Block 1 Flashcards
3 filament types and their thicknesses
- Actin: 5-9nm,
- Intermediate filaments: 10nm
- Microtubules: 25nm
2 motor proteins, and the directions go
- Kinesin: towards + end, anterograde movement
* Dynein: towards - end, retrograde movement
Types of tubulin subunits
alpha/beta dimers gamma tubulin (minus end cap)
List intermediate filament proteins
Nuclear lamins Vimentin Desmin Keratin Neurofilaments
F actin and G actin
F actin (filamentous) polymerizes from G actin (globular). Subunit binding and ATP hydrolysis are not a coupled process.
Emery-Dreifuss muscular dystrophy
What is the cause
Mutation in lamins A/C
Epidermolysis bullosa simplex
What is the cause
Mutations in keratin. Skin easily blisters.
Structure of intermediate filaments
Monomers form dimers.
Dimers bind into antiparallel tetramers.
Action of phalloidins and cytochalasins
• Phalloidins lock F actin units together.
• Cytochalasin inhibits polymerization.
(Both are from mushrooms)
Actin concentration in cells, and critical concentration.
Actin is > 1mM, and critical concentration is 0.1µM.
What is an actin comet
When a mycobacterium utilizes cellular actin polymerization to move around the cell.
4 classes of actin binding proteins
- Regulation (thymosin beta4, profilin, tropomodulin, capping protein).
- Severing (ADF/cofilin, gelsolin).
- Cross-linking (spectrin, dystrophin, fimbrin, filamin, actin-actinin).
- Motor (myosin)
Myosin I vs. Myosin II
- Myosin I binds to membranes (with the head directed towards cytoplasm)
- Myosin II forms thick filaments
Amoeboid movement pathway
Dendritic nucleation model
Actin polymerizes with Arp2/3 branch points, with lamellopodia forming at Wiskitt-Aldrich protein on cell wall.
RBC ghosts consist mostly of
Spectrin, actin, ankyrin, band 4.1, glycophorin, and anion exchanger
Hereditary spherocytosis
What it is and what causes it
RBC lose their shape and become fragile. Caused by mutations in spectrin, ankyrin or band 4.1
Symptoms of immotile cilia syndrome (ICS)
- infertility (because their sperm are immotile)
- chronic sinusitis and bronchitis (because cilia in their respiratory tracts cannot effectively move mucous toward the pharynx).
Axoneme structure
9 + 2
9 MT doublets (13 + 11 protofilaments), and 2 normal MTs
Membrane ER is continuous with
Nuclear membrane
4 post-translational processes that take place in ER
- Glycosylation
- Disulphide bonds
- Folding
- Subunit assembly
Location where steroids are made. Cellular structure that is visually developed in high-demand synthesis.
Mitochondria inner surface
Mechanisms of taxol and vinblastine
- Taxol inhibits MT depolymerization
* Vinblastine detaches MT minus ends
Types of proteins synthesized by ER-bound ribosomes
• Transmembrane proteins
• Secretory proteins
• Lysosome proteins
(These all go to the Golgi next)
Types of proteins synthesized by cytosolic ribosomes
• Mitochondrial proteins
• Nuclear proteins
• Peroxisome proteins
(These all go directly)
Signal Recognition Peptide (SRP) pathway
SRP on nascent peptide directs cytosolic ribosome to ER surface. Peptide is fed through peptide translocation complex, which is GTP-dependent.
Features of the SRP
Usually at N-terminus, hydrophilic, net positive charge, 13-48aa (no consensus sequence), contains an alpha helix, becomes non-polar at carboxyl end of sequence. Similar structure in all SRPs.
Signal peptidase
ER transmembrane protein, with catalytic side on lumen side. Cleaves SRP co-translationally.
Stop transfer sequences
Hydrophobic sequence that contains an alpha helix. Translocation into ER stops at this sequence, and peptide remains embedded.
Structure and function of Golgi apparatus
- 4-12 cisternae
- Cis Golgi is close to ER; distinct compartments that modify membrane proteins differentially
- Trans Golgi network (TGN) is a reticulum where proteins are sorted according to where they will be transported
Regulated secretory pathway vs. Constitutive secretory pathway
- All cells have constitutive secretory pathway; Regulated secretory pathway is only in exocrine, endocrine, and neurons.
- Secretory granules store proteins for later release.
V-type ATPases
What do they do
Pump H+ into the vacuoles: endosomes and lysosomes (pH = 5.0)
Lysosome functions
- Protein disposal
- Downregulate surface receptors, such as EGFR
- Releases of endocytosed nutrients
- Degradation of phagocytosed pathogens
- Autophagy
Lysosome storage diseases (LSDs)
• Incidence
• Cellular hallmark
• Treatment
- 1 in 5000 live births
- Enlarged lysosomes (Inclusion bodies)
- Enzyme replacement therapy (ERT)
How are enzyme replacement therapy (ERT) drugs tagged to ensure they localize to lysosomes
They have a mannose-6-phosphate tag
Mucolipidosis II (I-cell disease) What is the cause
Lack of GlcNAc phosphotransferase, which normally adds a mannose-6-phosphate to proteins to target them to the lysosome. Pan-deficiency of lysosomal enzymes.
How do ER vesicles target to the Golgi?
ER v-SNAREs bind to the Golgi t-SNAREs.
v is for vesicle and t is for target
Tetanus toxin and botulinum toxin
Compare the mechanisms
Both are SNARE peptidases
• Tetanus toxin prevents GABA release; spastic paralysis.
• Botulinum prevents ACh release at NMJ; flaccid paralysis.
Receptor-mediated endocytosis pathway
Clathrin-coated pits with receptors collect ligand before endocytosing. Clathrin then disengages.
Four types of receptor-mediated endocytosis, with examples
• Ligand degrades / Receptor recycled (LDL, peptide hormones, viruses) • Both degraded. (EGF, Immune complexes) • Both are recycled. (Transferrin, MHC) • Both are transported to different side. (Maternal IgG, IgD)
Transferrin pathway
- Apotransferrin scavenges Fe3+, becoming holotransferrin
- Holotransferrin binds to transferrin receptor
- Receptor-mediated endocytosis
- Clathrin dissociates, vesicle fuses to acidified endosome
- Fe3+ dissociates as Fe2+, and is pumped into cytosol
- Apotransferrin-bound receptor is exocytosed
Familial hypercholesterolemia (FH)
• Prevalence
• Symptoms
• Cause
• 1 in 500 are heterozygotes; 1 in 1,000,000 are homozygotes. Partial dominance.
• Elevated LDL, cholesterol depositions.
• LDL receptor mutations (over 400 documented)
Can interfere with synthesis, transport, binding, clustering, or recycling.