Questions and Answers
What are the main characteristics of integral membrane proteins?
Which factor is associated with peripheral proteins?
Which type of integral membrane protein has a single transmembrane helix with the amino-terminal domain outside of the cell?
What is NOT a feature of amphitropic proteins?
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How do integral membrane proteins exhibit lateral movement?
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How are transmembrane domains formed in Type V integral proteins?
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What does the amphipathic nature of membrane lipids contribute to?
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Which statement accurately reflects the function of recognition factors in membranes?
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What is a characteristic of membrane dynamics?
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Which of the following statements about membrane permeability is correct?
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Which enzyme is NOT involved in the catalysis of transverse diffusion in membranes?
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What is required for spontaneous flipping of lipids from one leaflet to another?
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How do flippases typically operate during lipid movement?
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Which property is NOT a physical characteristic of membranes?
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What primarily holds type IV proteins to the lipid bilayer?
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Which type of protein features both transmembrane helices and lipid anchors?
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Which of the following is NOT a function of membrane proteins?
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What is the transition temperature (Tm) related to in membrane fluidity?
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How does the presence of cholesterol affect membrane fluidity when the membrane is already rigid?
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Which of the following statements about fatty acid composition is true?
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Which of the following molecules serves as a lipid anchor for some membrane proteins?
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What effect do unsaturated lipids have on membrane fluidity?
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What role do external proteins play in cellular membranes?
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What occurs when the temperature exceeds Tm in terms of membrane fluidity?
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Study Notes
Membrane Components
- Phosphatidylethanolamine (PE) and phosphatidylserine (PS) are key components of cell membranes.
- Membranes interact with extracellular (ECF) and intracellular (ICF) fluids, regulating the movement of polar molecules.
Types of Membrane Proteins
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Integral Proteins:
- Span the entire membrane and exhibit asymmetry.
- Tightly associated with the membrane; can only be removed by detergents.
- Capable of lateral movement within the membrane.
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Peripheral Proteins:
- Loosely attached to membrane via interactions with polar head groups.
- Removed by disrupting ionic interactions (e.g., high salt or pH changes).
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Amphitropic Proteins:
- Sometimes associated with membranes, bound loosely.
Types of Integral Membrane Proteins
- Type I & II: Each has a single transmembrane helix; amino-terminal domain orientation differs between types.
- Type III: Contains multiple transmembrane helices within a single polypeptide.
- Type V: Transmembrane domains from different polypeptides combine to form channels.
Physical Properties of Membranes
- Membranes are dynamic and flexible, capable of existing in various phases.
- Not permeable to large polar solutes and ions, while small polar solutes and nonpolar compounds can pass through.
Membrane Dynamics
- Transverse Diffusion: Rare spontaneous flips from one leaflet of the membrane to another; lateral diffusion of lipids is fast and requires no catalysis.
Enzyme-Catalyzed Transverse Diffusion
- Specialized enzymes (flippases, floppases, scramblases) facilitate lipid movement across the membrane.
- Some flippases utilize ATP to transport lipids against the concentration gradient.
Lipid Anchors
- Some proteins in membranes are considered lipoproteins, containing covalently linked lipid molecules like long-chain fatty acids and isoprenoids.
- These lipid anchors enable proteins to be reversibly secured to the membrane, allowing for targeted positioning.
Functions of Membrane Proteins
- Receptors detect external signals (light, hormones, neurotransmitters).
- Serve as channels, gates, pumps, and pores facilitating nutrient and ion transport.
Membrane Attachment to Cytoskeleton
- Cell membranes anchor to the cytoskeleton, with proteins extending into interstitial spaces to perform functions like self-identification and receptor activities.
Membrane Fluidity
- Transition temperature (Tm) determines fluidity:
- Above Tm, membranes are too fluid; below Tm, they become rigid.
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Lipid Composition:
- Long-chain fatty acids decrease fluidity; short-chain fatty acids increase it.
- Saturated lipids reduce fluidity; unsaturated lipids increase it.
-
Cholesterol:
- Cholesterol's presence can decrease fluidity in fluid membranes and increase it in rigid membranes.
Membrane Composition Adaptation
- Organisms can modify membrane composition primarily through fatty acid adjustments to maintain appropriate fluidity.
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Description
Explore the crucial components of cell membranes, including phosphatidylethanolamine and phosphatidylserine. This quiz will help you understand how these components interact with extracellular fluid and their roles in membrane properties.
