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Questions and Answers
What is a characteristic of single-pass transmembrane proteins?
What is a characteristic of single-pass transmembrane proteins?
- They contain multiple transmembrane segments.
- They contain only polar amino acids.
- They have one α-helix traversing the lipid bilayer. (correct)
- They must be energetically favorable to transfer molecules.
What distinguishes multipass transmembrane proteins from single-pass proteins?
What distinguishes multipass transmembrane proteins from single-pass proteins?
- They consist of several α-helices that span the lipid bilayer. (correct)
- They have a soluble form when not embedded.
- They exist only as dimers.
- They require energy for molecule transfer.
Which structural feature is crucial for the passage of water molecules through aquaporin channels?
Which structural feature is crucial for the passage of water molecules through aquaporin channels?
- Presence of 5 α-helices.
- Tetramer formation with four monomers. (correct)
- Configuration of a single α-helix.
- A large β barrel structure.
What type of interactions are important for the dimerization of Glycophorin A?
What type of interactions are important for the dimerization of Glycophorin A?
Which of the following best describes the properties of β barrels in multipass transmembrane proteins?
Which of the following best describes the properties of β barrels in multipass transmembrane proteins?
What is a characteristic of peripheral membrane proteins?
What is a characteristic of peripheral membrane proteins?
How do lipid anchors affect membrane proteins?
How do lipid anchors affect membrane proteins?
What type of layer does the glycoproteins form on the extracellular surface of the cell membrane?
What type of layer does the glycoproteins form on the extracellular surface of the cell membrane?
Which property distinguishes transmembrane α-helices from peripheral proteins?
Which property distinguishes transmembrane α-helices from peripheral proteins?
What role do polar amino acids play in the structure of membrane proteins?
What role do polar amino acids play in the structure of membrane proteins?
Which term refers to long polysaccharide chains that are linked to proteins?
Which term refers to long polysaccharide chains that are linked to proteins?
What is the main function of the glycoproteins and proteoglycans within the glycocalyx?
What is the main function of the glycoproteins and proteoglycans within the glycocalyx?
How are Rab proteins categorized based on their attachment mechanisms?
How are Rab proteins categorized based on their attachment mechanisms?
What primarily characterizes the Src family of proteins?
What primarily characterizes the Src family of proteins?
What role does the glycocalyx play in cellular interactions?
What role does the glycocalyx play in cellular interactions?
Which of the following is NOT a function of the glycocalyx?
Which of the following is NOT a function of the glycocalyx?
What type of molecules are generally used by the Ras family for membrane attachment?
What type of molecules are generally used by the Ras family for membrane attachment?
What role do detergents play in the solubilization of membrane proteins?
What role do detergents play in the solubilization of membrane proteins?
Which property distinguishes mild nonionic detergents from harsher detergents?
Which property distinguishes mild nonionic detergents from harsher detergents?
What is one application of purified membrane proteins after solubilization?
What is one application of purified membrane proteins after solubilization?
What structural characteristic do nanodiscs provide for studying membrane proteins?
What structural characteristic do nanodiscs provide for studying membrane proteins?
Bacteriorhodopsin is notable for which of the following features?
Bacteriorhodopsin is notable for which of the following features?
Why is single-particle electron microscopy a valuable technique for studying membrane proteins?
Why is single-particle electron microscopy a valuable technique for studying membrane proteins?
What happens to protein mobility within the cell membrane?
What happens to protein mobility within the cell membrane?
How are detergent micelles formed during the solubilization of membrane proteins?
How are detergent micelles formed during the solubilization of membrane proteins?
What is primarily restricted to the apical surface of epithelial cells?
What is primarily restricted to the apical surface of epithelial cells?
How can membrane proteins restrict their lateral diffusion?
How can membrane proteins restrict their lateral diffusion?
What role does spectrin play in the erythrocyte membrane?
What role does spectrin play in the erythrocyte membrane?
Which proteins are involved in the attachment to the basal plasma membrane of epithelial cells?
Which proteins are involved in the attachment to the basal plasma membrane of epithelial cells?
What is a function of membrane-bending proteins?
What is a function of membrane-bending proteins?
Which mechanism is NOT involved in restricting lateral diffusion of membrane proteins?
Which mechanism is NOT involved in restricting lateral diffusion of membrane proteins?
What distinguishes intestinal epithelial cells from other cells?
What distinguishes intestinal epithelial cells from other cells?
What feature defines transmembrane proteins?
What feature defines transmembrane proteins?
What is the primary function of lipid rafts in cellular membranes?
What is the primary function of lipid rafts in cellular membranes?
Which process do lipid rafts NOT participate in?
Which process do lipid rafts NOT participate in?
What characterizes the lipid composition of the outer monolayer in cell membranes?
What characterizes the lipid composition of the outer monolayer in cell membranes?
How do lipid droplets influence membrane synthesis?
How do lipid droplets influence membrane synthesis?
What is the role of phosphatidylserine translocation during apoptosis?
What is the role of phosphatidylserine translocation during apoptosis?
Which type of receptors are typically found in lipid rafts?
Which type of receptors are typically found in lipid rafts?
What is NOT a characteristic of lipid droplets?
What is NOT a characteristic of lipid droplets?
The difference in lipid compositions between the inner and outer monolayers results in what phenomenon?
The difference in lipid compositions between the inner and outer monolayers results in what phenomenon?
What processes are associated with lipid rafts during endocytosis?
What processes are associated with lipid rafts during endocytosis?
Which enzyme is involved in lipid metabolism and associated with lipid droplets?
Which enzyme is involved in lipid metabolism and associated with lipid droplets?
What is primarily found in the inner monolayer of cell membranes?
What is primarily found in the inner monolayer of cell membranes?
What defines the mechanism of action in b cell receptors when interacting with an antigen?
What defines the mechanism of action in b cell receptors when interacting with an antigen?
What constitutes the fundamental role of a scramblase in the membrane?
What constitutes the fundamental role of a scramblase in the membrane?
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Study Notes
Membrane Structure and Function
- Lipid Rafts: Domains in membranes where lipids and proteins are concentrated, facilitating protein-protein, protein-lipid, and lipid-lipid interactions.
- Signal Transduction: B cell receptors dimerize in lipid rafts upon antigen interaction, initiating signaling for antibody production.
- Endocytosis: Lipid rafts play a role in endocytosis through caveola and transport vesicle formation, containing G-protein coupled receptors aiding in neurotransmitter transport.
Lipid Droplets
- Lipid droplets store excess neutral lipids, serving as building blocks for membrane synthesis or energy.
- Encased by a phospholipid monolayer with associated enzymes critical for lipid metabolism.
- Created by budding from the endoplasmic reticulum (ER), found in adipocytes and fatty-acid-rich cells.
Monolayer Composition Differences
- Outer Monolayer: Comprises phosphatidylcholine and sphingomyelin with choline heads.
- Inner Monolayer: Contains phosphatidylethanolamine and phosphatidylserine, generally negatively charged.
- Proteins like Protein Kinase C (PKC) interact with lipids on the inner monolayer.
Phosphatidylserine Translocation
- Apoptotic cells translocate phosphatidylserine from the inner to the outer layer, signaling macrophages for phagocytosis.
Membrane Protein Types
- Single-pass Transmembrane Proteins: Contain one α-helix that spans the membrane.
- Multipass Transmembrane Proteins: Multiple α-helices traverse the lipid bilayer, crucial for channel or transporter functions.
Aquaporin Channel
- Functions as a water channel, formed by a tetramer of four monomers, each with six α-helices, with NPA motif for substrate specificity.
β Barrels in Proteins
- Multipass transmembrane proteins form β-barrels, commonly found in bacterial outer membranes, mitochondria, and chloroplasts.
- Channel functions facilitated by polar side chains lining the protein pores.
Peripheral Membrane Proteins
- Located outside the lipid bilayer, attached via amphipathic α-helices or covalent lipid modifications.
- Solubilized easily by salt solutions or extremes in pH.
Lipid Anchors and Protein Localization
- Lipid anchors (e.g., myristoylation) dictate membrane localization of signaling proteins.
- Src family tyrosine kinases and Ras family GTPases are examples of proteins linked to membranes via lipid modifications.
Sidedness of Membrane Proteins
- Membrane protein orientation assessed through techniques like electrophoresis, demonstrating distinct upper and lower domains.
Glycoproteins and Glycocalyx
- Glycoproteins feature oligosaccharides or polysaccharide chains, contributing to the glycocalyx that serves protective and adhesive functions; found on the extracellular surface.
Detergent Use in Membrane Protein Studies
- Detergents solubilize membrane proteins while maintaining functionality.
- Mild nonionic detergents can isolate proteins for functional studies, allowing reconstitution into nanodiscs.
Bacteriorhodopsin Functionality
- Acts as an H+ pump identified by electron crystallography, composed of seven α-helices and essential for ATP production.
Protein Domain Restrictions
- Protein movement is restricted to specific membrane domains; for instance, in epithelial cells, proteins are localized to apical or basal surfaces.
Mechanisms of Protein Diffusion Restriction
- Self-assembly into aggregates, tethered interactions with macromolecules, or interactions with neighboring cell proteins.
Cortical Cytoskeleton Structural Role
- Spectrin forms a membrane skeleton, maintaining erythrocyte shape and elasticity through interactions with band 3 and other cytoplasmic proteins.
Membrane-Bending Proteins
- Proteins can deform lipid bilayers through hydrophobic domain insertion, lipid anchor attachment, and clustering of membrane lipids.
Summary
- Membrane function primarily ascribed to diverse transmembrane proteins.
- Proteins exhibit complex arrangements and roles across the bilipid layers, contributing to cellular functions and signaling pathways.
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