Mastering Biology: The Working Call

Enzymes speed reactions mainly by ... lowering EA. raising the kinetic energy of the reactants. protecting the catalysts. providing activation energy. None of the above.

lowering EA (activation energy). Yes! Enzymes always lower EA, though they may have other effects as well. With a lower EA, more collisions can produce the transition state.

How do cells use ATP to raise the energy level of reaction substrates? ATP is hydrolyzed to release its energy. The ADP part of ATP is bound to the substrate. The terminal phosphate of ATP is bound to the substrate. All of the above

The terminal phosphate of ATP is bound to the substrate. Good going! The bond between Pi and the substrate preserves much of the energy that was in ATP.

What name is given to the process by which water crosses a selectively permeable membrane? osmosis diffusion phagocytosis passive transport pinocytosis

osmosis Osmosis is the passive transport of water.

Chemical energy is a form of _____ energy. kinetic heat potential entropic motion

potential Chemical energy is a form of stored energy.

Why is ATP a good source of energy for biological reactions? Links between adenine and sugar are unstable. Links between sugar and phosphate are unstable. Peroxide links are highly reactive. The answer is still unknown. Triphosphate chains are unstable.

Triphosphate chains are unstable. Yes! The instability is associated with high energy, favoring reactions that break the triphosphate chain.

Succinylcholine is structurally almost identical to acetylcholine, but if combined with the enzyme that normally hydrolyzes acetylcholine, the enzyme is no longer able to hydrolyze acetylcholine. This suggests that _____. succinylcholine must regulate the activity of this enzyme by negative feedback the active site must have the wrong configuration to permit succinylcholine binding succinylcholine must be a noncompetitive inhibitor succinylcholine must be a competitive inhibitor of acetylcholine

succinylcholine must be a competitive inhibitor of acetylcholine Competitive inhibition occurs when a molecule mimics the substrate. Noncompetitive inhibition occurs when a molecule dissimilar to the substrate interacts with the enzyme.

In the figure below, working from the inside out, what would be the order of components observed? Quiz Image water, hydrophobic tail, hydrophilic head, hydrophilic head, hydrophobic tail, water hydrophobic tail, water, hydrophilic head, hydrophilic head, water, hydrophobic tail water, hydrophilic tail, hydrophobic head, hydrophobic head, hydrophilic tail, water water, hydrophilic head, hydrophobic tail, hydrophobic tail, hydrophilic head, water

water, hydrophilic head, hydrophobic tail, hydrophobic tail, hydrophilic head, water Correct. The hydrophilic heads would orient themselves so that they are in contact with the aqueous surroundings, forming water bubbles, with the hydrophobic tails oriented toward each other.

A pharmaceutical company wishes to focus on an enzyme to develop new medications. What type of study would be of the greatest benefit? Knowing the structure of enzymes may make it possible to design enzymes that raise the activation energy above that of the spontaneous reaction to allow more efficient drug synthesis. Studying the structure of an enzyme would help pharmaceutical companies determine the enzyme's substrate. Studying the structure would help pharmaceutical companies create enzymes that are not destroyed during reactions. Understanding the enzyme's structure would help pharmaceutical companies design molecules that fit to the binding site and alter activity.

Understanding the enzyme's structure would help pharmaceutical companies design molecules that fit to the binding site and alter activity. Enzymes are the most common targets of drugs. By understanding the details of enzyme structure, new drugs can be designed and existing drugs can be better understood and potentially modified.

Which of these is hydrophobic like the interior of the plasma membrane? The figure shows the structure of a cell membrane. There are a lipid bilayer, the cytoplasm, and the extracellular fluid. Several molecules are placed in the extracellular fluid, and they are labeled from A to D. Lipid soluble molecule is labeled as A, water as B, glucose as C, and a hydrogen ion as D. D C B A C and D

A Lipid soluble molecules are hydrophobic.

In cells, what is usually the immediate source of energy for an endergonic reaction? ATP as spontaneous reactions, endergonic reactions do not need an addition of energy ADP sugar glucose

ATP The hydrolysis of ATP provides the energy needed for an endergonic reaction.

Which of the following is a difference between active transport and facilitated diffusion? Facilitated diffusion involves transport proteins, and active transport does not. Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. Active transport involves transport proteins, and facilitated diffusion does not. Active transport requires the expenditure of cellular energy, and facilitated diffusion does not.

Active transport requires the expenditure of cellular energy, and facilitated diffusion does not. Active transport can move substances against the concentration gradient, but it requires energy, usually in the form of ATP.

In an experiment with an enzyme, the 58th amino acid seems to form a covalent bond with a substrate molecule as part of the catalytic process. What would you say? There must be an error. Enzymes don't make covalent bonds with substrates. It couldn't happen. Catalysis doesn't alter the enzyme. This is possible in theory, but it's never been observed. This is probably a case where the enzyme changes the position of equilibrium. At some point the bond between the amino acid and the substrate must break.

At some point the bond between the amino acid and the substrate must break. Right! To work repeatedly, the enzyme must return to its original state at the end of each catalytic cycle. Some steps may form bonds or break bonds between the enzyme and substrate.

Cells A and B are the same size and shape, but cell A is metabolically quiet and cell B is actively consuming oxygen. Oxygen will diffuse more quickly into cell _____ because _____. A ... its membrane transport proteins will not be saturated B ... the oxygen molecules inside cell B have a higher kinetic energy A ... the diffusion gradient there is shallower B ... the diffusion gradient there is steeper

B ... the diffusion gradient there is steeper As long as a metabolically active cell consumes oxygen as it enters, diffusion into the cell will continue because the concentration gradient favors movement in that direction.

In this diagram of the plasma membranes of two adjoining cells, identify the protein indicated by the white arrow, including its function. A white arrow points to a protein that spans the membrane. The protein has a binding site on the exterior surface for a specific molecule. A dotted line with an arrow at the end extends into the cell. a receptor protein that binds with a signaling molecule and relays the message into the cell by activating other molecules inside the cell a protein involved in enzymatic activity an active transport protein that moves molecules across a membrane against their concentration gradient an attachment protein that provides structural support a glycoprotein that is involved in cell-cell recognition

a receptor protein that binds with a signaling molecule and relays the message into the cell Signaling proteins are part of signal transduction pathways that transmit external chemical signals into the cell.

Biologists use the fluid mosaic model to describe membrane structure. Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements. Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. Membranes include a mosaic, or mix, of carbohydrates embedded in a phospholipid bilayer. The kinky tails of some proteins help keep the membrane fluid by preventing the component molecules from packing solidly together. The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. The diverse proteins found in and attached to membranes perform many important functions.

Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. The diverse proteins found in and attached to membranes perform many important functions. Membranes consist of diverse proteins suspended in and attached to a phospholipid bilayer. Kinks in the unsaturated fatty acid tails of some phospholipids keep the membrane fluid, and a mosaic of proteins perform a variety of functions.

How do cells replace the energy-rich ATP that is destroyed in energy-coupled reactions? (a) Chloroplasts use light energy to synthesize ATP. (b) Mitochondria synthesize ATP using energy that's released by oxidizing sugars and fats. (c) Ribosomes use catalytic RNA to couple ADP with Pi. Both (a) and (b). (a), (b), and (c).

Both (a) and (b). (a) Chloroplasts use light energy to synthesize ATP. (b) Mitochondria synthesize ATP using energy that's released by oxidizing sugars and fats. Right! Plants have both chloroplasts and mitochondria. Animals lack chloroplasts; they get sugars and fats from other organisms to fuel their mitochondria.

How can "induced fit" influence the specificity of an enzyme? (a) It can not influence the specificity of an enzyme. (b) It moves the reactive portion of the enzyme closer to the substrate. (c) The enzyme's active site changes shape to fit the correct substrate but not other molecules. Both (b) and (c). None of the above.

Both (b) and (c). (b) It moves the reactive portion of the enzyme closer to the substrate. (c) The enzyme's active site changes shape to fit the correct substrate but not other molecules. Correct! The active site of the enzyme will change shape to make a better fit with only the appropriate substrate, which can bring the reactive portion of the enzyme closer to the substrate.

A reaction is said to be unfavorable if ... (a) it will be very slow without a catalyst. (b) the free energy change for the reaction is positive. (c) equilibrium favors the reactants, not the products. Both (a) and (b). Both (b) and (c).

Both (b) and (c). Good answer! If the free energy change for the reaction is positive, equilibrium favors the reactants and we say the reaction is unfavorable.

Which answer is true of the molecule shown here? There is a structure of the ion which contains an adenine group, a ribose group, and three phosphate groups connected in sequence. (a) Its energy is associated mainly with the adenine group. (b) If it had one less O atom, it could be a subunit for replicating DNA. (c) Protein kinases use it to control the action of some enzymes. Both (b) and (c). (a), (b), and (c).

Both (b) and (c). (b) If it had one less O atom, it could be a subunit for replicating DNA. (c) Protein kinases use it to control the action of some enzymes. The best choice. Protein kinases transfer one of ATP's phosphates to enzymes that are being controlled, and if it contained deoxyribose instead of ribose, it would be a subunit for making DNA.

In plant cells, carbon dioxide and water are joined to form carbohydrates. Plant cells can also break down carbohydrates such as glucose, releasing carbon dioxide, water, and energy. No one has ever observed such reactions between water and carbon dioxide outside of living cells. What allows simple molecules to assemble into more complex molecules, and also disassemble, in cells but not in other, nonbiological environments? Cells couple energy-releasing reactions to energy-requiring reactions. Cells are subject to only the first law, not the second law, of thermodynamics. Cells possess properties not seen in nonliving things, which allow them to run physical processes in reverse. Cells are far more efficient in energy transactions than are nonliving substances.

Cells couple energy-releasing reactions to energy-requiring reactions. One of the many things cells do well is the linking of metabolic reactions in ways that allow an energy-yielding reaction to be coupled to an energy-requiring reaction. ATP molecules are the key to energy coupling.

Life on this planet would be much less abundant without the process shown here. Which answer is helpful in explaining why this process is important? The figure shows the schemes of the mitochondrion and the chloroplast. In the chloroplast there are 2 ATP molecules, 2 ADP molecules, and 2 phosphate groups. The light penetrates into the chloroplast. ATP is a catalyst for some of life's most important reactions. Inorganic substances are low in free energy. Chemical fuels lack the energy needed to make ATP. Every event decreases the entropy of the universe. Every chemical reaction decreases free energy.

Every chemical reaction decreases free energy. Good thinking! Because all the events of life decrease free energy, organisms need to replace the losses by taking energy from outside themselves. Light is the ultimate energy source for most life on Earth.

Which of these is exhibiting kinetic energy? a person sitting on a couch while watching TV a space station orbiting Earth an archer with a flexed bow a rock on a mountain ledge the high-energy phosphate bonds of a molecule of ATP

a space station orbiting Earth Kinetic energy is energy of motion.

Which fact is most important in explaining how enzymes speed reactions? Large molecules collide more energetically than small molecules. High-energy collisions are less common than low-energy collisions. Very low potential energy tends to make molecules unstable. It takes less energy to break a hydrogen bond than a covalent bond. Every reaction step adds to the time required for the overall reaction.

High-energy collisions are less common than low-energy collisions. Good choice! Enzymes provide reaction pathways that have low activation energy requirements. This allows low-energy collisions to cause reactions.

In a theoretical world where all things are possible, how could you increase the amount of energy that could be stored in a molecule of ATP? Alter the first and third groups to make them positive. Convert the negative charge of the phosphate groups to a positive charge. Change the middle phosphate group from a negative to a positive charge. Increase the negative charge of each phosphate group.

Increase the negative charge of each phosphate group. Because the high energy of ATP hydrolysis depends on the strong charge repulsion between the negatively charged phosphates, anything that increases this repulsion would also increase the energy liberated when ATP is broken down to ADP + P.

What is the fate of the phosphate group that is removed when ATP is converted to ADP? It is broken down into one phosphorus and four oxygen atoms. It is acquired by a reactant in a spontaneous reaction. It is used to convert an ATP into an AQP. It is acquired by a reactant in an endergonic reaction. It is acquired by a reactant in an exergonic reaction.

It is acquired by a reactant in an endergonic reaction. By acquiring the phosphate group the reactant acquires energy.

What's false? (1) Enzymes may change shape when they bind substrates; (2) Enzymes provide no energy for the reaction, except collision energy; (3) Enzymes may release substrates. None of the statements is false. Statement 1 is false. Statement 2 is false. Statement 3 is false. All three statements are false.

None of the statements is false. Great! Enzymes do all these things.

Use the graph and your knowledge of enzymes to identify the three true statements about enzymes. Reactants cannot convert to products without an initial input of energy to start the reaction. Enzymes lower the overall energy input needed for a reaction to occur. Chemical reactions cannot occur without enzymes. Only reactions that are controlled by enzymes require activation energy. By binding to reactant molecules, enzymes make it easier for the bonds in the molecules to break apart.

Reactants cannot convert to products without an initial input of energy to start the reaction. Enzymes lower the overall energy input needed for a reaction to occur. By binding to reactant molecules, enzymes make it easier for the bonds in the molecules to break apart. For a chemical reaction to begin, chemical bonds in the reactant molecules must be broken. This process requires that the molecules absorb energy from their surroundings. The energy that must be invested to start a reaction is called activation energy because it activates the reactants and triggers the chemical reaction. Enzymes enable metabolism to occur by reducing the amount of activation energy required to break the bonds of reactant molecules.

When in solution, a molecule that moves slowly across an artificial membrane moves rapidly across a plasma membrane. This molecule rapidly enters the cell regardless of whether its concentration is higher inside or outside the cell. Using this information, which transport mechanism is most likely to be responsible for the movement of the molecule across a plasma membrane? active transport passive transport exocytosis phagocytosis

active transport Some transport proteins can move molecules against their concentration gradient in a process called active transport.

Dr. Haxton thinks a certain enzyme works by the steps shown in the animation below. What would a good student say about the proposed mechanism?

Right! Enzymes may give and take atoms and form temporary covalent bonds with substrates as they catalyze reactions.

Which of the following is an example of the second law of thermodynamics? The aerobic respiration of glucose generates heat. Photosynthesis enables plants to create energy from sunlight. All types of cellular respiration produce ATP. CO2 is exhaled as a by-product of aerobic respiration.

The aerobic respiration of glucose generates heat. The second law of thermodynamics states that every energy transformation makes the universe more disordered and that most energy transformations release heat.

Which of these is ATP? The figure contains the structure of a molecule. It has 3 phosphate groups, a ribose molecule, and an adenine molecule. The figure contains the structure of a molecule. It has 3 phosphate groups, a deoxyribose molecule, and an adenine molecule. The figure contains the structure of a molecule. It has 3 phosphate groups, a ribose molecule, and a thymine molecule. The figure contains the structure of a molecule. It has 2 phosphate groups, a ribose molecule, and an adenine molecule. The figure contains the structure of a molecule. It has 3 phosphate groups, a deoxyribose molecule, and a guanine molecule.

The figure contains the structure of a molecule. It has 3 phosphate groups, a ribose molecule, and an adenine molecule. This is ATP.

In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP? digestion redox potentiation cellular respiration anabolism

cellular respiration This is the name given to the process by which the body converts food energy to energy stored in ATP.

The reaction ADP + P --> ATP is a(n) _____ reaction. endergonic chemical hydrolysis exergonic spontaneous

endergonic Energy has been acquired from the surroundings.

Which of these reactions requires a net input of energy from its surroundings? endergonic hydrolysis ATP --> ADP + P exergonic catabolic

endergonic The products of endergonic reactions have more potential energy than the reactants.

"Conservation of energy" refers to the fact that _____. the entropy of the universe is always increasing if you conserve energy you will not be as tired the net amount of disorder is always increasing energy cannot be created or destroyed but can be converted from one form to another no chemical reaction is 100 percent efficient

energy cannot be created or destroyed but can be converted from one form to another This is what is meant by conservation of energy.

The reaction A --> B + C + heat is released in a(n) _____ reaction. anabolic exchange endergonic exergonic dehydration synthesis

exergonic Energy has been released.

A(n) _____ reaction occurs spontaneously. anabolic exergonic kinetic chemical endergonic

exergonic In exergonic reactions the products have less potential energy than the reactants.

The energy for an endergonic reaction comes from a(n) _____ reaction. ADP + P --> ATP anabolic glucose + glucose --> maltose synthesis exergonic

exergonic The energy released by an exergonic reaction can be used to drive an endergonic reaction.

Select the INCORRECT association. exergonic ... spontaneous exergonic ... uphill potential energy ... positional energy kinetic energy ... motion enzyme ... protein

exergonic ... uphill Exergonic reactions release energy.

Which statement is true of enzymes? (a) Enzymes can be either proteins or RNA molecules. (b) When a cell makes an enzyme, it makes many copies. (c) Their substrate specificity involves matching of shapes. Both (a) and (b). (a), (b), and (c).

(a), (b), and (c). (a) Enzymes can be either proteins or RNA molecules. (b) When a cell makes an enzyme, it makes many copies. (c) Their substrate specificity involves matching of shapes. Good choice! There are many copies of each enzyme; they're usually proteins but sometimes they are RNA; and they only attack substrates that fit the shape and charge of the active site.

The reaction A → B is unfavorable by itself, but through energy-coupling, cells can use ATP to convert A into B. How is this done? (a) Hydrolysis of ATP releases heat that is used by the unfavorable reaction. (b) ATP acts as a catalyst to speed the unfavorable reaction. (c) The unfavorable reaction is replaced by two favorable reactions. Both (a) and (b). Both (b) and (c).

(c) The unfavorable reaction is replaced by two favorable reactions. You got it! The first reaction transfers part of ATP to A, making a high-energy product. That product is then converted to B. Both reactions release energy, so both are favorable.

You are working on a team that is designing a new drug. For this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells? the nonpolar, hydrophobic nature of the drug molecule the phospholipid composition of the target cells' plasma membrane the concentration of the drug molecule that is transported in the blood the similarity of the drug molecule to other molecules that are transported into the target cells

the similarity of the drug molecule to other molecules that are transported into the target cells If the target cells have transport proteins that specifically bind to certain molecules, they may bind with and transport a drug that is similar in structure.

Which of these are by-products of cellular respiration? glucose and water heat and water ATP ATP and water water

heat and water These are the by-products of cellular respiration.

What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule? dehydration synthesis hydrolysis dehydration decomposition anabolism entropic

hydrolysis Hydrolysis involves breaking bonds with the addition of water.

This cell is in a(n) _____ solution. The figure shows a cell membrane, the extracellular fluid, and the cytoplasm. The concentration of the solute is higher outside the cell. The figure shows 2 states of the cell: when it was just placed in this solute and over the time. hypotonic and isotonic hypertonic or isotonic hypertonic hypotonic isotonic

hypertonic There is a greater concentration of solute outside the cell.

You know that this cell is in a(n) _____ solution because it _____. The figure shows a cell placed in a solution with a higher concentration than inside the cell. The movement of the water is directed outside the cell, and the cell is shrunken. hypertonic ... lysed hypotonic ... lysed hypertonic solution ... lost water hypotonic ... is turgid hypertonic ... gained water

hypertonic solution ... lost water A cell will lose water when placed in a hypertonic solution.

What is energy coupling? a description of the energetic relationship between the reactants and products in an exergonic reaction the hydrolysis of ATP to ADP + P the use of an enzyme to reduce EA the use of energy released from an exergonic reaction to drive an endergonic reaction a barrier to the initiation of a reaction

the use of energy released from an exergonic reaction to drive an endergonic reaction This is energy coupling.

You know that this cell is in a(n) _____ solution because the cell _____. The figure shows a cell membrane, the extracellular fluid, and the cytoplasm. The concentration of the solute is higher inside the cell. The figure shows 2 states of the cell: when it was just placed in this solute and over the time. hypertonic ... gained water hypertonic ... lost water isotonic ... neither lost nor gained water hypotonic ... shrunk hypotonic ... swelled

hypotonic ... swelled A cell will gain water when placed in a hypotonic solution.

This plant cell is _____. Click to launch animation in an isotonic solution losing water hypertonic solution in a hypotonic solution lysing

in a hypotonic solution In a hypotonic solution plant cells experience a net gain of water and become turgid.