UNIT 3 Membrane composition

What is a plasma membrane?

A selectively permeable lipid bilayer surrounding a cell.

What is a phospholipid?

An amphipathic lipid containing a phosphate-containing head group.

What is a phosphoglyceride?

A phospholipid built from glycerol, 2 fatty acids, phosphate, and a head group.

What makes phosphoglycerides amphipathic?

They have hydrophilic heads and hydrophobic fatty-acyl tails.

What is glycerol's role in phosphoglycerides?

It forms the 3-carbon backbone connecting tails and the phosphate head.

What is a fatty-acyl tail?

A hydrophobic fatty-acid-derived chain attached to glycerol.

What is a sphingolipid?

A membrane lipid built on a sphingosine backbone.

What is sphingosine?

A long-chain amino alcohol that forms the backbone of sphingolipids.

How do sphingolipid and phosphoglyceride tails differ?

Phosphoglycerides use glycerol; sphingolipids use sphingosine.

Where are hydrophobic lipid tails located in a bilayer?

Toward the membrane interior, away from water.

Where are hydrophilic lipid heads located?

At the membrane surfaces, contacting aqueous environments.

What is a triglyceride?

Glycerol attached to three fatty acids.

Why aren't triglycerides major membrane lipids?

They lack a hydrophilic head and are not sufficiently amphipathic.

What is a glycolipid?

A lipid with one or more covalently attached sugar molecules.

Are all glycolipids sphingolipids?

FALSE. Glycolipids can have different lipid backbones.

Are all glycolipids phosphoglycerides?

FALSE.

Are all glycolipids phospholipids?

FALSE. Glycolipids need not contain phosphate.

Are all glycolipids amphipathic?

TRUE. Their lipid portion is hydrophobic and sugar-containing region hydrophilic.

What primarily differs between phosphatidylcholine and phosphatidylethanolamine?

Their polar head groups.

What is cholesterol's major membrane role?

It buffers membrane fluidity and affects permeability.

What is an integral membrane protein?

A protein embedded in the hydrophobic membrane core.

What is a transmembrane protein?

An integral protein that spans the membrane.

What is a single-pass protein?

A transmembrane protein crossing the bilayer once.

What is a multi-pass protein?

A transmembrane protein crossing the bilayer multiple times.

Why must transmembrane proteins be amphipathic?

Hydrophobic regions contact lipid tails; hydrophilic regions contact water.

What does a hydropathy plot predict?

Hydrophobic regions likely to form membrane-spanning segments.

What usually indicates a transmembrane segment on a hydropathy plot?

A sustained region of high hydrophobicity.

How are phosphoglycerides and sphingolipids similar?

Both are amphipathic membrane lipids with hydrophobic tails.

How are phosphoglycerides and sphingolipids different?

They use different backbones: glycerol versus sphingosine.

What is self-assembly?

Spontaneous organization of molecules into stable structures.

What is a micelle?

A spherical structure with hydrophobic tails inside and heads outside.

What lipid shape favors micelle formation?

Cone-shaped amphipathic lipids with one tail.

What lipid shape favors bilayer formation?

Cylindrical-shaped lipids with two tails.

Why do bilayers close into spherical structures?

Closure eliminates exposed hydrophobic edges, lowering free energy.

What is lateral diffusion?

Movement of membrane lipids within the same membrane layer.

Why can phospholipids laterally diffuse?

They remain in the favorable hydrophobic environment of the bilayer.

Why is spontaneous flip-flop rare?

The polar head must cross the hydrophobic membrane core.

What does "2D liquid" mean for membranes?

Membrane molecules move laterally while remaining in the bilayer.

How does increasing temperature affect membrane fluidity?

Higher temperature generally increases fluidity.

Why does temperature affect membrane fluidity?

Higher thermal energy increases lipid movement.

How does increased fatty-acid unsaturation affect fluidity?

It increases fluidity by preventing tight packing.

Why do unsaturated tails increase fluidity?

Double bonds create kinks that prevent tight lipid packing.

How does increased fatty-acid saturation affect fluidity?

It decreases fluidity because straight tails pack tightly.

How does cholesterol help at low temperatures?

It prevents phospholipids from packing too tightly.

How does cholesterol help at high temperatures?

It restrains lipid movement and prevents excessive fluidity.