what phases does mitosis consist of?
Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Karyokinesis, Cytokinesis
what are the two checkpoints in G1?
G1 DNA-damage checkpoint
-monitor integrity of newly replicated DNA
G1 Restriction checkpoint
-the point of no return
-mediated by Rb
-evaluate replication potential for S phase
what happens during checkpoint at end of S phase?
S DNA-damage checkpoint
-check quality of newly replicated DNA
what are the two checkpoints of G2 phase?
1. unreplicated DNA checkpoint
-prevents progression into mitosis before completion of DNA synthesis
2. DNA-damage checkpoint
-monitor integrity of newly replicated DNA
what are the two checkpoints of the M phase?
1. spindle-assembly checkpoint
-make sure all chromosomes, spindles, kinetochores are attached
-prevents premature entry into anaphase
2. chromosome segregation checkpoing
-prevents cytokinesis until full separation of chromsomes
what is the kinetochore?
-large protein complex
-forms near centromere
-attaches chromosome to mitotic spindle
what happens during Interphase?
G2 -> M transition
-centrosomes move to opposite poles
-orientation of spindles determines cell's plane of division
what happens during Prophase?
-condensation of replicated chromosomes
-chromatids connected at centromere
-kinetochores form near centrosomes
-mitotic spindle assembly
what happens during Prometaphase?
-breakdown of nuclear envelope (dissolution of nuclear lamina)
-spindle microtubules bind to kinetochores
what happens during Metaphase?
-chromosomes align at equatorial, metaphase plate
-kinetochore microtubules attach sister chromatids to opposite poles
-motor proteins move chromatids into position
what happens during Anaphase?
-anaphase promoting complex (APC)
--> cleavage of chromatids
-sister chromatids separate
--> each pulled to opposite spindle poles by dyneins
what happens during Telophase?
-sister chromatids arrive at opposite poles and decondense
-nuclear envelope reassembly
-assembly of contractile ring
what happens during Cytokinesis?
-separation due to contractile ring
-creation of 2, genetically identical, diploid 2n daughter cells
-completion of cell cycle
explain the regulation of retinoblastoma protein Rb?
in resting cells of G1, Rb is active (hypophosphorylated)
--> binds E2F and is an inhibitor of cell cycle progression
in G1 -> S, Rb is inactive (hyperphosphorylation)
--> due to increased cyclin D, Cdk 4/6 activity, Rb dissociates from E2F (which is now free to activate gene expression)
what happens during G2 to M progression?
CdC 25 phosphatase removes inhibitory phosphorylatin of Cdk1 so Cdk1 can bind to cyclin B; this complex activates mitosis
what is the phase of anaphase promoting complex?
to separate sister chromatids
-degradation of securing
-activation of separate
-cleavage of cohesin complexes
degradation of M phase cyclin B
what are the proteins involved in G1 DNA Damage checkpoint?
p21 activation (Cdk inhibitor)
what are the proteins involved in S DNA Damage checkpoint?
BRCA1 activation (repairs double stranded DNA breaks)
what are tumor suppressor genes?
-genes that maintain normal cell growth
-prevent unregulated cell cycle progression
-loss of function mutations enhance susceptibility to cancer
how are cancer cells regulated?
-no cell cycle arrest (lack of p53)
-cell division with damaged DNA
-continued mutation, selection, and tumor progression
-increased genetic instability
what are protooncogenes?
genes whose protein products control cell growth, proliferation, and differentiation
what happens during leptotene?
-sister chromatids condense and connect to each other
-pairing of homologous maternal/paternal chromosomes beings
what happens during diplotene?
-synaptonemal complex begins to break down
-homologous chromosomes begin to separate
-chiasmata (newly formed junctions between chromosomes)
what happens during Metaphase I in Meiosis?
1. homologous chromosomes randomly align on equatorial plate at chiasmata
2. spindle microtubules attach to kinetochores
what happens during Anaphase I in Meiosis?
homologous maternal/paternal chromosomes pulled to opposite sides
what are the differences between Meiosis II and Mitosis?
-no DNA replication
-2nd meiotic division separates sister chromatids
-number of chromosomes in haploid gametes half the number of diploid parent
what are 4 types of chromosome damage or fragmentation?
-inversion (fragment reattaches to same chromosome but reversed)
-duplication (fragment treated as a separate chromosome)