Cell Bio Flashcards
NLS
Nuclear localization signal: short, basic amino acid sequence
Progeria
Mutation of Lamin A, characterized by rapid aging and cardiovascular disease; pts have shortered telomeres
Restrictive dermopathy
Laminopathy that prevents epithelium from growing; fetus “suffocates” in its own skin
Huntington’s disease
Neurodegenerative disease caused by improper localization of Huntingtin to the nucleus rather than the cytoplasm; caused by trinucleotide repeat expansion, acquires NLS
Factors affecting membrane fluidity:
- Number of double bonds
- Acyl chain length
- Temperature
More cis double bonds: more fluid
More trans double bonds: no kinks, less fluid
Longer acyl chains: less fluid
Lower temp: less fluid
Phospholipid fusogenicity: HIV/Measles vs. Rabies/Influenza
HIV and measles enter the cell by fusing with plasma membrane, whereas rabies/influenza enter by receptor mediated endocytosis and fuse with endosome membrane
Lysosomal storage disorders - causes
Defective lysosomes cannot break down sphingolipids, which then accumulate and cause disease
Fabry’s & Gaucher’s
Lysosomal storage diseases, sphingolipids cannot be metabolized correctly
Tay-Sach’s
Lysosomal storage disease; sphingolipid metabolism defect
Nuclear membrane assembly/disassembly
Nuclear lamins normally unphosphorylated
Early in mitosis, kinases phosphorylate lamins, causes chromatin-nuclear membrane connection to break, beginning disassembly
Late in mitosis, phosphorylase returns lamin to unphos. state, allowing chromosome decondensation and membrane assembly
Lipid raft
Microdomain comprised of stiffer phospholipids, moving through membrane to bring lipids and proteins together
Critical for signal transduction, endocytosis, rapid re-organization of membrane for ECM modification and motility
Steps of glucose transport into blood through intestinal epithelial cell
Lumen: low glucose, low Na+ (due to Na+/K+ pump moving K+ in and Na+ out); glucose moves against its gradient and Na+ moves with its gradient
Cell has higher conc. of glucose than lumen and bloodstream
Blood side: glucose pumped out by permease (no ATP required)
Na+/K+ ATPase moves more Na+ out
Familial hypercholesterolemia vs. Tangier’s disease
FH: defect in LDL receptor, build up cholesterol in blood causing atherosclerosis; revealed mech. of cholesterol transport into cells
TD: defect in ABC ATPase that pumps cholesterol out of cells, leading to atherosclerosis; revealed mech of cholesterol transport out of cells
I-cell disease
Caused by defect in M6Pase or defective M6P receptor; leads to buildup of lysosomal substrates since lysosomes lack their enzymes
Microtubules: subunit, accessory proteins, hyperstable structures; motors, functions, drugs, significance
Made of tubulin. MAPs and tau proteins are accessory. Comprise cilia, flagella, centrioles. ATPases are dynein (retrograde) and kinesin (orthograde). Function for motility of cell, form mitotic spindle, and transport organelles/cargo. Affected by taxol, vinca alkaloids. Significant in Karageners syndrome, chemotherapy, dementias (tau-opathies)
Microfilaments: subunit, accessory proteins, hyperstable structures; motors, functions, drugs, significance
Subunit is actin, acessory proteins are numerous (importantly profilin). Structure: sarcomere, microvilli with myosin motors. Functions in phagocytosis, cytokinesis, cell motility, force generation, membrane stabilization. Important in hereditary spherocytosis, listeria, vaccinia
Intermediate filaments: subunit, accessory proteins, hyperstable structures; motors, functions, significance
Made of lamins, keratin, neurofilamin, vimentin, desmin, GFAP. No accessory proteins. Comprise desmosome and hemidesmosome. No motors. Functions in mechanical integrity (nucleus, cell-cell, cell-matrix). Significant in laminopathies, blistering diseases, cancer diagnosis
Vimentin
Intermediate filament present in most mesenchymal cells, incl. endothelial cells and fibroblasts
Desmin
Intermediate filament present in muscle cells
Glial fibrillary acidic protein (GFAP)
Intermediate filament present in glial cells (astrocytes)
Neurofilamin
Intermediate filament present in neurons
Keratin
Intermediate filament present in epithelial cells
Eicosanoids: classes and functions
Prostaglandins: PGE2 induces uterine contractions, vasodilation
Thromboxanes: TXA induces platelet aggregation, vasoconstriction
Leukotrienes: LTC4, LTD4, LTE4 induce vasodilation and bronchoconstriction in asthma; also play a role in anaphylaxis
Hereditary spherocytosis
Mutation in protein involved with membrane-cytoskeleton interactions in erythrocytes – results in misshapen erythrocytes, which cannot squeeze through splenic capillaries –> hepatosplenomegaly
Diseases involving phagocytosis
Legionnaire’s, streptococcus, tuberculosis, leprosy, leishmaniasis, toxoplasmosis/coccidosis, listeriosis
Diseases of receptor-mediated endocytosis
Familial hypercholesterolemia, rabies, influenza
Diseases of ABC ATPase transporters
Cystic fibrosis, tumor drug resistance (MDR), Tangier disease
Destination of proteins translated on membrane-bound ribosomes
ER, plasma membrane, secretory vesicles, lysosomes, and Golgi apparatus
Destinations of proteins translated on free ribosomes
Peroxisomes, nucleus, mitochondria, cytoplasm
Nuclear localization signal
Peptide sequence that indicates a molecule should be transported into the nucleus, typically Lys-Lys-Arg-Pro-Arg. Mutations in this sequence result in localization in the cytoplasm
Diseases of defective peroxisomal targeting
Zellweger syndrome, neonatal adrenoleukodystrophy (NALD)
Key events in Golgi
Sorting - phosphorylation of oligosaccharides on lysosomal proteins
Trim sugars
Trim and add sugars
Add sugars
Process and sort, send to lysosome, plasma membrane, secretory vesicle
Neoplasia
Irreversible proliferation of cells which continues even in the absence of an external stimulous
Regeneration
One-for-one replacement of cells: new cells replace old, damaged cells in a precise way
i.e. renewal of damaged endothelial cells in blood vessels after angioplasty
Hyperplasia
An increase in the number of cells in a tissue, where all cells are fully differentiated and functional
Grave’s disease
Hyperplasia of thyroid cells leads to an increase in thyroid hormone and hyperthyroidism
Restenosis
Hyperplasia of smooth muscle cells following vascular surgery, leading to re-blockage of the blood vessel
Metaplasia
Pathologic, adaptive substitution of one cell type by another; commonly seen in the lung tissue of smokers and in sufferers of chronic inflammatory pelvic disease
In both cases, normal cells are replaced by tougher and more protective squamous epithelium
Dysplasia
Changes in mitotic rate of cells, loss of positional control, and loss in uniformity of cell shape; often a precursor to cancer
Pleiotropy
Where a change in a single gene causes multiple phenotypic effects
Benign neoplasia
Proliferation of cells absent external factors where positional control is maintained
i.e. uterine fibroids - grow in place, don’t metastasize
Malignant neoplasia
Loss of proliferation and position control - cancer
Stages of the cell cycle
G0 - quiescent state characterized by decreased protein synthesis, increased protein degradation, decreased RNA synthesis, decreased number of polyribosomes, and changes in cell morphology G1 - cell prepares to replicate DNA S - synthetic phase, DNA replicated G2 - cell prepares to undergo mitosis M - mitosis
R point
Stage in the latter part of G1 where decision is made to either commit to mitosis; once decision is made, cell either completes division or undergoes apoptosis
CDK
Cyclin-dependent kinase - regulate cell cycle/mitosis, regulate activation and inactivation of mitosis promoting factor (MPF); target specific substrates, i.e. Cyclin B/Cdk1 act on lamins & histones
G1 phase cyclin/Cdk pair
Cyclin D & Cdk4 or Cdk6, upon sufficient accumulation, along with Cyclin E/Cdk 2, phosphorylate Rb protein to push cell into S phase
G1/S phase cyclin/Cdk pair
Cyclin E & Cdk 2; along with Cyclin D/cdk4-6 phosphorylate Rb protein to push cell into S phase
S phase cyclin/Cdk pair
Cyclin A & Cdk 2
M phase cyclin/Cdk pair
Cyclin B & Cdk 1
Rb protein
Retinoblastoma protein - exists in a hypophosphorylated state which suppresses cell growth; phosphorylation by Cyclins D & E inactivate Rb, releasing bound TF E2F, which initiates DNA transcription
Features of necrosis
- Triggered by sustained injury/insult, which causes cells to swell, organelle damage, and random chromatin degradation.
- Cells lyse, causing inflammation
Features of apoptosis
- Triggered by specific signals that activate apoptotic genes, which causes cell shrinkage while maintaining organelle morphology.
- Chromatin condenses and is systematically degraded, and the nucleus is broken up.
- Cell membrane blebs, and eventually phagocytosed; no inflammation
DNA gel shows ladders rather than smear of DNA, indicating systematic degradation
Polycystic kidney disease
- Disorder that results in uncontrolled apoptosis of kidney cells
- Tissue develops cysts that interfere with normal function
Phases of apoptosis
1) Induction - intrinsic (Bcl mediated) & extrinsic (Fas/TNF mediated) pathways
2) Modulation
3) Execution
1) Physiologic activators of apoptosis
2) Damage-related activators
3) Therapy-associated activators
1) TNF-alpha, FasL, GF withdrawal, glucocorticoids
2) Viral infection, heat shock, toxins, tumor suppressors, free radicals
3) UV/gamma irradiation, chemotherapy
Features of extrinsic apoptosis
- Receptor-mediated, Fas/TNF-alpha
- FasL binds to Fas, activates executioner caspases:
- break down cytoskeletal proteins
- activate endonucleases
Features of intrinsic apoptosis
- Caused by injury, mediated by Bcl proteins
- Bad phosphorylated, binds to Bcl-Xs at outer mitochondrial membrane
- Bax/BAK oligomerize and cause mitochondrial outer membrane permeabilization
- Cytochrome c released, binds to Apaf-1, which cleaves inactive zymogen to form caspase 9, which activates other caspases
Immunologic privilege
Conferred by extrinsic apoptosis: immune privileged express FasL, bind Fas on T cells and cause them to apoptose
Hashimoto disease
Apoptosis of thyrocytes caused by autoimmune targeting by T lymphocytes
Polydactyly/syndactyly
Extra/fused fingers, caused by abnormal apoptosis between digits during fetal development
Caspases
Cytosolic aspartate-specific cysteine proteases
Activated by cleavage of zymogens, regulated by Bcl-2 family proteins
Involved in apoptotic cascade
Bcl-2 family proteins
Pro- or anti-apoptotic proteins found on mitochondrial membrane
Ratio of pro-apoptotic vs anti-apoptotic Bcl members determins life and death of cells
Inducers of apoptosis: physiologic, damage, therapy, proteins
Physiologic activators: i.e. TNF-alpha, FasL; glucocorticoids
Damage related activation: viral infection, heat shock, free radicals
Therapy: UV/gamma radiation, chemo
p53: triggers DNA degradation and apoptosis
IAPs in stroke: clinical significance
Inhibitors of apoptosis can protect stroke victims from excessive loss of neurons
Scurvy
Vitamin C deficiency that results in faulty cross-linking of collagen fibrils
Leads to spots on skin, spongy gums, bleeding from mucous membranes
Ehler-Danlos syndrome
Connective tissue disorder caused by defect in collagen synthesis and assembly
Osteogenesis imperfecta
Genetic disorder caused by mutation in type I collagen, results in multiple fractures and brittle bones
Menke’s disease
X-linked recessive disease, causes deficiency in copper utilization resulting in faulty collagen cross-linking
Alport syndrome
Genetic disorder in which collagen IV is absent or non-functional
2nd most common inherited cause of kidney failure
Goodpasture syndrome
Autoimmune disease in which antibodies against collagen IV destroy basement membrane
Proteoglycans
- Comprised of hyaluronan (long repeating sugars), have protein cores attached to them surrounded by sugars
- Regulate hydration state of tissues & cartilage
- Resistance to impact in cartilage
- Reservoir for GFs and cytokines
Chondrodysplasia
Disorder in which chondrocytes do not mature and differentiate, causing malformed cartilage
Matricellular proteins
Fibronectin - cellular “glue” - binds cells and ECM, made by mesenchymal cells
Laminins - made by epithelial cells, bind ECM, anchored in cell and attached to actin fibers
CCN family of proteins
CCN proteins
CCN1 & CCN2: placentation, angiogenesis, fibrosis
CCN3: tumor formation & metastasis
CCN5: inhibit smooth muscle cells
Integrins
Mediate cell-cell and cell-ECM interactions
Literally thousands of combinations of alpha and beta chain subunits
Cadherins
Adhere cells, important part of desmosomes
Pemphigus
Autoimmune disease where antibodies destroy (hemi)desmosomes
Elastin
Major structural protein, present in laminae of large arterial walls and provide structural strength and flexibility
Marfan’s Syndrome
Individuals posses a defect in fibrillin that cross-links elastin in artery wall, resulting in aorta aneurysm
