Cell Division & Genetics UNIT #3: Cell Division & Genetics

*Living things are produced from other living things of same kind. *Continuity exists among all life forms. History: "THOSE FOOLS!" *Myths: 1. eels come from slime at bottom of rivers/ oceans 2. Maggots arose from decaying meat

WHAT DO YOU THINK ABOUT THIS? *These myths were hypotheses at one time– scientists didn’t use proper controls and, thus, skewed data. *Led to belief of SPONTANEOUS GENERATION: Living organisms can arise from nonliving things WHAT DO YOU THINK ABOUT THIS?

"Genius at Work" *1668: Francesco Redi: *observed maggots developing into flies; flies always near decaying meat. *Hypothesis: suspected flies laid eggs  maggots in meat (not that the maggots came from meat itself) *Experiment: 2 jars w/ meat, 1 covered tightly with cloth *Results: open jar– maggots b/c flies had access to meat

*1675- microorganisms discovered– spontaneous generation battle began again *Louis Pasteur (1864) French Scientist: *early experiments revealed existence of spores *believed spores became active when nutrients were available *@ the time: air = essential ingredient for spont. gen.

*Boiled infusions to kill present microorg’s Experiment: *He knew he had to prevent microorg’s but not air from entering infusions *designed a S-shaped neck flask- believed curve would trap dust and spores (nothing would grow in infusions) *Boiled infusions to kill present microorg’s *HE WAS CORRECT! Disproved spontaneous generation! *led to THEORY OF BIOGENESIS: all org.’s produced from other organisms (FYI: Cell theory came about, too)

*REPRODUCTION OF BODY CELLS *Cell reproduction occurs when parent cells divide 1 parent cell  2 daughter cells *Cell rep. important for: *growth *repair of damaged tissue *replace cells lost *different cell types *resistance to disease

“BIGGER is not always BETTER” *As cells grow, volume of cytoplasm increases faster than surface area of membrane *More and more nutrients pass through to keep large cells functioning; surface area too small to meet needs of cell *Leads to lack of nutrients or buildup of wastes UNLESS… CELL DIVIDES!!!!!!!!!!

Cell Cycle = Interphase + Mitosis *Interphase: non-reproducing stage *new cell parts produced; DNA wound like spools of protein eventually form chromosomes *Midway: DNA replicates (so future daughter cells have DNA) *MITOSIS: Process by which chromosomes are duplicated and distributed to daughter nuclei

mitosis

About 10 hours DNA replicates About 2 hours About 4 hours Cell grows Cell prepares for mitosis M I T O S About 10 hours DNA replicates About 2 hours About 4 hours Cell grows

STAGE 1 of MITOSIS: PROPHASE *Nucleoli disintegrate *chromatin condense to form chromosomes *nuclear membrane breaks down *in animals: centrioles migrate to opposite ends *SPINDLE forms: football-shaped structure formed from microtubules; f(x) is to move chromosomes *CHROMATID: each strand of double-stranded chromosome *strands join at CENTROMERE

STAGE 2: METAPHASE *Chromosomes scattered in area of former nucleus move towards the middle **REMEMBER: “M” and “M”– “metaphase” and “Middle”

STAGE 3: ANAPHASE *centromeres split– sister chromatids separate and move to opposite poles of cell *@ end of anaphase: one set of single-stranded chromosomes are @ each end of cell

*STAGE 4 (FINAL): TELOPHASE *plasma membrane pinches together at center (due to contraction of microfilaments) *Plants: cell wall prevents this so a CELL PLATE appears (made from golgi bodies or ER) *CELL PLATE: gives rise to plasma membranes of 2 cells; Cell wall forms between these *Nucleoli reappear *Nuclear membrane encloses chromosomes (N.M. from ER) *Chromosomes  chromatin (mass) *daughter cells = same genetic material as parent!

*100 trillion cells in the human body FACT: *100 trillion cells in the human body *25 trillion cell divisions/ second in adult body FACT:

RATE OF CELL DIVISION: Math Time: 1024 !!! *Different types of cells divide at different rates *ex. Blood cells = rapid (less than 1 hour) *ex. Mature nerve cells/some muscle NEVER reproduce ***BALANCE must be kept– “can’t have too much of a good thing” *OR problems like CANCER arise: uncontrolled growth which disrupts other cells Math Time: *1 cell goes through 10 cell cycles. How many cells are present after the 10th cycle? 1024 !!!

DEMO: Germinate corn seeds DEMO: Germinate corn seeds. Once the root is about 1 cm in length, cut 10 mm from the tip. After 5 days, have students observe the root again and note any changes. Measure the distance between the new roots and the end of the primary root. Where are the roots farthest apart? Where are most of the cells undergoing mitosis located?

*REGULATION OF THE CELL CYCLE *1 factor: cell to cell contact: cells divide until contact is made w/ other cells, then stop *stop just before DNA replication begins in interphase (point of no return) *CYCLINS control cell cycle (interact w/ cell division cycle proteins (CDC); with cancer– CYCLINS not f(x) correctly

*CELL REPRODUCTION IN PROKARYOTES *1 chromosome present (circular) *no cell cycle: but still replicate DNA: *BINARY FISSION: prokaryotes reproduce- DNA replicates and distributes equally to daughter cells *Chromosomes attach to membranes: new cell mem/wall forms between attachment sites– elongates cell; middle grows inward until creates 2 cells

QUESTION: During prophase of mitosis, the nuclear membrane disappears QUESTION: During prophase of mitosis, the nuclear membrane disappears. It reappears at the end of telophase. Where is the nuclear membrane during mitosis? Electron microscope studies show that during prophase, small saclike vesicles appear in the cytoplasm. In late anaphase, these disappear. MAKE A HYPOTHESIS to explain what might be happening to the nuclear membrane during mitosis.