Bio Ch10 Cell Division

• in nuclei of eukaryotes
• in most animal cells as pairs
• pairs are called -diploids

• Example: humans have 46 chromosomes (23 pairs)
• Every species has diff. # of chromosomes

made of chromatin (40%DNA 60%PROTEIN)

• Dna has to coil up to fit
• During cell divison all dna is coiled up (condensed)
• Rest of time- DNA is uncondensed (its being used)

DNA uncondensed- being used

DNA stays condensed all the time

pair of cells

• 
• Cohesion- helps hold together

1 copy of eacch chromosome (sex cells)

• overall appearancee/array of chromosomes in a cell
• -used to diagnose some defects

• INTERPHASE:
• 1) G1: gap phase 1 long, lots of growth
• 2) S: DNA synthasized
• 3) G2: gap phase 2, more synthesize
• 4) Mitosis - division of 1 nucleus into 2 nuclei (not cell division)
• 5)Cytokinesis - Division of 1 cell into 2 cells

• 1879 Flemming:
• working w salamander larvae he described mitosis

• Phases:
• Prophase: chromsomes condense, become visible, nuclear membrane disapears, everything organized

Metaphase: lined up on equator of cell(microtubules attached)

Anaphase: Seperation of chromatids -->become chromosomes

Telophase: finale destination--> 2 nuclei

• Diploid has 2 copies (2N cell)
• Haploid has 2 copy (1N cell)

if diploid cell undergoes mitosis it produces 2-2N cells (identical)

• 2 cells from 1 cell (divison of 2 cells)
• Plant cells:
• 

• 3 checkpoints:
• 1) G1/S checkpoint - is cell big enought to divide?

• 2) G2/M checkpoint - is dna ok? Gene called P53 checks on DNA. If there is a problem - a)repair b) apoptosis-cell suicide
• 

3) Spindle checkpoint - is spindle properly attached? Are chromosome attached properly to spindle?

• 2 kinds of proteins:
• 1) Cdks - cyclin-dependent kinase (activation molecule)
• 2) cyclins - attach to Cdk

Cdks: measured (cell size/DNA ratio) = when this ratio is big enojugh it will divide.

• Sense density of neighboring cells signals:
• a) inhibitory signals - slow things down
• b) growth factors (signals that have receptors & small amounts) - PDGF "Platelet Divide Growth Factor"
• plateletes involved in clotting blood... need to heal wound--> platelets produce PDGF to send signal to nearby cells (fibroblasts) to heal wound.