Biomembranes: Structure, Function & Transport

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Questions and Answers

Explain how the asymmetry of lipid composition between the inner and outer leaflets of a biomembrane contributes to its overall function. Provide a specific example related to cell signaling or protein localization.

Asymmetry in lipid composition affects membrane curvature, protein interactions, and signal transduction. For instance, phosphatidylserine exposure on the outer leaflet signals apoptosis.

Describe the role of cholesterol in modulating membrane fluidity. How does its effect differ at high versus low temperatures, and why is this important for cellular function?

Cholesterol maintains fluidity by disrupting hydrophobic interactions at low temperatures and preventing excessive fluidity at high temperatures. This ensures proper membrane function across a range of temperatures.

Differentiate between integral and peripheral membrane proteins, detailing how their interactions with the lipid bilayer differ and how these differences impact their respective functions.

Integral proteins span the bilayer, interacting hydrophobically with the lipid tails, enabling them to act as transporters or receptors. Peripheral proteins bind to the membrane surface via electrostatic interactions or hydrogen bonds, often participating in signaling or cytoskeletal support.

Explain how the glycocalyx, formed by glycolipids and glycoproteins, contributes to cell-cell recognition and immune response. Give a specific example of a disease state linked to altered glycosylation patterns.

The glycocalyx mediates cell-cell interactions and immune recognition via specific carbohydrate moieties. Altered glycosylation patterns are implicated in cancer metastasis and autoimmune diseases. Signup and view all the answers

Describe how the 'Fluid Mosaic Model' explains the dynamic behavior of biomembranes. What experimental evidence supports the concept of lateral diffusion of lipids and proteins within the membrane?

The Fluid Mosaic Model describes the membrane as a dynamic structure where lipids and proteins can move laterally. FRAP (Fluorescence Recovery After Photobleaching) experiments support this by demonstrating the recovery of fluorescence after photobleaching a membrane region. Signup and view all the answers

Contrast the mechanisms of action for channel proteins and carrier proteins in facilitated diffusion. Provide an example of each and explain how their structures dictate their function.

Channel proteins form pores for rapid ion or molecule transport down a concentration gradient (e.g., aquaporins). Carrier proteins undergo conformational changes to bind and translocate specific molecules (e.g., GLUT4 glucose transporter). Signup and view all the answers

Explain the mechanism by which ionophores facilitate ion transport across biomembranes. Differentiate between channel-forming and carrier ionophores, providing an example of each.

Ionophores increase membrane permeability to specific ions. Channel-forming ionophores like gramicidin create a pore, while carrier ionophores like valinomycin bind and shuttle ions across the membrane. Signup and view all the answers

Describe the role of aquaporins in maintaining cellular water balance. How does their structure prevent the passage of protons while allowing efficient water transport?

Aquaporins facilitate rapid water transport across membranes, maintaining osmotic balance. Their narrow pore lined with hydrophobic amino acids prevents proton passage via a 'water wire' arrangement. Signup and view all the answers

Compare and contrast the processes of endocytosis and exocytosis. Provide specific examples of cargo transported via these pathways and discuss the roles of key proteins involved.

Endocytosis imports material into the cell (e.g., receptor-mediated endocytosis of LDL), while exocytosis exports material out of the cell (e.g., neurotransmitter release). Clathrin, SNAREs, and Rab proteins are crucial for vesicle formation, targeting, and fusion. Signup and view all the answers

Explain the mechanism of action of a passive mediated transport system, focusing on the kinetics and specificity. How does the presence of a competitive inhibitor affect the transport rate, and why?

Passive mediated transport involves a carrier protein that binds a specific solute, facilitating its movement down the concentration gradient. A competitive inhibitor decreases the transport rate by competing for the same binding site on the carrier protein. Signup and view all the answers

Flashcards

Lipid behavior in water

Form spontaneously when amphipathic lipids are placed in an aqueous environment; can form bilayers, micelles, or liposomes.

Major membrane lipids

Phospholipids, glycosphingolipids, and cholesterol.

Integral membrane proteins

Proteins embedded within the lipid bilayer of the membrane.

Peripheral membrane proteins

Proteins associated with the membrane surface through interactions with integral proteins or lipid head groups.