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. (B)</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. (D)</p> Signup and view all the answers

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

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

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

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

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

<p>Thermodynamics (C)</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. (D)</p> Signup and view all the answers

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

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

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

<p>Chemical energy (A)</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 (B)</p> Signup and view all the answers

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

<p>Light energy (C)</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. (A)</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. (C)</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. (C)</p> Signup and view all the answers

How do water molecules primarily travel through the cell membrane?

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

What is the primary consequence of plasmolysis in plant cells?

<p>Cell death and wilting (A)</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 (C)</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. (B)</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. (B)</p> Signup and view all the answers

What type of transport is facilitated diffusion classified as?

<p>Passive transport utilizing concentration gradients (B)</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. (C)</p> Signup and view all the answers

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

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

What characterizes aquaporins in the context of cell membranes?

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

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

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

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

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

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

<p>Glucose (B)</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. (C)</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. (A)</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. (D)</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. (A)</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. (A)</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. (A)</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. (B)</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. (A)</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. (C)</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. (C)</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. (A)</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. (C)</p> Signup and view all the answers

What type of reaction is photosynthesis classified as?

<p>Endergonic reaction that absorbs energy to produce glucose. (C)</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. (B)</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. (A)</p> Signup and view all the answers

Flashcards

Cofactor

A nonprotein helper molecule that binds to an enzyme's active site and aids in catalysis.

Coenzyme

An organic cofactor.

Inhibitor

A chemical that interferes with an enzyme's activity.

Competitive inhibitor

A type of inhibitor that resembles the enzyme's substrate and competes with it for the active site.

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Noncompetitive inhibitor

A type of inhibitor that binds to a site on the enzyme other than the active site, changing the enzyme's shape and making it less effective.

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Transport Protein

A type of membrane protein that allows specific molecules to cross the cell membrane, contributing to its selective permeability.

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Energy

The ability to cause change or perform work.

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Kinetic Energy

Energy associated with motion. For example, the movement of your legs on a bike.

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Aquaporins

A class of membrane proteins that facilitate rapid water transport across cell membranes.

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Osmotic Swelling

The phenomenon where a cell swells due to the movement of water into the cell, driven by a difference in water concentration.

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Potential Energy

Energy stored due to an object's position or structure.

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Hypotonic Solution

A solution with a lower concentration of solutes compared to another solution. Water will tend to move into this solution.

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Chemical Energy

Potential energy stored in the arrangement of atoms in a molecule.

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Messenger RNA (mRNA)

A molecule that carries genetic information from DNA to ribosomes, where protein synthesis takes place.

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Thermodynamics

The study of energy transformations within a system.

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Translation

The process by which a cell synthesizes proteins based on the genetic code carried by mRNA.

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Law of Energy Conservation

The first law of thermodynamics - energy cannot be created or destroyed, only transformed.

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Plasma Membrane

The outer layer of a cell that acts as a barrier, regulating what enters and exits the cell.

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Open System

A system that exchanges both energy and matter with its surroundings.

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Selective Permeability

The ability of a membrane to allow certain substances to pass through while blocking others.

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Exocytosis

The process by which cells release substances to the outside.

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Exergonic Reactions

Reactions that release energy into the surroundings, like burning wood, where the reactants have more potential energy than the products.

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Osmosis

The movement of water molecules across a selectively permeable membrane from a region of high water concentration to a region of low water concentration, driven by the concentration gradient.

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Endergonic Reactions

Reactions that require energy input from the surroundings, like photosynthesis, where the products have more potential energy than the reactants.

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ATP (Adenosine Triphosphate)

The molecule used by cells as an immediate source of energy. It stores energy in its chemical bonds.

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Plasmolysis

The shrinking of a cell's cytoplasm due to water loss in a hypertonic environment.

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Cellular Respiration

A process that releases energy stored in glucose molecules through a series of chemical reactions, providing energy for the cell.

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Photosynthesis

The process by which plants capture light energy and convert it into chemical energy stored in sugar molecules.

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Facilitated Diffusion

A type of passive transport that allows specific molecules or ions to cross a cell membrane with the help of specialized transport proteins.

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Active Transport

The process of moving substances across a cell membrane against their concentration gradient, requiring energy.

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Entropy

The state of disorder or randomness in a system. The universe tends to move towards greater disorder.

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Diffusion

The movement of molecules from an area of high concentration to an area of low concentration, driven by the tendency towards greater randomness.

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Fluid Mosaic Model

The structure of a cell membrane is described as a "fluid mosaic" because it's composed of diverse proteins embedded within a fluid phospholipid bilayer. Think of it like a sea of phospholipids with protein icebergs floating about.

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Phospholipids

Phospholipids are the primary building blocks of cell membranes. They have a hydrophilic head that likes water and a hydrophobic tail that hates water.

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Membrane Proteins

Membrane proteins are embedded within the phospholipid bilayer, performing various functions such as transporting molecules, receiving signals, or attaching to other cells.

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Homeostasis

The process by which cells maintain a stable internal environment is called homeostasis. For example, cells regulate water balance by controlling the movement of water across their membranes.

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Importance of Homeostasis

The ability of a cell to maintain a stable internal environment is crucial for its survival. This is because cells are constantly exchanging materials with their surroundings.

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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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Chapter 5 - The Working Cell PDF

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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