What is used to check for PS flippage?
Annexin V bound to fluorescent dyes
What PLs are found on the outer leaflet?
What PLs are found on the inner leaflet?
What can you use to extract peripheral and integral membrane proteins?
- Peripheral - salt
- Integral - detergent
Classes of membrane proteins
What type of membrane protein is catenin?
Peripheral - connects cell receptors to the cytosol
What type of membrane protein is cadherin?
Integral membrane protein
Is lateral or cross-membrane diffusion (flippage) a commonly occuring event?
- lateral diffusion - the PL bilayer is viscous.
- Limited diffusion in polarized cells though: tight junctions, cytoskeletal attachment
What is a lipid rapid, and what is it composed of?
A localized region of the PM enriched in cholesterol and sphingolipids.
How do lipid rafts participate in cell signaling?
It concentrates membrane proteins in a unique environment, and by closer proximity, facilitates signaling.
What are the surface of cells coated with? What is it composed of?
A glycocalyx - carbohydrate coat
What is the function of the glycocalyx?
- Protection of cell-surface
- Cell-cell and cell-matrix interactions
- leukocyte homing (selectins)
A defective glycocalyx may result in what?
- Cystic fibrosis (airway surface layer)
- Dry eye (corneal epithelium)
What is leukocyte homing?
During an inflammatory process, cytokines and chemokines are released, causing endothelial cells to express selectins (lectin receptors) on their surface. As leukocytes roll along, their lectin moiety binds to the selectin, causing it to slow then stall. The WBC changes shape, and squeezes between endothelial cells into the site of inflammation.
What molecules can passively diffuse through a membrane?
gases, hydrophobic, and small polar molecules
What molecules CANNOT passively diffuse through a membrane?
large polar molecules and charged molecules (ions)
Facilitated diffusion is drive by.....
an electrochemical gradient. Substances move down their gradient (from higher to lower concentration).
Active transport requires....
Energy in the form of ATP.
What types of proteins are involved in transport of materials across a membrane?
- Carrier proteins
- Channel proteins: ligand and voltage-gated
Basic steps in neuronal cell-signaling:
- 1) neurotransmitter in synaptic vesicles fuse with pre-synaptic membrane.
- 2) Neurotransmitters are released into the synaptic cleft.
- 3) binding of neurotransmitters to receptors on the post-synaptic membrane to ligand-gated channels allow for opening of the channels.
What are VEGFs?
Vascular Endothelial Growth Factors - stimulate growth/synthesis of blood vessels (during embryonic development, after injury, building of muscle, etc.).
How can VEGFs assist in cancer?
- Solid tumors only grow to the size of a pea (no blood supply), unless they release their own GFs.
- Diabetic retinopathy also occurs in a similar manner.
Prostaglandin synthesis is mediated by....
A target for limiting inflammation is...
COX 1 or COX 2
What are phagosomes and phagolysosomes?
- Phagosomes - Cells engulf large particles via elaboration of their pseudopodium and membrane fusion to form phagosomes that move through the cytosol.
- Phagosolysosome - fusion of a phagosome with a lysosome.
Diseases associated with defective membrane function:
- Muscular Dystrophy
- Cystic Fibrosis
- Retinitis Pigmentosa
- Familial Hypercholesterolemia
Physical manifestation of MD:
Muscle weakness and atrophy
Most common MD is....and it is caused by....
- Duchenne's MD
- Caused by a defect in the dystophin-assoicated protein complex. The role of this complex is to stabilize the sarcolemma during stress of a muscle contraction.
Clinical manifestation of retinitis pigmentosum
Night blindness precedes loss of peripheral vision.
Retinitis pigmentosa is caused by....
A defect in the gene for the photoreceptors.
Characteristics of CF:
- common inheritance - 1/4000
- autosomal recessive
- defect in Cl-ion channels
- poor growth, excessive mucus production
Characteristics of familial hypercholesterolemia:
- Genetic disorder resulting in high LDL levels and CV disease.
- Atherosclerotic plaques form from LDL buildup.
- Defect in LDL receptor (this receptor is associated with clathrin).
Steps in secreting proteins:
- Synthesis in ER
- Transfer to Golgi
- Movement to membrae in secretory vesicles
- SECRETORY PROTEINS NEVER SEE THE CYTOPLASM!
Function of Sarcoplasmic Reticulum?
Serves as a calcium storage in muscles. Spreads the action potential from the sarcolemma throughout the cytoplasmic compartment.
In what types of cells would you find a highly developed Golgi?
- In secretory cells such as Plasma cells which are making and secreting antibodies.
- Exocytotic pathway
Function of exocytotic vessicles?
carries substances to be released outside of the cell and renews membrane components (receptors, etc).
What types of cells have constitutive exocytosis?
Immunoglobulins - releasing antibodies
What are SNAREs?
The ligand and receptor on the donor and target organelle for transport of vesicles.
Steps in receptor-mediated endocytosis...
- Clathrin surrounds the invaginated membrane section, forming an endosome.
- The endosome is uncoated in the cytosol and fuses with a lysosome.
- The receptor is recycled back to the PM.
Ex of clathrin-independent endocytosis
Uptake of HDL (good cholesterol)! Mediated by cavinolin
What is cavinolin?
Mediates small invaginations in the PM in lipid rafts, to form caveolae.
Primary vs secondary lysosome
- Primary - new lysosome filled with hydrolytic contents.
- Secondary - lysosome that fuses with phagosome.
Functions of lysosomes
- Phagocytosis (primary and secondary lysosomes)
- Autophagy (of old organelles)
Two main lysosomal storage diseases
- Tay-Sachs Disease
- Gauchers Disease
Clinical characteristics of Tay-Sach's Disease
- Cherry red macula
- Infants unable to sit up, poor motor skills, exaggerated startle reflex, floppy
- Infant mortality
Cause of Tay-Sach's Disease
- Accumulation of gangliosides due to defect in Hexoaminidase A enzyme.
- Ganglioside accumulation inside nerve cells of CNS.
Clinical characteristics of Gaucher's Disease
- Extremely enlarged spleen and liver.
- Skeletal abnormalities
- Neurologic complications
Where are peroxisomal proteins synthesized?
Main function of peroxisomes?
FA oxidation - holds oxidative proteins
Describe Zellwegger Disease
- A peroxisomal disease - no oxidative proteins...empty peroxisome
- Death within the first year of life.
- Multiple organs involved.
- Presents with muscle weakness, seizures, respiratory and cardiac failure.
- Due to a defect in the tRNA for lysine.
- Optic Neuritis...the optic nerve has a high metabolic demand.
- Sudden loss of vision in 2nd or 3rd decade.
- Usually bilateral, but may be unilateral.