p.9
Transmission of Nerve Impulses and Ion Channels
What happens when large areas of the neuronal membrane are depolarized?
An electrochemical disturbance propagates in a wave-like form, generating a nerve impulse.
p.5
Artificial Membranes Model
What are the advantages of using artificial membrane systems?
They allow for variation in lipid content, incorporation of purified membrane proteins, controlled environments, and entrapment of compounds like drugs and genes.
p.9
Transmission of Nerve Impulses and Ion Channels
How do neuronal cells maintain electrical potential?
By maintaining an asymmetry of inside-outside voltage and using voltage-gated channels.
p.4
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What structure do amphipathic phospholipids form in water?
Micelles, where hydrophobic regions are shielded from water and hydrophilic polar groups are immersed in the aqueous environment.
p.9
Membrane Selectivity and Transport Mechanisms
How does glucose enter adipocytes and skeletal muscle?
Through the GLUT4 transporter, which is enhanced by insulin.
p.2
Fluid Mosaic Model of Membrane Structure
What is the structure of the lipid bilayer in membranes?
Asymmetric with distinct inner and outer surfaces or leaflets.
p.4
Fluid Mosaic Model of Membrane Structure
What is lateral diffusion in the context of membrane proteins?
The movement of proteins within the membrane; many nonmobile proteins do not exhibit this due to being anchored to the cytoskeleton.
p.7
Membrane Selectivity and Transport Mechanisms
What are transporters in the context of membrane transport?
Specific proteins involved in facilitated diffusion and active transport.
p.10
Cell Communication via Gap Junctions and Extracellular Vesicles
What is transmembrane signaling?
The process involved in generating second messenger signaling molecules like cyclic nucleotides and calcium.
p.10
Diseases Associated with Membrane Protein Mutations
How can mutations in membrane proteins affect health?
They can lead to diseases by altering the function of receptors, transporters, ion channels, and enzymes.
p.1
Cell Communication via Gap Junctions and Extracellular Vesicles
How do membranes contribute to cell communication?
They contain gap junctions that allow adjacent cells to communicate by exchanging materials.
p.6
Membrane Selectivity and Transport Mechanisms
What is facilitated diffusion?
The passive transport of a solute from a higher to a lower concentration mediated by a specific protein transporter.
p.5
Fluid Mosaic Model of Membrane Structure
What is the fluid mosaic model of membrane structure?
A model proposed by Singer and Nicolson in 1972, describing membranes as having phospholipids that undergo rapid lateral diffusion and are influenced by lipid composition.
p.9
Endocytosis and Exocytosis Mechanisms
What is endocytosis?
The process by which cells take up large molecules.
p.2
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What is sphingomyelin and how is it formed?
A phospholipid formed from sphingosine and a fatty acid, esterified to phosphorylcholine.
p.10
Endocytosis and Exocytosis Mechanisms
What is exocytosis?
The process of releasing macromolecules to the exterior of the cell.
p.8
Membrane Selectivity and Transport Mechanisms
What are ionophores?
Molecules that act as membrane shuttles for various ions, such as valinomycin for K+.
p.2
Maintenance of Intracellular and Extracellular Environments
What is the fraction of total body water represented by extracellular fluid (ECF)?
1/3, distributed between plasma and interstitial compartment.
p.1
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What are the major lipids found in mammalian membranes?
Phospholipids, glycosphingolipids, and cholesterol.
p.4
Membrane Selectivity and Transport Mechanisms
How do small gas molecules like oxygen and carbon dioxide interact with the lipid bilayer?
They readily diffuse through the hydrophobic regions of the membrane due to their small size and low interaction with solvents.
p.10
Endocytosis and Exocytosis Mechanisms
What is phagocytosis?
Ingestion of large particles such as viruses, bacteria, or cellular debris, occurring in specialized cells like macrophages.
p.1
Membrane Selectivity and Transport Mechanisms
What are aquaporins?
Proteins that form water channels in certain membranes.
p.10
Cell Communication via Gap Junctions and Extracellular Vesicles
What are gap junctions?
Structures that allow direct transfer of small molecules between neighboring cells, composed of connexins.
p.8
Active Transport Systems and Energy Requirements
What is the function of the Na+ - K+ - ATPase?
It regulates intracellular concentrations of Na+ and K+, maintaining low Na+ and high K+ concentrations.
p.2
Maintenance of Intracellular and Extracellular Environments
What are the major ions stored in intracellular and extracellular fluids?
Na+, Ca2+, Cl−, K+, Mg2+, and phosphate.
p.1
Active Transport Systems and Energy Requirements
What is the significance of the Na+-K+-ATPase enzyme?
It regulates intracellular concentrations of sodium and potassium, requiring energy for active transport.
p.3
Composition of Membranes: Lipids, Proteins, and Carbohydrates
Is cholesterol present in plant cells?
No, it is absent in plant cells.
p.7
Membrane Selectivity and Transport Mechanisms
What is the difference between symport and antiport systems?
Symport moves two solutes in the same direction, while antiport moves two molecules in opposite directions.
p.7
Membrane Selectivity and Transport Mechanisms
What is the role of cotransporters?
They use the gradient of one substrate created by active transport to drive the movement of another substrate.
p.9
Active Transport Systems and Energy Requirements
What is the function of Na+ - K+ - ATPase?
It pumps three Na+ out and two K+ into cells.
p.11
Diseases Associated with Membrane Protein Mutations
What chloride level in sweat indicates a potential issue related to pancreatic function?
Elevated levels of chloride in sweat (>60 mmol/L).
p.2
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What are the main components of membranes?
Lipids, proteins, and carbohydrate-containing molecules.
p.4
Fluid Mosaic Model of Membrane Structure
What is the significance of the α-helical structure in membrane proteins?
It minimizes the hydrophilic character of peptide bonds, allowing them to be amphipathic and form integral parts of the membrane.
p.5
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What are caveolae and their relation to lipid rafts?
Caveolae derive from lipid rafts and contain the protein caveolin-1, which may be involved in their formation.
p.7
Membrane Selectivity and Transport Mechanisms
What is a uniport system?
A transport system that moves one type of molecule bidirectionally.
p.3
Fluid Mosaic Model of Membrane Structure
What effect do double bonds in lipid side chains have on membrane fluidity?
They increase the number of kinks, making the membrane more fluid.
p.7
Membrane Selectivity and Transport Mechanisms
What are ligand-gated channels?
Channels that open in response to a specific molecule binding to a receptor.
p.8
Transmission of Nerve Impulses and Ion Channels
What are the four key features of ion channels?
1. Overall structures, 2. Rapid ion conduction, 3. Selectivity, 4. Gating properties.
p.5
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What are the main structural components of membranes?
They span as a bundle of α-helical transmembrane segments, are amphipathic and globular, and are asymmetrically distributed in the membrane bilayer.
p.6
Active Transport Systems and Energy Requirements
What is active transport?
Vectorial movement of a solute across a membrane against a concentration gradient, requiring energy.
p.4
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What role do membrane proteins play?
They function as enzymes, pumps, transporters, channels, structural components, antigens, and receptors.
p.10
Endocytosis and Exocytosis Mechanisms
What is pinocytosis?
A process of cellular uptake of fluid and its contents, also known as 'cell drinking'.
p.10
Diseases Associated with Membrane Protein Mutations
What is a problematic aspect of receptor-mediated endocytosis?
Viruses like hepatitis, poliomyelitis, AIDS, and COVID-19 can enter cells via this mechanism.
p.3
Membrane Selectivity and Transport Mechanisms
How do detergents interact with membrane proteins?
The hydrophobic end binds to hydrophobic regions, displacing bound lipids.
p.6
Endocytosis and Exocytosis Mechanisms
What role do flask or tube-shaped indentations of the cell membrane play?
They likely play a role in endocytosis (cellular uptake of various components).
p.6
Membrane Selectivity and Transport Mechanisms
What are the two types of passive diffusion mentioned?
Simple diffusion and facilitated diffusion.
p.5
Artificial Membranes Model
What are liposomes?
Vesicles surrounded by a lipid bilayer with an aqueous interior, formed through mild sonication.
p.1
Fluid Mosaic Model of Membrane Structure
What is the fluid mosaic model of membrane structure?
It describes membranes as dynamic structures with lipid rafts, caveolae, and tight junctions.
p.6
Membrane Selectivity and Transport Mechanisms
What factors affect net diffusion of a substance?
Concentration gradient, electrical potential, permeability coefficient, hydrostatic pressure gradient, and temperature.
p.5
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What are lipid rafts?
Specialized areas of the exoplasmic leaflet of the lipid bilayer enriched in cholesterol, sphingolipids, and certain proteins.
p.4
Maintenance of Intracellular and Extracellular Environments
How can lipids enter membranes?
Through transport from the ER in vesicles, direct contact between membranes, or via phospholipid exchange proteins.
p.7
Active Transport Systems and Energy Requirements
What is required for active transport?
Energy, usually in the form of ATP, as it occurs against an electrical or chemical gradient.
p.1
Biochemical Importance of Membranes
What is the biochemical importance of plasma membranes?
They have selective permeabilities, act as barriers, and facilitate exchanges with the extracellular environment through exocytosis and endocytosis.
p.1
Maintenance of Intracellular and Extracellular Environments
What is the role of membranes in maintaining intracellular and extracellular environments?
They compartmentalize the body's internal water and regulate ionic compositions of fluids.
p.4
Fluid Mosaic Model of Membrane Structure
What is the primary driving force for the self-assembly of lipid bilayers?
The hydrophobic effect, which describes the tendency of nonpolar molecules to self-associate in an aqueous environment.
p.10
Endocytosis and Exocytosis Mechanisms
What is required for endocytosis?
Energy (usually from ATP hydrolysis), Ca2+, and cytoskeletal elements.
p.1
Endocytosis and Exocytosis Mechanisms
How do cells transport macromolecules across the plasma membrane?
Through endocytosis and exocytosis mechanisms.
p.2
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What are glycosphingolipids (GSLs)?
Sugar-containing lipids built on a ceramide backbone.
p.7
Membrane Selectivity and Transport Mechanisms
What is the function of cotransport systems?
The transfer of one solute depends on the simultaneous or sequential transfer of another solute.
p.3
Membrane Selectivity and Transport Mechanisms
What role do detergents play in relation to membrane proteins?
They solubilize and purify membrane proteins.
p.7
Membrane Selectivity and Transport Mechanisms
What do mechanically gated channels respond to?
Mechanical stimuli such as pressure and touch.
p.11
Diseases Associated with Membrane Protein Mutations
What are some conditions associated with pancreatic exocrine insufficiency?
Fat maldigestion, infertility in males due to abnormal development of the vas deferens, and elevated levels of chloride in sweat (>60 mmol/L).
p.6
Membrane Selectivity and Transport Mechanisms
What is simple diffusion?
The passive flow of a solute from a higher to a lower concentration due to random thermal movement.
p.2
Maintenance of Intracellular and Extracellular Environments
What are the major functions of extracellular fluid?
Bidirectional delivery system, brings nutrients, O2, ions, hormones, and removes waste products.
p.1
Membrane Selectivity and Transport Mechanisms
What is the function of ion channels in membranes?
They allow the selective entry of various ions across the membrane.
p.4
Membrane Selectivity and Transport Mechanisms
What is the role of translocases (flippases) in membranes?
They transfer certain phospholipids from the inner to the outer leaflet of the membrane.
p.3
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What does it mean for membrane lipids to be amphipathic?
They contain both hydrophobic and hydrophilic regions.
p.10
Cell Communication via Gap Junctions and Extracellular Vesicles
What are extracellular vesicles?
Lipid bilayer-enclosed structures that can include exosomes and microvesicles, delivering distinct 'payloads' to target cells.
p.6
Membrane Selectivity and Transport Mechanisms
What do tight junctions prevent?
They prevent the diffusion of macromolecules between cells.
p.5
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What are peripheral proteins and how do they interact with membranes?
Peripheral proteins do not interact directly with the hydrophobic cores of phospholipids and are bound to the hydrophilic regions of integral proteins and phospholipid head groups.
p.9
Transmission of Nerve Impulses and Ion Channels
What role do myelin sheaths play in nerve signal propagation?
They provide electrical insulation and speed up the propagation of the nerve impulse.
p.6
Membrane Selectivity and Transport Mechanisms
What factors limit simple diffusion across the membrane?
Thermal agitation of the molecule, concentration gradient, and solubility of the solute.
p.5
Fluid Mosaic Model of Membrane Structure
How does cholesterol affect membrane fluidity?
Cholesterol buffers membrane fluidity by increasing fluidity below Tm and limiting disorder above Tm.
p.10
Endocytosis and Exocytosis Mechanisms
What are the two types of pinocytosis?
Fluid-phase pinocytosis (nonselective) and absorptive pinocytosis (receptor-mediated).
p.4
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What distinguishes integral proteins from peripheral proteins?
Integral proteins interact extensively with phospholipids and require detergents for solubilization, while peripheral proteins do not.
p.7
Membrane Selectivity and Transport Mechanisms
How do hydrophilic molecules pass through the lipid bilayer?
By facilitated diffusion or active transport.
p.7
Membrane Selectivity and Transport Mechanisms
What distinguishes facilitated diffusion from simple diffusion?
Facilitated diffusion can be saturated and involves specific transporters.
p.7
Membrane Selectivity and Transport Mechanisms
What factors affect the permeability of ion channels?
Size, extent of hydration, and charge density of the ion.
p.8
Fluid Mosaic Model of Membrane Structure
What is the structure of the K+ channel (KvAP)?
An integral membrane protein composed of four identical subunits with two trans-membrane segments, creating an inverted 'V' structure.
p.8
Membrane Selectivity and Transport Mechanisms
What role do aquaporins play in cells?
They form water channels that facilitate the movement of water across certain membranes.
p.11
Diseases Associated with Membrane Protein Mutations
What abnormality in males can result from pancreatic exocrine insufficiency?
Infertility due to abnormal development of the vas deferens.
p.8
Maintenance of Intracellular and Extracellular Environments
Why is maintaining ionic gradients important for cells?
It is crucial for maintaining a net negative electrical potential inside the cell.
p.5
Fluid Mosaic Model of Membrane Structure
What is the transition temperature (Tm) in membrane structure?
The temperature at which membrane structure transitions from an ordered to a disordered state.
p.9
Endocytosis and Exocytosis Mechanisms
What happens to most endocytotic vesicles?
They fuse with primary lysosomes to form secondary lysosomes for intracellular disposal.
p.3
Composition of Membranes: Lipids, Proteins, and Carbohydrates
What orientation do the polar head groups of phospholipids face?
They face the aqueous environment.
p.10
Diseases Associated with Membrane Protein Mutations
What is cystic fibrosis?
A recessive genetic disorder caused by mutations in the CFTR gene, leading to chronic bacterial infections.
p.7
Membrane Selectivity and Transport Mechanisms
What are ion channels?
Transmembrane proteins that allow the selective entry of various ions.
p.9
Membrane Selectivity and Transport Mechanisms
What is the role of the Na+ - glucose symporter in glucose transport?
It allows glucose to enter cells by binding with Na+, which moves down its electrochemical gradient.
p.10
Endocytosis and Exocytosis Mechanisms
What are the three fates of molecules released by exocytosis?
They can remain as membrane proteins, become part of the extracellular matrix, or enter extracellular fluid to signal other cells.
p.7
Membrane Selectivity and Transport Mechanisms
What drives passive transport?
The transmembrane gradient of the substrate.
p.7
Membrane Selectivity and Transport Mechanisms
What triggers voltage-gated channels to open or close?
Changes in membrane potential.
p.3
Fluid Mosaic Model of Membrane Structure
How do saturated and unsaturated fatty acids differ in membrane structure?
Saturated fatty acids form straight tails, while unsaturated fatty acids form kinked tails.
