Ch.12 - Mol bio
Page 1: Transporters and Pumps
Examples of Transporters: Summary of various ion pumps and channels.
H+ Pumps
Found on thylakoid membrane (chloroplast) and inner mitochondrial membrane.
Function to transport protons.
Table 12-2: Some Examples of Transmembrane Pumps
Transporter | Location | Energy Source | Function
Na+-driven glucose pump | Apical plasma membrane of kidney and intestinal cells | Na+ gradient | Active import of glucose (glucose-Na+ symport)
Na+-H+ exchanger | Plasma membrane of animal cells | Na+ gradient | Active export of H+ ions, pH regulation
Na+ pump | Plasma membrane of most animal cells | ATP hydrolysis | Active export of Na+ and import of K+ (Na+-K+ ATPase)
Ca2+ pump (Ca2+ ATPase)
On plasma membrane of eukaryotic cells | ATP hydrolysis | Active export of Ca2+
On sarcoplasmic reticulum membrane of muscle cells | ATP hydrolysis | Active import of Ca2+ for muscle contraction
H+ pump (H+ ATPase)
On plasma membrane of plant cells, fungi, and bacteria | ATP hydrolysis | Active export of H+
On lysosomal membranes of animal cells | ATP hydrolysis | Active export of H+ from cytosol into vacuoles
Bacteriorhodopsin | Plasma membrane of some bacteria | Light | Active export of H+
Page 2: Transporters vs. Ion Channels
Transporters
Solute-binding site facilitates movement across the cell membrane.
Ion Channels
Allow specific ions to pass through when open.
Page 3: Ion Channel Characteristics
Selectivity
Only certain ions can enter.
Gating
Ion channels can open/close in response to stimuli.
Page 4: Functioning of Ion Channels
Example: Bacterial K+ Channel
Allows hydrated K+ ions through a selective filter, showcasing the channel protein's structure and functions in membrane dynamics.
Page 5: Gating Mechanisms of Ion Channels
Types of Gated Ion Channels:
Voltage-Gated: Opens/closes based on membrane potential.
Ligand-Gated: Opens/closes upon binding of a molecule (either extracellular or intracellular ligand).
Mechanically-Gated: Opens in response to mechanical stress or deformation.
Structural Changes
Gating involves conformational changes in protein structure.
Page 6: Quiz Question Concept
Understanding Gated Channels: Flow of ions through an ion channel can activate voltage-gated channels, indicative of membrane potential changes.
Page 7: K+ Leak Channels
Important in maintaining resting membrane potential.
Page 8: Ion Considerations
Need to consider both concentration and voltage gradients for ions.
Membrane Potential
Represents voltage differences across a membrane; equilibrium may not equal zero.
Page 9: Conceptual Understanding of Nernst Equation
Do not memorize but understand conceptually the implications for ion distribution and membrane potential.
Page 10: K+ Leak Channels
Driving Force:
Concentration and voltage gradients affect potassium ion movement.
K+ Leak Channels: Critical for cellular resting membrane potential stability.
Page 11: Mechanically Activated Ion Channels
Example: Auditory Hair Cells
Sound vibrations cause stereocilia to tilt, opening mechanically gated ion channels, allowing positive ions to flow in, leading to changed membrane potential and neuronal activation.
Page 12: Voltage-Gated Na+ Channel Dynamics
States of the Channel:
Closed, Open, Inactivated states during action potentials, showcasing the action potential's key stages.
Page 13: Acetylcholine Receptors
Function in Skeletal Muscle
Nicotinic acetylcholine receptors demonstrate channel behavior with charged amino acid interactions, relevant during synaptic signaling.
Page 14: Ion Channel Importance in Neuroscience
Table 12-3: Examples of Ion Channels
Ion Channel | Location | Function
K+ leak channel | Plasma membrane of most animal cells | Maintenance of resting membrane potential.
Voltage-gated Na+ channel | Plasma membrane of nerve cell axon | Generation of action potentials.
Voltage-gated K+ channel | Plasma membrane of nerve cell axon | Return to resting potential after action.
Voltage-gated Ca2+ channel | Plasma membrane of nerve terminal | Stimulation of neurotransmitter release.
Acetylcholine receptor | Plasma membrane of muscle cell | Excitatory synaptic signaling.
Glutamate receptor | Plasma membrane of neurons | Excitatory synaptic signaling.
GABA & Glycine receptors | Various neurons | Inhibitory synaptic signaling.
Mechanically-activated cation channel | Auditory hair cell | Sound vibration detection.
Page 15: Importance of Ion Channels in Neurons
Structure of Neurons
Insights into how ion channels are distributed across the nerve terminal, cell body, dendrites, and axons.
Page 16: Action Potential Mechanics
Phases of Action Potential Propagation in Neurons
Changes in states of Na+ channels (Closed, Open, Inactivated) and their role during transmission.
Page 17: Neurotransmitter Activation of Action Potential
Mechanism of neurotransmitter binding leading to action potential propagation down the neuron.
Page 18: Transmission of Signals via Action Potentials
Action Potential:
A temporary shift in the membrane's potential resulting from ion fluxes.
Page 19: Understanding Action Potentials
Voltage-gated Na+ channels responsible for action potential propagation.
Page 20: Action Potential Graph
Graphical Representation:
Shows the change from resting potential to action potential over time.
Page 21: Na+ Channel Dynamics during Action Potential
Continued actions of Na+ channels along the axon during action potential propagation.
Page 22: Neurotransmitter-Induced Responses
Mechanism: Conversion of action potentials to neurotransmitter release.
Page 23: Factors Influencing Membrane Potential
Discusses the trigger for voltage-gated sodium channels activation based on cell type.
Page 24: From Neurotransmitter Activation to Action Potential
Explores how neurotransmitters induce changes in membrane potentials across synapses.
Page 25: Maintaining Sodium and Potassium Gradients
The importance of consistent sodium (Na+) and potassium (K+) gradients for cellular functions.
Page 26: Chapter 12 Outline
Topics Covered:
Review of membrane structure and selective permeability.
Rules of membrane transport.
Transporters.
Ion channels.
Nerve cell signaling.