ATP-Driven Pumps in Cellular Transport
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Questions and Answers

What determines the diffusion rate of a molecule across a protein-free lipid bilayer?

  • The charge of the molecule
  • The concentration of the molecule
  • The shape of the molecule
  • The size and hydrophobicity of the molecule (correct)

    • What is the primary function of ATP-driven pumps?

  • To pump ions or other solutes across a membrane (correct)
  • To synthesize ATP from ADP and phosphate
  • To regulate gene expression
  • To generate energy for the cell

    • Why are protein-free lipid bilayers essentially impermeable to charged molecules?

  • Because of their shape
  • Because of their hydrophobicity
  • Because of their large size
  • Because of their high degree of hydration (correct)

    • What is the characteristic of P-type pumps?

    <p>They are structurally and functionally related to multipass transmembrane proteins</p> Signup and view all the answers

    What is a characteristic of transporter proteins?

    <p>They bind to specific solutes and undergo conformational changes</p> Signup and view all the answers

    What is the primary function of channel proteins?

    <p>To form a pore across the bilayer for specific solutes</p> Signup and view all the answers

    What is the function of V-type proton pumps?

    <p>To acidify the interior of organelles</p> Signup and view all the answers

    What is the advantage of ion channels over transporters?

    <p>They are faster and can pass up to 100 million ions per second</p> Signup and view all the answers

    What is the main difference between transporter and channel proteins?

    <p>Their function and mechanism of transport</p> Signup and view all the answers

    Which of the following molecules would be most likely to diffuse across a protein-free lipid bilayer?

    <p>A small, hydrophobic molecule</p> Signup and view all the answers

    What is the primary function of ion channels?

    <p>To allow specific inorganic ions to diffuse rapidly down their electrochemical gradients</p> Signup and view all the answers

    What is the characteristic of aquaporins?

    <p>They allow water to move more rapidly</p> Signup and view all the answers

    What is the role of conformational changes in transporter proteins?

    <p>To facilitate transport of the solute across the bilayer</p> Signup and view all the answers

    Why are protein-free lipid bilayers important for understanding membrane transport?

    <p>They demonstrate the principles of membrane transport</p> Signup and view all the answers

    What is the difference between ATP-driven pumps and ion channels?

    <p>ATP-driven pumps are involved in active transport, while ion channels are involved in passive transport</p> Signup and view all the answers

    What is the primary function of ABC transporters?

    <p>To pump small organic molecules across the cell membrane</p> Signup and view all the answers

    What happens during facilitated diffusion?

    <p>The solute moves through the lipid bilayer directly</p> Signup and view all the answers

    What is the main difference between passive and active transport?

    <p>The energy required for transport</p> Signup and view all the answers

    What is the role of a conformational change in a transporter?

    <p>To mediate passive transport</p> Signup and view all the answers

    What is the purpose of ATP-driven pumps?

    <p>To drive active transport</p> Signup and view all the answers

    What is the characteristic of uniporters?

    <p>They facilitate the passive movement of a single solute</p> Signup and view all the answers

    What problem do water channels in the kidney and exocrine cells need to solve?

    <p>To allow the rapid passage of water molecules while maintaining ion gradients</p> Signup and view all the answers

    What is the difference between symporters and coupled transporters?

    <p>The number of solutes transported</p> Signup and view all the answers

    What is a characteristic of ion channels that distinguishes them from aqueous pores?

    <p>Their ion selectivity</p> Signup and view all the answers

    How can active transport be driven?

    <p>By either ATP-driven pumps or ion-concentration gradients</p> Signup and view all the answers

    What is the function of gated channels in ion channels?

    <p>To open and close briefly to regulate ion flow</p> Signup and view all the answers

    What is the role of a transporter in active transport?

    <p>To couple uphill transport to the hydrolysis of ATP</p> Signup and view all the answers

    What type of gated channel is opened by a mechanical stress?

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

    What is the main contributor to the membrane potential in animal cells?

    <p>The K+ gradient across the plasma membrane</p> Signup and view all the answers

    What is the result of a difference in electrical charge on the two sides of a membrane?

    <p>A membrane potential</p> Signup and view all the answers

    What is the purpose of ion channels?

    <p>To allow the passage of ions across the membrane</p> Signup and view all the answers

    What is an example of a mechanically gated channel?

    <p>A bacterial mechanosensitive channel</p> Signup and view all the answers

    Study Notes

    ATP-Driven Pumps

    • ATP-driven pumps are also called transport ATPases, which hydrolyze ATP to ADP and phosphate and use the energy released to pump ions or other solutes across a membrane.
    • There are four types of ATP-driven pumps: P-type, ABC transporters, V-type, and F-type ATPases.

    P-Type Pumps

    • P-type pumps are structurally and functionally related to multipass transmembrane proteins.
    • They are called "P-type" because they phosphorylate themselves during the pumping cycle.
    • This class includes many of the ion pumps that set up and maintain gradients of Na+, K+, H+, and Ca2+ across cell membranes.

    ABC Transporters

    • ABC transporters primarily pump small organic molecules across cell membranes.

    V-Type Pumps

    • V-type pumps are turbine-like protein machines constructed from multiple different subunits.
    • The V-type proton pump transfers H+ into organelles, such as lysosomes, synaptic vesicles, and plant or yeast vacuoles to acidify the interior of these organelles.

    F-Type ATPases

    • F-type ATPases are found in mitochondria and chloroplasts.

    Ion Channels

    • Most channels in the plasma membrane of animal and plant cells that connect the cytosol to the cell exterior have narrow, highly selective pores that can open and close rapidly.
    • Ion channels are concerned specifically with inorganic ion transport.
    • They have an advantage over transporters, as they can pass up to 100 million ions through one open channel each second – a rate 10^5 times greater than even the fastest transporter.
    • Ion channels cannot be coupled to an energy source to perform active transport, so the conductance they mediate is always passive (downhill).

    Aquaporins

    • Aquaporins (water channels) allow water to move more rapidly.

    Protein-Free Lipid Bilayers

    • Protein-free lipid bilayers are impermeable to charged molecules (ions), regardless of size, due to their charge and high degree of hydration.
    • The smaller the molecule and the less strongly it associates with water, the more rapidly it diffuses across the bilayer.

    Transport Proteins

    • There are two main classes of membrane transport proteins: transporters and channels.
    • Transporters alternate between two conformations, allowing the solute-binding site to be sequentially accessible on one side of the bilayer and then on the other.
    • Channels form continuous pores across the bilayer, allowing specific solutes to pass through at a much faster rate.

    Active Transport

    • Active transport is mediated by transporters coupled to an energy source.
    • It involves movement of the solute against its concentration or electrochemical gradient and requires an input of metabolic energy.

    Conformational Change in Transporters

    • A conformational change in a transporter mediates the passive movement of a solute.
    • The transporter has three conformational states: outward-open, occluded, and inward-open states.

    Three Ways of Driving Active Transport

    • Coupled transporters harness the energy stored in concentration gradients to couple the uphill transport of one solute to the downhill transport of another.
    • ATP-driven pumps couple uphill transport to the hydrolysis of ATP.

    Uniporters, Symporters, and Coupled Transport

    • Uniporters facilitate the passive movement of a single solute from one side of the membrane to the other.
    • Symporters (co-transporters) involve the transfer of one solute strictly dependent on the transport of a second solute in the same direction.
    • Coupled transport involves the intimately coupled transfer of two solutes in the same direction.

    Ion Channels

    • Ion channels are ion-selective and fluctuate between open and closed states.
    • They have two important properties: ion selectivity, permitting some inorganic ions to pass but not others, and gating, which allows them to open briefly and then close again.
    • Voltage-gated channels are gated by a change in the voltage across the membrane.
    • Mechanically gated channels are gated by a mechanical stress.
    • Ligand-gated channels are gated by the binding of a ligand.

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    Molecular Biology of the Cell Chapter 11 PDF

    Description

    This quiz covers ATP-driven pumps, also known as transport ATPases, which use ATP hydrolysis to pump ions and solutes across cell membranes. It focuses on P-type pumps, including ion pumps responsible for setting up and maintaining ionic gradients.

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