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Questions and Answers
What defines the fluid nature of the cell membrane?
What defines the fluid nature of the cell membrane?
Which function is NOT typically associated with biological membranes?
Which function is NOT typically associated with biological membranes?
What role do membrane proteins play in cellular processes?
What role do membrane proteins play in cellular processes?
How does the saturation level of fatty acids in phospholipids influence membrane fluidity?
How does the saturation level of fatty acids in phospholipids influence membrane fluidity?
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What is the primary lipid found in biological membranes?
What is the primary lipid found in biological membranes?
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Which of the following is NOT a function of membranes?
Which of the following is NOT a function of membranes?
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What best describes the shape of lipids in membrane structure?
What best describes the shape of lipids in membrane structure?
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What allows for the formation of transmembrane domains in membrane proteins?
What allows for the formation of transmembrane domains in membrane proteins?
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What is the main function of ATP synthase in mitochondria?
What is the main function of ATP synthase in mitochondria?
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What distinguishes a uniporter from other transport proteins?
What distinguishes a uniporter from other transport proteins?
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What is the result of the Na+/K+ ATPase activity?
What is the result of the Na+/K+ ATPase activity?
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Which statement about glucose uptake is true?
Which statement about glucose uptake is true?
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What does the term 'electrogenic' refer to in the context of the Na+/K+ ATPase?
What does the term 'electrogenic' refer to in the context of the Na+/K+ ATPase?
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How many ATP molecules does ATP synthase generate for every three protons that pass through?
How many ATP molecules does ATP synthase generate for every three protons that pass through?
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What is the role of the F1 unit in ATP synthase?
What is the role of the F1 unit in ATP synthase?
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What is observed in equilibrium without an electrostatic potential across the membrane?
What is observed in equilibrium without an electrostatic potential across the membrane?
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What role do membrane proteins such as alpha-helices and beta-barrels play in cellular function?
What role do membrane proteins such as alpha-helices and beta-barrels play in cellular function?
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Which factors affect the rate of simple diffusion across membranes?
Which factors affect the rate of simple diffusion across membranes?
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How do transporter proteins facilitate the movement of solutes across the membrane?
How do transporter proteins facilitate the movement of solutes across the membrane?
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What characterizes active transport mechanisms in cells?
What characterizes active transport mechanisms in cells?
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Which transporter is involved in primary active transport through phosphorylation?
Which transporter is involved in primary active transport through phosphorylation?
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What is the main purpose of lipid rafts in the plasma membrane?
What is the main purpose of lipid rafts in the plasma membrane?
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What happens when electrically neutral solutes move across a membrane?
What happens when electrically neutral solutes move across a membrane?
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What defines the function of a uniporter in membrane transport?
What defines the function of a uniporter in membrane transport?
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Which of the following statements about simple diffusion is accurate?
Which of the following statements about simple diffusion is accurate?
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What is the primary role of the Na+/K+ ATPase pump?
What is the primary role of the Na+/K+ ATPase pump?
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Study Notes
Membrane Structure
- Biological membranes primarily form bilayers, studded with membrane-bound and transmembrane proteins.
- Cell membranes exhibit fluidity, enabling lateral movement of lipids and proteins. This is described by the Fluid Mosaic Model.
- Lipid bilayer thickness is approximately 5 nm.
- Transverse diffusion ("flip-flop") is very slow (t½ in days), while flippase-catalyzed transverse diffusion is fast (t½ in seconds). Lateral diffusion is very fast (1 μm/s).
Overview of Membrane Functions
- Compartmentalization: Membranes create enclosed intracellular compartments.
- Scaffold for biochemical activities: Membranes organize enzymes for efficient interaction.
- Selectively permeable barrier: Membranes regulate substance exchange between compartments.
Membrane & Storage Lipids
- Storage lipids: primarily energy storage (e.g., triglycerides)
- Membrane lipids: are polar.
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Phospholipids are the major lipids found in biological membranes.
- Glycerophospholipids: have a glycerol backbone, two fatty acid chains, and a phosphate head group. The head group is substituted with other molecules like choline, serine, or inositol.
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Glycolipids: have a carbohydrate head group attached
- Sphingolipids: are similar to glycerophospholipids but have a sphingosine backbone instead of glycerol.
- Archaebacterial ether lipids: have different backbone structures.
Phospholipid Structure
- Glycerophospholipids (general structure):
- Glycerol backbone
- Two fatty acid chains (saturated or unsaturated)
- Phosphate head group with a polar substituent (e.g., choline, serine)
Fatty Acids
- Saturated fatty acids: have no double bonds between carbon atoms; example: palmitic acid.
- Unsaturated fatty acids: have one or more double bonds between carbon atoms; example: oleic acid.
- Saturation affects membrane fluidity; unsaturated fatty acids increase fluidity.
Lipid Ordered and Disordered States
- Lipid-ordered state (gel): lipids are tightly packed.
- Lipid-disordered state (fluid): lipids are more fluid and less ordered.
- Temperature influences the transition between these states.
Membrane Asymmetry
- Phospholipid composition differs between the inner and outer leaflets of membranes.
- Different phospholipids are preferentially located in either the inner or outer layer.
Membrane Proteins
- Membrane proteins are categorized as integral or peripheral.
- Integral proteins are embedded within the lipid bilayer.
- Peripheral proteins are associated with the membrane surface.
- Transmembrane domains: Integral proteins have transmembrane domains which can be composed of α helices or β barrels.
Glycophorin
- Glycophorin is an integral membrane protein.
- Its structure is shown with an amino terminus on the outside and a carboxyl terminus on the inside.
Types of Transporter Proteins
- Uniporter: Transports one solute across a membrane.
- Symporter: Transports two or more solutes in the same direction across a membrane.
- Antiport: Transports two or more solutes in opposite directions across a membrane.
Glucose Transporters
- GLUT1 - ubiquitous, basal glucose uptake
- GLUT2 - liver, pancreas; glucose uptake; insulin regulation
- GLUT3 - basal glucose uptake
- GLUT4 - muscle and fat; insulin induced glucose uptake
- Other transporters (GLUTs 5-12) exist with specialized roles and distributions
Microdomains (Lipid Rafts) in Plasma Membrane
- Lipid rafts are specialized regions in the plasma membrane that are enriched in sphingolipids and cholesterol.
- They play a role in localized signal transduction modules.
Active and Passive Transport
- Passive transport: Movement of molecules across a membrane without energy input.
- Active transport: Movement of molecules across a membrane with energy input.
Membrane Potentials
- Membrane potential is the electrical potential difference across a membrane.
- Electrochemical gradient determines movement of charged particles
- Ion concentration gradients are maintained by active transport
ATP Synthase
- ATP Synthase is a multisubunit protein involved in the synthesis and use of ATP
- ATP synthase uses energy from a proton gradient to catalyze ATP synthesis
- 3 protons for 1 ATP
- It's located in mitochondria or chloroplasts.
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Description
Explore the fundamental aspects of biological membranes, including their structure, fluidity, and key functions. This quiz covers the Fluid Mosaic Model, lipid bilayers, and the roles of membranes in cellular compartmentalization and selectively permeable barriers.
