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Questions and Answers
Which type of proteins can act as receptors, channels, and agents for electron transport?
Which type of proteins can act as receptors, channels, and agents for electron transport?
What type of detergents are required to isolate integral membrane proteins?
What type of detergents are required to isolate integral membrane proteins?
What can help identify transmembrane segments in integral proteins based on amino acid sequence?
What can help identify transmembrane segments in integral proteins based on amino acid sequence?
Which type of fatty acids can resemble a straight, flexible rod?
Which type of fatty acids can resemble a straight, flexible rod?
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What is crucial for the movement of molecules in the membrane?
What is crucial for the movement of molecules in the membrane?
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At higher temperatures, in what state do membrane lipids exist?
At higher temperatures, in what state do membrane lipids exist?
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What is the approximate thickness of the plasma membrane?
What is the approximate thickness of the plasma membrane?
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Which type of microscope is required to detect the plasma membrane?
Which type of microscope is required to detect the plasma membrane?
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What do the 2 dark-staining layers in the electron micrographs correspond to primarily?
What do the 2 dark-staining layers in the electron micrographs correspond to primarily?
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Which model describes the structure of the plasma membrane as a mosaic of components including phospholipids, cholesterol, and proteins?
Which model describes the structure of the plasma membrane as a mosaic of components including phospholipids, cholesterol, and proteins?
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Which component is NOT a part of the lipid composition of membranes?
Which component is NOT a part of the lipid composition of membranes?
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What is the outer boundary of the cell that separates it from the external environment?
What is the outer boundary of the cell that separates it from the external environment?
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Which type of lipids have longer, more saturated fatty acyl chains than phosphoglycerides?
Which type of lipids have longer, more saturated fatty acyl chains than phosphoglycerides?
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Which lipids are prominent in brain and nerve cells, with deficiency causing serious neurological disease?
Which lipids are prominent in brain and nerve cells, with deficiency causing serious neurological disease?
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What makes up to 50% of animal membrane lipids?
What makes up to 50% of animal membrane lipids?
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What are liposomes primarily used to treat?
What are liposomes primarily used to treat?
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What do stealth liposomes contain to protect against immune destruction?
What do stealth liposomes contain to protect against immune destruction?
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What provides evidence for the fluid mosaic model of the membrane?
What provides evidence for the fluid mosaic model of the membrane?
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What is the primary function of plasma membranes?
What is the primary function of plasma membranes?
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What is the lipid composition of membranes?
What is the lipid composition of membranes?
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What did early 19th-century studies by E. Gorter and F. Grendel propose about cell membranes?
What did early 19th-century studies by E. Gorter and F. Grendel propose about cell membranes?
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What do membrane proteins primarily determine?
What do membrane proteins primarily determine?
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What do gated channels in membranes control?
What do gated channels in membranes control?
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What do membrane receptors transduce signals from?
What do membrane receptors transduce signals from?
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What factors affect membrane fluidity?
What factors affect membrane fluidity?
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What is the role of cholesterol in membrane fluidity?
What is the role of cholesterol in membrane fluidity?
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What contributes to membrane remodeling?
What contributes to membrane remodeling?
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How do phospholipids move within the plasma membrane?
How do phospholipids move within the plasma membrane?
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What facilitates the movement of certain phospholipids between membrane leaflets?
What facilitates the movement of certain phospholipids between membrane leaflets?
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How is protein mobility in the membrane limited?
How is protein mobility in the membrane limited?
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What factors affect membrane fluidity?
What factors affect membrane fluidity?
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What is the role of cholesterol in membrane fluidity?
What is the role of cholesterol in membrane fluidity?
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What contributes to membrane remodeling?
What contributes to membrane remodeling?
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How do phospholipids move within the plasma membrane?
How do phospholipids move within the plasma membrane?
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What facilitates the movement of certain phospholipids between membrane leaflets?
What facilitates the movement of certain phospholipids between membrane leaflets?
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How is protein mobility in the membrane limited?
How is protein mobility in the membrane limited?
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What is the approximate thickness of the plasma membrane?
What is the approximate thickness of the plasma membrane?
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What is the primary function of plasma membranes?
What is the primary function of plasma membranes?
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What did early 19th-century studies by E. Gorter and F. Grendel propose about cell membranes?
What did early 19th-century studies by E. Gorter and F. Grendel propose about cell membranes?
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What is the role of cholesterol in membrane fluidity?
What is the role of cholesterol in membrane fluidity?
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What type of microscope is required to detect the plasma membrane?
What type of microscope is required to detect the plasma membrane?
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Which model describes the structure of the plasma membrane as a mosaic of components including phospholipids, cholesterol, and proteins?
Which model describes the structure of the plasma membrane as a mosaic of components including phospholipids, cholesterol, and proteins?
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Study Notes
Membrane Proteins and Lipids: Key Facts and Functions
- Membrane proteins can be integral, peripheral, or lipid-anchored, each with different interactions with the lipid bilayer
- Integral proteins, which make up 25-30% of all encoded proteins, act as receptors, channels, and agents for electron transport
- Isolating integral membrane proteins requires detergents like ionic SDS or nonionic Triton X-100
- Some challenges in studying integral proteins include low numbers per cell, instability in detergents, and glycosylation
- Transmembrane domains in integral proteins can be identified by a string of nonpolar amino acids spanning the lipid bilayer
- Hydropathy plots can help identify transmembrane segments based on amino acid sequence
- Peripheral proteins are easily solubilized and have a dynamic relationship with the membrane
- Lipid-anchored proteins are covalently linked to lipid molecules and can act as adhesion molecules or enzymes
- Membrane fluidity is crucial for the movement of molecules and is affected by the physical state of membrane lipids
- At higher temperatures, membrane lipids exist in a relatively fluid state, while at lower temperatures, they form a frozen crystalline gel
- Saturated fatty acids resemble a straight, flexible rod, while unsaturated fats can be cis or trans, with crooks in the chain at the sites of a double bond
- The structure of the lipid bilayer depends on temperature, with individual lipids able to rotate around their axis or move laterally within the plane
Overview of Plasma Membrane Functions and Composition
- Plasma membrane functions include compartmentalization, scaffold for biochemical activities, selective permeability barrier, solute transportation, response to external signals, intercellular interaction, and energy transduction
- Membranes enclose cells and intracellular compartments, sequestering hydrolytic enzymes and acid hydrolases in membrane-bound vacuoles
- Membranes act as scaffolds and sites for enzyme localization, such as CO2 fixation in the outer surface of chloroplasts
- Gated channels in membranes control the movement of selected molecules, allowing rapid penetration of water molecules through the plasma membrane
- Membrane proteins facilitate the movement of substances against concentration gradients, such as H+ ions
- Membrane receptors transduce signals from outside the cell in response to specific ligands, like the plant hormone Abscisic acid controlling Calcium efflux and stomatal closure
- Membranes mediate recognition and interaction between adjacent cells, allowing the flow of material through plasmodesmata
- Membranes are involved in processes converting one type of energy into another, such as the conversion of ADP to ATP in the inner mitochondrial membrane
- Studies on plasma membrane structure led to the discovery that the outer layer of cells is composed of lipids, based on the principle "like dissolves in like"
- Early 19th-century studies by E. Gorter and F. Grendel proposed that cell membranes might contain a lipid bilayer, supported by RBC experiments
- Cell physiologists determined that membranes contain proteins, which are single proteins or part of complexes, explaining the permeability and surface tensions of membranes
- Membranes are lipid-protein assemblies held together by noncovalent bonds, with the lipid bilayer as a structural backbone and barrier, and proteins determining specialized activities. Lipid composition includes phosphoglycerides, sphingolipids, and cholesterol, with phosphoglycerides having hydrophilic head groups and hydrophobic fatty acyl chains.
Membrane Lipids and Fluidity
- Cis fats are beneficial, promoting good cholesterol, while trans fats are harmful to cardiovascular health
- Factors affecting membrane fluidity include the degree of saturation of fatty acids, the length of fatty acyl chains, and the presence of cholesterol
- Cholesterol abolishes sharp transition temperatures and creates a condition of intermediate fluidity in membranes
- Membrane lipid composition changes in response to temperature fluctuations, with cells remodeling phospholipids for cold resistance
- Desaturation of single bonds in fatty acyl chains and reshuffling of chains between phospholipid molecules contribute to membrane remodeling
- Phospholipids can move laterally within the same leaflet of the plasma membrane with ease, while flipping between leaflets is less favorable
- Enzymes called flippases facilitate the movement of certain phospholipids between membrane leaflets
- Membrane proteins are not stagnant and can move within the plasma membrane
- Cell fusion techniques have revealed that membrane proteins can move between fused cells
- Fluorescence recovery after photobleaching (FRAP) and single particle tracking (SPT) are used to measure the diffusion rates of membrane proteins
- The extent of fluorescence recovery in FRAP provides a measure of the percentage of mobile molecules
- Protein mobility in the membrane can be limited by interactions with other integral proteins, the cytoskeleton, and directed interactions with other proteins
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Description
Explore the key facts and functions of membrane proteins, lipids, and fluidity, including integral, peripheral, and lipid-anchored proteins, and the influence of factors like temperature and fatty acid composition on membrane fluidity. Learn about the essential roles of plasma membranes in compartmentalization, selective permeability, signal transduction, and energy transduction.
