Kaplan Biochemistry Ch. 8: Biological Membranes

List the following membrane components in order from most plentiful to least plentiful: carbohydrates, lipids, proteins, nucleic acids

1. Lipids - phospholipids, cholesterol 2. Proteins - channels and receptors (transmembrane), membrane associated, embedded proteins 3. Carbohydrates - glycoprotein coat and signaling molecules 4. Nucleic Acids - essentially absent

What are the three classes of membrane proteins? How are they each most likely to function?

1. Transmembrane proteins: serve as channels or receptors. 2. Embedded membrane proteins: have catalytic activity linked to nearby enzymes 3. membrane-associated (peripheral) proteins: involved in signaling and recognition molecules on the extracellular surface

Given the following data, calculate the resting membrane potential of this cell:

-60 mV use the goldman equation

Which of the following is true of diffusion and osmosis? A. Diffusion and osmosis rely on the electrochemical gradient of only the compound of interest. B. Diffusion and osmosis rely on the electrochemical gradient of all compounds in a cell. C. Diffusion and osmosis will proceed in the same direction if there is only one solute. D. Diffusion and osmosis cannot occur simultaneously.

A. The movement of any solute or water by diffusion or osmosis is dependent only on the concentration gradient of that molecule and on membrane permeability.

Which lipid type is LEAST likely to contribute to membrane fluidity? A. Unsaturated glycerophospholipids B. trans glycerophospholipids C. Cholesterol D. Unsaturated sphingolipids

B Compounds that contribute to membrane uidity will lower the melting point or disrupt the crystal structure. Choles- terol, choice (C), and unsaturated lipids, choices (A) and (D), are known for these functions. trans glycerophospho- lipids tend to increase the melting point of the membrane and therefore decrease membrane uidity.

Which of the following is LEAST likely to be the resting membrane potential of a cell? A. -70 mV B. -55 mV C. 0 mV D. +35 mV

C Cell membranes are most likely to have a resting membrane potential that is nonzero because the resting membrane potential creates a state that is capable of responding to stimuli. Signaling molecules and channels would not be as useful with a membrane potential of zero. The values given in the answer choices correspond to different stages of the action potential, but the key information is that a resting potential of 0 mV does not maintain gradients for later activity.

pinocytosis

Cell drinking (ingestion of fluids and dissolved particles)

How does cholesterol play a role in the fluidity and stability of the plasma membrane?

Cholesterol interferes with the crystal structure of the cell membrane and occupies space between phospholipid molecules at low temperatures, and restricts excessive movement at high temperatures.

Which of the following is a sphingolipid? A. Lecithin B. Phosphatidylinositol C. Cholesterol D. Ganglioside

D Gangliosides, along with ceramide, sphingomyelin, and cerebrosides, are sphingolipids.

A membrane receptor is most likely to be a(n): A. embedded protein with catalytic activity. B. transmembrane protein with sequestration activity. C. membrane-associated protein with sequestration activity. D. transmembrane protein with catalytic activity.

D Membrane receptors must have both an extracellular and intracellular domain; therefore, they are considered trans- membrane proteins. In order to initiate a second messenger cascade, they typically display enzymatic activity, although some may act strictly as channels.

Osmotic pressure equation

II=iMRT i: # of particles in solution M: molarity R: gas constant T: tempt in Kelvins

Compare two types of active transport. What is the difference between symport and antiport?

Primary active transport - uses ATP as energy to move solutes against their gradient Secondary Active transport - uses electrochemical gradient to power the transport Symport - moves particles in secondary active transport across the membrane in the same direction Antiport: moves particles across the cell membrane in the opposite direction

What distinguishes the inner mitochondrial membrane from other biological membranes? What is the pH gradient between the cytoplasm and the intermembrane space?

The mitochondrial membrane doesn't have cholesterol (BIG DIFFERENCE) there is no pH gradient between the cytoplasm and the intermembrane space because the outer mitochondrial membrane has such high permeability to biomolecules ***The proton motive force of the mitochondria is across the inner mitochondrial membrane, not the outer.

Nernst equation

an equation predicting the voltage needed (equilibrium potential) to just counterbalance the diffusion force pushing an ion across a semipermeable membrane from the side with a high concentration to the side with a low concentration

What is the relationship between osmotic pressure and the direction of osmosis through a semipermeable membrane?

as osmotic pressure increases, more water will flow into the compartment to decrease solute concentration osmotic pressure is often considered a sucking pressure because water will move toward the compartment with highest osmotic pressure

Desmosomes between cells

binds adjacent cells by anchoring their cytoskeletons. formed by interactions between transmembrane proteins associated with intermediate filaments inside adjacent cells.

How is the resting membrane potential maintained?

by a sodium-potassium pump, which moves 3 Na+ out of the cell and 2 + into the cell. also due to a minor leak channel that allows passive transport of ions like k+

What is the primary thermodynamic factor responsible for passive transport?

entropy

Describe the role of flippases and lipid rafts in biological membranes

flippases: responsible for the movement of phospholipids between layers of the plasma membrane because it is otherwise energetically unfavorable. lipid rafts: they are aggregates of specific lipids in the membrane that function as attachment points for other biomolecules and plays a role in cell signaling.

Contrast gap junctions and tight junctions.

gap junctions: allow intercellular transport of materials and do not prevent paracellular transport of materials -discontinuous bunches around the cell tight junctions: not used for intercellular transport but do prevent paracellular transport. -forms bands around the cell