Cell Membranes BME 2104

What is the lipid bilayer made of

Two layers of phospholipids and related compounds, with cholesterol controlling fluidity and stability.

What is the basic structure of a phospholipid

A glycerol backbone, two fatty acid chains, and a phosphate group.

What are the hydrophobic and hydrophilic parts of a phospholipid

Fatty acid tails = hydrophobic; phosphate head = hydrophilic.

What is phosphatidic acid

The core structure of phospholipids that can attach different alcohol groups (choline, serine, ethanolamine) to form variants.

What drives lipid bilayer formation?

The amphipathic nature of lipids (having hydrophilic and hydrophobic regions).

What structures do fatty acids and phospholipids form in water

Fatty acids form micelles; phospholipids form bilayers.

What is the fluid mosaic model?

A model where proteins are embedded in a semi-fluid lipid bilayer, allowing lateral movement of molecules.

What are the three types of membrane proteins

Peripheral (surface-attached), lipid-anchored (bound to lipids), and integral (embedded or spanning the bilayer).

What are transmembrane proteins?

A type of integral protein that crosses the entire membrane.

How thick is a cell membrane?

About 4 nanometers (nm)

What is the typical size of a cell?

About 10 micrometers (µm) in diameter.

What is a hydrophobic alpha helix in membrane proteins?

A structure where non-polar side chains face fatty acid tails, and the polar backbone is stabilized by hydrogen bonds.

How many amino acids are in one turn of an alpha helix?

3.6 amino acid residues per turn (≈0.54 nm per turn).

What is the main function of the lipid bilayer?

Acts as a transport barrier controlling what enters and exits the cell.

What functions do membrane proteins perform?

Transport, signaling, recognition, and enzymatic activity.

What does compartmentalization do

Separates regions for localized functions and increases local concentrations.

How do membranes regulate transport

By controlling movement of nutrients, ions, and waste.

What happens during signal reception and transduction?

Receptors bind ligands, triggering internal cellular responses

Why are cell interactions important?

They enable tissue structure, communication, and movement

Why is membrane fluidity important

Too little fluidity disrupts protein function; fluidity allows flexibility and normal function.

What factors increase or decrease membrane fluidity

• Unsaturated fatty acids → increase

• Saturated fatty acids → decrease

• Trans fats → decrease

What role does cholesterol play in membranes?

Acts as a fluidity buffer: prevents freezing at low temps and excess fluidity at high temps.

What are lipid rafts

Cholesterol-rich nanodomains in the membrane composed of sphingolipids and proteins.

What is the function of lipid rafts

Organize signaling, assist in protein sorting and trafficking, and play roles in immune response and pathogen entry