Transmembrane Proteins

What are the primary structural components of biological membranes?

Complex lipid-based structures forming pliable sheets, composed of various lipids and proteins.

What is the primary function of the cell membrane?

To separate the cell from its surrounding environment.

List three major functions of biological membranes.

Defining cell boundaries, allowing selective import/export of substances, and providing internal compartmentalization.

How does compartmentalization benefit eukaryotic cells?

It separates energy-producing reactions from energy-consuming ones and sequesters proteolytic enzymes away from vital cellular proteins.

What is the structural arrangement of the membrane bilayer?

Two leaflets of lipid monolayers where hydrophilic head groups face water and hydrophobic fatty acid tails are packed inside.

What does the 'Fluid Mosaic Model' propose regarding membrane structure?

Lipids form a viscous, two-dimensional solvent into which proteins are integrated to varying depths.

What is the difference between integral and peripheral membrane proteins?

Integral proteins are firmly associated with the membrane, often spanning the bilayer, while peripheral proteins are weakly associated and easily removed.

Name three functional categories of membrane proteins.

Receptors, channels/gates/pumps, and enzymes.

What are the cellular roles of transmembrane (TM) proteins?

Cell-to-cell communication, organelle-cytosol communication, ion/nutrient transport, links to the extracellular matrix, viral receptors, and cytoskeleton connections.

Why are transmembrane proteins significant in medicine?

They are key factors in many diseases (e.g., cancer, diabetes, depression) and serve as targets for over 75% of pharmaceuticals.

What are the two main requirements for a polypeptide chain to be stable within a lipid bilayer?

It must contain many hydrophobic amino acids and fold to satisfy backbone hydrogen-bond propensity.

What are the two general topologies of transmembrane proteins?

Single/helical bundles and beta-barrels.

Where are beta-barrel transmembrane proteins typically found?

In the outer membrane of gram-negative bacteria and some non-constitutive membrane-acting toxins.

What is the approximate thickness of a biological lipid bilayer?

Approximately 30 Angstroms (30Å).

What method is used to predict which amino acids form membrane-spanning alpha-helices?

Hydropathy plot analysis.

Why do transmembrane helices often contain charged residues at their ends?

To interact with the lipid head groups of the membrane.

What is the primary reason passive diffusion of polar molecules through a lipid membrane is difficult?

It involves desolvation, which creates a high activation energy barrier.

What are proteins that provide an alternative diffusion path for solutes called?

Transporters or permeases.

What is the function of aquaporins?

They allow for the rapid passage of water through biological membranes.

What percentage of proteins in complete genomes are estimated to be transmembrane proteins?

Over 25%.

What is the most common topology for transmembrane proteins?

Single helix or helical bundles (comprising over 99% of TM proteins).

What is an example of a 7TM receptor?

G protein-linked receptors.

What is the role of ATP synthase (F0F1 ATPase) in the membrane?

It is an enzyme involved in ATP synthesis, often utilizing a proton gradient.