Chapter 8 - Introduction to Metabolism

3/7/13 10:35 PMChapter 8 - Introduction to Metabolism

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Chapter 8 - Introduction to Metabolism

Due: 9:00am on Monday, March 11, 2013

Note: You will receive no credit for late submissions. To learn more, read your instructor's Grading Policy

Activity: Energy Transformations

Click here to complete this activity.

Then answer the questions.

Part A

Which of these is exhibiting kinetic energy?

ANSWER:

Correct

Kinetic energy is energy of motion.

Part B

"Conservation of energy" refers to the fact that _____.

ANSWER:

Correct

This is what is meant by conservation of energy.

Biol 1002 - Spring 2013

Chapter 8 - Introduction to Metabolism Resources

the high-energy phosphate bonds of a molecule of ATP

a rock on a mountain ledge

a space station orbiting Earth

an archer with a flexed bow

a person sitting on a couch while watching TV

energy cannot be created or destroyed but can be converted from one form to another

if you conserve energy you will not be as tired

the entropy of the universe is always increasing

no chemical reaction is 100 percent efficient

the net amount of disorder is always increasing

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Part C

Chemical energy is a form of _____ energy.

ANSWER:

Correct

Chemical energy is a form of stored energy.

Part D

In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP?

ANSWER:

Correct

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

Part E

Which of these are by-products of cellular respiration?

ANSWER:

Correct

These are the by-products of cellular respiration.

ATP and Energy

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

Part A - Identifying the highest energy form of adenosine

kinetic

heat

potential

motion

entropic

potentiation

redox

digestion

anabolism

cellular respiration

carbon dioxide and water

glucose, carbon dioxide, and water

heat, carbon dioxide, and water

ATP, carbon dioxide, and water

ATP and carbon dioxide



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. Thephosphates 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:

Correct

Because adding phosphate groups to the ribose component of an adenosine molecule gives the molecule usable energy, the adenosinewith the most phosphate groups has the highest energy content, and the one with no phosphate groups has the lowest energy content.

ANSWER:



Correct

Adenosine triphosphate (ATP) is the high-energy form of adenosine because it contains the most phosphate groups (three). This molecule fuelsmany different endergonic (energy-requiring) enzymatic processes in biological organisms. ATP molecules diffuse or are transported to the placewhere 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 threephosphate 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:



ANSWER:

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.

Activity: Chemical Reactions and ATP



-phosphate (the phosphate closest to ribose)

-phosphate (the middle phosphate)

-phosphate (the terminal phosphate)

adenine group

ribose sugar





Part A

In this reaction _____.

ANSWER:

Correct

This is what is shown by the graph.

Part B

In this reaction _____.

ANSWER:

Correct

The potential energy of the products is less than that of the reactants.

Part C

The reaction A --> B + C + heat is released in a(n) _____ reaction.

entropy has decreased

AC is a reactant

CD is a product

the products have been rearranged to form reactants

the products have less potential energy than the reactants

the chemical energy of the products is greater than that of the reactants

disorder has decreased

the kinetic energy of the reactants is less than that of the products

entropy has decreased

heat has been released to the environment



ANSWER:

Correct

Energy has been released.

Part D

A(n) _____ reaction occurs spontaneously.

ANSWER:

Correct

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

Part E

Which of these reactions requires a net input of energy from its surroundings?

ANSWER:

Correct

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

Part F

In cells, what is usually the immediate source of energy for an endergonic reaction?

ANSWER:

exchange

exergonic

dehydration synthesis

endergonic

anabolic

chemical

endergonic

exergonic

kinetic

anabolic

hydrolysis

ATP --> ADP + P

endergonic

catabolic

exergonic



Correct

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

Part G

The reaction ADP + P --> ATP is a(n) _____ reaction.

ANSWER:

Correct

Energy has been acquired from the surroundings.

Part H

The energy for an endergonic reaction comes from a(n) _____ reaction.

ANSWER:

Correct

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

Part I

What is the fate of the phosphate group that is removed when ATP is converted to ADP?

ANSWER:

sugar

ADP

ATP

as spontaneous reactions, endergonic reactions do not need an addition of energy

glucose

chemical

endergonic

spontaneous

exergonic

hydrolysis

ADP + P --> ATP

exergonic

anabolic

glucose + glucose --> maltose

synthesis

It is acquired by a reactant in an exergonic reaction.

It is used to convert an ATP into an AQP.

It is acquired by a reactant in an endergonic reaction.

It is broken down into one phosphorus and four oxygen atoms.

It is acquired by a reactant in a spontaneous reaction.



Correct

By acquiring the phosphate group the reactant acquires energy.

Part J

This graph illustrates a(n) _____ reaction.

ANSWER:

Correct

The products contain more potential energy than the reactants.

Part K

Select the INCORRECT association.

ANSWER:

Correct

Exergonic reactions release energy.

Part L

What is energy coupling?

ANSWER:

exergonic

catabolic

hydrolysis

spontaneous

endergonic

potential energy ... positional energy

enzyme ... protein

kinetic energy ... motion

exergonic ... uphill

exergonic ... spontaneous



Correct

This is energy coupling.

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 thereaction. As the concentration of substrate increases, the reaction rate increases, until the point where the active site is saturated with substrate. When theenzyme is saturated, 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

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

ANSWER:

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?

the use of energy released from an exergonic reaction to drive an endergonic reaction

the hydrolysis of ATP to ADP + P

a description of the energetic relationship between the reactants and products in an exergonic reaction

a barrier to the initiation of a reaction

the use of an enzyme to reduce EA

region A

region B

region C



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 thereaction rate independent of substrate concentration?

ANSWER:

Correct

Part C

Consider a situation in which the enzyme is operating at optimum temperature and , and has been saturated with substrate. What is your best

option for increasing the rate of the reaction?

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:

Hint 2. Select the correct meaning of optimum

What does the term optimum mean in this context?

ANSWER:

region A

region B

region C

The added substrate molecules would bind to the active site.

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

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 .



Correct

ANSWER:

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 someactivator to the reaction. But otherwise, increasing the enzyme concentration is the only option.

Enzyme Inhibition

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

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:

Increase the .

Increase the temperature.

Increase the enzyme concentration.

Increase the substrate concentration.

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 thesubstrate concentration.



Correct

A competitive inhibitor has the same structure as the substrate with which it competes. Like the substrate, a competitive inhibitor binds atthe enzyme’s active site, although relatively weakly. The competitive inhibitor reduces enzyme activity, but the effect can be reversed byincreasing the substrate concentration.

Hint 2. What are the characteristics of noncompetitive inhibitors?

Which of the following statements correctly describe(s) noncompetitive inhibitors?


ANSWER:

Correct

A noncompetitive inhibitor binds to the enzyme away from the active site, which alters the shape of the enzyme. This affects the enzyme’sability to bind to the substrate and decreases the enzyme’s activity. Like a competitive inhibitor, a noncompetitive inhibitor also bindsrelatively weakly and its effect can be reversed because it can be removed.

Hint 3. What are the characteristics of irreversible inhibitors?

Which of the following statements correctly describe(s) irreversible inhibitors?


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 theenzyme.

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.



ANSWER:

Correct

Competitive inhibitors compete physically and structurally with the substrate for an enzyme’s active site; they can be outcompeted by adding extrasubstrate. Noncompetitive inhibitors do not compete for the active site, but inhibit the enzyme by binding elsewhere and changing the enzyme’sshape. Irreversible inhibitors bind directly to the active site by covalent bonds, which change the structure of the enzyme and inactivate itpermanently. 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?


To answer this question, think about the properties of irreversible inhibitors. What do they do to an enzyme? If you have inhibited an enzymewith 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:

Irreversible inhibitors usually form covalent bonds within the active site, preventing the substrate from entering the active site orpreventing 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.



Correct

An irreversible inhibitor binds covalently to the enzyme, which alters the enzyme’s chemical structure. The inhibitor cannot be removedeasily.

ANSWER:

Correct

Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive. Some drugs areirreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (whichinhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).

Part C - Reversible inhibition

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and noticethat the reaction slows down.

What can you do to speed the reaction up again?


To answer this question, think about the properties of competitive inhibitors. How do they work? Is there a way to remove them from the activesite of the enzyme once they are in it? If so, what is it?

Hint 2. How does a competitive inhibitor work?

Which of the following statements most accurately describes a competitive inhibitor?

ANSWER:

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.

Removing the irreversible inhibitor should get the reaction working again.

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.

Adding more substrate will increase the rate of reaction.

Adding more inhibitor should get the reaction up to speed again.

A competitive inhibitor has a structure that is so similar to the substrate that it can bind to the enzyme in the same way as thesubstrate.

The structure of a competitive inhibitor does not resemble the substrate and does not compete for the active site.

Most competitive inhibitors are toxic substances that destroy enzymes.

Competitive inhibitors bind at the enzyme's active site, where the enzyme converts them into the reaction product(s).

Add more inhibitor to speed up the reaction.

Add more substrate; it will outcompete the inhibitor and increase the reaction rate.

Increase the temperature.

Increase the pH.



Correct

Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor. Many drugs used to treat different medicalconditions, including hypertension, are competitive inhibitors. It is fairly easy to make a molecule that is similar in structure to a particular substratebecause the known enzyme’s shape can be used as a model of what the molecule needs to look like. It is more difficult to make a noncompetitiveinhibitor because it is less obvious what the noncompetitive inhibitor’s shape and structure should be.

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 reactioncatalyzed by two different enzymes.

Rank these by reaction rate, as measured by the rate of product formation (from the most product formed to the least product formed). Torank 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 energythat the reactants must absorb before a chemical reaction will start.

Hint 2. How does activation energy affect reaction rate?

Complete the following statement.

ANSWER:

Correct

ANSWER:

The higher the activation energy, the more

less product formed per unit time.



Correct

Enzymes lower the activation energy of a chemical reaction. This means that a catalyzed reaction is more likely to proceed than an uncatalyzedreaction, 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 convertstwo reactants, or substrates, into two products.)

Hint 2. Which factors affect enzyme activity?

Choose the factors that affect enzyme activity by altering either the enzyme’s shape or its effectiveness.




ANSWER:

Correct

An enzyme will denature, or change its shape and lose its biological activity, when the reaction's environmental temperature is too high forthat enzyme, or when the pH is outside of that enzyme’s optimal range. Cofactors, including inorganic ions and vitamins, often bind toenzymes and affect catalysis.

ANSWER:

All attempts used; correct answer displayed

A substrate binds at an enzyme’s active site; the enzyme typically recognizes the specific shape of its substrate. A cofactor, such as an inorganicion or vitamin, may bind to the enzyme and assist in catalyzing the reaction. The reaction environment must be appropriate for catalysis toproceed. 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’soptimal range.

Activity: How Enzymes Work

temperature

pH

inorganic ions and vitamins

activation energy





Part A

In general, enzymes are what kinds of molecules?

ANSWER:

Correct

Enzymes are proteins.

Part B

Enzymes work by _____.

ANSWER:

Correct

Enzymes work by reducing the energy of activation.

Part C

An enzyme _____.

ANSWER:

lipids

minerals

proteins

carbohydrates

nucleic acids

adding energy to a reaction

increasing the potential energy difference between reactant and product

adding a phosphate group to a reactant

reducing EA

decreasing the potential energy difference between reactant and product





Correct

Enzymes are proteins that behave as catalysts.

Part D

What name is given to the reactants in an enzymatically catalyzed reaction?

ANSWER:

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:

Correct

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

Part F

What is the correct label for "A"?

can bind to nearly any molecule

is an organic catalyst

is a inorganic catalyst

increases the EA of a reaction

is a source of energy for endergonic reactions

products

active sites

EA

reactors

substrate

loses energy

loses a phosphate group

is unchanged

permanently alters its shape.

is used up



ANSWER:

Correct

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

Regulating Enzyme Action

Organisms require many different small molecules for their moment-to-moment activities. These small molecules are often produced in enzymaticpathways that have three or more enzymes making modifications to the substrate. These pathways must be regulated so that the small molecules arepresent in appropriate amounts.

The image shows a hypothetical enzymatic pathway with four enzymes, labeled E1, E2, E3, andE4. The enzymes make products, labeled 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?


In an enzymatic pathway such as the one depicted, there is a normal pattern of feedback inhibition. The inhibition usually involves the firstenzyme 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 offwhen 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:

ANSWER:

energy of activation

substrate energy

enzyme energy

uphill

ATP

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.



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 end-product inhibition.

Chapter 8 Question 1

Part A

Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _______ is to _______.

ANSWER:

Correct

Activity: Build a Chemical Cycling System



Part A

What process occurs in structure H?

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.

exergonic; endergonic

work; energy

entropy; enthalpy

exergonic; spontaneous

free energy; entropy





ANSWER:

Correct

Chloroplasts are the sites of photosynthesis.

Part B

What molecules belong in space A and B?

ANSWER:

Correct

Photosynthesis produces glucose and releases oxygen into the atmosphere.

Part C

What organelle is indicated by the letter C?

ANSWER:

protein synthesis

ribosome synthesis

intracellular digestion

photosynthesis

cellular respiration

glucose and carbon dioxide

glucose and oxygen


oxygen and water

carbon dioxide and oxygen



Correct

Mitochondria are the sites of cellular respiration.

Part D

What molecules belong in spaces E and F?

ANSWER:

Correct

Carbon dioxide and water are by-products of cellular respiration.

Activity: Overview of Cellular Respiration



Part A

What process occurs in Box A?

Golgi apparatus

peroxisome

chloroplast

mitochondrion

lysosome

oxygen and water

glucose and oxygen


glucose, water, carbon dioxide, and oxygen

carbon dioxide and oxygen





ANSWER:

Correct

Glycolysis occurs in the cytosol.

Part B

What process occurs within Box B?

ANSWER:

Correct

The citric acid cycle transfers electrons to NADH and FADH2.

electron transport and oxidative phosphorylation

electron transport

glycolysis

oxidative phosphorylation

the citric acid cycle

oxidative phosphorylation

photophosphorylation

the citric acid cycle

electron transport

glycolysis



Part C

What molecule is indicated by the letter D?

ANSWER:

Correct

Oxygen is the final electron acceptor of cellular respiration.

Activity: Redox Reactions

Click here to view this animation.


Part A

Which term describes the degree to which an element attracts electrons?

Hint 1.

Which is a property of atoms?

ANSWER:

ATP

water

pyruvate

oxygen

glucose





Correct

Electronegativity is the tendency of an atom to attract electrons toward itself.

Part B

Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?

Hint 1.

How does the electrical state of each atom change?

ANSWER:

Correct

Each atom will carry a charge from the transfer of electrons.

Part C

Which of the following statements is true of the bonds in a water molecule?

Hint 1.

Consider the atomic properties of oxygen and hydrogen.

ANSWER:

Correct

The oxygen and hydrogen atoms in water have partial charges, but the molecule has a net charge of zero.

Part D

Which of the following statements is not true of most cellular redox reactions?

Hint 1.

Electronegativity.

Reduction.

Oxidation.

Polarity.

Proton and electron.

Polar and nonpolar.

Anion and cation.

Ionic and covalent.

There is equal sharing of the electrons between the oxygen atom and the two hydrogen atoms, and the net charge is zero.

The electron in each hydrogen atom is completely transferred to the oxygen atom, and each hydrogen atom has a net charge of +1.

Oxygen acts as the electron acceptor and is oxidized.

Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero.



What happens to the electrons and bonds during a redox reaction?

ANSWER:

Correct

A hydrogen atom (proton, or H+) is often transferred to the atom that gains an electron.

Part E

What kind of bond is formed when lithium and fluorine combine to form lithium fluoride?

Hint 1.

Consider the electrons in the outermost shell of each atom.

ANSWER:

Correct

The complete transfer of an electron from lithium to fluorine results in a stable compound in which both atoms have full outermost shells.

Part F

Gaseous hydrogen burns in the presence of oxygen to form water:

2H2 + O2 → 2H2 O + energy

Which molecule is oxidized and what kind of bond is formed?

Hint 1.

How are the electrons transferred?

ANSWER:

Correct

Hydrogen loses electrons to oxygen, which is more electronegative and thus pulls the electrons closer to itself in the water molecule.

A hydrogen atom is transferred to the atom that loses an electron.

The electron acceptor is reduced.

The reactant that is oxidized loses electrons.

Changes in potential energy can be released as heat.

Redox.

Nonpolar covalent.

Ionic.

Polar covalent.

Oxygen, polar.

Oxygen, nonpolar.

Hydrogen, polar.

Hydrogen, nonpolar.



Cellular Respiration (2 of 5): Glycolysis (BioFlix tutorial)

In glycolysis, the first stage of cellular respiration, one molecule of glucose is oxidized totwo molecules of pyruvate, with the production of ATP and NADH. As you watch theGlycolysis animation, pay attention to the reactions involved in the production of NADH.These reactions, called redox (oxidation-reduction) reactions, play a key role in cellularrespiration. Also pay attention to the mechanism by which ATP is synthesized. Thinkabout how ATP synthesis at this stage differs from ATP synthesis during oxidativephosphorylation, where most of the ATP in cellular respiration is made.

Part A - Redox (oxidation-reduction) reactions in glycolysis

In glycolysis, as in all the stages of cellular respiration, the transfer of electrons from electron donors to electron acceptors plays a critical role in theoverall conversion of the energy in foods to energy in ATP. These reactions involving electron transfers are known as oxidation-reduction, or redox,reactions.

Drag the words on the left to the appropriate blanks on the right to complete the sentences.

Hint 1. Redox reactions

Under normal circumstances, redox reactions always occur in pairs. In the first of the two reactions, the electron donor is oxidized (it loseselectrons). In the second reaction, the electron acceptor is reduced (it gains the electrons lost by the first compound). A generic redox reactionshowing the transfer of two electrons is illustrated here.

Note that compounds A and B each exist in two forms: One form is reduced (it carries the extra electrons) while the other form is oxidized (itdoes not carry the extra electrons). In the reaction shown here, the electron donor is the reduced form of compound A and the electron acceptoris the oxidized form of compound B.

Hint 2. The oxidation of carbon-containing compounds

In the net reaction of cellular respiration, glucose (C6H12O6) is completely oxidized to CO2.



In reality, glucose is not oxidized to CO2 in a single step, as suggested by the net reaction. Instead, there is a step-wise removal of 12 pairs ofelectrons from the carbon-containing intermediates of glucose catabolism (one pair at a time) until all of the carbons exist in the form of CO2.Two of the 12 pairs of electrons are removed in the reactions of glycolysis.

Hint 3. What are the electron carriers in glycolysis?

In glycolysis and the other stages of cellular respiration, electrons removed from intermediates in glucose catabolism are not passed directly toO2. Instead, electron carriers shuttle the electrons from the oxidation of the carbon-containing compounds to the eventual reduction of O2 towater.

In glycolysis, which molecule picks up the electrons released by the oxidation of glucose?

Hint 1. Redox reactions involving NAD+ and NADH

Recall that compounds involved in redox reactions occur in pairs, an oxidized form and a reduced form. The most common pair ofelectron carriers in cellular respiration is NAD+ (the oxidized form) and NADH (the reduced form).

ANSWER:

Correct

ANSWER:

ATP

O2

NAD+

NADH



All attempts used; correct answer displayed

In the net reaction for glycolysis, glucose (the electron donor) is oxidized to pyruvate. The electrons removed from glucose are transferred to theelectron acceptor, NAD+, creating NADH.

Part B - Energy from glycolysis

Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?

Hint 1. Energy in carbon-containing compounds

In the overall process of cellular respiration, glucose is oxidized to carbon dioxide and much of the energy generated by the breakdown ofglucose is used to make ATP. In glycolysis, however, glucose is only oxidized to pyruvate; no carbon dioxide is produced in this stage ofrespiration. In addition, only a small fraction (<10%) of the total ATP produced by cellular respiration is generated in glycolysis. Consider whatthis means in terms of the energy content of pyruvate and its oxidation in subsequent stages of cellular respiration.

Hint 2. ATP-- the energy currency of cells

The interconversion of ATP and ADP + Pi is a key step in the transfer of energy between reactions that release energy and those that requirean input of energy.

Most of the ATP produced in our cells comes from the oxidation of foods in cellular respiration. The reverse reaction, the hydrolysis of ATP toADP and Pi, powers most of the energy-requiring reactions that take place in cells, such as active transport and muscle contraction.

Hint 3. What is the fate of NADH produced by glycolysis?

Is the NADH produced in glycolysis used in any other reactions of cellular respiration where ATP is produced?

ANSWER:

ANSWER:

Yes, NADH is an input to the citric acid cycle, where more ATP is produced.

Yes, NADH is an input to oxidative phosphorylation, where more ATP is produced.

Yes, NADH is an input to both the citric acid cycle and oxidative phosphorylation, where more ATP is produced.

No, NADH is used in oxidative phosphorylation, but no additional ATP is produced.

No, NADH is not used in any subsequent stages of cellular respiration.

ATP and NADH only

CO2 only

pyruvate, ATP, and NADH

NADH only

ATP only

pyruvate and ATP only

O2 only



Correct

ATP is the main product of cellular respiration that contains energy that can be used by other cellular processes. Some ATP is made in glycolysis.In addition, the NADH and pyruvate produced in glycolysis are used in subsequent steps of cellular respiration to make even more ATP.

Part C - ATP synthesis in glycolysis: substrate-level phosphorylation

The ATP that is generated in glycolysis is produced by substrate-level phosphorylation, a very different mechanism than the one used to produce ATPduring oxidative phosphorylation. Phosphorylation reactions involve the addition of a phosphate group to another molecule.

Sort the statements into the appropriate bin depending on whether or not they correctly describe some aspect of substrate-levelphosphorylation in glycolysis.

Hint 1. The reactions of glycolysis are catalyzed by soluble enzymes

All of the reactions of glycolysis are catalyzed by soluble enzymes located in the cytosol of the cell. None of the enzymes is associated withmembranes.

Hint 2. Oxidative phosphorylation and ATP synthesis

In oxidative phosphorylation, the last stage of cellular respiration, energy released from the oxidation of NADH and FADH2 is used to produceATP from ADP and free inorganic phosphate (Pi) ions.

ANSWER:

Correct

In substrate-level phosphorylation, an enzyme transfers a phosphate group from one molecule (an intermediate in the breakdown of glucose topyruvate) to ADP to form ATP. This is very different from the mechanism of ATP synthesis that takes place in oxidative phosphorylation.

Pathways for Pyruvate

In most organisms, the end product of glycolysis is pyruvate. Pyruvate still contains a substantial amount of energy, which can be further extracted.Whether the organisms are operating under aerobic or anaerobic conditions determines the metabolic pathway that pyruvate undergoes to produce moreATP. In this tutorial, you will identify the end products of these metabolic pathways.



Part A - Products of pyruvate metabolism

Match each product of pyruvate metabolism with the condition under which it is produced.

Drag each item to the appropriate bin.

Hint 1. Is the formation of acetyl CoA oxidation or reduction?

When pyruvate is _____ to acetyl CoA, NAD+ is reduced to NADH.

ANSWER:

Hint 2. An example of fermentation

Recall that wineries use fermentation to turn grape sugar into alcohol. This may help you remember that alcohols are a typical product offermentation.

Hint 3. Fermentation in muscle cells

When animal muscles metabolize glucose faster than they can be supplied with oxygen, fermentation takes place, producing lactate rather thanacetyl CoA. Organisms that normally produce energy using oxygen as an electron acceptor can use fermentation instead to generate energywhen oxygen is absent.

ANSWER:

oxidized

reduced



Correct

In the presence of oxygen, human cells carry out aerobic respiration, which yields acetyl CoA. In the absence of oxygen, human cells can carryout lactic acid fermentation, which yields lactate. Yeasts and many bacteria carry out alcohol fermentation, which takes place under anaerobicconditions, and produces ethanol.

Part B - Reactants and products of lactic acid fermentation

Sort the following items according to whether they are reactants or products in the anaerobic reduction of pyruvate during lactic acid fermentation.

Drag each item to the appropriate bin.


During a reduction-oxidation reaction such as the anaerobic reduction of pyruvate in lactic acid fermentation, there are always two entitiesinvolved. One of them gets reduced (gains electrons), and the other one gets oxidized (loses electrons). In the case of the reduction of pyruvate(the reducing agent), you need to determine which form of nicotinamide adenine dinucleotide gets oxidized.



Hint 2. What is the reduced form of nicotinamide adenine dinucleotide?

Which of the following molecules is the reduced form of nicotinamide adenine dinucleotide?

ANSWER:

ANSWER:

Correct

When an animal engages in strenuous usage of its muscles, anaerobic conditions ensue, and pyruvate is reduced to lactate. In the process,NADH is oxidized to NAD+. This NAD+ can further oxidize glyceraldehyde-3-phosphate to produce more ATP.

NAD+

NADH

NADH2

FADH2



Activity: Fermentation



Part A

In muscle cells, fermentation produces _____.

ANSWER:

Correct

These are the products of fermentation as it occurs in muscle cells.

Part B

In fermentation _____ is reduced and _____ is oxidized.

ANSWER:

Correct

The pyruvate from glycolysis is reduced to either lactate or ethanol, and NADH is oxidized to NAD+.

Misconception Question 40

Part A

carbon dioxide, ethanol, NADH, and ATP

carbon dioxide, ethanol, and NAD+

pyruvate

lactate and NAD+

lactate, NADH, and ATP

NAD+ ... pyruvate

NADH ... lactate

lactate ... NADH

lactate ... ethanol

pyruvate ... NADH





Which statement about the binding of enzymes and substrates is correct?

ANSWER:

Correct

As the substrate enters the active site, the enzyme changes shape slightly due to interactions between the substrate’s chemical groups andchemical groups on the side chains of the amino acids that form the active site. This shape change makes the active site fit even more snuglyaround the substrate. This induced fit is like a clasping handshake.

Score Summary:

Your score on this assignment is 85.4%.You received 13.67 out of a possible total of 16 points.

Substrate molecules bind to the active site of the enzyme only by weak bonds, such as hydrogen bonds or hydrophobic attraction.

When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape.

Substrate molecules fit into the active site of an enzyme like a key fits into a lock.

Documents

Chapter 8 - Introduction to Metabolism