AP Bio Unit 4B Test Cell Cycle

Cytoplasmic signals…

chemicals (relay proteins, kinases, etc. in pathways) in the cell regulate cell cycle

Physical signals..

density dependent inhibition (as density increases amount of nutrients decreases slowing growth)

anchorage dependence (must be attached to divide; connection between substrate and plasma membrane and cytoskeleton)

fusing cells at two different phases of the cell cycle makes the molecules present in the cytoplasm of cells in S or M phase control the progression of the phase.

Cell Cycle Control System…

molecules in the cell trigger and coordinate key events in the cell cycle

G1 checkpoint…

a signal must be received to proceed through the process and then proteins are made to help synthesize dna

no signal = exit the cell cycle and enter G0

G2 checkpoint…

checks for mutations in dna

G0…

non-dividing state

mature nerve and muscle cells never divide

cells like liver cells exist in G0 until growth factors (due to injury) are present

significance: prevents the over accumulation of cells throughout the body; allows the organism to replace dead or damaged cells as needed.

M (metaphase) checkpoint…

checking to see if there are spindle fibers to each side and pole of the sister chromatids to prevent the entire chromosome from being pulled in one direction

Protein Kinase…

enzyme that transfers phosphate from ATP (converting it to ADP) to a protein

changes confromational shape, changing its function; activate or inactivate a protein

de/phosphorylation caused by protein kinases regulates the cell cycle (mitosis)

abnormalities can cause abnormal cells growth, contributing to the development of cancer

Cyclins (cytoplasmic signals)

class of proteins like enzymes

proteins that cyclically fluctuates concentration in cell cycle

binds/activate kinases to regulate cell cycle

cycling concentrations rise in cell during G1, S, G2 = they bind to and activate protein kinases called cyclin dependent kinases (CDKs)

M Phase Promoting Factor (MPF)…

a specific cyclin dependent dependant kinase that triggers the cell’s passage past G2 checkpoint into M phase.

triggers events like chromatin condensation, nuclear envelope breakdown, and spindle formation

G2 Checkpoint (Cyclins and Cyclin Dependent Kinases)…

synthesis of cyclin begins in S phase and accumulates

cyclin (key regulatory protein that controls cell cycle, binds to CDK) + CDK (type of protein kinase) = producing MPF, initiating mitosis (pass G2 checkpoint)

Each MPF promotes mitosis by phosphorylating proteins…

hundreds of different MPF molecules that act on different cellular structures

example: phosphorylates proteins in nuclear envelope to cause fragmentation or phosphorylates tubulin protein to cause the formation of the spindle fibers

significance: all necessary MPF molecules must be present and activated to achieve two genetically identical daughter cells

Internal Signals - Regulation of Anaphase…

does not occur until all the chromosomes are attached to the spindle at the metaphase plate

kinetchores send a molecular signal that causes the sister chromatids to remain together delaying anaphase while motor proteins remain inactive

significance: prevents daughter cells from having extra or missing chromosomes

External signals - Growth Factors…

proteins released by certain cells that stimulate other cells to divide

example: platelet-derived growth factors (PDGF) produced and released by blood cells called platelets results in the growth of fibroblast cells. these cells have PDGF protein receptors on cell surface and once they bind together, the cell passes G1 checkpoint and divides (increasing production of cyclin).

significance: there are over 50 different external growth factors that can trigger cells to divide.

Cancer cells…

cancer cells lose both density dependent inhibition and anchorage dependence

Benign…

abnormal cells remain at the original site

doesn’t affect organic function

Malignant…

invasive and impairs the function of one or more; results in cancer

excessive proliferation, can have abnormal numbers of chromosomes, can have a disabled metabolism

Metastasis…

cancer cells move from their original location to other sites in the body