Membrane Proteins Flashcards

Study Notes

Classifications of Membrane Proteins

Integral Proteins: Span the lipid bilayer; require detergents for removal; penetrate the hydrophobic core.
Peripheral Proteins: Loosely attached to the bilayer via non-covalent bonds; removed by salts or pH changes; do not penetrate hydrophobic core.
Lipid-Anchored Proteins: Associate outside the bilayer; anchored by fatty acids or prenyl groups; removed by detergents and require phospholipids.

Transmembrane Proteins

Can exist as single helix, multiple helices, or beta barrels.
Anchored by various means including helices, lipid attachments, oligosaccharide linkers, or non-covalent bonds.
Monotopic proteins have polypeptide chains that do not fully cross the bilayer.

Lipid-Anchored Membrane Proteins

GPI Anchors: Located on external surfaces; require phospholipids for insertion.
Functions include acting as receptors, enzymes, and cell adhesion molecules.
Lipoproteins: Attach to cytoplasmic side using long hydrocarbon chains; do not penetrate the hydrophobic core; important signaling molecules.

Alpha Helical Conformation

Most transmembrane proteins have polypeptide chains crossing the lipid bilayer in an alpha helical form.
These proteins are amphipathic, featuring both polar (hydrophilic) and non-polar (hydrophobic) domains.

Protein Structure Characteristics

Polar amino acid residues are typically located on the protein surface.
Nonpolar residues are found in the interior, often influencing protein folding and functionality.

Non-Polar Side Chains

Key non-polar amino acids: Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Phenylalanine, Tryptophan, Proline.
Mnemonic: "Grandma Always Visits London In May For Winston's Party."

Polar/Uncharged Side Chains

Key polar uncharged amino acids: Serine, Threonine, Cysteine, Asparagine, Glutamine, Tyrosine.
Mnemonic: "Santa's Team Crafts New Quilts Yearly."

Polar/Electrically Charged Side Chains

Key charged amino acids: Aspartate, Glutamate, Lysine, Arginine, Histidine.
Mnemonic: "Dragons Eat Knights Riding Horses."

Unique Side Chains

Glycine: Non-polar, has a single hydrogen, fits in both hydrophilic and hydrophobic environments.
Cysteine: Polar and forms disulfide bonds with other cysteine residues.
Proline: Non-polar, features a unique structure disrupting secondary protein folding.

Role of Aquaporins

Aquaporins create hydrophilic channels in the membrane, facilitating water transport across the bilayer.

Multipass Membrane Proteins

Single-pass proteins cross the membrane one time, while multipass proteins weave in and out, creating complex membrane topologies.

Description

Test your knowledge on membrane proteins with this flashcard quiz. Covering the three classes of membrane proteins, including integral and peripheral proteins, you'll deepen your understanding of their structures and functions. Perfect for biology students and enthusiasts!