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Questions and Answers
Who are Jablonski diagrams named after?
Who are Jablonski diagrams named after?
Fluorescence typically occurs at higher energies or shorter wavelengths than the energy of absorption.
Fluorescence typically occurs at higher energies or shorter wavelengths than the energy of absorption.
False
What phenomenon was first observed by Sir G.G. Stokes in 1852?
What phenomenon was first observed by Sir G.G. Stokes in 1852?
The Stokes Shift
A typical Jablonski diagram depicts the singlet ground state as ______.
A typical Jablonski diagram depicts the singlet ground state as ______.
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Match the following states with their corresponding energy levels:
Match the following states with their corresponding energy levels:
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What is one common cause of the Stokes shift?
What is one common cause of the Stokes shift?
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Spectrofluorometers can only record emission spectra.
Spectrofluorometers can only record emission spectra.
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What do fluorophores typically decay to after being excited?
What do fluorophores typically decay to after being excited?
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What is a defining characteristic of biological membranes?
What is a defining characteristic of biological membranes?
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Lateral diffusion of lipids in a bilayer occurs rapidly at all temperatures.
Lateral diffusion of lipids in a bilayer occurs rapidly at all temperatures.
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What is the primary mechanism of energy transfer in FRET?
What is the primary mechanism of energy transfer in FRET?
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What are the three states of lipid bilayers at different temperatures?
What are the three states of lipid bilayers at different temperatures?
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FRET requires the emission of a photon for energy transfer to occur.
FRET requires the emission of a photon for energy transfer to occur.
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What is the Förster distance in FRET?
What is the Förster distance in FRET?
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Trans-bilayer movement of lipids from one leaflet to another requires _______ due to its energetically unfavorable process.
Trans-bilayer movement of lipids from one leaflet to another requires _______ due to its energetically unfavorable process.
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FRET occurs between a donor molecule in the excited state and an acceptor molecule in the ______ state.
FRET occurs between a donor molecule in the excited state and an acceptor molecule in the ______ state.
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Match the following states of lipid bilayers with their characteristics:
Match the following states of lipid bilayers with their characteristics:
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What is the method used to measure the rate of lateral diffusion of lipids?
What is the method used to measure the rate of lateral diffusion of lipids?
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Which factor does NOT influence the rate of energy transfer in FRET?
Which factor does NOT influence the rate of energy transfer in FRET?
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Lipid molecules can move freely across the bilayer without any barriers.
Lipid molecules can move freely across the bilayer without any barriers.
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Match the terms in FRET with their correct definitions:
Match the terms in FRET with their correct definitions:
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What phenomenon involves lipids behaving as if they are corralled by 'fences'?
What phenomenon involves lipids behaving as if they are corralled by 'fences'?
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How is FRET commonly used in biological research?
How is FRET commonly used in biological research?
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Atomic force microscopy (AFM) uses a light source to visualize membrane proteins.
Atomic force microscopy (AFM) uses a light source to visualize membrane proteins.
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Which property of fluorophores refers to their ability to absorb and emit light?
Which property of fluorophores refers to their ability to absorb and emit light?
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Fluorophores are generally unreactive and do not change when exposed to light.
Fluorophores are generally unreactive and do not change when exposed to light.
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Name one commonly used fluorophore.
Name one commonly used fluorophore.
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Fluorophores can be categorized into types such as organic dyes, fluorescent proteins, and _____.
Fluorophores can be categorized into types such as organic dyes, fluorescent proteins, and _____.
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Match the following applications with their descriptions:
Match the following applications with their descriptions:
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What is one key benefit of modern fluorophores compared to earlier generations?
What is one key benefit of modern fluorophores compared to earlier generations?
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Wavenumber is expressed in units of nm.
Wavenumber is expressed in units of nm.
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What are the typical units for wavelength when discussing fluorophores?
What are the typical units for wavelength when discussing fluorophores?
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What is the primary mechanism by which solutes move from a region of higher concentration to a region of lower concentration across a membrane?
What is the primary mechanism by which solutes move from a region of higher concentration to a region of lower concentration across a membrane?
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Ion channels allow transmembrane movement at rates approaching the limit of unhindered diffusion.
Ion channels allow transmembrane movement at rates approaching the limit of unhindered diffusion.
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What are the two broad categories of transporters mentioned?
What are the two broad categories of transporters mentioned?
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The force opposing ion movements that increase membrane potential is produced by a _______ gradient.
The force opposing ion movements that increase membrane potential is produced by a _______ gradient.
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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Which of the following statements about electrochemical gradients is FALSE?
Which of the following statements about electrochemical gradients is FALSE?
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The Na+ K+ ATPase is an example of a channel that allows rapid ion transport.
The Na+ K+ ATPase is an example of a channel that allows rapid ion transport.
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The random distribution of molecules is in accordance with the second law of _______.
The random distribution of molecules is in accordance with the second law of _______.
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What is the primary function of integrins in the plasma membrane?
What is the primary function of integrins in the plasma membrane?
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Cadherins interact with dissimilar cadherins in adjacent cells.
Cadherins interact with dissimilar cadherins in adjacent cells.
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What technique allows for the observation of a single lipid molecule in the plasma membrane?
What technique allows for the observation of a single lipid molecule in the plasma membrane?
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________ serve as receptors and signal transducers in cell adhesion.
________ serve as receptors and signal transducers in cell adhesion.
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Which of the following statements about membrane proteins is true?
Which of the following statements about membrane proteins is true?
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Match the following membrane proteins with their functions:
Match the following membrane proteins with their functions:
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Solute transport across membranes is exclusively passive and does not require energy.
Solute transport across membranes is exclusively passive and does not require energy.
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In the process of facilitated diffusion, a solute moves down its ________ gradient.
In the process of facilitated diffusion, a solute moves down its ________ gradient.
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Study Notes
Membrane Dynamics
- Biological membranes are flexible, changing shape without losing integrity.
- Noncovalent interactions between lipids in the bilayer allow this flexibility. Lipids aren't covalently bonded.
- Membrane dynamics involves motions and transient structures of the lipids.
- At low temperatures, lipids form a semisolid gel phase (paracrystalline).
- At high temperatures, lipid acyl chains rotate, producing a liquid-disordered state (fluid).
- At intermediate temperatures, lipids exist in a liquid-ordered state with less motion in acyl chains, but lateral movement still happens.
Trans-bilayer Movement of Lipids
- At physiological temperatures, trans-bilayer ("flip-flop") movement of lipids is slow if it occurs at all in most membranes.
- Moving polar/charged head groups into the hydrophobic bilayer interior requires a large, positive free energy change.
- This process is generally slow.
- Lipids will move laterally within a membrane bilayer leaflet much faster.
Lipids and Proteins Diffuse Laterally
- Lipids and proteins diffuse laterally in the bilayer.
- Fluorescence recovery after photobleaching (FRAP) is used experimentally to measure the rate of this lateral diffusion.
- FRAP shows movement from one region to a nearby region is inhibited.
- Membrane proteins are often in a "sea of lipids."
- Single particle tracking allows for observing the movement of a single lipid molecule.
Some Membrane Proteins Aggregate
- Some membrane proteins aggregate into large patches on cell surfaces or organelles.
- Individual proteins in these patches don't move relative to each other.
- Acetylcholine receptors are examples of proteins forming patches in neuron plasma membranes at synapses
Certain Integral Proteins Mediate Cell-Cell Interactions
- Integral proteins in plasma membranes mediate cell-cell interactions and adhesion.
- Integrins are heterodimeric proteins anchored to the plasma membrane, serving as both receptors and signal transducers.
- Cadherins interact homophilically with identical cadherins in neighboring cells.
- Immunoglobulin-like proteins and selectins are also involved in cell adhesion.
Solute Transport across Membranes
- Membrane proteins facilitate solute diffusion down concentration gradients.
- Transport against gradients requires energy (ATP hydrolysis).
- Ions can move via ion channels or ionophores.
- Electrochemical gradients (combined electrical and concentration gradients) influence ion movement.
Passive Transport
- Solutes diffuse from higher to lower concentration (simple diffusion) until equal concentration.
- Ions move down a transmembrane electrical gradient (membrane potential). This involves membrane potential influencing ion movement.
Key Properties of Fluorophores
- Excitation and emission wavelengths
- Quantum yield
- Photostability
- Fluorescence lifetime
Types of Fluorophores
- Organic dyes
- Fluorescent proteins
- Quantum dots
- Fluorescent nanoparticles
Applications of Fluorophores
- Fluorescence microscopy
- Flow cytometry
- Molecular probes/diagnostic tools
- Immunofluorescence
- Live-cell imaging
- In vivo imaging
Atomic Force Microscopy
- AFM uses a sharp tip of a microscopic probe to image uneven surfaces, like cell membranes.
- Electrostatic and van der Waals forces produce a force on the probe, measured by laser deflection that helps maintain constant force.
- Images are created from detected motion in the z-dimension.
Single Molecules of Bacteriorhodopsin
- AFM shows bacteriorhodopsin forms highly regular structures in membranes.
Fluorescence Resonance Energy Transfer (FRET)
- FRET is an electrodynamic phenomenon that can be explained by classical physics.
- Energy transfer occurs between a donor molecule in the excited state and an acceptor in the ground state.
- The emission of the donor overlaps with the absorption spectrum of the acceptor.
- The rate and efficiency depend on spectral overlap, quantum yields of donor, orientation, distance between the molecules.
- FRET is used to measure distances between protein molecules, indicating binding or changes in protein shape.
Immunofluorescence
- Direct immunofluorescence uses a primary antibody labeled with a fluorophore.
- Indirect immunofluorescence uses a secondary antibody labeled with a fluorophore, that binds to the primary antibody.
Membrane Protein Interactions
- FRET relies on distance dependence to study protein interactions, as binding changes the distance between the FRET pair, altering fluorescence.
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Description
Explore the fascinating world of biological membranes with this quiz focusing on membrane dynamics and the trans-bilayer movement of lipids. Test your knowledge about the flexibility, phases, and movement of lipids in biological membranes at varying temperatures.
