MCB exam 1 p3
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40 Terms
Q: What is the lipid bilayer?
A: A flexible, two-dimensional fluid sheet made of lipids with proteins embedded in it.
Q: Why is the plasma membrane important?
A: Separates inside of cell from outside
Selectively permeable barrier
Scaffold for biochemical reactions
Cell–cell interactions
Signal transduction
Q: What is a key difference between prokaryotic and eukaryotic cells?
A: Eukaryotic cells have extensive internal membranes that form organelles
Q: What do membranes define in eukaryotic cells?
A: Membrane-bound organelles with unique soluble and membrane proteins.
Q: What does “amphipathic” mean?
A: Molecule has hydrophilic head and hydrophobic tail.
Q: Why do bilayers form automatically in water?
A: Hydrophobic tails avoid water; heads interact with water.
Q: What lipids make up membranes?
A:Phospholipids
Sterols (cholesterol)
Glycolipids
Q: How do unsaturated fatty acid tails affect membranes?
A: Create kinks → looser packing → more fluid membrane.
Q: Where is cholesterol found?
A: In eukaryotic membranes; in both leaflets.
Q: Leaflet distribution of lipids?
A:PC & SM → exoplasmic
PE & PS → cytosolic
Cholesterol → both
Q: What are lipid rafts?
A: Tightly packed, ordered membrane microdomains.
Q: Components of lipid rafts?
A: Cholesterol, sphingolipids, specific proteins (e.g., GPI-anchored).
Q: Functions of lipid rafts?
A: Cell signaling, protein sorting, membrane trafficking.
Q: Three classes of membrane proteins?
A:Integral
Lipid-anchored
Peripheral
Q: What defines an integral membrane protein?
A: Amino acids interact directly with lipid bilayer.
Q: What defines a lipid-anchored protein?
A: Covalently attached lipid holds protein in membrane.
Q: What defines a peripheral protein?
A: Indirectly associated via other proteins (noncovalent).
Q: What structure usually forms transmembrane regions?
A: Hydrophobic alpha helices (20–30 nonpolar AAs).
Q: Single-pass vs multipass proteins?
A: Single crosses once; multipass crosses 2+ times.
Q: What movements can lipids make?
A: Lateral diffusion, flexion, rotation (flip-flop is rare).
Q: Do membrane proteins move?
A: Many move laterally; some are anchored.
Q: What is FRAP?
A: Fluorescence Recovery After Photobleaching; measures lateral mobility.
Q: What does faster FRAP recovery mean?
A: Higher protein mobility.
Q: What did cell fusion experiments show?
A: Membrane proteins can move laterally.
Q: What is single particle tracking?
A: Tracks movement of individual membrane proteins.
Q: Levels of protein structure?
A: Primary, Secondary, Tertiary, Quaternary.
Q: What determines secondary structure?
A: Hydrogen bonds; dictated by primary sequence.
Q: Forces stabilizing tertiary structure?
A: H-bonds, hydrophobic interactions, ionic bonds, van der Waals, disulfide bonds.
Q: What is quaternary structure?
A: Multiple protein subunits forming a complex.
Q: What is affinity?
A: Strength of binding between molecules.
Q: Relationship between Kd and affinity?
A: Lower Kd = higher affinity.
Q: What does Kd equal?
A: koff / kon
Q: When is equilibrium reached?
A: When on-rate = off-rate.
Q: What helps proteins fold correctly?
A: Chaperones and chaperonins.
Q: What family is Hsp70?
A: Heat shock protein chaperones; use ATP.
Q: Where are disulfide bonds common?
A: Oxidizing environments (ER, extracellular), not cytoplasm.
Q: Where are most membrane proteins glycosylated?
A: ER and Golgi.
Q: Orientation of membrane glycoprotein sugars?
A: Face extracellular side.
Q: How to show a protein is membrane-associated?
A:
Immunofluorescence
Cell fractionation
Lipid requirement for function
Protease protection assays
Q: Why are proteases useful in topology studies?
A: They only cut accessible regions.
Note 
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