Active Transport Mechanisms in Cells
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Questions and Answers

What is the main function of the rough endoplasmic reticulum?

  • Synthesize lipids for cellular membranes
  • Synthesize and release new proteins (correct)
  • Conduct the synthesis of ATP
  • Store calcium ions for muscular contraction
  • What modification occurs to proteins within the endoplasmic reticulum?

  • Post-translational modifications (correct)
  • Phosphorylation to recycle ADP
  • Enzymatic hydrolysis to release energy
  • Methylation for long-term storage
  • Which of the following statements is FALSE regarding endocytosis?

  • It can involve fusion with lysosomes for degradation.
  • It involves the uptake of materials into the cell.
  • It only recycles content without redistribution. (correct)
  • It removes substances from the extracellular space.
  • What is a unique characteristic of the smooth endoplasmic reticulum?

    <p>It packages proteins into transport vesicles.</p> Signup and view all the answers

    Which type of junction prevents leakage of substances between cells?

    <p>Tight Junctions</p> Signup and view all the answers

    How does the mitochondria contribute to cellular function?

    <p>It produces ATP for energy.</p> Signup and view all the answers

    What is the primary reason that mature red blood cells lack endoplasmic reticulum?

    <p>They are designed solely for hemoglobin transport.</p> Signup and view all the answers

    What role do gap junctions play in cardiac muscle cells?

    <p>Allow synchronized contraction through electrical impulse spread.</p> Signup and view all the answers

    What is the main function of the sodium-potassium pump?

    <p>It transports sodium and potassium ions against their concentration gradients.</p> Signup and view all the answers

    Which mechanism primarily uses ATP directly to move molecules against their concentration gradient?

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

    How does the nervous system differ from the endocrine system in terms of communication?

    <p>The nervous system relies on membrane potentials to transmit signals, whereas the endocrine system relies on hormone-mediated communication.</p> Signup and view all the answers

    What creates the membrane potential in living cells?

    <p>The separation of positive and negative charges across the plasma membrane.</p> Signup and view all the answers

    What is the typical membrane potential maintained by a typical cell?

    <p>-70mV</p> Signup and view all the answers

    Which statement about secondary active transport is true?

    <p>It uses the energy created by the primary transport of ions to move other substances.</p> Signup and view all the answers

    Which example best illustrates tertiary active transport?

    <p>Hydrogen/Peptide symporter in the small intestine</p> Signup and view all the answers

    What defines passive transport across a cell membrane?

    <p>Movement from high concentration to low concentration without energy</p> Signup and view all the answers

    What happens to potassium ions when they move out of the cell?

    <p>They help to establish a negative membrane potential.</p> Signup and view all the answers

    Which types of molecules can freely diffuse across the lipid bilayer?

    <p>Hydrophobic molecules such as oxygen and carbon dioxide</p> Signup and view all the answers

    What is a characteristic of facilitated diffusion?

    <p>It uses specific carrier proteins for transport</p> Signup and view all the answers

    How does the sodium-potassium pump primarily function?

    <p>By actively transporting sodium out and potassium into the cell</p> Signup and view all the answers

    What is the concentration gradient responsible for in passive transport?

    <p>Driving the movement of substances from high to low concentration</p> Signup and view all the answers

    Which statement best describes secondary active transport?

    <p>It relies on the energy from the primary active transport of another substance</p> Signup and view all the answers

    In what manner do gated channels regulate transport across membranes?

    <p>They open or close in response to specific stimuli</p> Signup and view all the answers

    What role do intrinsic membrane proteins play in passive transport?

    <p>They transport non-lipid soluble substances across cell membranes</p> Signup and view all the answers

    Study Notes

    Active Transport

    • Movement of molecules against the concentration gradient (low to high concentration).
    • Requires energy (ATP) and involves transport proteins called pumps.
    • Example: sodium-potassium pump

    Primary Active Transport

    • Directly uses the energy of ATP to move sodium and potassium.
    • Example: sodium-potassium pump (present in all cells).

    Secondary Active Transport

    • Indirectly uses the energy of ATP to transport substances.
    • Examples:
      • Sodium/Hydrogen Antiporter (in kidney cells).
      • Sodium/Glucose Symporter (in the small intestine and kidney cells).

    Tertiary Active Transport

    • Example: Hydrogen/Peptide Symporter (in the small intestine).

    Membrane Potential

    • All living cells have a membrane potential (electrically polarized).
    • This potential is the separation of opposite charges across the plasma membrane.
    • The separation of charges across the membrane is called "potential" because it has the potential to do work.
    • This work can be used for communication.

    How Sodium and Potassium ATPases influence Membrane Potential

    • They maintain the sodium and potassium gradients across the cell membrane.
    • A large population of potassium leak channels allows a lot of potassium to leak out of the cell.
    • A small population of sodium leak channels allows some sodium to leak into the cell.
    • Net Effect: A typical cell maintains a membrane potential of about -70mV, relative to the extracellular space.

    Potassium

    • The concentration gradient for potassium tends to move this ion out of the cell.
    • The outside of the cell becomes more positive as potassium ions move to the outside down their concentration gradient.
    • The membrane is impermeable to the large intracellular protein anion.

    Osmosis

    • Movement of solvent (water) across a semipermeable membrane from a high to low solvent concentration.
    • Only the solvent moves.

    Transport Across a Plasma Membrane

    • One main function of the plasma membrane is to serve as a permeability barrier.
    • It is a selective membrane.
    • Lipid-soluble substances are free to diffuse, other substances must be transported across the membrane.

    Fick’s Equation for Diffusion Across a Lipid Membrane

    • Q = the speed at which particles or molecules move from areas of high concentration to areas of low concentration.
    • Triangle C: Concentration Gradient of that Substance.
    • P = Permeability of that substance (P = lipid partition coefficient).
    • A = Surface Area of the barrier (membrane).
    • MW = molecular weight of the substance (square root of MW approximates molecular radius).
    • Triangle X: Membrane Thickness.

    What is the lipid bilayer permeable to?

    • Hydrophobic Molecules (oxygen, carbon dioxide, nitrogen, steroids).
    • Small Uncharged Polar Molecules (water, glycerol, urea, ethanol).
    • These molecules move by diffusion.

    What is the lipid bilayer not permeable to?

    • Large uncharged polar molecules (glucose and sucrose).
    • Ions (sodium, potassium, calcium, hydrogen, chloride).

    Passive Transport

    • Movement of molecules across the cell membrane from an area of high concentration to low concentration (down the concentration gradient).
    • This kind of movement does not require the use of energy.
    • Examples: diffusion, osmosis, and facilitated diffusion.

    Passive Transport Examples

    • Non-lipid-soluble substances cross cell membranes via intrinsic membrane proteins (channels and carriers).
    • Channels select what gets through based on size and charge.
    • In gated channels, there is a "gate" that opens static pores.
    • There are temperature-gated, pH-gated, phosphorylation, and mechanically-gated channels.
    • Carriers select what gets through based on binding specificity.
    • Facilitated diffusion via carriers relies on specific recognition of the transported substance by the carrier protein AND a concentration gradient.
    • Ionic transport via channels relies on specific recognition of the transported ion and a concentration and/or electrical gradient.

    Active Transport (in the context of protein synthesis)

    • The rough ER, in association with its ribosomes, synthesizes and releases new proteins into the ER lumen.
    • Within the ER lumen, a newly synthesized protein is folded into a final conformation and may be modified.
    • A new protein is not able to traverse the ER membrane.
    • Transport vesicles that fuse with the Golgi complex are formed.
    • As the vesicles travel through the ER and Golgi complex they are modified to their final form by post-translational modifications. Contents are sorted, packaged, and directed to final destinations.
    • Secretory vesicles receive signals that initiate their fusion and release of vesicle contents by exocytosis.
    • The smooth ER does not contain ribosomes but packages the new proteins into transport vesicles.

    Endocytosis

    • Recycling of Content.
    • Fusion with Lysosome for Degradation.
    • Reuse and Redistribution.

    Endoplasmic Reticulum in Different Cell Types

    • Muscle Cell: Sarcoplasmic Reticulum stores calcium.
    • Plasma Cell: Secretes huge amounts of antibodies. ER is very developed and occupies the whole cytoplasm.
    • Mature Red Blood Cell: It has no nucleus and no ER. After maturation, it becomes a packet of circulating hemoglobin.

    Mitochondria

    • The site of MOST ATP production.
    • Source of energy of the cell and recharges an ADP with phosphate.

    The ATP Cycle

    • When a cell needs energy, ATP is broken down, or hydrolyzed, into ADP and phosphate, which releases energy.
    • The ADP produced is recycled back into ATP by adding a phosphate group.

    Specialized Cell Junctions

    • Desmosomes: Anchor adjacent cells together, providing mechanical stability and strength to tissues. They involve cytoskeletal components and other proteins.
    • Tight Junctions: Create a barrier to prevent the passage of molecules and ions between cells.
      • Intestinal Epithelium: Tight junctions prevent leakage of nutrients and pathogens from the gut lumen into the bloodstream.
      • Blood-Brain Barrier: Restricts the movement of harmful substances.
    • Gap Junctions: Intercellular connections that allow direct communication between adjacent cells. They contain protein channels called connexons, which enable the transfer of ions, small molecules, and signaling compounds.
      • Cardiac Muscle: Gap junctions allow for synchronized contraction of heart cells by enabling the rapid spread of electrical impulses.

    Diffusion

    • Movement of molecules from high concentration to low concentration.
    • Both the solute and solvent move.

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    Description

    Explore the various types of active transport mechanisms, including primary, secondary, and tertiary active transport. This quiz covers key examples like the sodium-potassium pump and the significance of membrane potential in cellular functions.

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