Membranes and Membrane Proteins

What percentage of the human genome encodes membrane proteins?

~30% of the human genome encodes membrane proteins.

What is the target of over 50% of all known drugs?

Membrane proteins are the target of over 50% of all known drugs.

What percentage of cytosolic volume is made up of lipid membranes?

Lipid membranes make up only 6–12% of cytosolic volume.

How many known protein folds are classified as membrane protein folds?

Out of ~1195 known protein folds, only 58 (~5%) are membrane protein folds.

What family does the GLP-1 receptor belong to?

The GLP-1 receptor belongs to the GPCR (G-Protein Coupled Receptors) family.

What is one key function of the GLP-1 receptor?

It regulates glucose homeostasis.

What drug targets the GLP-1 receptor?

The drug Semaglutide targets the GLP-1 receptor.

What is the composition of membranes?

Membranes are composed of lipids (15–75%) and proteins.

What does it mean for a membrane to be selectively permeable?

It allows specific molecules to pass through.

Name two types of bacterial membranes.

Gram-positive and Gram-negative.

What is a characteristic of Gram-negative bacteria?

Gram-negative bacteria have two membranes with a thin peptidoglycan layer in the periplasmic space.

What is a characteristic of Gram-positive bacteria?

Gram-positive bacteria have a thick peptidoglycan wall and a single membrane.

What are double lipid bilayers found in eukaryotic membranes?

They are found in organelles such as mitochondria and the nucleus.

What are common features of membranes?

Sheet-like structure, hydrophilic head and hydrophobic tail regions, non-covalent assembly, asymmetric, fluid, and electrically polarized.

What are the four major biomolecule groups?

Lipids, nucleic acids, proteins, and polysaccharides.

What are phosphoglycerides characterized by?

They have a glycerol backbone, 2 fatty acids, and a phosphate at C3.

What is cardiolipin (CL) and where is it found?

Cardiolipin is found in the inner mitochondrial membrane and makes up 20% of lipids there.

What role does cholesterol play in the plasma membrane?

Cholesterol makes up 30–40% of plasma membrane lipids and rigid structure decreases fluidity.

What is an aspect of lipid diversity?

Lipid composition varies by chemical structure and ratio, affecting behavior.

What is the permeability of membranes to ions and most polar molecules?

Membranes are impermeable to ions and most polar molecules.

What is the significance of phosphatidylserine (PS) in membranes?

PS normally on inner leaflet signals apoptosis when found on the outer leaflet.

What does hop diffusion refer to in membrane dynamics?

It refers to rapid local diffusion of lipids with occasional hopping across barriers.

What defines the cell shape in erythrocytes?

The membrane skeleton, primarily consisting of spectrin, helps define cell shape.

What are the types of membrane proteins?

Integral, peripheral, and amphitropic proteins.

What model describes the structure of membranes?

The Fluid Mosaic Model describes how proteins float in a lipid sea.

What is glycophorin and its role in erythrocytes?

Glycophorin is a protein important for malaria invasion and blood group determination.

What is the hydropathy scale used for?

It is used to predict membrane-spanning segments of proteins.

What are the principles of β-barrel membrane proteins?

They consist of an even number of β-strands, with N/C-termini in the periplasm and antiparallel strands.

What is the function of porins?

Porins are channels for small hydrophilic molecules found in the outer membrane of Gram-negative bacteria.

What affects the location of amino acids in membrane proteins?

Amino acids are located based on their interaction with the membrane core, interface, or aqueous phase.

What are lipid rafts?

Lipid rafts are domains rich in sphingolipids and cholesterol that are thicker, more ordered, and less fluid.

What challenges are faced when working with integral membrane proteins?

Challenges include low expression levels, poor solubility in detergents, difficult purification, and crystallization issues.