Questions and Answers
What are the 3 classes of membrane proteins?
Integral proteins, peripheral proteins, lipid-anchored proteins.
Which of the following describes transmembrane proteins?
What is GPI in the context of lipid-anchored membrane proteins?
Glycosyl-phosphatidylinositol anchored protein.
What structural conformation do most transmembrane proteins take?
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What is the role of nonpolar residues in protein structure?
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What does the acronym 'Grandma Always Visits London In May For Winston's Party' represent?
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What does the acronym 'Santa's Team Crafts New Quilts Yearly' represent?
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What does the acronym 'Dragons Eat Knights Riding Horses' represent?
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What does 'Grandma Craft Party' illustrate in terms of amino acids?
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What role do aquaporins play in the membrane?
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How do single-pass and multi-pass membrane proteins differ?
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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.
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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!
