Lecture 11, 12 Flashcards
List and describe the sequence of events occurring in interphase.
Cell Cycle: 2 phases:
- Interphase
a: Gap 1 (G1)
- end of mitosis
- longest phase
- cell growth (synthesize RNA + proteins)
b: DNA synthesis (S)
- DNA synthesis/ replication
- DNA doubled
- new sister chromatids are formed
c: Gap 2 (G2)
- cell prepares for division
- cell growth
- organization of cellular organelles
List and describe the sequence of events occurring in mitosis.
Cell Cycle: 2 phases:
1. Interphase
- Mitosis
a: Karyokinesis - division of nucleus
b: Cytokinesis - division of cell cytoplasm
5 stages:
- prophase
- mitotic spindle
- centrosome
- kinetochores
- nucleulous disassembles
- chromatids bound by centromere - prometaphase
- nuclear envelope disassembles
- spindle microtubules bind to kinetochores - metaphase
- chromatids align
- kinetochore microtubules attach sister chromatics to opposite poles
- motor proteins move chromatids into position - anaphase
- sister chromatids migrate towards opposite poles
- APC: anaphase promoting complex
- sister chromatids separate by dyneins (pull towards e.g. end)
- anaphase A: kinetochore microtubules get shorter
- anaphase B: microtubules overlap and lengthen - telophase
- nuclear envelope forms
- chromatids decondense
- karyokinesis
Describe the structure and function of the centromere, kinetochore, centrosome and mitotic spindle.
Centromere:
- hold sister chromatids together
- centric heterochromatin
- interphase
- form kinetochore
Kinetochore:
- protein complex
- form near centromere
- attach chromosome to mitotic spindle
Centrosome: slide 30
- Microtubule organizing center (MTOC)
- pair of centrioles
- position of centrioles determine location of mitotic
spindle poles
- found in G1
Mitotic Spindle: - have centrosomes - microtubules - motor proteins; dynein (towards minus) kinesin (towards positive)
Describe the role of cyclins and cyclin-dependent kinases in cell cycle regulation.
LOOK AT SLIDE 46-47
Cyclin:
- levels fluctuate
Cyclin Dependent Kinases
- depend on cyclin
- kinases phosphorylate
- stable levels
Cyclin Dependent Kinase Inhibitors (CDKI)
- inhibit the cyclin- CDK complex
List and describe the checkpoints in cell cycle regulation.
Checkpoints in Cell Cycle:
- G1:
a: G1 DNA- damage checkpoint:
- monitor integrity of newly replicated DNA
b: G1 restriction checkpoint
- point of no return
- mediated by Rb protein
2: S:
a: S DNA damage checkpoint
- monitor quality of replicating DNA
3: G2:
a: Unreplicated DNA checkpoint
- critical regulatory point in the cell cycle
- prevent cell from going to mitosis prior to DNA synthesis completion in S phase
b: G2 DNA damage checkpoint
- monitor integrity of newly replicated DNA
4: Mitosis
a: Spindle assembly checkpoint
- cannot go onto anaphase
- microtubules attach to spindle so that can’t enter anaphase until everything is lined up
b: Chromosome segregation checkpoint
- prevent cytokinesis util the separation of chromosomes
- without this: then would cause anaploidy etc
Describe the role of the anaphase-promoting complex in mitosis and cell cycle regulation.
APC:
- sister chromatids separate by dyneins (pull towards e.g. end)
- increase separate
- decrease securing
- cleave cohesin
List and describe the sequence of events occurring in meiosis.
Meiosis:
have 2 chromosomes (2n)
4 sister chromatids (4d)
1: Meiosis 1:
separate homologous chromosomes
chromosome #: 2n –> 1 n
DNA content: 4d –> 2 d
2: Meiosis 2:
separation of sister chromatids
equatorial division
DNA content: 2d –> 1d
List and describe the 5 stages of prophase I in meiosis I.
Meiosis 1 –> Prophase 1:
1. Leptotone
- chromatin condensation
sister chromatids condense and connect to each other
- pair homologous maternal/ paternal chrom
- Zygotene
- synapsis (close association of homologous chrome)
- form synaptonemal comlex (chrom bind together)
3. Pachytene
– Synaptonemal complex complete
– Crossover
- Transposition of DNA strands between 2 different
chromosomes
4. Diplotene – The synaptonemal complex begins to break down – Homologous chromosomes begin to separate – Newly formed junctions between chromosomes (chiasmata) may be apparent • Chiasmata indicate crossover may have occurred – Sister chromatids remain closely associated
5. Diakinesis – Homologous chromosomes condense – Nucleolus disappears – Nuclear envelope disintegrates
List and describe the two events in meiosis that increase genetic diversity.
- recombination
- crossover (increase genetic diversity)
- meiosis 1 - independent assortment
- anaphase 1 of meiosis 1
Describe the intrinsic and extrinsic apoptosis pathways.
Apoptosis pathways:
1. Extrinsic (signal from outside)
- binding of ligand to death receptor
- death inducing signaling complex:
caspase cascade
a: caspase 8: activation of initiator caspase
b: caspase 3: activation of effector caspase
Note: caspase: protein family of cistern-aspartic proteases that target nuclear and cytoplasmic proteins
- Intrinsic (signal from inside)
a: death signal i.e.: DNA damage
b: proapoptotic protein upregulated ie: bax
c: MT released cytochrome c
d: form apoptosome via: Apaf 1, cytochrom c, and procaspase 9
e: caspase cascade- initiator: caspase 9
- effector: cspase 3
Describe the role of the retinoblastoma (Rb) and p53 tumor suppressor genes in the cell cycle and cancer.***
Rb: tumor suppressor
Active: Rb is hypophosphorylates –> cell stays stable and does not move onto G1-> S
- active means its a tumor suppressor so stops cell from doing cell cycle
Inactive: Rb is hyperphosphorylated –> cell keeps going through cycle
- inactive means Rb is not working as a suppressor so the cell goes G1 -> S
Define proto-oncogene, oncogene and tumor suppressor gene.
Proto-onco genes:
- protein products control cell growth, proliferation, and differentiation
- normal cells have this
Oncogenes:
- mutated proto-oncogenes
Explain the role of telomerase in cell senescence and tumor growth.
Telomerase: elongates telomeres
Somatic cells lack telomerase
- each division chromosomal DNA gets smaller
- senescence
Cell senescence:
- after a few cycles telomerase stops working and p53is activated = cell arrest
Explain how abnormal cell division can result in clinical syndromes.
Anaploidy:
- abnormal # of chrom in cell
- nondisjunction during mitosis or meiosis
a: trisomy: 3 chrom
b: monosomy: 1 chrom
c: nullisomy: loss of both chrom
i. e. breast cancer (48 chrom instead of 46)
Polyploidy
- whole sets of extra chrome
- triploids (3 N)
- tetraploids (4 N)
Name the mitochondrial enzyme which is released into cytoplasm in apoptosis from many different causes.
Cytochrome C
