FINAL 07 2020, questions and answers PDF

Preview

Summary

Module_5_ Ch_08...

Description

6/13/2020

Module #5: Ch 08

Module #5: Ch 08 Due: 11:59pm on Thursday, July 1, 2021 You will receive no credit for items you complete after the assignment is due. Grading Policy

ATP and Energy Biological processes involve both catabolism, the breaking down of high-energy molecules into simple molecules, and anabolism, the building of complex molecules from simple ones. In general, catabolic processes generate energy, whereas anabolic processes require energy. The energy is usually stored in intermediate energy-carrying molecules such as adenosine triphosphate (ATP).

Part A - Identifying the highest energy form of adenosine Select the highest energy form of adenosine from the following images.

Hint 1. How adenosine gains energy The addition of phosphates to the ribose component (a pentose sugar) of an adenosine molecule gives the molecule usable energy. The phosphates can be broken off by an enzyme, and the energy freed from the release of the phosphate group can drive endergonic (energy-requiring) chemical reactions in the cell. Hint 2. Which molecule has the highest energy? Rank the following molecules from highest to lowest energy content. To rank molecules as equivalent, overlap them. ANSWER:

Reset

Help

ANSWER:

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

1/18

6/13/2020

Module #5: Ch 08

Correct Adenosine triphosphate (ATP) is the high-energy form of adenosine because it contains the most phosphate groups (three). This molecule fuels many different endergonic (energy-requiring) enzymatic processes in biological organisms. ATP molecules diffuse or are transported to the place where the energy is needed and deliver chemical energy from the breaking of their phosphate bonds.

Part B - Energy release from ATP Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?

Hint 1. The general structure of adenosine triphosphate (ATP) Adenosine triphosphate (ATP) is made up of three main structural parts: the nitrogenous base adenine, the ribose sugar, and the three phosphate groups bonded together by phosphodiester bonds.

Hint 2. What are the different parts of the ATP molecule? Complete the following vocabulary exercise relating to the parts of the ATP molecule. ANSWER:

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

2/18

6/13/2020

Module #5: Ch 08

Reset

1. The beta-phosphate

2. The adenine group

3. The ribose sugar

Help

is the phosphate group attached to the alpha-phosphate.

is the nitrogenous base attached to the ribose sugar.

is the scaffold that provides the backbone for the entire adenosine triphosphate

molecule. 4. The gamma-phosphate

is the third phosphate group and is attached to the beta-phosphate,

farthest from the ribose sugar, where it is most likely to participate in energy-releasing reactions. 5. The alpha-phosphate

is the phosphate group closest to the ribose sugar.

ANSWER:

-phosphate (the phosphate closest to ribose) -phosphate (the middle phosphate) -phosphate (the terminal phosphate) adenine group ribose sugar

Correct The -phosphate is the primary phosphate group on the ATP molecule that is hydrolyzed when energy is needed to drive anabolic reactions. Located the farthest from the ribose sugar, it has a higher energy than either the - or -phosphate.

Enzyme and Substrate Concentrations In general, an enzyme has one active site at which catalysis can occur. When the substrates are bound to the active site, the enzyme will catalyze the reaction. A the concentration of substrate increases, the reaction rate increases, until the point where the active site is saturated with substrate. When the enzyme is saturate the rate of the reaction will not increase with the concentration of substrates.

Part A Look at the graph of reaction rate versus substrate concentration for an enzyme. In which region does the reaction rate remain constant?

Hint 1. How to read the graph

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

3/18

6/13/2020

Module #5: Ch 08

On this graph, changes in reaction rate are shown by vertical (up or down) movement of the line. A constant reaction rate would be represented by a flat portion of the line (one that moves neither up nor down).

ANSWER:

region A region B region C

Correct In region C of the graph, the reaction rate is independent of substrate concentration.

Part B Refer again to the graph. In which region is the enzyme saturated with substrate?

Hint 1. How to approach the problem When the enzyme is saturated, adding more substrate molecules will not increase the rate of reaction. In which region of the graph is the reaction rate independent of substrate concentration?

ANSWER:

region A region B region C

Correct

Part C Consider a situation in which the enzyme is operating at optimum temperature and increasing the rate of the reaction?

, and has been saturated with substrate. What is your best option for

Hint 1. Select what would happen if the substrate concentration were increased If the enzyme is saturated, what would happen if the substrate concentration were increased? ANSWER:

The added substrate molecules would bind to the active site. The added substrate molecules would not bind to the active site.

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

4/18

6/13/2020

Module #5: Ch 08

Hint 2. Select the correct meaning of optimum What does the term optimum mean in this context? ANSWER:

It means that adjusting the temperature or

can improve the enzyme activity a little.

It means that adjusting the temperature or

can improve the enzyme activity quite a bit.

It means that the

or temperature is such that the enzyme is not active.

It means that the enzyme has maximum activity and cannot be improved by adjusting temperature or

.

ANSWER:

Increase the

.

Increase the temperature. Increase the enzyme concentration. Increase the substrate concentration.

Correct If an enzyme is saturated with substrate, and it is operating at optimum and optimum temperature, there is very little that can be done except to increase the enzyme concentration. Some enzymes can be activated further by allosteric activators, in which case one might add some activator to the reaction. But otherwise, increasing the enzyme concentration is the only option.

How Enzymes Function Enzymes are biological catalysts. They can increase the rate of chemical reactions as much as a millionfold by lowering the energy barrier of a reaction.

Part A - Enzymes and activation energy The graph presents three activation energy profiles for a chemical reaction (the hydrolysis of sucrose): an uncatalyzed reaction, and the same reaction catalyzed by two different enzymes.

Rank these by reaction rate, as measured by the rate of product formation per unit time, from lowest reaction rate to highest reaction rate. To rank items as equivalent, overlap them.

Hint 1. Definition of activation energy Activation energy (also called free energy of activation) is the initial investment of energy needed to start a reaction. It is the amount of energy that the reactants must absorb before a chemical reaction will start. Hint 2. How does activation energy affect reaction rate? Complete the following statement. ANSWER:

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

5/18

6/13/2020

Module #5: Ch 08 more

The higher the activation energy, the

less

product formed per unit time.

ANSWER:

Reset

uncatalyzed reaction

reaction catalyzed by enzyme A

Help

reaction catalyzed by enzyme B

Correct Enzymes lower the activation energy of a chemical reaction. This means that a catalyzed reaction is more likely to proceed than an uncatalyzed reaction, and it forms products more rapidly than an uncatalyzed reaction.

Part B - Factors that affect enzymes Complete this vocabulary exercise relating to enzymes. Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column.

Hint 1. How enzymes work This diagram shows the process by which an enzyme converts reactant molecules into product molecules. (In this case, the enzyme converts two reactants, or substrates, into two products.)

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

6/18

6/13/2020

Module #5: Ch 08

Hint 2. Which factors affect enzyme activity? Choose the factors that affect enzyme activity by altering either the enzyme’s shape or its effectiveness. Select all that apply. ANSWER:

temperature pH inorganic ions and vitamins activation energy

ANSWER:

Reset

Help

1. An enzyme is denatured when it loses its native conformation and its biological activity.

2. An enzyme is considered a catalyst because it speeds up chemical reactions without being used up. 3. An enzyme is considered specific because of its ability to recognize the shape of a particular molecule. 4. A cofactor , such as a vitamin, binds to an enzyme and plays a role in catalysis.

5. When properly aligned, the enzyme and substrate form an enzyme-substrate (ES) complex .

6. A substrate binds to an enzyme at the active site , where the reaction occurs.

7. In a catalyzed reaction a reactant is often called a substrate .

Correct A substrate binds at an enzyme’s active site; the enzyme typically recognizes the specific shape of its substrate. A cofactor, such as an inorganic ion or vitamin, may bind to the enzyme and assist in catalyzing the reaction. The reaction environment must be appropriate for catalysis to proceed. An enzyme will denature, or change its shape and lose its biological activity, at too high a temperature or at a pH outside the enzyme’s optimal range.

Activity: How Enzymes Work

Click here to complete this activity.

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

7/18

6/13/2020

Module #5: Ch 08

Then answer the questions.

Part A In general, enzymes are what kinds of molecules? ANSWER: proteins minerals lipids nucleic acids carbohydrates

Correct Enzymes are proteins.

Part B Enzymes work by _____. ANSWER: adding energy to a reaction increasing the potential energy difference between reactant and product decreasing the potential energy difference between reactant and product reducing EA adding a phosphate group to a reactant

Correct Enzymes work by reducing the energy of activation.

Part C An enzyme _____. ANSWER:

is an organic catalyst is a inorganic catalyst can bind to nearly any molecule increases the EA of a reaction is a source of energy for endergonic reactions

Correct Enzymes are proteins that behave as catalysts.

Part D What name is given to the reactants in an enzymatically catalyzed reaction? ANSWER:

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

8/18

6/13/2020

Module #5: Ch 08 EA reactors active sites substrate products

Correct This is the name given to the reactants in an enzymatically catalyzed reaction.

Part E As a result of its involvement in a reaction, an enzyme _____. ANSWER:

loses a phosphate group loses energy permanently alters its shape. is used up is unchanged

Correct Enzymes are not changed as a result of their participation in a reaction.

Part F What is the correct label for "A"?

ANSWER:

uphill substrate energy enzyme energy energy of activation ATP

Correct The energy of activation must be overcome in order for a reaction to proceed.

Regulating Enzyme Action https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

9/18

6/13/2020

Module #5: Ch 08

Organisms require many different small molecules for their moment-to-moment activities. These small molecules are often produced in enzymatic pathways that have three or more enzymes making modifications to the substrate. These pathways must be regulated so that the small molecules are present in appropriate amounts. The image shows a hypothetical enzymatic pathway with four enzymes, labelled E1, E2, E3, and E4. The enzymes make products, labelled P0, P1, P2, P3, and P4.

Part A Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown?

Hint 1. How to approach the problem In an enzymatic pathway such as the one depicted, there is a normal pattern of feedback inhibition. The inhibition usually involves the first enzyme in the pathway, since this enzyme catalyzes what is commonly known as the "committed step" of the pathway. To answer the question, think about what would be the most efficient way of regulating an enzymatic pathway, so that it is on when the products are needed, and off when there is too much of the product. Hint 2. Identify how to regulate an enzymatic pathway Which of the following is the most logical way to regulate an enzymatic pathway if you are trying to keep a constant level of product around? ANSWER:

The initial reactant deactivates the last enzyme. The initial reactant deactivates the first enzyme. The final product inhibits the first enzyme. The final product activates the last enzyme.

ANSWER:

P0 binds E4 and activates it. P2 binds E2 and activates it. P4 binds E1 and deactivates it. P3 binds E2 and activates it P4 binds E3 and deactivates it.

Correct Many enzymatic pathways are regulated by the feedback inhibition model described here. In fact, it is so common that another name for it is endproduct inhibition.

Enzyme Inhibition Molecules other than substrates bind to enzymes. Some of these other molecules slow down the rate of the enzymatic reaction. These molecules are called enzyme inhibitors.

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

10/18

6/13/2020

Module #5: Ch 08

Part A - Types of enzyme inhibitors Complete this vocabulary exercise relating to the three types of enzyme inhibitors. Drag the words on the left to the appropriate blanks in the sentences on the right. Each word is used only once.

Hint 1. What are the characteristics of competitive inhibitors? Which of the following statements correctly describe(s) competitive inhibitors? Select all that apply. ANSWER:

A competitive inhibitor competes with the substrate for the active site of the enzyme. A competitive inhibitor binds irreversibly to the enzyme and renders it useless. The structure of a competitive inhibitor is very similar to that of the substrate. At sufficient concentration, a competitive inhibitor reduces enzyme activity; enzyme activity can be regained by increasing the substrate concentration.

Hint 2. What are the characteristics of noncompetitive inhibitors? Which of the following statements correctly describe(s) noncompetitive inhibitors? Select all that apply. ANSWER:

A noncompetitive inhibitor binds to the active site on an enzyme. The effect of a noncompetitive inhibitor is reversible; enzyme activity is restored when the noncompetitive inhibitor is removed from the enzyme. The structure of a noncompetitive inhibitor is similar to that of the substrate. A noncompetitive inhibitor distorts the enzyme’s shape when it binds to the enzyme.

Hint 3. What are the characteristics of irreversible inhibitors? Which of the following statements correctly describe(s) irreversible inhibitors? Select all that apply. ANSWER:

Irreversible inhibitors usually form covalent bonds within the active site, preventing the substrate from entering the active site or preventing catalytic activity. Irreversible inhibitors include nerve gases and insecticides, which act on acetylcholinesterase. Irreversible inhibitors can be competed out of an active site by adding more substrate. Irreversible inhibitors act by breaking the enzyme apart.

ANSWER:

https://session.masteringbiology.com/myct/assignmentPrintView?assignmentID=8245659

11/18

6/13/2020

Module #5: Ch 08

Reset

1. A (n) competitive

Help

inhibitor has a structure that is so similar to the substrate that it can bond to the

enzyme just like the substrate. 2. A (n) noncompetitive

inhibitor binds to a site on the enzyme that is not the active site.

3. Usually, a(n) irreversible

inhibitor forms a covalent bond with an amino acid side group within the

active site, which prevents the substrate from entering the active site or prevents catalytic activity. 4. The competitive inhibitor competes with the substrate for the active site

on the enzyme.

5. When the noncompetitive inhibitor is bonded to the enzyme, the shape of the enzyme

is distorted.

6. Enzyme inhibitors disrupt normal interactions between an enzyme and its substrate .

Correct Competitive inhibitors compete physically and structurally with the substrate for an enzyme’s active site; they can be outcompeted by adding extra substrate. Noncompetitive inhibitors do not compete for the active site, but inhibit the enzyme by binding elsewhere and changing the enzyme’s shape. Irreversible inhibitors bind directly to the active site by covalent bonds, which change the structure of the enzyme and inactivate it permanently. Most medications are enzyme inhibitors of one kind or another.

Part B - Irreversible inhibition You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme?

Hint 1. How to approach the problem To answer this question, think about the properties of irreversible inhibitors. What do they do to an enzyme? If you have inhibited an enzyme with an irreversible inhibitor, what—if anything— can be done to activate the enzyme? Hint 2. What is the description of an irreversible inhibitor? Which of the following statements most accurately describes an irreversible inhibitor? ANSWER: An irreversible inhibitor binds to the active site of an enzyme and can easily be removed. An irreversible inhibitor binds to a different location than the substrate and can easily be removed. An irreversible inhibitor binds covalently to the active site of an enzyme and cannot be removed easily. An irreversible inhibitor binds to the substrate and removes it from solution so it cannot react with the enzyme.

ANSWER:

Removing the irreversible inhibitor should get the...