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- 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
- Cohesion- helps hold together
1 copy of eacch chromosome (sex cells)
- overall appearancee/array of chromosomes in a cell
- -used to diagnose some defects
Cell Cycle "process of growth and divison"
- 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
- 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:
Cell cycle control:
- 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?
Control of the cell cycle at molecular level:
- 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.
Control of cell cycle at multicellular level:
- 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.