The Working Cell - Membrane Functions
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Questions and Answers

What role do cofactors play in enzyme activity?

  • They are proteins that enhance enzyme stability.
  • They serve as substrates for enzyme reactions.
  • They bind to the active site and assist in catalysis. (correct)
  • They are waste products produced during enzymatic reactions.
  • Which of the following statements about enzyme inhibitors is true?

  • Non-competitive inhibitors bind only to the enzyme-substrate complex.
  • Competitive inhibitors can be overcome by reduced substrate concentration.
  • Competitive inhibitors mimic the substrate and compete for the active site. (correct)
  • All inhibitors decrease the affinity of the enzyme for its substrate.
  • How does a cell regulate its enzymatic activity?

  • By permanently inhibiting all enzyme activity in the cell.
  • By simultaneously activating all metabolic pathways.
  • By turning the genes on or off that encode for specific enzymes. (correct)
  • Through uncontrolled genetic expression of enzymes.
  • What is the significance of coenzymes in relation to vitamins?

    <p>Coenzymes are synthesized from nutrients, including vitamins.</p> Signup and view all the answers

    What defines a competitive inhibitor in enzyme activity?

    <p>It competes with the substrate for accessing the active site.</p> Signup and view all the answers

    What type of energy involves the motion of objects performing work?

    <p>Kinetic energy</p> Signup and view all the answers

    Which form of energy is primarily utilized by cells to perform work?

    <p>Chemical energy</p> Signup and view all the answers

    What is described as energy transformation occurring in a collection of matter?

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

    According to the first law of thermodynamics, what is true about energy in the universe?

    <p>Energy remains constant.</p> Signup and view all the answers

    Which type of energy is associated with the random movement of atoms or molecules?

    <p>Kinetic energy</p> Signup and view all the answers

    What form of potential energy is possessed by molecules because of their atomic structure?

    <p>Chemical energy</p> Signup and view all the answers

    An organism's exchange of energy and matter with its environment characterizes it as what type of system?

    <p>Open system</p> Signup and view all the answers

    What type of energy can be harnessed during processes like photosynthesis?

    <p>Light energy</p> Signup and view all the answers

    What role do aquaporins play in a cell's membrane?

    <p>They serve as channels specifically for the movement of water.</p> Signup and view all the answers

    Which statement about the phospholipid bilayer is correct?

    <p>The fluid mosaic model describes a dynamic arrangement of proteins in the bilayer.</p> Signup and view all the answers

    What can happen if kidney cells produce too many aquaporins?

    <p>There could be an overabsorption of water, leading to fluid retention.</p> Signup and view all the answers

    How do water molecules primarily travel through the cell membrane?

    <p>By using aquaporins, specialized water channels.</p> Signup and view all the answers

    What is the primary consequence of plasmolysis in plant cells?

    <p>Cell death and wilting</p> Signup and view all the answers

    How do transport proteins assist polar molecules in crossing cell membranes?

    <p>By providing specific channels or binding sites</p> Signup and view all the answers

    What is a potential consequence of defective aquaporins in individuals?

    <p>They might require excessive water intake to avoid dehydration.</p> Signup and view all the answers

    What was the unexpected discovery made by Peter Agre's research team?

    <p>A new protein enabled rapid transport of water in cells.</p> Signup and view all the answers

    What type of transport is facilitated diffusion classified as?

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

    Which describes the significance of the fluid mosaic model in relation to cell membranes?

    <p>It highlights the diversity and movement of proteins within the lipid bilayer.</p> Signup and view all the answers

    What is the primary composition of the lipid bilayer in a cell membrane?

    <p>Phospholipids and cholesterol.</p> Signup and view all the answers

    What characterizes aquaporins in the context of cell membranes?

    <p>They rapidly facilitate water diffusion.</p> Signup and view all the answers

    What method did Dr. Agre's team use to identify the smaller protein in their sample?

    <p>Using antibodies to bind and label the protein.</p> Signup and view all the answers

    What might increase the synthesis of aquaporin proteins in certain cells?

    <p>Pregnancy and associated fluid retention.</p> Signup and view all the answers

    What significant role does the newly discovered protein play in kidney cells?

    <p>It facilitates rapid water transport.</p> Signup and view all the answers

    What happens to food-spoiling bacteria in concentrated salt solutions?

    <p>They plasmolyze and may eventually die.</p> Signup and view all the answers

    Which substance is most likely to utilize facilitated diffusion to cross cell membranes?

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

    Which experimental condition was used to test the hypothesis about the new protein's function?

    <p>Injecting messenger RNA into frog eggs.</p> Signup and view all the answers

    What phenomenon was observed in the RNA-injected frog eggs when subjected to a hypotonic solution?

    <p>They exhibited rapid bursting.</p> Signup and view all the answers

    Why is plasmolysis particularly lethal to plant cells?

    <p>It leads to dehydration and loss of turgor pressure.</p> Signup and view all the answers

    In terms of water balance, how does the contractile vacuole function in freshwater Paramecium?

    <p>It expels excess water to prevent cell swelling.</p> Signup and view all the answers

    Which cells were found to express the newly discovered protein more abundantly than red blood cells?

    <p>Certain kidney cells.</p> Signup and view all the answers

    What conclusion did the researchers reach regarding the smaller protein after initial tests?

    <p>It was identical to a predicted water channel protein.</p> Signup and view all the answers

    Why did Dr. Agre's team initially believe the smaller protein was a breakdown product?

    <p>It was much less abundant than the larger protein.</p> Signup and view all the answers

    Which statement best describes the function of cellular respiration in relation to energy?

    <p>Cellular respiration releases energy gradually through multiple reactions.</p> Signup and view all the answers

    How do endergonic reactions differ from exergonic reactions?

    <p>Endergonic reactions absorb energy, producing products with higher potential energy than the reactants.</p> Signup and view all the answers

    What does the second law of thermodynamics imply about the process of diffusion across a membrane?

    <p>Diffusion leads to an increase in entropy within the universe.</p> Signup and view all the answers

    Which of the following accurately describes an exergonic reaction?

    <p>Releases energy by breaking down complex molecules into simpler ones.</p> Signup and view all the answers

    In the context of cellular reactions, what is the significance of storing energy as ATP?

    <p>ATP provides immediate energy for cellular activities.</p> Signup and view all the answers

    What type of reaction is photosynthesis classified as?

    <p>Endergonic reaction that absorbs energy to produce glucose.</p> Signup and view all the answers

    Why is burning wood considered an exergonic reaction?

    <p>It releases more energy than it requires to break bonds.</p> Signup and view all the answers

    What role does entropy play in the context of living cells?

    <p>Cells maintain low entropy while contributing to overall universal entropy increase.</p> Signup and view all the answers

    Study Notes

    The Working Cell

    • Cells have a membrane that allows water to flow across.

    • This membrane is a lipid bilayer made of phospholipids.

    • The heads of the phospholipids are hydrophilic (water-loving).

    • The tails of the phospholipids are hydrophobic (water-fearing).

    • Membrane proteins called aquaporins form water channels.

    • Aquaporins allow billions of water molecules to flow through the membrane every second, far more than can travel through the lipid bilayer on their own.

    • Aquaporins are essential for water balance, like in the kidneys

    • Some people have defective aquaporins which leads to drinking 20 liters of water per day to prevent dehydration.

    • Membranes are fluid mosaics of lipids and proteins.

    • A cell membrane's structure enables many functions such as regulating transport across the membrane.

    • Some membrane proteins are enzymes.

    • Membrane proteins may form intercellular junctions that attach adjacent cells.

    • Some proteins attach to the ECM and cytoskeleton helping support the membrane and coordinate internal / external changes.

    • Membrane proteins can form intercellular junctions, regulate traffic across the membrane, and perform other functions.

    • A cell's metabolic reactions transform energy, using ATP to drive cellular work.

    • Enzymes speed up a cell's chemical reactions and provide precise control of metabolism.

    • The spontaneous formation of membranes was critical for the origin of life.

    • Substances like phospholipids can spontaneously self-assemble into simple membranes.

    • Membranes allow chemical differences and regulate chemical exchanges with the environment.

    • Passive transport is diffusion across a membrane without energy.

    • Diffusion is the tendency of particles to spread out into available space.

    • Passive transport across the membrane occurs through concentration gradients.

    • Oxygen (O2) and carbon dioxide (CO2) easily diffuse across cell membranes.

    • Osmosis is the diffusion of water across a membrane.

    • Tonicity refers to the ability of a surrounding solution to cause a cell to gain or lose water.

    • Isotonic solutions have equal solute concentration inside and outside the cell.

    • Hypotonic solutions have lower solute concentrations than inside the cell.

    • Hypertonic solutions have higher solute concentrations than inside the cell.

    • Cells in a hypotonic solution gain water, swell and may burst.

    • Cells in a hypertonic solution lose water and shrink.

    • Transport proteins facilitate diffusion across membranes.

    • Hydrophilic substances use transport proteins to cross hydrophobic layers.

    • Transport proteins speed up water transport.

    • Transport proteins are essential for regulating water transport in various cell types.

    • Cells expend energy in active transport of a solute.

    • Active transport moves solutes against their concentration gradient, requiring energy (ATP).

    • Transport proteins are essential for active transport.

    • Active transport is vital for maintaining internal conditions different from the surroundings (e.g., K+ and Na+ in animal cells)

    • Exocytosis and endocytosis transport large molecules.

    • Exocytosis moves large molecules out of the cell using vesicles.

    • Endocytosis moves large molecules into the cell using vesicles

    • Phagocytosis is a type of endocytosis involving engulfing large particles.

    • Receptor-mediated endocytosis takes in specific molecules using specific receptors.

    • Cells transform energy as they perform work.

    • Kinetic energy is energy of motion.

    • Potential energy is stored energy.

    • Chemical energy is stored in molecular bonds.

    • Thermal energy is random atomic / molecular movement (heat).

    • The first law of thermodynamics states that energy cannot be created nor destroyed.

    • The second law of thermodynamics states that energy transfers increase entropy (disorder) of the surrounding.

    • Enzymes speed up reactions by lowering activation energy.

    • Enzymes have specific shapes and fit substrates in a region called the active site.

    • The activation energy barrier protects ordered molecules from breaking down spontaneously.

    • Heat speeds up molecules and reactions.

    • Enzyme inhibition regulates enzymatic activity.

    • Inhibitors can be competitive (blocking the active site), or non-competitive (inhibiting the enzyme in another part).

    • Feedback inhibition is a regulatory mechanism where the product of a reaction inhibits an enzyme earlier in the pathway.

    • Many drugs, pesticides, and poisons are enzyme inhibitors.

    • Inhibitors interfere with enzyme function, either reversibly or irreversibly.

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    Description

    Explore the essential functions of cell membranes in regulating water transport and maintaining cellular environments. This quiz covers the structure and roles of phospholipids and aquaporins in cell membrane functionality, as well as the implications of defective aquaporins. Test your knowledge on these vital cellular components!

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