7. Energy and Metabolism

Enzymes

What are enzymes?

Some bacteria are metabolically active in hot springs because
a. they are able to maintain a lower internal temperature.
b. high temperatures make catalysis unnecessary.
c. their enzymes have high optimal temperatures.
d. their enzymes are completely insensitive to temperature.

Add labels to the figure that follows, which illustrates the breakdown of a disaccharide inside a cell. <img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/f3e56f9e4bcc60a7-1677226509215.jpg" style="width: 300px;">

Which of the following is a false statement regarding enzymes?
a. Enzymes are proteins that speed up metabolic reactions;
b. Enzymes have specific substrates;
c. Enzymes supply ATP to their substrates;
d. An enzyme may be used many times.

Functions of Enzymes

Enzymes increase the rate of a reaction by raising the activation energy for reactions.

Enzymes react with their substrate (form chemical bonds), forming an enzyme-substrate complex, which irreversibly alters the enzyme.

No. Some enzymes do form covalent bonds with their substrates, but these bonds are eventually broken before the products are released. All enzymes are unchanged as a result of their participation in a reaction.

The more heat that is added to a reaction, the faster the enzymes will function.

No. If heated too much, an enzyme will no longer function efficiently because excess heat will denature the enzyme.

No. Just one of the listed responses is correct.

Enzymes speed up the rate of the reaction without changing the DG for the reaction.

Consider the characteristics of enzymes that are related to their function.

Which of the following statements about enzymes is/are true?

No. Moderate increase in temperature will accelerate the reaction; more dramatic changes in temperature will affect the structure of the enzyme and therefore the rate at which it can catalyze a reaction.

No. This will slow down molecular motion, which will therefore slow the rate of contact between enzyme and substrate. The consequence of this is that the reaction rate will slow.

No. Up to the saturation point of the enzyme, the reaction rate will increase as a function of increased substrate concentration.

No. Changes in proton concentration around the enzyme can change the ionization state of functional groups in the enzyme active site and on the substrate. Both of these changes could affect reaction rate.

Recall that enzymes are proteins.

Which of the following environments or actions would not affect the rate of an enzyme reaction?

Enzymes can greatly speed up reactions, but they cannot change the net energy output because they cannot change the activation energy.

No. Enzymes can speed up reactions because they can lower the activation energy.

Enzymes can change the equilibrium point of reactions, but they cannot speed up reactions because they cannot change the net energy output.

No. Enzymes cannot change the equilibrium point, but they can speed up reactions.

Enzymes can greatly speed up reactions, but they cannot change the activation energy because they cannot change the net energy output.

No. Enzymes speed up reactions by lowering the activation energy.

Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output.

Think about the activation energy and free energy change of an enzyme-catalyzed reaction.

Which of the following statements about enzyme function is correct?

No. The magnitude of &Delta;G is a function of the relative G values for the reactants and products.

No. The G value for substances cannot be changed unless a reaction occurs.

No. Enzymes can change the rate of a reaction, but as they cannot change the G of the reactants and products, enzymes cannot make an endergonic reaction exergonic or vice versa.

No. Enzymes cannot change the G value for any molecule&#8212;that is an inherent property of the molecule.

Consider how an enzyme affects the different aspects of a reaction. and

Which of the following is changed by the presence of an enzyme in a reaction? and

Enzymes: Mr. W's Enzyme Song

Heat from the environment is necessary for substrates to get over the activation energy barrier.

No. This is a true statement, but is this the only correct answer?

The kinetic energy of the substrates is increased as the amount of heat in the system is increased.

Increasing the amount of heat in a system will always increase the rate of enzyme-catalyzed reactions.

No. This is true only for a limited temperature range. With increasing temperatures, the enzyme will eventually denature, leading to a lower rate of the reaction.

The second and third choices are correct.

No. At least one of the second and third choices is incorrect.

The first and second choices are correct.

Think about the relationship between heat, temperature, activation energy, and enzyme function.

Which of the following statements correctly describe(s) the role or roles of heat in biological reactions?

Enzymes usually function best at an optimal pH and temperature. The following graph shows the effectiveness of two enzymes at various temperatures.
(c) From what you know about enzyme structure, explain why the rate of the reaction catalyzed by enzyme A slows down at temperatures above 40°C (140°F).

Enzymes (Updated)

ENZYMES (1/2) - Definition/Cofactors/Models

No. This is a reasonable generalization; most enzymes are proteins even though exceptions exist.

An enzyme is very specific in terms of the substrate to which it binds.

No. This is a true statement. Enzymes bind very specifically to their substrate or substrates because of the enzyme's unique three-dimensional shape.

An enzyme lowers the activation energy of a chemical reaction.

No. This is a true statement. Enzymes do lower the activation energy of a reaction; lowering activation energy allows the reaction to proceed rapidly.

Enzymes can be used to accelerate both anabolic and catabolic reactions.

No. This is a true statement. Enzymes can speed up reactions that are anabolic or catabolic.

An enzyme is consumed during the reaction it catalyzes.

Consider the structure and function of enzymes.

Which of the following statements about enzymes is incorrect?

What are Enzymes & How Do They Work?

Enzymes Example 1

If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to
a. add more of the enzyme.
b. heat the solution to 90°C.
c. add more substrate.
d. add a noncompetitive inhibitor.

most substrates do not function well at high or low pH

No. Although pH can affect the structure of the substrate, it is more likely to affect something else.

No. Enzymes that function in the stomach function optimally at very low pH.

changes in pH can cause loss of cofactors from the enzyme

No. Although pH changes can cause an enzyme to lose a cofactor, even enzymes without cofactors are affected by changes in pH.

the binding of hydrogen ions to the enzyme absorbs energy and thus there may not be enough energy to overcome the activation energy barrier

No. Binding of hydrogen ions does not affect the energy that is available to overcome the activation energy barrier.

high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

Remember that enzymes are usually proteins.

Enzyme activity is affected by pH because __________.

Enzymes usually function best at an optimal pH and temperature. The following graph shows the effectiveness of two enzymes at various temperatures.
(b) One of these enzymes is found in humans and the other in thermophilic (heat-loving) bacteria. Which enzyme would you predict comes from which organism?

A lactase enzyme breaking down lactose sugar in the small intestine.

A DNA polymerase enzyme synthesizing new strands of DNA.

A lipase enzyme breaking down fats (lipids) in the small intestine.

A helicase enzyme unraveling DNA so it can be replicated.

Which of the following are examples of the functions of enzymes?a) A lactase enzyme breaking down lactose sugar in the small intestine.b) A DNA polymerase enzyme synthesizing new strands of DNA.c) A lipase enzyme breaking down fats (lipids) in the small intestine.d) A helicase enzyme unraveling DNA so it can be replicated.e) All of the above.

An enzyme that functions properly at 70 degrees Fahrenheit and at a neutral pH.

An enzyme that functions properly at 98 degrees Fahrenheit and at an acidic pH.

An enzyme that functions properly at 98 degrees Fahrenheit and at a neutral pH.

An enzyme that functions properly at 70 degrees Fahrenheit and at an acidic pH.

Which characteristics are likely associated with an enzyme isolated from a human stomach where conditions are strongly acidic.a) An enzyme that functions properly at 70 degrees Fahrenheit and at a neutral pH.b) An enzyme that functions properly at 98 degrees Fahrenheit and at an acidic pH.c) An enzyme that functions properly at 98 degrees Fahrenheit and at a neutral pH.d) An enzyme that functions properly at 70 degrees Fahrenheit and at an acidic pH.

Enzymes usually function best at an optimal pH and temperature. The following graph shows the effectiveness of two enzymes at various temperatures. 
(a) At which temperature does enzyme A perform best? Enzyme B?<img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/bf69d3f1166705f4-1677714294214.jpg" style="width: 300px;">

Environmental Factors Affecting Enzyme Activity

Animation: How Enzymes Work

Animation: Enzymes: Steps in a Reaction

Enzymes | Cells | Biology | FuseSchool

Enzymes and How They Work: An Introduction

How Enzymes Work

Evaluate these statements about Koch’s postulates, which are used to establish a causative link between a specific microbe and a specific disease. Select True or False for each statement.
T/F The microbe must be present in individuals suffering from the disease and absent from healthy individuals.
T/F The microbe must be isolated and grown in pure culture.
T/F If organisms from the pure culture are injected into a healthy experimental animal, the disease symptoms should appear.
T/F The microbe does not have to be isolated from the experimental animal as long as the disease is present.

The active site has a fixed structure (shape).

No. The active site of an enzyme changes when it binds to its substrate or substrates&mdash;the change in enzyme shape is called “induced fit.”

Coenzymes are rarely found in the active site of an enzyme.

No. Some coenzymes are bound to active sites.

The structure of the active site is not affected by changes in temperature.

No. As temperature increases, the structure of the active site will eventually be lost as the protein denatures.

The active site allows the reaction to occur under the same environmental conditions as the reaction without the enzyme.

No. The active site often changes the local environment to one that favors the reaction by lowering the activation energy.

The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.

Think about the function of the active site in enzyme catalysis.

Which of the following statements about the active site of an enzyme is correct?

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