Cell Biology and Membrane Dynamics Quiz
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Questions and Answers

What is the main purpose of single particle tracking in the study of membrane dynamics?

  • To follow the movement of lipid molecules over a long time scale
  • To track the movement of a single lipid molecule on a shorter time scale (correct)
  • To visualize all lipid molecules simultaneously
  • To analyze the composition of lipid bilayers

What characteristic of integrins makes them essential for cell adhesion?

  • They are soluble proteins that do not interact with membranes
  • They contain multiple identical subunits that facilitate adhesion
  • They solely provide structural support without signaling
  • They are anchored to the plasma membrane by hydrophobic transmembrane helices (correct)

Which type of interaction do cadherins typically engage in to mediate adhesion between cells?

  • Homophilic interactions with identical cadherins (correct)
  • Hydrophilic interactions with extracellular matrix proteins
  • Heterophilic interactions with integrins
  • Non-specific interactions with any membrane protein

What is a key function of integral membrane proteins beyond cell adhesion?

<p>They may serve as receptors and signal transducers (D)</p> Signup and view all the answers

What type of transport occurs when solutes move against their concentration gradient?

<p>Active transport (C)</p> Signup and view all the answers

How might ions cross the plasma membrane according to the provided information?

<p>Via ion channels or carried by ionophores (A)</p> Signup and view all the answers

What role do selectins play in cell interactions?

<p>They mediate cell adhesion through weak interactions (D)</p> Signup and view all the answers

What drives the transport of solutes against a concentration gradient?

<p>Energy directly from ATP hydrolysis or from ion movements (A)</p> Signup and view all the answers

What do the labels S0, S1, and S2 in a Jablonski diagram represent?

<p>Electronic energy states (B)</p> Signup and view all the answers

What is typically observed regarding the energy of emission compared to absorption?

<p>Emission energy is lower than absorption energy (D)</p> Signup and view all the answers

What is one common cause of the Stokes shift?

<p>Rapid decay to the lowest vibrational level of S1 (D)</p> Signup and view all the answers

Which of the following statements about fluorescence spectroscopy instrumentation is false?

<p>Fluorescence spectrometers can only measure emission spectra. (B)</p> Signup and view all the answers

The phenomenon of fluorescence typically results in which of the following?

<p>Emission at lower energies or longer wavelengths (B)</p> Signup and view all the answers

What significant observation was made by Sir G.G. Stokes related to fluorescence?

<p>The energy of absorption is always higher than that of emission (D)</p> Signup and view all the answers

Which process occurs after a fluorophore absorbs light?

<p>It typically reaches thermal equilibrium quickly (B)</p> Signup and view all the answers

Which factor does NOT contribute to the Stokes shift?

<p>Structural change at ground state (C)</p> Signup and view all the answers

What primarily contributes to the flexibility of biological membranes?

<p>Noncovalent interactions among lipids (A)</p> Signup and view all the answers

At low temperatures, how do lipids in a bilayer behave?

<p>They form a semisolid gel phase. (B)</p> Signup and view all the answers

What is the status of trans-bilayer diffusion of lipids at physiological temperature?

<p>It occurs very slowly or not at all. (C)</p> Signup and view all the answers

What happens during lateral diffusion of lipids in the membrane?

<p>Lipids can occasionally jump over barriers. (B)</p> Signup and view all the answers

What is the main reason that trans-bilayer movement of lipids requires catalysis?

<p>It requires energy input to overcome a positive free-energy change. (D)</p> Signup and view all the answers

What technique is commonly used to measure the lateral diffusion of lipids?

<p>Fluorescence recovery after photobleaching (FRAP) (C)</p> Signup and view all the answers

What occurs at intermediate temperatures in lipid bilayers?

<p>Lipids exist in a liquid-ordered state. (C)</p> Signup and view all the answers

Why is it that lipid molecules in bilayers are not covalently anchored?

<p>To allow for lipid movement and flexibility. (B)</p> Signup and view all the answers

What is the primary mechanism by which solutes move from an area of higher concentration to an area of lower concentration across a membrane?

<p>Simple diffusion (A)</p> Signup and view all the answers

What term is used to describe the combined effect of transmembrane electrical gradients and concentration gradients on ion movement?

<p>Electrochemical gradient (B)</p> Signup and view all the answers

Which type of transporters bind substrates with high specificity but operate at lower transport rates?

<p>Carriers (C)</p> Signup and view all the answers

What is the role of ion-selective channels in the plasma membrane?

<p>To allow selective and rapid ion movement (D)</p> Signup and view all the answers

What is the result of rapid changes in ion channel activity in neurons?

<p>Changes in membrane potential (A)</p> Signup and view all the answers

How do ion pumps, such as the Na+ K+ ATPase, contribute to the function of a plasma membrane?

<p>They control ion permeability and concentrations (B)</p> Signup and view all the answers

During muscle contraction, which ions are released as a result of channel opening in the sarcoplasmic reticulum?

<p>Ca2+ ions (C)</p> Signup and view all the answers

What principle do the processes of solute movement adhere to, as reflected in the content?

<p>Second law of thermodynamics (B)</p> Signup and view all the answers

What defines the ability of a fluorophore to absorb and emit light?

<p>Photoreactivity (B)</p> Signup and view all the answers

Which of these is NOT listed as a key property of fluorophores?

<p>Solubility (C)</p> Signup and view all the answers

Which of the following is one of the applications of fluorophores?

<p>Fluorescence Microscopy (D)</p> Signup and view all the answers

What is the usual unit for measuring wavelength in the context of fluorophores?

<p>Nanometers (B)</p> Signup and view all the answers

Which of the following fluorophores is stated as being popular for antibody labeling?

<p>Fluorescein (D)</p> Signup and view all the answers

Derivatives of which of the following compounds are considered common fluorophores?

<p>Rhodamine (C)</p> Signup and view all the answers

What characteristic improvement is noted in the most recent generations of fluorophores?

<p>Higher brightness (B)</p> Signup and view all the answers

Which type of fluorophore is categorized under organic dyes?

<p>Fluorescent Dyes (C)</p> Signup and view all the answers

What is the primary phenomenon that FRET describes?

<p>Energy transfer without the emission of a photon (B)</p> Signup and view all the answers

Which factor does NOT influence the rate of energy transfer in FRET?

<p>Temperature of the environment (B)</p> Signup and view all the answers

The Förster distance is defined as the distance at which RET is what percentage efficient?

<p>50% (B)</p> Signup and view all the answers

In FRET, what is the state of the donor molecule when energy transfer occurs?

<p>In the excited state (B)</p> Signup and view all the answers

Which distance range typically indicates the Förster distance for FRET?

<p>20 to 60 Å (A)</p> Signup and view all the answers

What effect does a protease have on FRET between two fluorophores?

<p>Inhibits energy transfer (D)</p> Signup and view all the answers

How does the orientation of donor and acceptor molecules impact FRET efficiency?

<p>Optimal orientation increases energy transfer (A)</p> Signup and view all the answers

In what application is FRET commonly used?

<p>Studying protein-protein interactions (D)</p> Signup and view all the answers

Flashcards

Trans-bilayer diffusion

The movement of a lipid molecule from one leaflet of the bilayer to the other.

Membrane flexibility

The ability of a membrane to change shape without losing its integrity and becoming leaky.

Gel phase

The state of a lipid bilayer at relatively low temperatures where lipids form a semi-solid gel-like structure.

Liquid-disordered state

The state of a lipid bilayer at relatively high temperatures where individual hydrocarbon chains are in constant motion.

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Liquid-ordered state

The state of a lipid bilayer at intermediate temperatures where there is less thermal motion than in the liquid-disordered state, but lateral movement still occurs.

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Lateral diffusion

The movement of lipids within the plane of the bilayer.

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Fluorescence Recovery After Photobleaching (FRAP)

A technique used to measure the rate of lateral diffusion of lipids in a membrane.

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Lipid fences

Barriers that restrict the movement of lipids within the plane of the bilayer.

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Simple Diffusion

The movement of molecules from a region of high concentration to low concentration across a permeable membrane.

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Concentration Gradient

The difference in concentration of a solute across a membrane.

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Membrane Potential

The difference in electrical potential across a membrane.

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Electrochemical Gradient

The combined effect of the concentration gradient and membrane potential on the movement of ions across a membrane.

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Transporters

Membrane proteins that facilitate the movement of solutes across a membrane.

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Carriers

Transporters that bind their substrate with high specificity and catalyze transport at lower rates.

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Channels

Transporters that allow transmembrane movement at much faster rates, approaching unhindered diffusion.

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Ion-Selective Channels

Ion channels that allow the rapid movement of specific ions across membranes.

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Single Particle Tracking

A technique that allows scientists to track the movement of individual lipid molecules in a membrane within a very short timeframe.

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Protein Aggregation

The process of a cell membrane protein permanently attaching to a specific spot or forming a group with other proteins. These proteins then remain fixed, unable to move freely.

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Integral Membrane Proteins

Proteins that act like connectors between cells or between a cell and the surrounding environment.

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Integrins

A type of integral membrane protein with two different subunits that attach and can serve as both receptors and signal transmitters. They help transfer information across the cell membrane.

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Cadherins

A type of integral membrane protein that binds to similar proteins on adjacent cells, allowing for their attachment.

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Passive Transport

The movement of molecules across a membrane from an area of higher concentration to an area of lower concentration, not requiring any energy.

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Active Transport

The movement of molecules across a membrane from an area of lower concentration to an area of higher concentration, requiring energy.

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Ionophores

Small molecules that can act as 'carriers' for ions across a membrane. They mask the ion's charge, allowing them to pass through the lipid bilayer.

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Jablonski Diagram

A diagram showing the energy levels of a fluorophore, including electronic and vibrational states.

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Light Absorption

The process where a molecule absorbs light and jumps to a higher energy state.

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Light Emission

The process where a molecule emits light as it transitions to a lower energy state.

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Stokes Shift

The difference in energy between the absorbed and emitted light, resulting in a longer wavelength (lower energy) emission.

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Vibrational Relaxation

The process where a molecule loses energy by returning to the lowest vibrational level of the excited state.

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Spectrofluorometer

A specialized instrument that measures both the absorption and emission of light by a sample.

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Emission Spectrum

A spectrum showing the intensity of light emitted at different wavelengths when the sample is excited at a fixed wavelength.

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Absorption Spectrum

A spectrum showing the intensity of emitted light at a fixed wavelength as the excitation wavelength is varied.

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What is a fluorophore?

A molecule that absorbs light energy and then emits light at a longer wavelength. These are useful for tagging and visualizing cells, molecules, and proteins

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What is Excitation Wavelength?

The wavelength of light that a fluorophore absorbs to become excited.

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What is Emission Wavelength?

The wavelength of light that a fluorophore emits after being excited.

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What is Quantum Yield?

A measure of the efficiency of a fluorophore in converting absorbed light energy into emitted light.

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What is Photostability?

The ability of a fluorophore to withstand repeated excitation without degrading.

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What is pH sensitivity?

A fluorophore's ability to emit light at different wavelengths depending on its environment. For example, its pH.

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What is Fluorescence Microscopy?

A technique that uses fluorescence to visualize and analyze cells and molecules.

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What is Flow Cytometry?

A technique that uses fluorescence to identify, count, and sort cells and particles.

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FRET (Fluorescence Resonance Energy Transfer)

A technique that uses the interaction of fluorescent molecules to measure distances between them. It relies on the transfer of energy from a donor molecule in the excited state to an acceptor molecule in the ground state without the emission of a photon.

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Förster distance

The distance at which the efficiency of FRET is 50%.

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FRET to show protein-protein interactions

A type of FRET that occurs when two proteins come close enough together through binding, allowing the fluorescent proteins attached to them to interact and transfer energy.

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Atomic Force Microscopy (AFM)

A microscopy technique that scans a sharp tip across a surface to create a 3D image. It can visualize membrane proteins by detecting the force exerted by them on the probe.

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AFM to visualize membrane proteins

The use of AFM to visualize membrane proteins. The tip scans the surface and detects the force exerted by proteins on the probe.

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Rate of energy transfer in FRET

A phenomenon where the rate of energy transfer between donor and acceptor molecules in FRET depends on their distance, the spectral overlap between their emission and absorption spectra, and the relative orientation of their transition dipoles.

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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 are not covalently anchored to each other.
  • Membrane dynamics involve various lipid motions.
  • Lipid bilayer structure is stable, individual phospholipid and sterol molecules have freedom of motion.

Lipid States

  • At low temperatures, lipids form a semisolid gel phase (paracrystalline).
  • At high temperatures, lipids are in constant motion, forming a liquid-disordered (fluid) state.
  • At intermediate temperatures, lipids exist in a liquid-ordered state, showing less thermal motion in acyl chains, but still allowing lateral movement.

Trans-bilayer Lipid Movement

  • Trans-bilayer ("flip-flop") movement of lipids is slow at physiological temperatures, as polar or charged head groups must leave the aqueous environment and enter the hydrophobic interior.
  • Trans-bilayer movement requires significant energy input.

Lateral Lipid Diffusion

  • Lipids and proteins diffuse laterally in the membrane.
  • Fluorescence recovery after photobleaching (FRAP) shows this lateral movement.
  • Lipids move as if corralled by fences, occasionally jumping regions.
  • Many membrane proteins are mobile.
  • Single-particle tracking visually confirms this lateral movement.

Membrane Protein Aggregates

  • Some membrane proteins aggregate to create patches on a cell surface.
  • Protein molecules do not move relative to each other within the patches.
  • Acetylcholine receptors form dense patches on neuron plasma membranes in synapses.

Integral Proteins and Cell Interactions

  • Integral proteins mediate cell-cell interactions and adhesion.
  • Integrins are heterodimeric and anchored to the plasma membrane by a hydrophobic transmembrane helix.
  • Integrins are not just adhesives, but also act as signal transducers.
  • Other families, like cadherins, undergo homophilic interactions with identical cadherins in adjacent cells.
  • Immunoglobulin-like proteins and selectins are involved in cell-cell interactions.

Solute Transport Across Membranes

  • Membrane proteins facilitating solute diffusion are called transporters or permeases.
  • Transporters bind substrates with high stereospecificity and catalyze transport, occurring below free diffusion rates.
  • Channels allow rapid transmembrane movement, nearly at the limit of unhindered diffusion.

Ion Selective Channels

  • Ion-selective channels facilitate ion movement across membranes.
  • Channels, along with ion pumps (e.g., Na+/K+ ATPase), regulate ion concentrations and membrane potential.
  • Rapid channel activity changes cause membrane potential changes in neurons (e.g., action potentials).
  • Ca²⁺ channel opening in myocytes triggers muscle contraction.

Fluorescence Resonance Energy Transfer (FRET)

  • FRET is an electrodynamic phenomenon explaining energy transfer between molecules.
  • FRET occurs between a donor (excited) molecule and an acceptor (ground) molecule.
  • Donor emission wavelengths often overlap with acceptor absorption wavelengths.
  • Energy transfer happens without photon appearance, through dipole-dipole interactions.
  • The rate of energy transfer depends on spectral overlap, donor quantum yield, dipole orientation, and distance.
  • FRET is used to analyze protein-protein interactions.

Atomic Force Microscopy (AFM)

  • AFM is used for visualizing membrane proteins.
  • A sharp cantilever tip is scanned over a surface.
  • Electrostatic and van der Waals forces between tip and surface are measured.
  • The technique can visualize features down to the nanometer scale.

Other topics

  • Jablonski diagrams explain light absorption and emission processes.
  • Fluorophores absorb and emit light in predictable ways and are used for various applications, like labeling compounds and visualizing cellular structures.
  • The Stokes shift describes the difference between excitation and emission wavelengths in fluorescence.
  • Spectrofluorometers measure fluorescence and absorption spectra.

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Membrane Dynamics PDF

Description

Test your knowledge on key concepts related to membrane dynamics and cell adhesion. This quiz covers topics including single particle tracking, integrins, cadherins, and transport mechanisms across the plasma membrane. Assess your understanding of the roles different proteins play in cellular interactions.

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