Membranes and Membrane Transport Flashcards
Cholesterol is a precursor to which of the following?
Vit C, NADH, nucleic acids, or steroid hormones?
Steroid hormones
True or False: Peripheral membrane proteins are located near the cell membranes, while integral membrane proteins extend through the cell membrane.
True
Which statement is true regarding passive/active transport?
a) Passive moves solutes against gradient
b) Passive requires ATP hydrolysis
c) Active requires net input of energy
C
Which substance would most easily cross lipid bilayer through passive diffusion?
O2, water, glucose, or Na+?
O2
What are isoprenoids? Where are they found
Repeating five-carbon units (isoprene units).
Found in terpenes, vit E, vit K, ubiquinone
What are terpenes?
Contain a number of isoprene units, found in plant essential oils
What is prenylation?
Attachment of isoprene to a protein. Helps tether protein to membrane.
What is cholesterol?
4 ring structure with side chain and OH at C3 (sterol).
Membrane component–embedded in lipid bilayer.
Precursor to all steroid hormones, vitamin D, and bile salts.
How is cholesterol stored in cells?
Stored as fatty acid esters, to keep it out of the membrane.
Basic steroid structure?
3 6-carbon rings and one 5-carbon ring.
What are lipoproteins?
Proteins linked to a lipid group. Usually refer to plasma macromolecules.
Transport lipid molecules in blood. Why? Lipids aren’t water soluble.
3 components of lipoprotein?
Apolipoprotein- protein component
Phospholipid, cholesterol, other proteins
Cholesteryl esters/triacyl glycerols
How are lipoproteins classified?
According to density.
HDL, LDL, VLDL, ULDL.
HDL has more protein relative to the amount of cholesterol than LDL.
Describe the cell membrane.
Heterogeneous mixture of lipids and proteins.
Inner and outer leaflets. Fluid mosaic.
Membrane features vary greatly between cell types. E.g. mitochondrial membrane has more protein, red blood cell membrane has more carbohydrates.
What is one function of membranes in cells?
Compartmentalization. Hydrophobic barrier and specialized proteins allow micro-environments.
Specialization of function.
Describe membrane fluidity. What affects this?
Viscosity depends on composition.
Un/saturated fatty acid and cholesterol content.
Lateral movement of lipids. Lipid transfer between leaflets–flippase, floppase, and scramblase are enzymes that catalyze this.
Describe membrane permeability.
Selectively permeable.
What can move across a membrane?
Lipophilic molecules, very small and uncharged polar molecules, water (somewhat)
What cannot move across a membrane?
Ions, large molecules, charged and polar molecules
What functions are membrane proteins involved in?
Transport, catalysis, signal transduction
What is the difference between peripheral and integral proteins?
Peripheral = located near cell membrane. Non-covalent, prenylation, GPI anchor, etc.
Integral = traverse the membrane, or are embedded.
What does cholesterol do in the membrane?
How does it affect fluidity?
Cholesterol has a rigid hydrophobic structure and is interspersed among phospholipids.
Acts as a buffer to fluidity. As temperature increases, cholesterol stabilizes neighboring phospholipids. At lower temperature, spaces out phospholipids to prevent solidification.
Generally, more cholesterol = more stability, less fluidity.
What are lipid rafts?
Segment of the plasma membrane that contains higher proportion of cholesterol and sphingolipids (saturated FA tails). Doesn’t move around as much as typical phospholipids.
What do lipid rafts do?
Membrane sections–microdomains–form ordered and rigid structure, help stabilize groups of proteins.
