Understanding Membranes: Key Concepts in Membrane Transport
School
University of Melbourne**We aren't endorsed by this school
Course
BIOCH 10001
Subject
Biology
Date
Dec 12, 2024
Pages
4
Uploaded by JusticeOryx2934
B2.1 Membranes and Membrane TransportGuiding Questions Sub-Topic ClarificationQuestionsB2.1.1—Lipid bilayers as the basis of cell membranesPhospholipids and other amphipathic lipids naturally form continuous sheet-like bilayers in water.1.Define the term plasma membrane. 2.Explain the concept of amphipathic molecules in the context of lipid bilayers.3.Draw a diagram of a single phospholipid molecule. Label the hydrophobic and hydrophilic sections.4.Explain how hydrophobic and hydrophilic properties of the phospholipid bilayer allow a membrane to maintain its structure.B2.1.2—Lipid bilayers as barriersStudents should understand that the hydrophobic hydrocarbon chains that form the core of a membranehave low permeability to large molecules and hydrophilic particles, including ions and polar molecules, so membranes function as effective barriers between aqueous solutions.5.Define selectively permeable in the context of the plasma membrane.6.Explain why the phospholipids must form a bilayer when introduced into an aqueous environment.7.Why are lipid bilayers considered effective barriers in biological systems?B2.1.3—Simple diffusion across membranesUse movement of oxygen and carbon dioxide molecules between phospholipids as an example of simple diffusion across membranes.8.What is simple diffusion, and how does it differ from other forms of passive transport across membranes?9.What types of molecules can undergo simple diffusion across a lipid bilayer, and why?10.What are some factors that can affect the rate of simple diffusion, aside from temperature and concentration gradient?B2.1.4—Integral and peripheral proteins in membranesEmphasize that membrane proteins have diverse structures, locations and functions. Integral proteins are embedded in one or both of the lipid layers of a membrane. Peripheral proteins are attached to one orother surface of the bilayer.11.List the six main functions of the membrane proteins:12.Describe the structure of integral membrane proteins and how they interact with the hydrophobic core of the lipid bilayer.13.Provide examples of integral membrane proteins and their functions.14.Explain how peripheral proteins can be easily removed from the membrane compared to integral proteins.B2.1.5—Movement of water molecules across membranes by osmosis and therole of aquaporinsInclude an explanation in terms of random movement of particles, impermeability of membranes to solutes and differences in solute concentration.15.Osmosis occurs not just by simple diffusion, but also by facilitated diffusion.a.State the name of the specialized type of membrane protein used to transport water.b.Give examples of cells that use facilitated diffusion as well as simple diffusion.c.Why is facilitated diffusion used if water can move by simple diffusion?16.Explain what would happen to the cells of tissues and organs immersed in these solutions:a.Isotonic b.Hypertonic c.Hypotonic B2.1.6—Channel proteins for facilitated diffusionStudents should understand how the structure of channel proteins makes membranes selectively permeable by allowing specific ions to diffuse throughwhen channels are open but not when they are closed.17.Explain the concept of selectivity in channel proteins. How do channel proteins ensure that only specific molecules can pass through them?18.Provide examples of channel proteins and the types of molecules they transport.19.How are channel proteins regulated, and what are some factors that can affect their activity?20.Draw and annotate a diagram to show how protein channels are used in the facilitated diffusion of potassium in axons.B2.1.7—Pump proteins for active transportStudents should appreciate that pumps use energy from adenosine triphosphate (ATP) to transfer specificparticles across membranes and therefore that they can move particles against a concentration gradient.21.What is active transport, and how does it differ from passive transport mechanisms like diffusion and facilitated diffusion?22.Provide examples of pump proteins and the molecules or ions they transport.23.Discuss the importance of the sodium-potassium pump (Na+/K+ pump) in maintaining the resting membrane potential of neurons and muscle cells.
24.Annotate the diagram below to show how a protein pump is used in the active transport of sodium and potassium ions across the plasma membrane of axons.B2.1.8—Selectivity in membrane permeabilityFacilitated diffusion and active transport allow selective permeability in membranes. Permeability bysimple diffusion is not selective and depends only on the size and hydrophilic or hydrophobic properties of particles.25.Complete the chart on the next page by indicating whether, and why, the substance will or will not be able to cross the Bilayer.a.B.2.1.9—Structure and function of glycoproteins and glycolipidsLimit to carbohydrate structures linked to proteins or lipids in membranes, location of carbohydrates on theextracellular side of membranes, and roles in cell adhesion and cell recognition.26.Draw a diagram of a glycoprotein and a glycolipid.27.State the functions of glycolipids found in the plasma membrane28.State the functions of glycoproteins found in the plasma membraneB2.1.10—Fluid mosaic model of membrane structureStudents should be able to draw a two-dimensional representation of the model and include peripheral and integral proteins, glycoproteins, phospholipids and cholesterol. They should also be able to indicate hydrophobic and hydrophilic regions.29.Draw and label a simplified (2D) diagram of the plasma membrane. Include: phospholipid bilayer, integral and peripheral proteins, glycoproteins and cholesterol. 30.Outline the Singer-Nicholson fluid mosaic model of the cell membrane.31.How does the fluid mosaic model describe the structure of biological membranes?B2.1.11—Relationships between fatty acid composition of lipidbilayers and their fluidity AHLUnsaturated fatty acids in lipid bilayers have lower melting points, so membranes are fluid and therefore flexible at temperatures experienced by a cell. Saturated fatty acids have higher melting points and make membranes stronger at higher temperatures. Students should be familiar with an example of adaptations in membrane composition in relation to habitat.32.How does the fluidity of the lipid bilayer impact its function in biological membranes?33.Explain the relationship between the degree of saturation of fatty acids in phospholipids and the fluidity of the lipid bilayer.34.Discuss the role of membrane fluidity in cell adaptation to temperature changes.35.How do organisms that inhabit extreme environments (e.g., polar regions or hot springs) adapt the composition of their membrane lipids to maintain membrane fluidity?B2.1.12—Cholesterol and membrane fluidity in animal cells AHLStudents should understand the position of cholesterol molecules in membranes and also that cholesterol acts as a modulator (adjustor) of membrane fluidity, stabilizing membranes at higher temperatures and preventing stiffening at lower temperatures.36.Cholesterol is a type of lipid, but it is not a fat or oil. What group does it belong to?37.Cholesterol makes up around about 20% of the mass of cell membranes. This percentage varies greatly and some membranes, e.g. bacteria, do not contain it at all.a.Where in the plasma membrane can cholesterol be found?b.What properties cause it to be located in this position?38.The presence of cholesterol in the membrane restricts the movement of phosolipids and other molecules.How does this affect the physical properties of the membrane?39.The presence of cholesterol disrupts the regular packing of the of the hydrocarbon tails of phospholipid molecules. What impact does this have on the physical properties of the membrane?40.What chemical properties of the membrane are affected by cholesterol?B2.1.13—Membrane fluidity and the fusion and formation of vesicles AHLInclude the terms “endocytosis” and “exocytosis”, and examples of each process.41.Exocytosis is often characterized as being either pinocytosis or phagocytosis. Distinguish between between the two terms.42.Describe how the plasma membrane breaks and reforms during exocytosis and endocytosis. How does the fluidity of the membrane allow this? 43.Complete and annotate the diagram below to show the process of vesicle transport of a protein molecule through a eukaryote cell. Begin with protein synthesis in the Rough ER and finish with exocytosis though MoleculeElectrical ChargeSizeCross the Membrane?Explanation (Why/Why Not)Oxygen Gas (O2)NoSmallSodium Ion [Na]+Yes: (+)SmallGlucosePolarLargeWaterPolarSmallCarbon Dioxide (CO2)NoSmallChloride Ions [Cl]-Yes: (-)Small
the plasma membrane. Label all organelles shown. B2.1.14—Gated ionchannels in neurons AHL Include nicotinic acetylcholine receptors as an example of a neurotransmitter-gated ion channel and sodium and potassium channels as examples of voltage-gated channels.44.What are gated ion channels, and how do they function in neuronal signaling?45.Explain the concept of ion selectivity in gated ion channels. Why is ion selectivity important for their function?46.Provide an example of a neurotransmitter-gated ion channel and describe its role in neuronal communication.B2.1.15—Sodium–potassium pumps as an example of exchange transporters AHLInclude the importance of these pumps in generating membrane potentials47.What is the sodium-potassium pump, and where is it found in cells?48.Describe the role of voltage-gated sodium channels in neuronal action potentials. How do they contributeto the depolarization phase of an action potential?49.Explain the function of voltage-gated potassium channels in neuronal action potentials. How do they contribute to repolarization and hyperpolarization phases?50.Explain the importance of the sodium-potassium pump in maintaining the resting membrane potential of neurons..B2.1.16—Sodium-dependent glucosecotransporters as an example of indirect active transport AHLInclude the importance of these cotransporters in glucose absorption by cells in the small intestine and glucose reabsorption by cells in the nephron.51.What are sodium-dependent glucose cotransporters (SGLTs), and where are they found in the body?52.Explain the concept of indirect active transport as exemplified by SGLTs.53.What is the importance of SGLTs in glucose absorption by the small intestine?54.Discuss the importance of SGLTs in glucose reabsorption in the nephron.B2.1.17—Adhesion of cells to form tissues AHLInclude the term “cell-adhesion molecules” (CAMs) and the understanding that different forms of CAM areused for different types of cell–cell junction. Students are not required to have detailed knowledge of the different CAMs or junctions.55.What is cell adhesion, and why is it essential for the formation of tissues in multicellular organisms?56.Define cell-adhesion molecules (CAMs) and explain their role in cell adhesion.