Cell Division Flashcards
Where do you find the highest rate of cell division?
Embryonic cells. Divide every 12 hours or so.
Cells in a section of tissue are intensely positive for an enzyme histochemical stain for acid phosphatase. This would be indicative of the presence of a large number of:
Lysosomes. This is the right answer for any of the hydrolytic enzymes.
- protease
- nuclease
- glycosidase
- aryly sulfatase
- lipase
- phospholipase
When cancer treatment bluntly blocks cell division, what are some common symptoms as a result?
Anemic: development of new blood cells in the bone marrow is blocked
GI problems: epithelium in gut is killed off and not replaced.
What does the chromosome cycle consist of?
- DNA synthesis
- Karyokinesis
chromosomes are duplicated; seperated; put into new daughter nuclei
tight regulation; need to divide with identical porportions of dna into daughter cells
When does cytokinesis occur?
During mitosis. The cell divides.
What does interface consist of?
G1 (gap 1), S (synthesis), Gap 2 (g2; rest phase)
What phase do skeletal cells and neurons get arrested in?
Gap 1
What happens during interphase?
- Cell increases in size and content
- Replicates genetic material (during S)
prepares for division
In what phase do centrioles replicate? What do they eventually form?
During S phase (in interphase). Form mitotic spindles.
What controls rate of cell cycle?
Extrinsic:
- availability of nutrients; starve a cell (don’t grow)
- growth factors (kinases, signals, typically limited, so limit rate cell can go through cell cycle)
Intrinsic factors cell senescence (can only divide a pre-set number of times throughout life)
How do extrinsic factors such as growth factors affect tumor genesis?
cancer: mutations in receptors for growth factors; become constitutively active; cells go through cell cycle more rapidly; causing tumor genesis
What does a patient with Werner’s Syndrome suffer from?
Pre-mature aging, person becomes physiologically old; caused by mutation in gene that encodes DNA helicase; unwinds DNA during replication; faulty DNA replication; can’t go through cell cycle
What does a patient with Progeria suffer from?
Premature aging. Mutation in intermediate filaments that line nuclear envelope, mutation in Lamin A. Prevents ability to divide. Provides support for nuclear envelope, some DNA is actually attached to these lamins.
Levels of which cyclins must increase before cell moves past restriction point into S phase.
D & E.
As DNA is replicated, what cyclin level increases and pushes the cell into G2?
Cyclin A
When cyclin B appears what phase is the cell irrevocably pushed into?
M (mitosis)
During S phase the autosomal cell goes from 2n to?
4n. Centrosome is also duplicated. Cyclin A is built up and pushes cell into Gap 2.
What does the metaphase chromosome consist of?
Two sister chromatids.
What are two sister chromatids connected by?
Centromere. Also site of kinetochore microtubule eventually.
What are the distinguishing features of prophase?
Chromosomes condense.
Kinetochores assemble on centromeres.
Centrosomes (MTOCs) migrate to poles
Spindle begins to form
In what phase of mitosis does the nuclear envelope disappear and chromosomes begin to migrate to poles (microtubules attach to kinetochores)?
Prometaphase.
In what phase are chromosomes lined up?
Metaphase. Chromosomes are maximally condensed and lined up on metaphase plate.
Where are minus ends of microtubules embedded?
In spindle poles.
In what phase are sister chromatids pulled apart?
Anaphase.
Nuclear envelope begins to form and chromosomes decondense in what phase?
Telophase. Also see cleavage furrow.
What does the cancer drug Colchicine act on?
Disrupts mitotic spindle formation.
Taxol and vincristine do the same thing.
What does the cancer drug 5-fluorouracil act on?
Inhibits DNA synthesis.
Methotrexate and cytosine arabinoside does the same.
In what phase of meiosis do homologous chromosomes pair up?
Prophase I
During Anaphase I in meiosis, what gets pulled to opposite sides of the cell?
Homologous chromosomes. Cell is still 2n. Have two copies of each chromosome.
Where does crossing-over happen?
During prophase I.
During meiotic prophase I, in which of the five stages do chromosomes condense?
Lepotene. Form long strands. Remain attached to nuclear lamin.
During which phase of meiotic prophase does recombination occur?
Pachytene. Chiasmata (crossing over sites) form as random exchange of genetic material occurs between homologous chromosomes.
Oocytes become arrested in what phase?
Diplotene.
At what phase of meiotic prophase I do homologous chromosomes pair up?
Zygotene.
At what phase of meiotic prophase I does nucleolus and nuclear envelope disapear?
Diakinesis.
Human chromosomes are not normally found in what structure?
Telocentric.
What isTrisomy 21 (Down’s Syndrome) caused by?
Non-disjunction of chromosomes during first meiotic division. Homologs not pulled apart, ended up in same cell. 21 has extra chromosome.
What do double minute chromosomes contain?
Associated with aggressive tumors, has fragments of DNA that code for growth factors.
What is chronic myelogenous leukemia caused by?
Short chromosome 22 due to translocation with chromosome 9. Philadelphia chromosome-22q.
Has just signaling gene, express constant growth signals.
Wild replication of cells within bone marrow.
