Unit7-Biomembranes and signal transduction
Page 1: Introduction
Course and Context
Dr. Manisha Ray, Chem 361/Biol 366 at Loyola University Chicago.
Textbook: Biochemistry: An Integrative Approach with Expanded Topics by John T. Tansey.
Focus: Overview of Biomembranes and Signal Transduction.
Page 2: Membrane Function
Role in Cell Communication
Membranes act as communication channels between cells.
Define the boundaries of cells and organelles, critical for their functioning.
All cells possess membranes that seperate the interior from the exterior.
Signal transduction is vital for transmitting messages across the membrane barrier.
Page 3: Signal Transduction Basics
Definition and Function
Signal Transduction involves the conveyance of information from outside to inside the cells.
Page 4: Lipid Types in Biomembranes
Chapter Concept Checks
Key question: What types of lipids predominantly make up biomembranes?
Structure description of phospholipids is essential.
Page 5: Phospholipid Structure
Characteristics of Phospholipids
Composed of hydrophobic fatty acid tails and a hydrophilic polar head.
Example: Glycerophospholipid structure (1,2-dihexanoyl-sn-glycero-3-phosphocholine).
Includes key components like acyl chain (hydrophobic) and alcohol head group (hydrophilic).
Page 6: Plasma Membrane Structure
Fluid Mosaic Model (1972)
Membrane consists of two asymmetric leaflets of phospholipids.
Thickness of lipid bilayers is typically 45 Å.
Page 7: Membrane Variation
Different Membrane Types in Organisms
Plasma membranes differ across cell types: mitochondria, endoplasmic reticulum, etc.
Common components include cholesterol and various phospholipids like phosphatidylcholine and phosphatidylethanolamine.
Page 8: Membrane Chemical Properties
Permeability Factors
Lipid bilayers allow gases like O2, CO2, and N2 to diffuse through.
Plasma membranes are hydrophobic, selectively excluding ions and large organic molecules.
Solubility of molecules decreases with their size; glucose is less soluble than smaller molecules.
Water's diffusion through membranes is complex and under investigation.
Page 9: Membrane Permeability
Gas Dissolution
O2 and CO2 readily dissolve across the lipid membrane.
Transport proteins help facilitate the movement of polar molecules.
Page 10: Transport Proteins
Functionality
Ions and large biomolecules like glucose require transport proteins to cross the membrane.
Page 11: Membrane Proteins
Classifications
Integral membrane proteins (IMP): embedded in the membrane; require detergent to solubilize.
Can be classified as ditopic or transmembrane proteins. Examples: Aquaporin, ß integrin.
Page 12: Integral Membrane Proteins (IMP)
Properties and Types
Subclassified into monotopic, ditopic, and bitopic based on structure.
Seven transmembrane receptors contain α helices that span the membrane.
Page 13: Peripheral Membrane Proteins (Part 1)
Characteristics
Associate with membrane surfaces, stabilized by hydrophobic interactions.
Can be solubilized through altering pH or ionic concentrations.
Page 14: Peripheral Membrane Proteins (Part 2)
Interaction with Membranes
Can have hydrophobic anchors (e.g., myristoyl, palmitoyl).
Play roles in membrane dynamics and interactions.
Page 15: Transport Mechanisms
Types of Transport Proteins
Carriers, pumps, and channel proteins facilitate the transport of molecules (e.g., ions, glucose).
Essential for neurotransmission and signal propagation.
Page 16: Understanding Diffusion
Definition and Factors
Movement down a concentration gradient; aligns with the second law of thermodynamics.
Affected by particle size, shape, solvent viscosity, and temperature.
Page 17: Osmosis
Definition
Movement of solvent across a semipermeable membrane from low to high solute concentration.
Page 18: Carrier Protein Mechanisms
Types of Transporters
Uniporters: transport one molecule/ion.
Symporters: couple the transport of two in the same direction.
Antiporters: couple transport of one molecule in the opposite direction.
Page 19: Secondary Active Transport
Mechanisms
Symporters and antiporters use gradients to transport secondary molecules.
Examples: Na+/Glucose transporter (symporter) and Na+/Ca2+ exchanger (antiporter).
Page 20: Active Transport Mechanisms
Overview
Pumps transport molecules against gradients, using ATP to ADP conversion.
Example: Na+/K+ ATPase pump is crucial for ion homeostasis.
Page 21: Comparison of Transport Mechanisms
Active vs Secondary Transport
Active: direct ATP expenditure.
Secondary: relies on ion gradients created by primary active transport.
Page 22: Channel Proteins
Types of Channels
Ligand-gated: opens upon ligand binding (e.g., Na+ channel)
Voltage-gated: responds to changes in membrane potential.
Page 23: Membrane Structures
Lipid Rafts
Cholesterol and sphingolipids form lipid rafts, aiding in membrane fluidity.
Page 24: Membrane Fusion and Budding
Mechanisms
Membranes can fuse or bud off, playing roles in secretion and cell communication.
Page 25: Signaling Basics
Signal Transduction Overview
Chemical signals activate responses through receptor binding, conformational changes, and intracellular cascades.
Page 26: Signal Transduction Requirements
Essential Components
Signal, a receptor, and mechanisms for cellular response are necessary for signal transduction.
Page 27: Terminology in Signal Transduction
Key Definitions
Signal: chemical compound released for communication.
Second messenger: amplifies signals inside the cell.
Cross talk: interaction between signaling pathways.
Page 28: PKA Signaling Pathway
Overview
PKA, a common signaling pathway activated by cAMP, widespread in metabolic processes (e.g., epinephrine response).
Page 29: PKA Signaling Mechanism
Process Description
Binding of catecholamines to β-adrenergic receptors activates a G protein, adenylate cyclase, and produces cAMP.
cAMP activates glycogen phosphorylase, facilitating glycogen breakdown.
Page 30: Second Messenger Overview
Common Second Messengers
cAMP and Ca2+ ions both function as second messengers, regulating various pathways.
Page 31: Kinase Cascades
Importance
Kinase cascades facilitate cross-talk, control, and signal amplification in response regulation.
Page 32: PKA Activation Regulation
Feedback Mechanisms
Regulatory proteins can inhibit PKA by binding to its regulatory domains.
Page 33: Cholera Toxin Effects
Mechanism
Activates G-protein signaling, leading to dehydration through excessive Cl- channel activation.
Page 34: Insulin Signaling Pathway
Multi-faceted Functions
Regulates glucose metabolism, different from PKA signaling by engaging Growth Factor pathways.
Page 35: Insulin Receptor Activation
Overview
Insulin binds, receptor dimerizes and autophosphorylates, recruiting IRS for glucose transporter activity.
Page 36: AMPK Signaling Pathway
Role and Function
AMPK acts as an energy sensor; regulates metabolism based on cellular energy status.
Page 37: AMPK Pathway Influence
Contrasting Signals
Signals low energy states, promoting ATP production through oxidation of substrates.
Page 38: Additional Pathways
Overview of Various Signal Transduction Pathways
Include JAK-STAT, MAPK, PKC, and CDK signaling pathways, each with distinct roles in cellular responses.
Page 39: JAK-STAT Pathway
Inflammation Role
Key mechanism in gene expression regulation, initiated by cytokine receptor activation.
Page 40: STAT Functionality
Mechanism Summary
Phosphorylation by JAK leads STAT translocation to the nucleus affecting gene expression.
Page 41: Mitogen-activated Protein Kinase (MAPK)
Growth Regulation
Kinase cascade activation leads to essential cell proliferation regulatory functions.
Page 42: MAPK Inhibition
Therapeutic Targets
Drugs like Gleevec inhibit MAPK pathways, useful in cancer treatment.
Page 43: Toll-like Receptor Signaling
Immunity Role
Essential for inflammatory responses, activated by pathogen-associated molecules like LPS.
Page 44: TLR Mechanism
Signaling Process
Ligand binding induces signaling cascades integrating PI3K and Akt pathways.
Page 45: Cyclin-dependent Kinases (CDK)
Cell Cycle Regulation
Important for cell growth and replication through kinase/cyclin interactions.
Page 46: CDK Structure
Explanation
Enzymatic functions independent of cross-talk with other signaling pathways.
Page 47: PKC Signaling
Calcium-dependent Activity
Activated through various receptors influencing transcription and enzymatic functions.
Page 48: PKC Isoform Diversity
Classification and Functions
Broad isoform classification enhances cellular signaling adaptability.
Page 49: Calcium-dependent Signaling
PKC Activation Steps
Involves ligand-receptor interactions and calcium dynamics influencing gene transcription.
Page 50: Nitric Oxide (NO) Signaling
Physiological Effects
NO serves as a signaling molecule in vascular regulation and cell communication.
Page 51: NO Production
Biosynthesis Overview
Involves multiple electron carriers synthesizing nitric oxide from arginine.
Page 52: NO in Medicine
Therapeutic Implications
NO pathway modulation by drugs (e.g., Sildenafil) aids in managing vascular conditions.
Page 53: Receptor-Ligand Interactions
Analogous Functions
Ligands can bind to receptors similarly to substrates in enzyme reactions, affecting intracellular signaling outputs.
Page 54: Nuclear Hormone Receptors
Functionality
Ligand binding triggers nuclear responses, critical in transcription activation.
Page 55: Membrane-bound Receptor Dynamics
Mechanism Summary
Ligand binding can induce conformational shifts, leading to signal propagation across the membrane.
Page 56: Ligand Binding Interaction
Binding Strength Influences
Weak interactions predominate in receptor-ligand binding; specific types include hydrogen bonds and hydrophobic effects.
Page 57: Types of Membrane-bound Receptors
Receptor Classifications
Ion channel-linked receptors: Control ion flow.
GPCRs: Activate multiple signaling networks.
Enzyme-linked receptors: Function as kinases upon ligand binding.
Page 58: Ion Channel Dynamics
Functionality Example
Binding of acetylcholine opens ion-selective channels, facilitating action potentials in muscle cells.
Page 59: G PCR Mechanism
Overview
GPCRs influence various pathways; examples include PKA and PKC signaling cascades.
Page 60: Enzyme-linked Receptor Activity
Insulin Receptor Role
Involved in phosphorylation cascades promoting glucose uptake.
Page 61: Receptor Activation Types
Comparative Analysis
Different receptor states affect signaling strengths; agonists can enhance or diminish receptor activity.
Page 62: Receptor-Ligand Binding Curves
Graph Representation
Typical binding curves show different characteristics based on ligand types: agonists, antagonists, etc.
Page 63: Summary
Membranes and Signal Transduction
Membranes serve as selective barriers enabling cellular compartmentalization
Signal transduction enables intercellular communication, crucial for maintaining physiological functions.