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
Describe the enzyme system which is the final effector mechanism for apoptosis.
caspases
- protein family of cysteine-aspartic proteases
List examples of physiological processes involving apoptosis.
physiological
Describe the structural changes that occur in cells after apoptosis is triggered.
Cell shrink plasma membrane blebbing aggregation of chromatin fragmentation of nucleus oligonucleosoma; DNA fragmentation caspase cascade activation
