L9: Biomembranes Flashcards
List the components of biological membranes.
- proteins, carbohydrates, lipids
State the location of carbohydrate covalently linked to membrane protein or lipid.
- Carbohydrate covalently linked to membrane proteins and lips are found on the extracellular face of a cells membrane or the luminal side of endoplasmic reticula/Golgi.
What is myasthenia gravis and cystic fibrosis. Name the defective ion channels in each.
- Myasthenia gravis: autoimmune disease characterized by muscle weakness and fatigue to the muscles involved with talking, swallowing, facial expression, chewing and eyelid movement. It is the result of self-antibodies targeting nicotinic ACh receptors at the NMJ - Cystic fibrosis: genetic disorder (pop in Caucasians) characterized by multi-organ disease, main manifestation is the accumulation of thick mucous secretions in lungs. Leading to recurrent infections. It is the result of a mutation to a chloride channel, leading to defects in fluid and electrolyte transport.
What is the role of cholesterol in membrane structure?
- Cholesterol can increase and decrease fluidity of the plasma membrane.
Compare and contrast gap junctions and the nicotinic-acetylcholine receptor.
- Gap junctions are protein pores that allow movement of small molecules between two adjacent cells. Connexons and are made up of 6 connexin subunits. Two connexons (each in a separate plasma membrane) when joined, form a continuous pore that allows movement of small molecules/ions. - Nicotinic acetylcholine receptors are ligand-gated sodium channels composed of five subunits. Present at neuromuscular junctions, these receptors bind Ach from the adjacent neurons, which causes a conformational change, opening the channel and allow sodium to flow in down its concentration gradient and into the cell.
Describe active transport, secondary active transport, symport, and antiport. Examples?
- Active transport: movement of a substance across a biomembrane against its concentration gradient, requiring input of energy. Examples: ATPases, pumps (Na/K) - Secondary active transport: energy from electrochemical ion gradients is used to drive transport of compound across biomembrane without direct use of energy. Examples: symport, antiport - Symport: moves two molecules/ions in same direction across biomembrane - Antiport: moves two molecules/ions in counter direction to one another across biomembrane
How does cholesterol increase and decrease the fluidity in the plasma membrane?
- Decreases fluidity: body temp, steroid rings (hydrophobic and rigid) interact with and immobilize fatty acyl chains - Increases fluidity: reduced temp, cholesterol prevents tight packing off fatty acyl tails and maintains fluidity
What is the typical ratio of protein to lipids in a biomembrane? Does this ratio always hold true?
- Most membranes contain roughly equal protein to lipid ratios. This ratio holds true with exceptions to the inner mitochondrial membrane (which is more protein) and myelin (which is more lipid).
Know some examples of α-neurotoxins and how these compounds exert their effects.
- alpha-conotoxin: produced by cone shell - alpha-cobratoxin: produced by cobra - alpha-bungarotoxin: produced by krait - tubocurarine: produced by plant These cause paralysis by blocking nicotinic ACh receptor on muscle.
What is the action of digitalis?
- Digitalis is an inhibitor of the Na/K ATPase. Causes increase in FOC, decrease in HR.
Define the following terms: integral membrane protein, peripheral membrane protein
- Integral: proteins embedded in the membrane - Peripheral: proteins associated with the inner or outer face of membrane
What is the function of the GLUT protein family?
- GLUT proteins function to move glucose across lipid bilayers down their concentration gradient. They can transport other monosaccharides, but affinity is highest for glucose. They are integral proteins.
Describe the Na+/K+ ATPase and how it functions. Name a drug that inhibits it.
- Na/K ATPase maintains Na/K gradient across the plasma membrane of every cell in the body. Sodium has highest concentration outside the cell, while potassium has highest concentration inside the cell. This ATPase binds 3 sodiums on the cytosolic side, is phosphorylated, moves 3 sodiums to extracellular side, binds 2 potassium, phosphate is hydrolyzed and potassium is broughto to cytosolic side. - Digitalis inhibits this ATPase.
What is Zellweger syndrome?
- Zellweger syndrome is a disorder of failure to produce functional peroxisomes and therefore failure to produce plasmalogens. Results in defective myelination, which leads to hypotonia, severe intellectual disability and is generally fatal in few few months of life. Infants present with poor weight gain, weak suck, hypotonia, high foreheads, flat broad nasal bridges and underdeveloped jaws.
List four ways that peripheral membrane proteins may be attached to the surface of the bilayer.
1.) electrostatic interactions between proteins and negatively charged head groups 2.) proteins covalently attached to hydrophobic tail groups 3.) proteins covalently attached to phosphatidylinositol via GPI-anchor (sugar structure) 4.) interactions with integral membrane proteins
Draw the structure of a glycerophospholipid (phosphoglyceride).
