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Molecular Biology of the CellFifth Edition
Molecular Biology of the CellFifth Edition
Chapter 10Membrane Structure
Chapter 10Membrane Structure
Copyright © Garland Science 2008
Alberts • Johnson • Lewis • Raff • Roberts • WalterAlberts • Johnson • Lewis • Raff • Roberts • Walter
Figure 10-1 Molecular Biology of the Cell (© Garland Science 2008)
Biological membranes tend to form bilayers studded with various membrane-bound & transmembrane proteins
The fluid nature of the cell membrane allows lateral movement of many lipid and protein components; a feature which is described in the Fluid Mosaic Model
Overview of Membrane Functions
• Compartmentalization – Membranes form continuous sheets that enclose intracellular compartments.
• Scaffold for biochemical activities – Membranes provide a framework that organizes enzymes for effective interaction.
• Selectively permeable barrier – Membranes allow regulated exchange of substances between compartments.
Overview of Membrane Functions
• Transporting solutes – Membrane proteins facilitate the movement of substances between compartments.
• Responding to external signals – Membrane receptors transduce signals from outside the cell in response to specific ligands.
• Intracellular interaction – Membranes mediate recognition and interaction between adjacent cells.
• Energy transduction – Membranes transduce photosynthetic energy, convert chemical energy to ATP, and store energy.
Membrane & storage lipids
Storage lipids = energy storage; dietary lipids (i.e., triglycerides)
Phospholipid structure
Phospholipids are the major lipid found in biological membranes
Figure 10-2 Molecular Biology of the Cell (© Garland Science 2008)
Fatty acids
Saturated Unsaturated
Effects on membrane fluidity?…….
Lipid-orderedstate
Lipid-disorderedstate
What effectdoes saturation vs.unsaturation of FAhave on natural fats?On phospholipid membrane structure?
Steroids
Shape of lipids can determine Overall structure of “membrane”
Figure 10-8 Molecular Biology of the Cell (© Garland Science 2008)
Lipid content reflects function
What kind of structures allow for transmembrane domains?
Membrane Proteins
Membrane Proteins
Alpha-helix or barrel are found in membrane proteins
Bacteriorhodopsin
TM: Transmembrane Domain (-barrel)
-hemolysintoxin
Glycophorin
Bacteriorhodopsin
Hydrophobicity plot: predicts location of transmembrane
domains in proteins
helices
sheets, i.e. barrels
Some typesof proteinlipidation: importanceis in localization of specific proteins to the membrane (i.e., duringsignal transduction pathway activation)
ER lumenCytosol
Microdomains (lipid rafts) in plasma membrane
Idea of localizedsignal transductionmodules
Molecular Biology of the CellFifth Edition
Molecular Biology of the CellFifth Edition
Chapter 11Membrane Transport of Small Molecules and the Electrical
Properties of Membranes
Chapter 11Membrane Transport of Small Molecules and the Electrical
Properties of Membranes
Copyright © Garland Science 2008
Alberts • Johnson • Lewis • Raff • Roberts • WalterAlberts • Johnson • Lewis • Raff • Roberts • Walter
Figure 11-1 Molecular Biology of the Cell (© Garland Science 2008)
For simple diffusion: solutes will have different rates of diffusion depending upon solute polarity, size, & solute concentration gradient
Figure 11-2 Molecular Biology of the Cell (© Garland Science 2008)
Figure 11-3a Molecular Biology of the Cell (© Garland Science 2008)
Types of membrane transport proteins
Figure 11-3b Molecular Biology of the Cell (© Garland Science 2008)
Types of membrane transport proteins
Figure 11-4a Molecular Biology of the Cell (© Garland Science 2008)
Active & Passive Transport
Figure 11-5 Molecular Biology of the Cell (© Garland Science 2008)
Movement of electrically neutral solutes occurs “down” its concentration gradient (fromhigh [S] to low [S]) until equilibrium is reached
Equilibrium without an electrical potential across the membrane has equal particles and equal charge on both sides
Net movement of electrically chargedsolutes is determinedby a combination ofelectrical potential(Vm) & the chemicalconcentration differenceacross the membrane
Just like M&M view of enzymes:T+Sout↔TS↔T+Sin
T = transporterS = solute
Simple diffusion: process ofhydration shell removal is endergonic, so activation energy for diffusion throughthe membrane is high
Transporter protein reduces activationenergy for solute transport by formingnoncovalent bonds with dehydratedsolute to replace H-bonding with water and by creating a hydrophilictransmembrane passageway
Figure 11-6 Molecular Biology of the Cell (© Garland Science 2008)
Figure 11-4b Molecular Biology of the Cell (© Garland Science 2008)
Membrane Potentials
Figure 11-7 Molecular Biology of the Cell (© Garland Science 2008)
3 ways of driving active transport
Figure 11-8 Molecular Biology of the Cell (© Garland Science 2008)
3 types of transporter-mediated movement
Transporters (consider 3 examples)
•Glucose transporters: –GLUT1 uniporter
–Facilitated diffusion (works with [glucose] gradient)
•Na+/K+ ATPase:–P-Type ATPase (channel becomes phosphorylated during transport)
–Antiporter
–Primary active transport (couples ATP hydrolysis [exergonic] with simultaneous movement of Na+ & K+ against their electrochemical gradients [endergonic])
•ATP synthase:–F-Type ATPases (reversible, ATP-driven proton pumps: protons can either move against concentration gradient (i.e. certain bacteria) or with gradient (i.e., ATP synthesis through oxidative phosphorylation in mitochondria)
–ATP synthase refers to scenario in which protons movement occurs with its gradient!
GLUT1: glucose transporter
A helical wheel diagramreveals an amphipathic-helix
Amphipathic -helices
-helical supermolecular structures.
[Glucose] high outside
cell
[Glucose]Low inside
cell
No energy needed!
Facilitated diffusion
Uniporter:glucose
permease
Insulin regulates glucose transporter expressionon the cell surface
Equilibrium without an electrostatic potential across the membrane has equal particles and equal charge on both sides. However, if there is an electrostatic potential difference, then the steady state will have unequal number of particles and charges on each side.
Vm is the electrostatic potential difference across the membrane. Also denoted or
Na+/K+-ATPase: The Electrogenic Pump
The term,electrogenic, refers to a transport-generated electrical potential.
This usually results when movement of an ion withoutan accompanying counteriontakes place.
The Na+/K+ ATPase pumps Na+ outward to maintain the Na+ gradientthat drives glucose uptake into the bloodstream
Energy required To pump glucoseFrom two sources:
1) [Na+]outside>>[Na+]inside
2) Transmembrane potential (inside-neg., so draws Na+ inward)
…this means[glucose]inside/[glucose]outside ~ 9,000!
Figure 11-11 Molecular Biology of the Cell (© Garland Science 2008)
K+ binding constant
Low
Low
High
Low
Na+ binding constant
High
High
Low
High
ATP Synthase is the last step in the electron transport chain
ATP Synthase
A multisubunit
transmembrane protein
(450 kD)
Two functional units,
F1 and Fo
Fo is a water-insoluble
transmembrane
proton pore
F1 is a water-soluble
peripheral membrane
protein complex
ATP Synthase
Generates 1 ATP for every 3 protonsthat pass through it
ENERGY COUPLING! Couples ATP synthesis (endergonic) with passive diffusion of protons through inner mito. Membrane (exergonic).
Visualizing ATP Synthase
Norbert Dencher and Andreas Engel
AtomicForceMicroscopy
C-subunits of F0 complex
From chloroplasts
Hibernation
The uncoupling of ETC from ATP synthesis
Occurs in brown fat:many mitochondriaand cytochromes
Oxidation of NADHuncoupled from ATP synthesis
The energy of ETC is released as heat!
Also found in mostnewborn mammals
The uncoupling of ETC from ATP synthesis
Oxidation of NADHuncoupled from ATP synthesis
Pore protein calledthermogeninallows protonsto flow down gradient
The energy of ETC is released as heat!(instead of ATP)