Cell Membrane Structure and Transport
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Questions and Answers

What is the most common type of movement of phospholipids in the cell membrane?

  • Flip-flop movement between monolayers
  • Lateral diffusion within the same monolayer (correct)
  • Movement aided by external forces
  • Rotation around their long axis

    • Which factor does NOT influence the fluidity of the cell membrane?

  • Temperature
  • Chemical structure of phospholipid tail
  • Size of the cell (correct)
  • Hydrophobic interactions

    • What is the rare type of phospholipid movement that involves transitioning between monolayers?

  • Flip-flop (correct)
  • Lateral diffusion
  • Tail flexion
  • Hydrophobic interaction

    • What effect do tightly packed hydrocarbon tails have on membrane fluidity?

    <p>Decrease fluidity due to hydrophobic interactions</p> Signup and view all the answers

    Which movement of phospholipids occurs at a rapid rate and involves the rotation around their long axis?

    <p>Tail flexion</p> Signup and view all the answers

    What is the primary function of the cell membrane?

    <p>To protect and enclose the cell</p> Signup and view all the answers

    Which of the following statements regarding the lipid bilayer is true?

    <p>Hydrophobic tails aggregate away from water.</p> Signup and view all the answers

    What percentage of the cell membrane is primarily made up of proteins?

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

    What allows membrane lipids and proteins to exhibit fluidity?

    <p>The ability to move freely within the membrane</p> Signup and view all the answers

    Which type of membrane has a double lipid bilayer?

    <p>Nucleus</p> Signup and view all the answers

    In the composition of the cell membrane, what are glycoproteins and glycolipids primarily made of?

    <p>Carbohydrates attached to proteins and lipids</p> Signup and view all the answers

    What is the effect of increased cholesterol in the cell membrane?

    <p>Increases membrane rigidity</p> Signup and view all the answers

    Which component of the cell membrane is primarily responsible for its semi-permeable nature?

    <p>Phospholipid arrangement in the bilayer</p> Signup and view all the answers

    What do channels specifically allow to pass through the membrane?

    <p>Ions of a particular size and charge</p> Signup and view all the answers

    What type of channel opens in response to a change in voltage across the membrane?

    <p>Voltage-gated channel</p> Signup and view all the answers

    What is an example of a mechanism that controls ligand-gated channels?

    <p>Binding of a molecule (ligand)</p> Signup and view all the answers

    What best describes the resting membrane potential?

    <p>A voltage difference across the membrane typically between -20 to -200 mV</p> Signup and view all the answers

    How does passive transport occur across the cell membrane?

    <p>From regions of high concentration to low concentration without energy</p> Signup and view all the answers

    Which type of transport protein closely resembles enzyme-substrate binding?

    <p>Transporters</p> Signup and view all the answers

    What can cause mechanically-gated channels to open?

    <p>Mechanical force</p> Signup and view all the answers

    What drives the movement of molecules during diffusion across a membrane?

    <p>Concentration gradients</p> Signup and view all the answers

    Which ion has a higher concentration inside the cell compared to outside?

    <p>K+</p> Signup and view all the answers

    What characteristic is specifically attributed to transporters compared to channels?

    <p>They exhibit specificity for the solute they transport.</p> Signup and view all the answers

    What effect does high temperature have on the movement of phospholipids in a cell membrane?

    <p>Phospholipids move more freely, increasing fluidity.</p> Signup and view all the answers

    How do saturated fatty acids differ from unsaturated fatty acids in terms of molecular structure?

    <p>Saturated fatty acids only contain single bonds between carbons.</p> Signup and view all the answers

    What is the role of cholesterol in maintaining cell membrane fluidity?

    <p>Cholesterol acts as a buffer to reduce extreme changes in fluidity.</p> Signup and view all the answers

    What characteristic of cis-unsaturated fatty acids contributes to increased membrane fluidity?

    <p>They have a bent shape which creates space.</p> Signup and view all the answers

    Which type of membrane protein spans across the lipid bilayer?

    <p>Integral proteins</p> Signup and view all the answers

    What is one function of membrane carbohydrates?

    <p>They aid in cell-cell recognition.</p> Signup and view all the answers

    Why are ions unable to cross the lipid bilayer directly?

    <p>Ions require transporter proteins to cross.</p> Signup and view all the answers

    What happens to membrane fluidity at low temperatures when cholesterol is present?

    <p>Cholesterol prevents freezing and maintains fluidity.</p> Signup and view all the answers

    How do short hydrocarbon tails affect membrane fluidity?

    <p>They create less interaction, increasing fluidity.</p> Signup and view all the answers

    What role do transport proteins play in the cell membrane?

    <p>They facilitate the movement of hydrophilic molecules across the membrane.</p> Signup and view all the answers

    Which type of fatty acid would likely lead to a more viscous membrane?

    <p>Saturated fatty acids.</p> Signup and view all the answers

    What is a primary characteristic of peripheral membrane proteins?

    <p>They are loosely attached to the membrane surface.</p> Signup and view all the answers

    Why is membrane fluidity important for cell signaling?

    <p>It allows membrane proteins to diffuse and interact.</p> Signup and view all the answers

    What structure is responsible for creating a selectively permeable barrier in the cell membrane?

    <p>Lipid bilayer</p> Signup and view all the answers

    What type of molecules primarily utilize simple diffusion to cross the lipid bilayer?

    <p>Small non-polar molecules</p> Signup and view all the answers

    Which statement describes facilitated diffusion?

    <p>It requires membrane transport proteins for the passage of large polar molecules.</p> Signup and view all the answers

    What combination of forces determines the direction of passive transport for charged molecules?

    <p>Electrochemical gradient and concentration gradient</p> Signup and view all the answers

    What is the primary energy source utilized for active transport mechanisms?

    <p>ATP hydrolysis</p> Signup and view all the answers

    During osmosis, water moves from areas of:

    <p>Low solute concentration to high solute concentration</p> Signup and view all the answers

    What role do aquaporins play in cellular transport?

    <p>They facilitate the movement of water across the cell membrane.</p> Signup and view all the answers

    What results when the concentration gradient and membrane potential work in opposite directions for a charged ion?

    <p>Slow efflux of ions</p> Signup and view all the answers

    Which of the following is NOT a characteristic of passive transport?

    <p>It requires energy input.</p> Signup and view all the answers

    Which molecules primarily require facilitated diffusion to cross the lipid bilayer?

    <p>Large polar molecules and ions</p> Signup and view all the answers

    Which process requires the use of special transporter proteins called pumps?

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

    Study Notes

    Cell Membrane Structure and Transport

    • Cell membranes are protective layers surrounding all cells.
    • Composed of lipids, proteins, and carbohydrates.
    • Semi-permeable; some molecules pass through, others do not.

    Lecture Objectives

    • Understand the basic structure and composition of the cell membrane.
    • Understand the lipid bilayer structure and factors influencing fluidity.
    • Understand the different mechanisms of molecule transport across membranes.

    Cell Membrane Composition

    • Lipids (40%): Phospholipids and cholesterol arrange in a bilayer.
    • Proteins (50%): Embedded in the bilayer, performing various functions.
    • Carbohydrates (10%): Attached to proteins (glycoproteins) and lipids (glycolipids), extending from the membrane surface.

    Organelle Membranes

    • Intracellular organelles also have membranes with lipid bilayers.
    • Compositions slightly differ from cell membranes.
    • Nucleus and mitochondria have double lipid bilayers.
    • Endoplasmic reticulum, Golgi, and lysosomes have single lipid bilayers.

    Lipid Bilayer Structure

    • Phospholipids and cholesterol are the main components.
    • Hydrophilic heads face water; hydrophobic tails face away from water, aggregating together.
    • This arrangement forms a bilayer.

    Phospholipids and Cholesterol

    • Phospholipids have a hydrophilic head and hydrophobic tails.
    • Cholesterol regulates membrane fluidity.

    Cell Membrane Lipid Bilayer

    • Membrane lipids are exposed to two forces: attraction to water by the hydrophilic heads, and hydrophobic tails avoiding water.
    • Formation of bilayer: Hydrophilic heads face water on both sides; hydrophobic tails stay within the bilayer interior.

    Cell Membrane Fluidity

    • Membrane lipids and proteins move freely within the membrane.
    • This creates a fluid structure.
    • Fluidity depends on factors such as temperature, phospholipid tail structure, and cholesterol levels.

    Cell Membrane Phospholipid Movement

    • Phospholipids move and change places within the same monolayer (lateral diffusion) catalyzed by enzymes.
    • Lipid molecules flex their tails and rotate rapidly around their long axes.
    • Flip-flop (movement from one monolayer to the other) is rare.
    • Fluidity depends on how tightly hydrocarbon tails pack together.

    Factors Determining Cell Membrane Fluidity

    • Temperature.
    • Chemical structure of phospholipid tails (saturated vs. unsaturated).
    • Cholesterol levels.

    Effect of Temperature

    • High temperatures increase fluidity as phospholipids have more energy to move and create spaces between them.
    • Low temperatures decrease fluidity as phospholipids have less energy, pack closely, and interact more strongly, reducing movement.

    Saturated vs. Unsaturated Fatty Acids

    • Saturated fatty acids have only single bonds and are usually solid at room temperature.
    • Unsaturated fatty acids contain double bonds, creating bends, and are typically liquid at room temperature.
    • Saturated fatty acids pack tightly; unsaturated fatty acids create spaces between them.

    Effect of Phospholipid Structure

    • Length of hydrocarbon tails.
    • Short hydrocarbon tails interact less increasing fluidity.
    • Double bonds in hydrocarbon chains cause bends increasing fluidity.

    Effect of Cholesterol

    • Cholesterol fits between phospholipid molecules.
    • Regulates membrane fluidity.
    • Acts as a buffer preventing extreme changes in fluidity at low and high temperatures.
    • At high temperatures, cholesterol reduces fluidity and prevents melting.
    • At low temperatures, cholesterol increases fluidity and prevents freezing.

    Importance of Cell Membrane Fluidity

    • Enables cells to adapt their shape and movement to different conditions.
    • Enables membrane proteins to diffuse and interact.
    • Ensures membrane molecules are distributed evenly between daughter cells when cells divide.
    • Allows membranes to fuse, e.g., vesicles fusing with each other.

    Membrane Proteins and Carbohydrates

    • Proteins are embedded in the membrane (integral or peripheral).
    • Integral proteins span the membrane, embedded in the lipid bilayer.
    • Peripheral proteins are attached to the membrane surface.
    • Proteins perform various functions: Transport, Receptors, Enzymes, Anchors

    Membrane Carbohydrates

    • Some lipids have sugars (glycolipids) attached to them.
    • Most membrane proteins have sugars attached (glycoproteins).
    • Important for protection, lubrication, and cell recognition.

    Membrane Transport Proteins

    • Cells and organelles must allow the passage of hydrophilic molecules such as inorganic ions, sugars, amino acids, and nucleotides.
    • Vital for metabolism and function.

    Types of Transport Proteins

    • Channels: Allow ions of a particular size and charge to pass; need to be open.
    • Transporters: Transport specific molecules that fit specific binding sites on the protein.
    • These are similar to enzyme-substrate interactions.

    The Cell Membrane is Semi-Permeable

    • The hydrophobic interior of the lipid bilayer stops most hydrophilic molecules from passing.
    • Lipid bilayer is selective.
    • Small, non-polar molecules (O2, CO2, N2, steroid hormones) cross rapidly.
    • Small polar molecules (H2O, ethanol) cross slowly.
    • Large polar molecules (glucose, amino acids) and ions cross extremely slowly, if at all, and need transporter proteins.

    Passive Transport

    • Molecules move from high to low concentration regions without energy.
    • Two types:
      • Simple diffusion: Small, non-polar molecules (e.g., gases) directly cross the lipid bilayer.
      • Facilitated diffusion: Large polar molecules and ions cross the lipid bilayer with the help of membrane transport proteins

    Passive Transport of Charged Molecules

    • For charged molecules, two forces determine the direction of transport:
      • Resting membrane potential: The inside of the cell is more negatively charged, attracting positively charged molecules.
      • Concentration gradient: Ions move from high to low concentration regions.

    Active Transport

    • Molecules move against their concentration gradient (from low to high concentration) requiring energy and pumps.
    • Facilitated by specialized transporter proteins (pumps).
    • Energy obtained from ATP hydrolysis or electrochemical gradients.

    Summary of Membrane Transport

    • Passive transport (simple diffusion, facilitated diffusion)
    • Active Transport

    Osmosis

    • Crucial for water movement inside cells.
    • Movement of water across the membrane is slow without special proteins called aquaporins.
    • Water moves from low solute concentration to high solute concentration (across the membrane).

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    Description

    Explore the intricate structure of cell membranes, including their lipid and protein compositions. This quiz covers the mechanisms of transport and the unique features of organelle membranes. Test your knowledge on how these components function to protect and regulate cells.

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