CHapter 11 Flashcards
Chapter 11: Biological Membranes and Transport
Page 1: Introduction
Overview of biological membranes and their importance in transport mechanisms.
Page 2: Lipids Aggregation
Three major structures formed by lipids:
Micelles
Liposomes
Bilayers
Structure formation depends on:
Type of lipid
Concentration
Page 3: Micelles
Description:
Formed by amphipathic molecules with larger polar heads than tails.
Contain a few dozen to a few thousand lipid molecules.
Critical micelle concentration (CMC) is key for micelle formation.
Examples: Fatty acids and sodium dodecyl sulfate.
Page 4: Vesicles (Liposomes)
Synthetic vesicle membranes can be created in vitro with inserted proteins.
Central aqueous cavity can contain dissolved molecules (e.g., drugs).
These are useful for transporting molecules and can fuse readily with cell membranes.
Small bilayers spontaneously seal into spherical vesicles based on concentration.
Page 5: Membrane Bilayer
Forms in aqueous solutions with lipids having polar head groups and more than one tail.
Composed of:
Two leaflets of lipid monolayers (e.g., phospholipids, sphingolipids).
Depicts hydrophobic (tails) and hydrophilic (heads) interactions.
Page 6: Exam Question Example
Question: Which change increases micelle diameter?
A: Increasing concentration of cholesterol
B: Increasing length of acyl chains
C: Increasing concentration of polyunsaturated fatty acids
D: Using lipids with more polar head groups.
Page 7: Membrane Definition
Membranes are complex lipid-based structures that form pliable sheets.
Composed of various lipids and proteins, defining boundaries of cells and compartments in eukaryotic cells.
Page 8: Membrane Functions
Define boundaries for cells.
Import/export nutrients (e.g., lactose) and waste (e.g., toxins).
Retain metabolites and ions, sense external signals, provide compartmentalization for reactions.
Important for energy storage (proton gradients) and nerve signal transmission.
Page 9: Common Features of Membranes
Sheet-like, flexible structure (30–100 Å thick).
Typically, two leaflets of lipids (bilayer).
Form spontaneously and are stabilized by noncovalent forces, particularly the hydrophobic effect.
Asymmetric distribution of lipids and carbohydrates attached outside.
Fluid structures where movement is prevalent.
Page 10: Fluid Mosaic Model
Proposed by Singer and Nicholson in 1972.
Describes the arrangement and movement of proteins within the lipid bilayer, both embedded and loosely associated.
Page 11: Variability in Composition
Membrane composition varies across organisms, tissues, and organelles:
Abundance and type of lipids and proteins, e.g., absence of cholesterol in mitochondria and abundant galactolipids in chloroplasts.
Page 12: Asymmetry in Membranes
Different lipid compositions in leaflets:
Outer leaflet often positively charged.
Specific functions associated with lipid positioning (e.g., blood clotting, cell signaling).
Page 13: Membrane Structure Highlights
Plasma membrane components and associated structures:
Golgi apparatus, endosomes, and lysosomes with specific lipid compositions.
Page 14: Exam Question
Question: Identify the false statement regarding biological membranes.
A: All membranes have the same composition.
B: All contain lipids.
C: Lipid bilayers are impermeable to polar solutes.
D: Membranes typically contain proteins.
Page 15: Membrane Proteins Overview
Membrane proteins categorized into:
Integral: span the entire membrane
Peripheral: loosely attached, interact with aqueous domains.
Page 16: Peripheral Membrane Proteins
They associate with polar head groups through ionic interactions.
Removed by disrupting interactions (e.g., high salt conditions).
Page 17: Lipid-Linked Proteins
Proteins covalently linked to lipids, influencing targeting and membrane function.
Examples include glycosylated phosphatidylinositol (GPI) anchors.
Page 18: Integral Membrane Proteins
Span entire membrane with hydrophobic transmembrane segments, interact with lipid bilayer.
Examples include channels for nutrient transport.
Page 19: Membrane Protein Composition
Composition includes various secondary structures, e.g., alpha-helices and beta-sheets.
Responsible for various membrane functions.
Page 20: Membrane Protein Functions
Functions of membrane proteins:
Receptors detecting external signals (e.g., hormones).
Ion channels for transporting ions and nutrients.
Enzymatic role in lipid metabolism (e.g., ATP synthase).
Page 21: Exam Questions on Membrane Proteins
Topics on amphitropic proteins:
Functions and characteristics within membranes.
Page 22: Effects on Membrane Fluidity
Membrane fluidity influenced by lipid composition and temperature, affecting biological functions.
Page 23: Membrane Dynamics
Lateral diffusion of lipids occurs rapidly.
Experimental techniques (e.g., FRAP) monitor lipid movement and dynamics.
Page 24: FRAP Methodology
Steps involved in the fluorescence recovery after photobleaching for studying membrane dynamics.
Page 25: Special Enzymes and Proteins
Flippases facilitate lipid movement across bilayers; significant for membrane asymmetry.
Page 26: Membrane Rafts
Lipid distribution is not random; specialized areas with particular lipid and protein clustering.
Page 27: Membrane Fusion
Membranes can fuse without exposure to solvent, a critical process in cellular communication.
Page 28: Membrane Transport Mechanisms
Transport must be energetically favorable, considering concentration and electrochemical gradients.
Page 29: Types of Membrane Transport
Different mechanisms:
Simple diffusion for nonpolar substances.
Passive diffusion versus facilitated diffusion via transport proteins.
Active transport mechanisms driven by ATP.
Page 30: Membrane Properties Summary
Membrane fluidity and dynamics are crucial for physiological functions, with varied effects based on lipid structures.
Page 31: Exam Questions on Transport
Questions about membrane depolarization, protein embedment, and hydrophobic segments in complex processes.
Feedback mechanisms that drive homeostasis and communication at cellular levels.