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Questions and Answers
Biological membranes are mainly composed of a lipid bilayer.
Biological membranes are mainly composed of a lipid bilayer.
True
The fluid mosaic model is the current model of the cell membrane.
The fluid mosaic model is the current model of the cell membrane.
True
Glycosphingolipids are built on a backbone of ceramide.
Glycosphingolipids are built on a backbone of ceramide.
True
Cholesterol resides within plasma membranes, but not within mitochondrial, Golgi complex, and nuclear membranes.
Cholesterol resides within plasma membranes, but not within mitochondrial, Golgi complex, and nuclear membranes.
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Membrane fluidity decreases as membrane fluidity increases.
Membrane fluidity decreases as membrane fluidity increases.
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Transporters, ion channels, and gap junctions are not important participants in membrane function.
Transporters, ion channels, and gap junctions are not important participants in membrane function.
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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Which of these statements is false about membrane lipids?
Which of these statements is false about membrane lipids?
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Which of these statements is true about integral proteins?
Which of these statements is true about integral proteins?
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What is the main difference between simple diffusion and facilitated diffusion?
What is the main difference between simple diffusion and facilitated diffusion?
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What are the three factors that limit simple diffusion?
What are the three factors that limit simple diffusion?
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Which of the following is NOT a type of active transport?
Which of the following is NOT a type of active transport?
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What is the main difference between passive transport and active transport?
What is the main difference between passive transport and active transport?
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Which of the following is an example of receptor-mediated endocytosis?
Which of the following is an example of receptor-mediated endocytosis?
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What is the main function of gap junctions?
What is the main function of gap junctions?
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Which of the following is NOT a characteristic of cystic fibrosis?
Which of the following is NOT a characteristic of cystic fibrosis?
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What is the main cause of Wilson disease?
What is the main cause of Wilson disease?
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Gap junctions are important for cell-cell communication.
Gap junctions are important for cell-cell communication.
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Mutations in the ATP7B gene can lead to Wilson disease.
Mutations in the ATP7B gene can lead to Wilson disease.
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The FGFR3 gene is involved in the conversion of cartilage to bone.
The FGFR3 gene is involved in the conversion of cartilage to bone.
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Exosomes are generated by budding from the plasma membrane of a source cell.
Exosomes are generated by budding from the plasma membrane of a source cell.
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Mutations in genes encoding ion channels can cause specific diseases.
Mutations in genes encoding ion channels can cause specific diseases.
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What is the main difference between exocytosis and endocytosis?
What is the main difference between exocytosis and endocytosis?
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The fluid mosaic model suggests that membrane proteins are immobile.
The fluid mosaic model suggests that membrane proteins are immobile.
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The fluid mosaic model was proposed by Singer and Nicolson in 1972.
The fluid mosaic model was proposed by Singer and Nicolson in 1972.
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Study Notes
Cell Membrane Structure and Function
- The cell membrane, also known as the plasma membrane, defines cell boundaries in eukaryotes.
- It separates intracellular and extracellular environments, maintaining different compositions.
- Membranes are primarily formed by a lipid bilayer with integral and peripheral proteins.
- The fluid mosaic model describes the membrane as a mosaic of proteins embedded in a fluid lipid bilayer (Singer and Nicolson, 1972).
- Major lipids include phospholipids, cholesterol, and glycosphingolipids.
Major Lipids in Mammalian Membranes
- Phospholipids: Consist of alcohol, a phosphodiester bridge, and diacylglycerol or sphingosine.
- Glycosphingolipids: Contain sugars attached to a ceramide backbone. Located in plasma membranes, displaying sugar components externally.
- Sterols (e.g., cholesterol): Modifies membrane fluidity, impacting permeability to small hydrophilic molecules.
Membrane Proteins
- Integral proteins: Firmly embedded within the lipid bilayer, often requiring detergents for removal.
- Peripheral proteins: Associated with the membrane via electrostatic interactions and hydrogen bonds, located on either the inner or outer surface.
Membrane Transport
- Passive transport: Movement of molecules down a concentration gradient, not requiring energy (e.g., simple diffusion, facilitated diffusion).
- Active transport: Movement of molecules against a concentration gradient, requiring energy (e.g., ATP-driven pumps, cotransport).
- Endocytosis: Cells take up large molecules by engulfing them into vesicles, including phagocytosis (ingestion of large particles) and pinocytosis (ingestion of fluid). Receptor-mediated endocytosis is highly specific.
- Exocytosis: Cells release molecules by fusing vesicles with the plasma membrane.
Specialized Membrane Structures
- Lipid rafts: Cholesterol- and sphingolipid-enriched microdomains in the membrane, possibly involved in signaling.
- Caveolae: Flask-shaped indentations of the membrane, sometimes containing caveolin-1.
- Tight junctions: Intercellular adhesion complexes in epithelia and endothelia, controlling paracellular permeability.
Membrane Transport Mechanisms
- Simple Diffusion: Passive movement of substances across the membrane directly through the lipid bilayer.
- Facilitated Diffusion: Passive movement of substances across the membrane via protein channels or carriers.
- Active Transport: Requires energy to move substances against their concentration gradient using specific protein pumps.
Cell Signaling and Membrane Proteins
- Membrane proteins act as receptors for signal transduction.
- Gap junctions facilitate direct cell-to-cell communication.
- Examples of Membrane Diseases cystic fibrosis and long QT syndrome arising from mutations in specific membrane proteins (CFTR and ion channels, respectively).
Other related concepts
- Osmosis: The net movement of water across a semipermeable membrane down its concentration gradient.
- Ion Channels: Proteins forming pores in the membrane selectively allowing specific ions to pass through.
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Description
Explore the critical components of cell membranes, including their structure, lipids, and proteins. Understand the fluid mosaic model and how major lipids like phospholipids and cholesterol impact membrane fluidity and functionality. This quiz is perfect for students studying cell biology and related topics.
