CM07: Membrane structure and transport

Define fusion and fission.

Fusion: Two membranes joining together.

Fission: One membrane separating into separate compartments.

What is the lipid bilayer composed of?

Composed of 2 leaflets (e.g. phospholipids, sphingolipids, and cholesterol)

What is the function of proteins in the membrane?

They determine the functional properties of membranes.

What does the membrane consist of?

It consist of a lipid bilayer, proteins, and carbohydrates.

What does amphipathic mean?

A substance with hydrophilic and hydrophobic regions.

What is the difference between saturated and unsaturated fats?

Saturated: straight chain.

Unsaturated: 30 degree bend which reduceflexibility.

What does phospholipids consist of?

head, tail, and a polar group

What are shingolipids?

They are long-chain FA (fatty acids) connected to a 18-carbon amino alcohol (sphingosine)

Where are sphingolipids found?

They are found on the outer leaflet of the cell membrane, which makes them mechanically resistant and chemically stable.

What are interchangeable R groups found on sphingolipids?

H - Ceramide

Sugar molecule - glycosphingolipid

Phosphocholine - sphingomyelin

What type of membrane is sphingomyelin commonly found?

It’s found in membrane that forms the myelin sheath.

What is cholesterol and what is it responsible for?

It is a flat and rigid molecule with a polar -OH group. (Also a weak polar)

It is responsible for membrane fluidity (by increase melting temp and decrease fluidity).

What is lipid important for in the membrane?

It is important for signaling and mechanical stability of the membrane.

What can cross the membrane?

• Gases (O2, CO2)

• Small and non-polar molecules

• Water-soluble molecules (polar) cannot easily cross the membrane (e.g. ions, amino acids, sugars, nucleotides)

What are passive modes of membrane transport? What are some examples?

Passive → meaning that it moves down a conc. gradient

Simple diffusion: small molecules pass through bilayer.

Faciliated diffusion: dependent on carrier and channel proteins to allow molecules through.

What are some modes of membrane transportation that require energy input?

Active transport

• Primary: require ATP

• Secondary: couples uphill movement to the downhill movement of another molecule (Na+)

Vesicular transport (endocytosis/exocytosis)

What are several factors that affect diffusion?

Temperature, solute size, solvent viscosity, and distance.

What is diffusion?

It is the constant and random movement of molecules due to kinetic energy.

What equation explains how diffusion through the membrane is affected?

Fick’s Law

What does Fick’s Law describe?

Flux (J) is directly proportional to diffusion coefficient (D), area (A), and concentration gradient.

What are some substances that have high permeability?

Gases (O2, CO2, N2), hydrophobic solutes, and small uncharged molecules.

What are some substances that have low permeability?

Ions (Na+, K+, Cl-, etc.), large uncharged polar molecules (e.g. glucose, sucrose), and charged molecules (amino acids, ATP, DNA).

What are ion channels?

They are channels composed of multiple subunits with hydrophilic regions.

Highly selective (e.g. Na+, K+, etc.) and regulated (e.g. permeability to ion changes).

What is carrier-mediated membrane transport?

It’s a type of transport that induce a conformational change.