Presentation on theme: "C ELL D IVISION C YCLE Kanokporn Boonsirichai. T WO T YPES OF C ELL D IVISION Mitosis Chromosome number is preserved. Meiosis Chromosome number is reduced."— Presentation transcript:
M EIOSIS Crossing over Meiosis does two things - 1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). 2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives.
F OUR CLASSES OF CYCLINS G1 cyclins promote the cell through “Start” or restriction point in late G1 G 1 /S-cyclins bind Cdks at the end of G1 and commit the cell to DNA replication S-cyclins bind Cdks during S phase and are required for initiation of DNA replication M-cyclins promote the events of mitosis wikipedia
M AJOR CYCLINS AND C DKS Cyclin- Cdk complex VertbrateBudding yeast CyclinCdkCyclinCdk G 1 -Cdkcyclin DCdk4, 6Cln3Cdk1 G 1 /S-Cdkcyclin ECdk2Cln1, 2Cdk1 S-Cdkcyclin ACdk2Cln5, 6Cdk1 M-Cdkcyclin BCdk1Cln1, 2, 3, 4 Cdk1
R OLES OF M-C DK IN M ITOSIS Induces the assembly of the mitotic spindle Ensures that replicated chromosomes are attached to the spindle Triggers chromosome condensation, nuclear envelope breakdown, actin rearrangement, reorganization of Golgi apparatus and ER
S PINDLE - ATTACHMENT CHECKPOINT Ensures that all chromosomes are properly attached to the mitotic spindle before sister- chromatid separation occurs Unattached kinetochores send out a negative signal that blocks activation of Cdc20-APC complex Binding of Mad2 to unattached kinetochore, leading to inhibition of Cdc20-APC and securin degradation
C REATION OF G1 PHASE Destruction of M-cyclin at the end of mitosis leads to: inactivation of Cdc20-APC activation of Hct1-APC activation of Sic1 CKI decrease in the transcription of M cyclin gene
T RANSITION THROUGH S TART Extracellular signals cause an accumulation of G 1 cyclin (not sensitive to Hct1-APC and Sic1) G 1 -Cdk stimulates transcription of G1/S cyclin gene G1/S-Cdk stimulates transcription of S-cyclin gene
E XTRACELLULAR S IGNALS Mitogens: stimulates cell division by relieving intracellular negative control Growth factors: stimulates cell growth by promoting synthesis of proteins and other macromolecules and inhibiting their degradation Survival factors: promotes cell survival by suppressing apoptosis
PDGF: P LATELET - DERIVED GROWTH FACTOR Functions as a mitogen Secreted by platelet cells to stimulate cell division during wound healing Can act on multiple cell types: fibroblasts, neuroglial cells, smooth muscle cells
M ITOGEN SIGNALING PATHWAY ( THROUGH GTP ASE R AS AND MAP KINASES )
O VERACTIVE MITOGENIC SIGNAL RESULTS IN CELL CYCLE ARREST OR APOPTOSIS
R EPLICATIVE C ELL S ENESCENCE Fibroblasts from normal human tissues can only go through 25-50 population doubling when cultured in standard mitogenic medium
G ROWTH FACTOR SIGNALING PATHWAY PI 3-kinase phosphorylates inositol phospholipid in the membrane activating S6 kinase which activates components of translational machinery
N ERVE CELLS GROWTH AND APOPTOSIS Survial factors are produced in limited amount Nerve growth factor (NGF)
A NCHORAGE - DEPENDENT CELL DIVISION Cells are growth over non-adhesive substratum with or without a patch of adhesive palladium, fed with 3 H-thymidine and autoradiographed.
Integrins (cell surface matrix receptors) interact with laminin and/or fibronectin (extracellular matrix molecules, leading to activation of FAK (focal adhesion kinase) and signaling pathways that promote cell survival, growth and division Actin is labeled in green and proteins with phosphotyrosines are labeled in red
E XTRACELLULAR NEGATIVE SIGNAL PROTEINS TGF- signal proteins inhibit the proliferation of many cell types (blocking progression through G 1 or stimulating apoptosis) BMP (bone morphogenetic protein) triggers apoptosis of cells between developing digits of a mouse paw
E XTRACELLULAR NEGATIVE SIGNAL PROTEINS Myostatin inhibits proliferation of myoblasts that fuse to form muscle cells Mutations in myostatin gene can cause an increase in muscle cell size and number
C ONTROL OF BODY SIZE Through the control of total cell mass Salamanders of different ploidy levels are of the same body size But their cell size and cell number are different Kidney tubules hindbrain Haploid Tetraploid
Q UESTION Describe a mechanism by which Cdk is activated during the cell cycle.