different haploid daughter cells

DNA in Eukaryotic Cells

• stored in the nucleus

• Takes form of chromatin

Chromatin- DNA+histone proteins

Chromosomes- condensed form of DNA

Centromere- specialized sequence of DNA where sister chromatids are joined

Kinetichore- protein complex where spindle fibers attach

Ploidy- refers to number of sets of chromosomes in a cell

Centrosomes- where spindle fibers are organized, come in pairs

Centrioles- centrosome for animal cells

The cell cycle is 89% preparation and 10% execution

Interphase

G1- growth phase, cells increase in volume by producing more cytoplasm and organelles

S phase- DNA replication takes place

G2- growth phase and preparation for mitosis, errors in DNA replication are addressed here

G2- nucleolus and nuclear envelope are still intact

Mitosis- also known as Karyokinesis

Prophase

• Chromatin fibers condense into chromatids

• Nucleolus and nuclear membrane dissolve

• Formation of spindle fibers (microtubules)

• Centrosomes start to migrate to the poles

Prometaphase- period of movement of chromosomes toward the center of the cell

Metaphase

• Chromosomes align at the middle (metaphase plate)

• Spindle fibers attach to the kinetochore

• Centrosome are at the pole producing both kinetochore and non-kinetochore microtubules

Anaphase

• Sister chromatids separate and migrate toward the opposite poles

• Motor proteins- located in kinetochore complex, digest the spindle fibers, pulls on sister chroamtids causing them to separate and move

• Spindle fibers facing away from the chromatids push on the cell, elongating it

Telophase

• Chromatid arrive at the opposite poles, becoming less condensed

• Spindle fibers dissolve

• Nuclear envelope and nucleus begin to reform

• Cleavage furrow- indentation in animal cells begin to form

• Cell plate- indentation in plant cells begin to form

Cytokinesis

• Cytoplasm is divided in half, forming 2 daughter cells

• At the end of this, chromatids are no longer condensed and nuclear envelope has reformed

• Nucleoli may be seen again

Meiotic Cell Division

• Reductional division

• One round of DNA replication (interphase) followed by two rounds of cell division (Meiosis I and Meiosis II)

• Gametogenesis- production of sperm and egg cells (n) from germ cells (2n)

• Primary basis for genetic variation in diploid organisms

Difference between Meiosis I and II?

• Meiosis I (2n→n) and Meiosis II (n→n)

• Meiosis I has interphase  (IPMAT) and Meiosis II does not

Interphase (2n)- Genetic material is replicated

Prophase I (2n) substages:

1. Leptotene- homology search

2. Zygotene- synapsis, pairing up

3. Pachytene- recombination

4. Diplotene- chiasmata formation

5. Diakinesis- separation

Prophase I- chromatin condense intro chromatid, Nuclear envelope and necleolos dissolve

Chiamata- crossing over,

Synaptonemal complex- holds synapsis together, chromosomes aligned

Homologous chromosomes- have the same DNA length, same genes, centromeres are in the precise location

Tetrads- homologous chromosomes align

Recombination- exchange of egentic information

Metaphase I (2n)- spindle fibers attach to both kinetochores of the sister chromatids

Anaphase I (2n)- chiasmata separate, homogous pair move toward opposite poles, sister chromatids are still attached

Telophase I + Cytokinesis (n)- forms 2 haploid daughter cells with sister chromatids attached to each other

Prophase II (n)- no pairing of homologous chromosomes, no crossing over

Metaphase II (n)- alignment, spindle fibers attach to the kinetochore

Anaphase II (n)- sister chromatids separate and move toward opposite poles

Telophase II + cytokinesis (n)- results to 4 haploid daughter cells

Fertilization- fusion of genetically diverse gametes