Cell Cycle Flashcards
Cell Cycle
process by which cells replicate their chromosomes and separate them into two new cells
- Resulting cells contain the same genetic material as the original
Prokaryotic
- Lack a true nucleus or sub cellular organelles
- Bacteria and archaea
Eukaryotic
- have a true nucleus and sub cellular organelles
- all other organisms on this planet (fungi, plants, and humans)
Prokaryotic cell cycle
Reproduce asexually
1.) Bacterial chromosome is replicated (copied)
2.) Two copies are anchored on opposite sides of the cell
3.) Binary fission
Binary fission
cell divides in half
- Each resulting cell has an identical copy of the bacterial chromosome = genetically identical
Who coined the term mitosis?
Walther Flemming observed cell division and coined term mitosis
Mitos
“warped thread”
- osis
process
Interphase
all other cells that are between mitosis
G1 of interphase
Gap (Growth) phase
- normal cellular function/preparation for S
G0 of interphase
cell cycle exit (arrest)
- normal cellular function WITHOUT dividing
S phase of interphase
Synthesis phase
- DNA replication
G2 phase of interphase
Gap (growth) phase
- preparation for mitosis
Mitosis
division of the nucleus
cytokinesis: division of the cytoplasm
Cell cycle control
controlled through reversible phosphorylation and dephosphorylation
Molecular switches
Addition of phosphate group turns activity of proteins on and/or off
Kinase
enzyme that adds phosphate groups
Phosphatase
enzyme that removes phosphate groups
- depends on protein (and/or the phosphorylation site), can either activate or repress a protein’s function
Cyclin Dependent Kinases (Cdks)
Add phosphates to other proteins
- drive transitions between phases of the cell cycle
Are Cdks always present in the cell?
Yes, but can be inactive
Activation of Cdks
1.) Bound to cyclin (cyclin levels fluctuate with the cell cycle; Cdk is only turned on when the cell wants to progress through the cell cycle)
2.) Addition of an activating phosphorylation (Cyclin-Cdks can auto phosphorylate themselves)
3.) Removal of inhibitory phosphates is done by phosphatase
Different cyclin-cdk complexes regulate different phases of the cell cycle
G1-Cdk
S-Cdk
M-Cdk
Activation of the next cyclin-Cdk complex induces inactivation of the previous phase cyclin-Cdk
Ex. what causes the destruction of S phase cyclin?
M-Cdk; turns off the S-Cdk during mitosis
How is Cyclin degradation done?
Via ubiquitin-mediated proteolysis
76 aa protein
Ubiquitin (Ub)
Phosphorylation of the cyclin is the signal for ubiquitylation
- Poly-Ub signal for protein to be degraded
~ Directs protein to proteasome - Ubiquitylated proteins (cyclin) degraded in proteasome
Two types of cell death
1.) Necrosis
2.) Apoptosis
Necrosis
Usually resulting from injury or disease
Characteristics of Necrosis
- Affects groups of neighboring cells
- Chromatin clumping/random DNA fragmentation
- Swollen cell/organelles
- Burst mitochondria
- Cellular lysing and release of intracellular components
- Inflammation of neighboring tissues
Apoptosis
Programmed cell death
Characteristics of Apoptosis
- Affects single cell
- Ordered (non-random) DNA fragmentation
- Nuclear compaction and fragmentation
- Mitochondria remain intact
- Cell membrane blebbing
- Phagocytosis by neighboring cells = no inflammation response
Which cell death shows distinctive blebbing from the cell surface?
Apoptosis
Critical part of many developmental processes
Apoptosis
(ex. frog losing its tadpole tail)
(ex. humans get rid of the webbing between fingers)
G0 Phase
Animal cells can exit the cell cycle and remain quiescent
G1 Phase
cell grows in size
- cell doubles organelles
- LONGEST phase
S Phase
DNA replication
G2 Phase
Proteins needed for division are synthesized
