Cell Transport
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Questions and Answers

What is the primary function of cell transport?

  • To regulate cell growth
  • To store genetic information
  • To synthesize proteins
  • To facilitate the movement of substances across the cell membrane (correct)

    • What type of substances can readily pass through a phospholipid bilayer?

  • Carbohydrates
  • Proteins
  • Lipid-soluble substances (correct)
  • Water-soluble substances

    • Which of the following is a characteristic of the cell membrane?

  • Porously permeable barrier
  • Permeable barrier
  • Semi-permeable barrier (correct)
  • Impermeable barrier

    • What is the term for the movement of water molecules through the cell membrane?

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

    What is the process of transporting substances out of the cell through the cell membrane?

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

    What is the role of membrane proteins in cell transport?

    <p>To provide an alternative pathway across the lipid bilayer</p> Signup and view all the answers

    What is the characteristic of facilitated diffusion?

    <p>Rate of transport is directly proportional to the concentration of the diffusing substance</p> Signup and view all the answers

    What is the main difference between simple diffusion and facilitated diffusion?

    <p>Simple diffusion occurs through the lipid bilayer, while facilitated diffusion occurs through specific proteins</p> Signup and view all the answers

    What is the term for the minimum pressure required to stop osmosis?

    <p>Osmotic pressure</p> Signup and view all the answers

    What is the primary function of aquaporins in the cell?

    <p>To facilitate the transport of water across the membrane</p> Signup and view all the answers

    What is the characteristic of active transport?

    <p>Molecules move against their concentration gradient</p> Signup and view all the answers

    What is the primary function of facilitated diffusion proteins?

    <p>To allow molecules to pass through the membrane</p> Signup and view all the answers

    What is the main characteristic of ion channels?

    <p>They are highly selective and allow passage of specific ions or molecules</p> Signup and view all the answers

    What is the purpose of aquaporins?

    <p>To allow water molecules to cross the membrane rapidly</p> Signup and view all the answers

    What is the main difference between voltage-gated and ligand-gated channels?

    <p>Voltage-gated channels open in response to changes in voltage, while ligand-gated channels open in response to ligand binding</p> Signup and view all the answers

    What is the energy source for primary active transport?

    <p>Breakdown of ATP or similar</p> Signup and view all the answers

    What is the mechanism of secondary active transport?

    <p>The transport of molecules using the energy from the concentration gradient of the driving ion</p> Signup and view all the answers

    What is the difference between symport and antiport?

    <p>Symport is the transport of two substances in the same direction, while antiport is the transport of two substances in opposite directions</p> Signup and view all the answers

    What is the purpose of transcellular transport?

    <p>To transport substances across the cell from one ECF compartment to another</p> Signup and view all the answers

    What is the mechanism of receptor-mediated endocytosis?

    <p>The binding of ligands to specific receptors on the cell surface</p> Signup and view all the answers

    What is the difference between constitutive secretion and regulated secretion?

    <p>Constitutive secretion does not need a signal, while regulated secretion needs a signal</p> Signup and view all the answers

    What is the primary function of the cell membrane as a barrier to substance movement?

    <p>To regulate the passage of substances into and out of the cell</p> Signup and view all the answers

    Which type of transport does not require energy input to occur?

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

    What determines the permeability of the cell membrane to certain substances?

    <p>The lipid solubility of the substance</p> Signup and view all the answers

    What is the primary function of osmosis in cell transport?

    <p>To maintain the balance of water and solutes within the cell</p> Signup and view all the answers

    What is the process by which cells take in external substances?

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

    Which type of transport does not require the cell to expend energy?

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

    What is the primary function of carrier proteins in facilitated diffusion?

    <p>To bind to molecules or ions and facilitate their transport across the membrane</p> Signup and view all the answers

    What determines the rate of simple diffusion across a membrane?

    <p>The lipid solubility of the substance</p> Signup and view all the answers

    Which type of molecules can diffuse directly through the lipid bilayer?

    <p>Small hydrophobic molecules</p> Signup and view all the answers

    What is the maximum rate of transport achieved by a carrier protein in facilitated diffusion?

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

    What is the primary function of carrier proteins in facilitated diffusion?

    <p>To bind to specific molecules and facilitate their passage across the membrane</p> Signup and view all the answers

    What is the characteristic of ion channels that allows them to be selective?

    <p>Their ability to allow only specific ions to pass through</p> Signup and view all the answers

    What is the function of aquaporins in the cell membrane?

    <p>To allow water molecules to cross the membrane more rapidly</p> Signup and view all the answers

    What is the term for the simultaneous transport of two substances across a membrane in the same direction?

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

    What is the primary function of voltage-gated channels?

    <p>To mediate the passage of ions across the plasma membrane in response to changes in voltage</p> Signup and view all the answers

    What is the mechanism of transcellular transport?

    <p>Active transport through the cell membrane on one side and facilitated diffusion on the other</p> Signup and view all the answers

    What is the function of receptor-mediated endocytosis?

    <p>To internalize specific molecules bound to receptors</p> Signup and view all the answers

    What is the primary function of ion channels in the plasma membrane?

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

    What is the term for the process of transporting molecules out of the cell through the cell membrane using part of the membrane itself as a carrier?

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

    What is the primary function of constitutive secretion?

    <p>To incorporate proteins into the plasma membrane or extracellular matrix</p> Signup and view all the answers

    What is the main function of the cell membrane in terms of substance movement?

    <p>To act as a semi-permeable barrier</p> Signup and view all the answers

    What is the characteristic of substances that can readily pass through a phospholipid bilayer?

    <p>They are lipid-soluble</p> Signup and view all the answers

    What is the purpose of the transport of substances across the cell membrane?

    <p>To maintain cellular homeostasis</p> Signup and view all the answers

    What is the key difference between passive and active transport?

    <p>The energy requirement</p> Signup and view all the answers

    What is the term for the movement of water molecules from an area of high concentration to an area of low concentration?

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

    What is the primary function of membrane proteins in cell transport?

    <p>To act as channels or carriers for molecule transport</p> Signup and view all the answers

    What determines the permeability of small hydrophobic molecules across the lipid bilayer?

    <p>The lipid solubility of the molecule</p> Signup and view all the answers

    What is the characteristic of facilitated diffusion that distinguishes it from simple diffusion?

    <p>It is specific to certain molecules or ions</p> Signup and view all the answers

    What is the role of aquaporins in the cell membrane?

    <p>To act as channels for the transport of water molecules</p> Signup and view all the answers

    What is the term for the movement of water molecules from an area of high concentration to an area of low concentration?

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

    What is the maximum rate of transport achieved by a carrier protein in facilitated diffusion?

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

    What is the primary mechanism of facilitated diffusion?

    <p>Passive transport with the help of carrier proteins</p> Signup and view all the answers

    What is the characteristic of ion channels that allows them to be selective?

    <p>All of the above</p> Signup and view all the answers

    What is the primary function of aquaporins?

    <p>To transport water molecules across the cell membrane</p> Signup and view all the answers

    What is the primary function of voltage-gated channels?

    <p>To transmit information along the length of a neuron</p> Signup and view all the answers

    What is the primary mechanism of receptor-mediated endocytosis?

    <p>The binding of a ligand to a specific receptor</p> Signup and view all the answers

    What is the primary function of facilitated diffusion proteins?

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

    What is the primary function of secondary active transport?

    <p>To couple the movement of an ion down its electrochemical gradient to the uphill movement of another molecule</p> Signup and view all the answers

    What is the primary function of ion channels in the plasma membrane?

    <p>To regulate the amount of ions in the cell</p> Signup and view all the answers

    What is the primary function of transcellular transport?

    <p>To transport molecules from one ECF compartment to another</p> Signup and view all the answers

    What is the primary function of constitutive secretion?

    <p>To transport molecules out of the cell without the need for a signal</p> Signup and view all the answers

    Study Notes

    Cell Transport

    • Cell transport is the movement of substances through the cell membrane.
    • The majority of biochemicals do not pass readily through a phospholipid bilayer, a semi-permeable barrier.

    Passive Transport (Diffusion)

    • Molecules move down their concentration gradient.
    • No cellular energy is required; uses kinetic energy.
    • Types of passive transport:
    • Simple Diffusion
      • Through the lipid bilayer (e.g., osmosis, diffusion of water)
      • No specific protein is needed
      • Rate of diffusion is directly proportional to the lipid solubility of the substance
    • Facilitated Diffusion
      • Through carriers or transporters
      • Specific proteins facilitate diffusion across the membrane
      • No cellular energy is required
      • Carrier/Channel only acts upon specific substrates
      • Rate of transport will reach a maximum based on the number of carriers available in the membrane

    Osmosis

    • The net movement of water caused by a concentration difference of water across a membrane.
    • Water can diffuse through the lipid bilayer and through selective protein channels called aquaporins.
    • Aquaporins are highly specialized, with at least 13 types in various cell types of mammals.
    • Pressure can also influence water diffusion.
    • The amount of pressure required to stop osmosis is called OSMOTIC PRESSURE.

    Active Transport

    • Molecules move against their concentration gradient.
    • Uses cellular energy to move molecules.
    • Types of active transport:
    • Primary Active Transport
      • Energy is derived directly from the breakdown of ATP or similar.
      • Transport is against a concentration/electrochemical gradient.
    • Secondary Active Transport
      • Energy is provided by the concentration gradient of the driving ion.
      • Transporter protein couples the movement of an ion (typically Na+ or H+) down its electrochemical gradient to the uphill movement of another molecule or ion against a concentration/electrochemical gradient.
      • CO-TRANSPORT or SYMPORT: The simultaneous transport of two substances across a membrane in the same direction.
      • COUNTER-TRANSPORT or ANTIPORT: The simultaneous transport of two substances across a membrane in opposite directions.

    Transcellular or Epithelial Transport

    • In some places of the body, substances must be transported across the cell from one ECF compartment to another.
    • Basic mechanism: Active transport through the cell membrane on one side, either simple diffusion or facilitated diffusion through the membrane on the opposite side.

    Endocytosis and Exocytosis

    • Impermeable molecules can be transported across the membrane by means other than membrane proteins, using part of the membrane itself as a carrier.

    • Endocytosis:

    • PHAGOCYTOSIS: Ingestion of large particles.

    • PINOCYTOSIS: Ingestion of small particles.

    • RECEPTOR MEDIATED ENDOCYTOSIS (e.g., Cholesterol).

    • Exocytosis:

    • CONSTITUTIVE SECRETION: All cells, no signal sequence, proteins are incorporated into the plasma membrane, and extracellular matrix or are signaling proteins.

    • REGULATED SECRETION: Specialized cells, need signal to stimulate fusion and release to the cell exterior.### Carrier Proteins

    • Responsible for facilitated diffusion of sugars, amino acids, and nucleosides

    • Bind to specific molecules, undergo conformational changes, and allow the molecule to pass

    • Facilitated diffusion proteins

    Channels

    • Open pores in the membrane, allowing ions and small hydrophilic molecules to pass
    • Many protein channels are highly selective, allowing passage of only one or a few specific ions or molecules
    • Selectivity comes from characteristics like diameter, shape, and nature of electrical charges and bonds along the inside surface

    Aquaporins

    • Water channels through which water molecules can cross the membrane much more rapidly than they can diffuse through the phospholipid bilayer
    • Increase speed of diffusion

    Ion Channels

    • Mediate the passage of ions across the plasma membrane
    • The gate of the channel controls ion permeability
    • Some are always open (leak channels), while others have gates
    • Several kinds of stimuli can open ion-gated channels, including changes in voltage, ligand binding, and mechanical stimuli

    Voltage-Gated Channels

    • Present in the plasma membrane of all excitable cells (nerve, muscle, endocrine, and egg cells)
    • Responsible for the neuron's ability to transmit information along its length and to release neurotransmitters
    • There is a range of membrane potentials that cause them to open
    • Channel's threshold is the minimum membrane potential that causes the opening of the channel

    Ligand-Gated Channels

    • Found in the membrane of skeletal muscle cells, some neurons of the autonomic nervous system, and brain
    • Channel opens in response to ligand binding
    • Example: Acetylcholine released from a neuron binds to Nicotinic Acetylcholine Receptor in skeletal muscle cells at the neuromuscular junction

    Active Transport

    • Primary active transport: energy is derived directly from the breakdown of ATP or similar
    • Transport is against a concentration/electrochemical gradient

    Secondary Active Transport

    • Energy is provided by the concentration gradient of the driving ion
    • Transporter protein couples the movement of an ion (typically Na+ or H+) down its electrochemical gradient to the uphill movement of another molecule or ion against a concentration/electrochemical gradient

    Co-Transport and Counter-Transport

    • Co-transport (or symport): the simultaneous transport of two substances across a membrane in the same direction
    • Example: Na+-D-Glucose co-transporter (SGLT-1)
    • Counter-transport (or antiport): the simultaneous transport of two substances across a membrane in opposite directions
    • Example: Na+ H+ antiporter in the kidney

    Transcellular or Epithelial Transport

    • In some places of the body, substances must be transported across the cell from one ECF compartment to another
    • Basic mechanism: active transport through the cell membrane on one side, and either simple diffusion or facilitated diffusion through the membrane on the opposite side

    Endocytosis and Exocytosis

    • Impermeable molecules can be transported across the membrane by means other than membrane proteins
    • Using part of the membrane itself as a carrier

    Endocytosis

    • Phagocytosis: ingestion of large particles
    • Pinocytosis: ingestion of small particles
    • Receptor-mediated endocytosis: example, cholesterol

    Exocytosis

    • Constitutive secretion: all cells, no signal sequence, proteins are incorporated into the plasma membrane, and extracellular matrix or are signaling proteins
    • Regulated secretion: specialized cells, need signal to stimulate fusion and release to the cell exterior

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    Related Documents

    Molecular and Cellular Bases of Physiology L02 - Summer 24 PDF

    Description

    Learn about the different types of cell transport, including passive and active transport, osmosis, endocytosis, and exocytosis. Understand how cells move molecules across their membranes and the processes involved.

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