Brian Santos per. 4/5 Mr. Veres

Pretest

1. Correct The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____. (Concept 8.1E-Book)

Your Answer: The first, second, and third choices are correct.

2. Correct Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy? (Concept 8.1E-Book)

Your Answer: the covalent bonds of a sugar molecule—potential energy

3. Correct Which of the following statements about the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O) is incorrect? (Concept 8.2E-Book)

Your Answer: The free energy lost in this combustion is greater than the energy that appears as heat.

4. Correct Which of the following statements about equilibrium of chemical reactions is correct? (Concept 8.3E-Book)

Your Answer: A reaction that is at equilibrium is not capable of doing any work.

5. Correct Which of the following statements about ATP (adenosine triphosphate) is incorrect? (Concept 8.3E-Book)

Your Answer: The energy release on hydrolysis of ATP is the result of breaking a high-energy bond.

6. Correct Enzymes are described as catalysts, which means that they _____. (Concept 8.4E-Book)

Your Answer: increase the rate of a reaction without being consumed by the reaction

7. Correct Which of the following would be unlikely to contribute to the substrate specificity of an enzyme? (Concept 8.4E-Book)

Your Answer: The free energy of the enzyme is greater than the free energy of the substrate, which attracts the substrate to the enzyme.

8. Correct Which of the following is not a way in which an enzyme can speed up the reaction that it catalyzes? (Concept 8.4E-Book)

Your Answer: The active site can provide heat from the environment that raises the energy content of the substrate.

9. Correct The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Which of the following could account for this observation? (Concept 8.4E-Book)

Your Answer: The first three choices are correct.

10. Correct Which of the following statements about feedback regulation of a metabolic pathway is incorrect? (Concept 8.5E-Book)

Your Answer: The products of the pathway become the reactants for a different reaction, and thus products are unable to accumulate.

Energy transformations

Energy is the capacity to cause change. Kinetic energy is the energy associated with motion. Energy that is not kinetic is called potential energy, and is energy that matter possesses because of its location or structure. Energy is neither created nor destroyed but converted from one form to another. This property is called the conservation of energy.

The bow and arrow start out with low potential energy . As the archer's arm pulls back the string, kinetic energy from the arm's motion is converted to potential energy in the tense bowstring and arrow.

When the bowstring is released, the stored potential energy is converted into the kinetic energy of the moving arrow. When the arrow hits the target, its motion ceases. If energy is neither created nor destroyed, where did the energy of the flying arrow go?

Let's rewind and look at kinetic energy in more detail. When energy is converted from potential energy to kinetic energy, some of the energy can be used to do work, but some energy ends up as heat, a type of kinetic energy. Heat is the random motion of atoms and molecules. Click on the archer's arm to fire the arrow again and watch the red glow, which indicates heat.

As the arrow flies through the air, heat is generated by friction between the arrow and air molecules. When the arrow strikes the target, all the energy becomes heat energy. The heat energy is rapidly transferred into the air and spreads out. Heat energy is a very disordered kind of energy. It has the highest amount of entropy, or disorder, of any kind of energy.

Where do our muscles get energy to perform work, such as pulling back a bowstring? Our bodies use the chemical energy from food to perform work. Chemical energy is a form of potential energy. When your body breaks down food molecules, the stored potential energy from food can be converted to kinetic energy.

The stored chemical energy in food is released in your muscle cells during the process of cellular respiration. Using oxygen, cellular respiration converts chemical energy from food to another form of chemical energy called ATP. Water (H2O) and carbon dioxide (CO2) are by-products of cellular respiration. The potential energy of ATP can be converted to kinetic energy. Some of the kinetic energy is used to do useful work, such as pulling back a bowstring, but the heat energy that is generated cannot be used to do work.

The structure of ATP

ATP powers nearly all forms of cellular work by providing energy stored in its chemical bonds. Construct an ATP molecule by dragging the appropriate molecules from the lower part of the box to the shaded region above.

During cellular respiration, glucose releases energy. This energy is stored when a phosphate group is added to ADP (adenosine diphosphate), forming ATP (adenosine triphosphate). ATP releases energy when the covalent bond between phosphate groups breaks during hydrolysis. This energy is used to drive other biochemical reactions. Move your cursor on and off the molecule to see the bond between phosphate groups being formed and broken.

Chemical reactions and ATP

Cells contain many different molecules that can engage in a variety of chemical reactions. When molecules react, for example when they collide and exchange parts, their atoms and bonds are rearranged. Reactants are rearranged to form products. Reactant and product molecules store potential energy in the arrangements of their atoms and bonds. Chemical reactions involve changes in bonding and changes in energy. We can plot potential energy on a graph and compare the potential energy of reactants and products.

In this reaction, energy is released to the surroundings as the reactants are rearranged to form products. The potential energy of the molecules drops. In the other reaction, the product molecules have more potential energy than the reactants. The reactants must absorb energy for this reaction to occur.

Chemical reactions that release energy are called exergonic reactions. You might call exergonic reactions "downhill" reactions. Other reactions, called endergonic reactions, are "uphill" changes; they absorb

energy from their surroundings. Click on the graph that shows the type of reaction that is most likely to occur spontaneously-- that is, without a net addition of energy.

Correct. Exergonic reactions occur spontaneously. The potential energy of the molecules decreases. It is easier for a cell to carry out a reaction that does not need additional energy input. A downhill change is easier than an uphill change.

Every working cell has to carry out thousands of endergonic reactions-- reactions in which products have more potential energy than reactants. By definition, an endergonic reaction does not occur spontaneously. Then what can a cell do to make an endergonic reaction happen? The trick is energy coupling-- obtaining chemical energy from an exergonic reaction and then using the energy to drive an endergonic reaction. ATP is the key to energy coupling in the cell. In an exergonic reaction, ATP becomes ADP as a phosphate is removed; a reactant molecule acquires the phosphate from ATP and gains energy. Now the reaction can proceed.

How enzymes work

If exergonic reactions occur spontaneously, what keeps molecules from breaking apart and cell chemistry from racing out of control? For any reaction to occur, even a downhill reaction, some energy must be added to get the reaction going. This energy is needed to break bonds in the reactant molecules. The energy needed to start a chemical reaction is called the energy of activation (EA). This required energy input represents a barrier that prevents even energy-releasing exergonic reactions from occurring without some added energy.

How does a living cell overcome the energy barrier so that its metabolic reactions can occur quickly and precisely? A special kind of protein called an enzyme is the answer. An enzyme serves as a biological catalyst, increasing the rate of a reaction without being changed into a different molecule. An enzyme does not add energy to a reaction; instead, it speeds up a reaction by lowering the energy barrier.

An enzyme is very selective. Its three-dimensional shape allows it to act only on specific molecules, referred to as the enzyme's substrates. As the substrates bind to the enzyme's active site, they are held in a position that facilitates the reaction. This takes less activation energy than the unaided reaction. Products form and are released. The enzyme emerges unchanged from the reaction.

Because of the specific fit between enzyme and substrate, each enzyme can catalyze only one kind of reaction involving specific substrates. Thousands of different enzymes may be required to carry out all of a cell's metabolic processes.

Investigation: how is the rate of enzyme catalysis measured?

Enzymes catalyze reactions by lowering the activation energy necessary for a reaction to occur. In this investigation, you will explore how the rate of enzyme catalysis is measured.

Enzymes catalyze reactions by lowering the activation energy necessary for a reaction to occur. The molecule that an enzyme acts on is called the substrate. In an enzyme-mediated reaction,

substrate molecules are changed and product is formed. The enzyme molecule is unchanged after the reaction, and it can continue to catalyze the same type of reaction over and over.

Each enzyme is specific for the reaction it will catalyze. In the example shown at left,

Enzyme = catalaseSubstrate = hydrogen peroxide (H2O2)Products = water and oxygen

If a small amount of catalase is added to hydrogen peroxide, you will observe bubbles of oxygen forming.

We can calculate the rate at which an enzyme converts substrate to product by measuring, over time, either the disappearance of substrate or the appearance of product (as in the graph at the left). For example, based on the graph, what is the rate, in moles/second, over the interval from 0 to 10 seconds?

Rate = Δy/Δx

So for this example, the rate would be

(7 moles - 0 moles)/(10 seconds - 0 seconds) =

7/10 =

0.7 moles/second

The rate would be 0.

Answers to the 2 questions

1.    Answered     during which interval is the enzyme working at its maximum rate: 0-60 seconds, 60-120 seconds, 120-180 seconds, or over the entire time course? ExplainYour Answer: the enzyme is working at its maximum rate over the entire time, because the graph keeps going up until it reaches a constant at that point the enzyme is working at the maximum capacity it can work at. Before that the enzyme is still working to reach the maximum.

2.    Answered     In order to keep the rate constant over the entire time course, what should be added: more enzymes or more substrate? Explain.Your Answer: to keep the constant over the entire time course more substrate would need to be added so that the enzymes would have a substance to to bind to, because if more enzymes were added the substrates already in the substance would be bonded to the enzyme and than after when all the products are made the rate of the constant would decrease, but if more substrates where added than the enzymes would have molecules to bind to and the rate of work that they are doing will remain constant.

Activities quiz

1.    Correct     Which of these is exhibiting kinetic energy? (Activity: Energy Transformations)Your Answer: a space station orbiting Earth 

2.    Correct     "Conservation of energy" refers to the fact that _____. (Activity: Energy Transformations)Your Answer: energy cannot be created or destroyed but can be converted from one form to another 

3.    Correct     Chemical energy is a form of _____ energy. (Activity: Energy Transformations)Your Answer: potential 

4.    Correct     In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP? (Activity: Energy Transformations)Your Answer: cellular respiration 

5.    Correct     Which of these are by-products of cellular respiration? (Activity: Energy Transformations)Your Answer: heat, carbon dioxide, and water 

6.    Correct     Which of these is ATP? (Activity: The Structure of ATP)Your Answer:

 

7.    Correct     What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule? (Activity: The Structure of ATP)Your Answer: hydrolysis 

8.    Correct     In this reaction _____. (Activity: Chemical Reactions and ATP)

Your Answer: the products have less potential energy than the reactants 

9.    Correct     In this reaction _____. (Activity: Chemical Reactions and ATP)

Your Answer: heat has been released to the environment 

10.    Correct     The reaction A --> B + C + heat is released in a(n) _____ reaction. (Activity: Chemical Reactions and ATP)Your Answer: exergonic 

11.    Correct     A(n) _____ reaction occurs spontaneously. (Activity: Chemical Reactions and ATP)Your Answer: exergonic 

12.    Correct     Which of these reactions requires a net input of energy from its surroundings? (Activity: Chemical Reactions and ATP)

Your Answer: endergonic 

13.    Correct     In cells, what is usually the immediate source of energy for an endergonic reaction? (Activity: Chemical Reactions and ATP)Your Answer: ATP 

14.    Correct     The reaction ADP + P --> ATP is a(n) _____ reaction. (Activity: Chemical Reactions and ATP)Your Answer: endergonic 

15.    Correct     The energy for an endergonic reaction comes from a(n) _____ reaction. (Activity: Chemical Reactions and ATP)Your Answer: exergonic 

16.    Correct     What is the fate of the phosphate group that is removed when ATP is converted to ADP? (Activity: Chemical Reactions and ATP)Your Answer: It is acquired by a reactant in an endergonic reaction. 

17.    Correct     This graph illustrates a(n) _____ reaction. (Activity: Chemical Reactions and ATP)

Your Answer: endergonic 

18.    Correct     Select the INCORRECT association. (Activity: Chemical Reactions and ATP)Your Answer: exergonic ... uphill 

19.    Correct     What is energy coupling? (Activity: Chemical Reactions and ATP)Your Answer: the use of energy released from an exergonic reaction to drive an endergonic reaction 

20.    Correct     Enzymes are _____. (Activity: How Enzymes Work)Your Answer: proteins 

21.    Correct     Enzymes work by _____. (Activity: How Enzymes Work)Your Answer: reducing EA

 

22.    Correct     An enzyme _____. (Activity: How Enzymes Work)Your Answer: is an organic catalyst 

23.    Correct     What name is given to the reactants in an enzymatically catalyzed reaction? (Activity: How Enzymes Work)Your Answer: substrate 

24.    Correct     As a result of its involvement in a reaction, an enzyme _____. (Activity: How Enzymes Work)Your Answer: is unchanged 

25.    Correct     What is the correct label for "A"? (Activity: How Enzymes Work)

Your Answer: energy of activation

Chapter quiz

1.    Correct     Which of the following correctly states the relationship between anabolic and catabolic pathways? (Concept 8.1 )

Your Answer: Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways. 

2.    Correct     Which of the following situations does not represent a transformation of one type of energy to another? (Concept 8.1 )Your Answer: a collision between one billiard ball and other balls, causing them to move 

3.    Correct     Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description? (Concept 8.1 )Your Answer: Organisms acquire energy from their surroundings. 

4.    Correct     Consider the growth of a farmer's crop over a season. Which of the following correctly states a limitation imposed by the first or second laws of thermodynamics? (Concept 8.1 )Your Answer: In order to obey the first law, the crop must represent an open system. 

5.    Correct     Which of the following states the relevance of the first law of thermodynamics to biology? (Concept 8.1 )Your Answer: Energy can be freely transformed among different forms as long as the total energy is conserved. 

6.    Correct     Which is the most abundant form of energy in a cell? (Concept 8.1 )Your Answer: chemical energy 

7.    Correct     Which of the following is an example of the second law of thermodynamics as it applies to biological reactions? (Concept 8.1 )Your Answer: The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water. 

8.    Correct     According to the second law of thermodynamics, which of the following is true? (Concept 8.1 )Your Answer: The decrease in entropy associated with life must be compensated for by an increase in entropy in the environment that life occurs in. 

9.    Correct     If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously? (Concept 8.2 )Your Answer: Energy input into the organism must be occurring in order to drive the decrease in entropy. 

10.    Correct     Which one of the following has the most free energy per molecule? (Concept 8.2)

Your Answer: a starch molecule 

11.    Correct     Which part of the equation G = H - TS tells you if a process is spontaneous? (Concept 8.2 )Your Answer: G 

12.    Correct     If, during a process, the system becomes more ordered, then _____. (Concept 8.2)

Your Answer: S is negative 

13.    Correct     When one molecule is broken down into six component molecules, which one of the following will always be true? (Concept 8.2 ) Your Answer: S is positive. 

14.    Correct     From the equation G = H - TS it is clear that _____. (Concept 8.2 )Your Answer: The first three choices are correct.  

15.    Correct     What must be true if the reaction AB + CD AC + BD occurs spontaneously? (Concept 8.2 )Your Answer: The difference between H and TS must be negative. 

16.    Correct     An exergonic (spontaneous) reaction is a chemical reaction that _____. (Concept 8.2 )Your Answer: releases energy when proceeding in the forward direction 

17.    Correct     Which of the following reactions would be endergonic? (Concept 8.2 )Your Answer: glucose + fructose sucrose 

18.    Correct     Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tend to keep these pathways away from equilibrium? (Concept 8.2 )Your Answer: The first and second choices are correct. 

19.    Correct     Which of the following is not an example of the cellular work accomplished with the free energy derived from the hydrolysis of ATP? (Concept 8.3 )

Your Answer: the production of heat, which raises the temperature of the cell 

20.    Correct     In general, the hydrolysis of ATP drives cellular work by _____. (Concept 8.3)Your Answer: releasing free energy that can be coupled to other reactions 

21.    Correct     Which of the following statements correctly describes some aspect of ATP hydrolysis being used to drive the active transport of an ion into the cell against the ion's concentration gradient? (Concepts 8.2 and 8.3 )Your Answer: This is an example of energy coupling. 

22.    Correct     Which compound could be most easily modified to form ATP? (Concept 8.3 )Your Answer: the RNA nucleotide adenosine 

23.    Correct     Much of the suitability of ATP as an energy intermediary is related to the instability of the bonds between the phosphate groups. These bonds are unstable because _____. (Concept 8.3 ) Your Answer: the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP 

24.    Correct     When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations? (Concept 8.3 )Your Answer: In the cell, the hydrolysis of ATP is coupled to other endergonic reactions. 

25.    Correct     What best characterizes the role of ATP in cellular metabolism? (Concept 8.3 )

Your Answer: The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate. 

26.    Correct     The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways? (Concept 8.3 )Your Answer: the hydrolysis of ATP 

27.    Correct     A chemical reaction is designated as exergonic rather than endergonic when _____. (Concepts 8.2 and 8.4 )Your Answer: the potential energy of the products is less than the potential energy of the reactants 

28.    Correct     What do the sign and magnitude of the G of a reaction tell us about the speed of the reaction? (Concepts 8.2 and 8.4 )Your Answer: Neither the sign nor the magnitude of G have anything to do with the speed of a reaction. 

29.    Incorrect     The mechanism of enzyme action is _____. (Concept 8.4 )Your Answer: lowering the free energy change of a reactionThe Correct Answer: lowering the energy of activation for a reaction 

30.    Correct     Which of the following statements about enzymes is true? (Concept 8.4 )Your Answer: Enzymes speed up the rate of the reaction without changing the G for the reaction. 

31.    Correct     Which of the following statements about enzyme function is correct? (Concept 8.4 )Your Answer: Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output. 

32.    Correct     A plot of reaction rate (velocity) against temperature for an enzyme indicates little activity at 10°C and 45°C, with peak activity at 35°C. The most reasonable explanation for the low velocity at 10°C is that _____. (Concept 8.4 )Your Answer: there is too little activation energy available 

33.    Correct     Which of the following statements about enzymes is incorrect? (Concept 8.4 )Your Answer: All of the above are correct statements about enzymes. 

34.    Correct     Which of the following statements about the active site of an enzyme is correct? (Concept 8.4 )Your Answer: The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits. 

35.    Correct     What is meant by the "induced fit" of an enzyme? (Concept 8.4 )Your Answer: The enzyme changes its shape slightly as the substrate binds to it. 

36.    Correct     Which of the following statements correctly describe(s) the role(s) of heat and temperature in biological reactions? (Concept 8.4 )Your Answer: The first and second choices are correct.  

37.    Correct     Above a certain substrate concentration, the rate of an enzyme-catalyzed reaction drops as the enzymes become saturated. Which of the following would lead to a faster conversion of substrate into product under these saturated conditions? (Concept 8.4 )Your Answer: The first and second choices are correct. 

38.    Correct     Which of the following environments or actions does not affect the rate of an enzyme reaction? (Concept 8.4 )Your Answer: all of the above 

39.    Correct     Enzyme activity is affected by pH because _____. (Concept 8.4 )Your Answer: high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site 

40.    Correct     Which of these statements about enzyme inhibitors is true? (Concept 8.4 )Your Answer: The action of competitive inhibitors may be reversible or irreversible. 

41.    Correct     Succinylcholine is structurally almost identical to acetylcholine. If succinylcholine is added to a mixture that contains acetylcholine and the enzyme that hydrolyzes acetylcholine (but not succinylcholine), the rate of acetylcholine hydrolysis is decreased. Subsequent addition of more acetylcholine restores the original rate of acetylcholine hydrolysis. Which of the following correctly explains this observation? (Concept 8.4 )Your Answer: Succinylcholine must be a competitive inhibitor with acetylcholine. 

42.    Correct     The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of _____. (Concept 8.5 )Your Answer: allosteric regulation 

43.    Correct     Which, if any, of the following statements is not true about allosteric proteins? (Concept 8.5 )Your Answer: They can bind to a range of substrates. 

44.    Correct     The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Which of the following best explains why this decrease occurs? (Concept 8.5 )Your Answer: The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site. 

45.    Correct     Under most conditions, the supply of energy by catabolic pathways is regulated by the demand for energy by anabolic pathways. Considering the role of ATP formation and hydrolysis in energy coupling of anabolic and catabolic pathways, which of the following statements is most likely to be true? (Concept 8.5 )Your Answer: High levels of ADP act as an allosteric activator of catabolic pathways