Cell VII Flashcards
True or false: the nucleolus is membrane bound?
False
How many nucleoli are usually observed in a typical nucleus?
1-2
What is the size of the nucleoli proportional to?
Amount of protein synthesis in the cell
What is the nucleoli particularly rich in (2)?
rRNA
Protein from free polyribosomes
What are the three components of the nucleoli?
- Nucleolar organizer DNA (sequence of bases that code for rRNA
- Pars fibrosa (new, naked rRNA)
- Part granulosa (maturing subunits of ribosomes)
How does the nucleolar organizer appear in the nucleolus (using EM)?
lighter, amorphous patches that is surrounded by darker patches
What does the pars fibrosis look like at the EM level?
encircles the nucleolar organizer, but is darker and more granulated
Where is the pars granuloso located in the nucleolus? What does it look like/
Center of the nucleolus, away from the nucleolar organizer. Granulated and darker than the NO
How does the nucleaolar associated chromatin appear under EM?
VERY dark area on the periphery of the nucleolus
What is nucleostemin? What happens to it as cells develop?
p53 binding protein found in UNdifferentiated cells.
Decreases as cells become differentiated
How is nucleostemin implicated in CA?
Its presence may play a role in unchecked proliferation of CA cells, since p53 is bound
What are the four stages of the cell cycle?
G1
S
G2
M
What is the most variable stage in the cell cycle?
G1 (9-12 hrs)
When does centriole duplication occur in the cell cycle?
S phase
True or false: DNA replication can occur without cytokinesis?
True–leads to polyploid cells
Where are the checkpoints in the cell cycle?
G1
S
G2
When is centriole replication complete?
Before or at the beginning of G2
What does the checkpoint at G2 check for/
Unreplicated DNA (replication forks)
DNA damage
What are two examples of cells in G0?
Striated muscle cells
Most neurons
What drives the cell cycle?
CDK and cyclins
In what part of mitosis do chromatids condense?
Prophase
In what part of mitosisdoes centrioles begin to migrate to opposite ends of the cell?
Prophase
When is prometaphase initiated?
When the nuclear lamins are phosphorylated and disassociate
What is the action of drugs like colchicine, vincristine, and vinblastine?
Inhibit polymerization of microtubules needed for centrioles
How is colchicine used to treat gout?
Prevent immune cells from entering joints (which is microtubule dependent)
What is the effect of Taxol?
Inhibits depolymerization of microtubules
In what part of mitosis are chromatids aligned in the center of the cell?
Metaphase
In what part of mitosis does colchicine arrest dividing cells?
at metaphase
In what phase of mitosis does separation of chromatids occur?
Anaphase
In what part of mitosis do nucleoli disappear?
early prometaphase
What is the protein that connects chromatids together?
Cohesin
What breaks cohesin (2)?
Anaphase promoting complex activates Separase
Why would you expect the cytoplasm to be eosinophilic in cells that are active in transcription?
Increased rER to synthesize protein.
What are the checkpoints in telophase?
Spindle assembly
Chromosome segregation
True or false: organelles such as mitochondria and Golgi are evenly separated with cytokinesis?
False-daughter cell may be shorted
What proteins are necessary to initiate the cleavage furrow?
Actin and myosin
How does cytochalasin B exert its effects on mitotic division/
Inhibits polymerization of actin microfilaments that divide the cell
What is the consequence of the lack of telomerase in somatic cells?
Telomers shorten, leading to senescence
What two types of cells normally express telomerase?
Stem cells and germinal cells
What are the two main mechanisms of cell death/
Necrosis
Apoptosis
What is the difference between necrosis and apoptosis?
Immune response is present in necrosis
What is phosphatidylserine’s role in apoptosis?
this phospholipid is normally located in the CYTOSOLIC lipid monolayer. When phosphatidylserine is translocated to the extracellular lipid monolayer, it marks the cell as dead. This marker signals neighboring cells to phagocytose and digest the dead cell.
What are the two pathways that initiate apoptosis?
Extrinsic and intrinsic
What are the two extrisic receptors that activate apoptosis?
Tumor necrosis factor +TNF receptor
Fas ligand + fas receptor
What cells express the ligand, Fas, that activate the Fas receptor on cell destined for apoptosis?
Cytotoxic T cell
What is the first major step in the intrinsic apoptosis pathway, after the cell has signalled that it is injured?
Mitochondria releases cytochrome C
What is the action of cytochrome C when released into the cytoplasm?
Activated caspase 8
What is the FasL counter attack?
When tumor cells express the Fas ligand-which is normally found only on cytotoxic T cells- and caused apoptosis of cytotoxic T cells
What is the function of the “Bad” apoptotic factor?
Bad is phosphorylated in the presence of estrogen, but if estrogen levels decrease (menopause), then it will not be phosphorylated, and will trigger the death of osteoblasts (osteopenia)
Where is apoptosis needed in development?
- Form spaces between fingers
- Connection b/t uterus and vagina
- Break anal and choanal membranes
- Immune cells
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