Cell cycle and mitosis Flashcards
What is the cell cycle?
Series of events that a cell passes through until it reproduces
Method of prokaryotic cell division
Binary fission
Two periods of eukaryotic cell division
Interphase
Mitosis (M phase)
What is interphase?
Period between cell divisions
What occurs during the M phase
Cell division stage
What are the stages of interphase?
G1 phase
S phase
G2 phase
What occurs during the G1 phase?
Cell growth
Synthesis of new proteins and organelles
Regular cell functioning
Longest phase of the cell cycle
What occurs during the S phase?
Chromosomes are replicated
Centromeres are synthesized
What occurs during the G2 phase?
Centrioles and molecules for cell division are produced
Final check before mitosis
Shortest stage of interphase
What are the checkpoints of the cell cycle?
Control points where signals regulate the cycle
3 major checkpoints are G1, G2 and M
What regulates the movement of cells through the cell cycle?
Protein kinases and enzymes
Which proteins function as internal regulators?
Cyclin Dependent Kinase (CDK)
Maturation Promoting Factor (MPF)
p53
p27
Function of CDK
Adds phosphate to proteins
Along with the kinases control movment of cells from nondividing → G1 → S → G2 → M
Function of MPF
Trigger progression through the cell cycle
MPF = Mitotic CDK + Mitotic Cyclin
Function of p53
Blocks the cell cycle in case of DNA damage
If severe DNA damage occurs, p53 triggers apoptosis
Function of p27
Binds to cyclin and CDK to block entry into the S phase
What controls the G2 checkpoint
Controlled by MPF
MPF phosphorylates and activates proteins involved in chromosome condensation, nuclear envelope breakdown, spindle assembly and cell death
What controls the G1 checkpoint?
Controlled by the G1 CDK cyclins
Additional levels of phosphorylation and dephosphorylation regulate
What factors regulate progression through the cell cycle?
Endogenous hormones: Auxin, cytokinins, abscisic acid, gibberellins and brassinosteroids (backgammon)
Environmental factors
What are the four classes of cyclins?
G1-cyclins promote progression through start of restriction point in late G1
G1/S-cyclins bind CDKs at the end of G1 (cell is now committed to DNA replication)
S-cyclins bind CDKs during S phase required to initiate DNA replication
M-cyclins promote mitotic events
What are external regulators in the cell cycle?
Proteins which respond to events outside the cell
What are the functions of external regulators?
Speed up or slow down the cell cycle
What are some examples of external regulators?
Growth factors speed up cell division
Molecules on surfaces of neighbouring cells slow down/stop the cell cycle
What occurs in cancer cells?
Uncontrolled cell growth (often because of defect in p53 gene)
Viewing cell under electron microscope during interphase
Chromosomes seen as chromatin under electron microscope
Nucleus in visible
What are the events of prophase?
Chromatin condenses into chromosomes
Nuclei and nuclear envelope break down
Spindle fibres grow from centrioles
Centrioles migrate to opposite poles of cell
What are the events of metaphase?
Chromosomes line up along the cell equator
Spindle fibres from the centrioles attach to the centromeres
Nuclear membrane has been completely degraded
What are the events of anaphase?
Centromeres split
Sister chromatids separate as each is pulled to an opposite pole
What are the events of telophase?
Chromosomes become longer and thinner
Nuclear membrane form
Nucleolus reappears
What is cytokinesis?
Cytoplasmic division which completes mitosis
