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Questions and Answers
What does the Hill coefficient indicate regarding ligand binding?
What does the Hill coefficient indicate regarding ligand binding?
- The degree of saturation of a binding site
- The rate at which ligands dissociate from receptors
- The amount of ligand present in solution
- The cooperativity of binding between multiple ligands (correct)
How does Gibb's free energy relate to the dissociation constant (Kd) of a binding interaction?
How does Gibb's free energy relate to the dissociation constant (Kd) of a binding interaction?
- Lower Kd indicates higher free energy
- Higher Kd indicates more stable binding
- Gibb's free energy is directly proportional to Kd
- Lower Kd indicates more favorable free energy (correct)
What mechanism is described by ligand-gated ion channels and how do they function?
What mechanism is described by ligand-gated ion channels and how do they function?
- They depend on voltage changes to open and close
- They open in response to the binding of specific ligands (correct)
- They allow ions to pass when they are selectively permeable
- They remain constantly open regardless of ligand presence
What is a characteristic of multipart ligands with regard to their affinity for targets?
What is a characteristic of multipart ligands with regard to their affinity for targets?
What role do non-covalent forces play in intermolecular interactions?
What role do non-covalent forces play in intermolecular interactions?
What is the primary difference between passive and active transport?
What is the primary difference between passive and active transport?
Which of the following statements about membrane permeability is accurate?
Which of the following statements about membrane permeability is accurate?
What role do aquaporins play in membrane transport?
What role do aquaporins play in membrane transport?
Which substance would require a transporter protein to move across a lipid bilayer?
Which substance would require a transporter protein to move across a lipid bilayer?
What is the significance of the dissociation constant (Kd) in relation to ligand binding?
What is the significance of the dissociation constant (Kd) in relation to ligand binding?
Which statement about cooperative binding is true?
Which statement about cooperative binding is true?
Which of the following molecules would cross a lipid bilayer most efficiently?
Which of the following molecules would cross a lipid bilayer most efficiently?
What distinguishes active transport from passive transport?
What distinguishes active transport from passive transport?
What is the primary mechanism of transport for carrier molecules?
What is the primary mechanism of transport for carrier molecules?
Which characteristic is NOT true about pores/channels in facilitated transport?
Which characteristic is NOT true about pores/channels in facilitated transport?
What distinguishes transporters from channels in facilitated transport?
What distinguishes transporters from channels in facilitated transport?
What is the unique feature of the Na+/K+-ATPase pump?
What is the unique feature of the Na+/K+-ATPase pump?
Which of the following ion concentration levels is NOT characteristic of the inside of a cell?
Which of the following ion concentration levels is NOT characteristic of the inside of a cell?
What happens during the uniport of glucose by GLUT transporters?
What happens during the uniport of glucose by GLUT transporters?
Which statement about facilitated transport is true?
Which statement about facilitated transport is true?
What type of transport does the Na+/K+-ATPase represent?
What type of transport does the Na+/K+-ATPase represent?
What does a small dissociation constant (Kd) indicate about the affinity of two molecules?
What does a small dissociation constant (Kd) indicate about the affinity of two molecules?
At what concentration of ligand (L) does the dissociation constant (Kd) represent?
At what concentration of ligand (L) does the dissociation constant (Kd) represent?
Which expression correctly relates the fraction bound (Y) to the ligand concentration [L] and the dissociation constant (Kd)?
Which expression correctly relates the fraction bound (Y) to the ligand concentration [L] and the dissociation constant (Kd)?
What is the significance of the Hill coefficient in binding interactions?
What is the significance of the Hill coefficient in binding interactions?
In the binding equation P + L ⇄ PL, what does 'P' represent?
In the binding equation P + L ⇄ PL, what does 'P' represent?
How can the affinity of multipart ligands compare to their individual components?
How can the affinity of multipart ligands compare to their individual components?
What does the term 'fraction bound' (Y) indicate in the context of molecular binding?
What does the term 'fraction bound' (Y) indicate in the context of molecular binding?
What is the primary role of the constants Kon and Koff in the binding equation?
What is the primary role of the constants Kon and Koff in the binding equation?
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Study Notes
Transport around the Cell
- There are two types of transport across a membrane:
- Passive transport: Does not require energy input.
- Active transport: Requires energy input.
Membrane Permeability
- Lipid bilayers: Are not permeable to polar molecules or ions, which require protein-mediated transport.
- Small, non-polar molecules (like CO2): Can cross the lipid bilayer more efficiently than larger, polar molecules.
- Water: Can cross lipid bilayers to some extent, but aquaporins (water channel proteins) facilitate water movement.
- Glucose and ions (MgSO4): Require transporter proteins facilitate their movement across membranes.
Methods of Facilitated Transport
- Carrier molecules: Form a hydrophobic shield around polar molecules, often ions.
- Pores/Channels: Transport can be facilitated by pores/channels, which are non-stoichiometric, fast, selective, and may be gated.
- Transporters: Conformational changes facilitate transport, and can be either passive or active (pumps).
Transport Protein Action
- Transporter proteins: Can move multiple ligands through conformational changes.
Uniport of Glucose
- Glucose transporters (GLUT): Bind glucose and facilitate its transport across membranes.
Effect of Na+/K+-ATPase on Cellular Ion Concentrations
- Na+/K+-ATPase: Is an ATP-dependent ion pump that maintains Na+ and K+ gradients across cell membranes.
- Importance of Na+/K+-ATPase: Uses one-third of total energy at rest.
Regulated Transport
- Ion channels: Can be gated (regulated) by voltage or small organic molecules.
- Ligand binding: Can open ion channels, allowing ions to cross the membrane.
The Nicotinic Acetylcholine Receptor
- Ligand-gated channel: The nicotinic acetylcholine receptor is an ion channel regulated by acetylcholine binding.
- Conformation change: Acetylcholine binding changes the receptor's conformation from closed to open, allowing ions to pass through.
Non-covalent Forces and Intermolecular Interactions
- Non-covalent forces: Drive intermolecular interactions, such as heme binding to O2, antibody binding, and transcription factor binding to DNA.
Quantitative Treatment of 1:1 Binding
- Dissociation constant (Kd): A measure of affinity between two molecules.
- Small Kd: Indicates high affinity.
- Kd: Can be determined by measuring rates or concentrations.
- Fractional saturation (Y): Represents the fraction of protein bound to ligand.
Classic Binding Curve
- Kd: Is equal to the concentration of ligand at which 50% of the protein is bound.
- Key point on the binding curve: When 50% of the protein is bound, [L] = Kd.
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