Biology Chapter 8 HW

FUN FACT:

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).

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.

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.

This graph illustrates a(n) _____ reaction.

endergonic The products contain more potential energy than the reactants.

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

endergonic; Energy has been acquired from the surroundings.

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

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

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

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

What is the correct label for "A"?

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

Select the INCORRECT association.

exergonic ... uphill Exergonic reactions release energy.

The following reactionA --> B + C + heatis a(n) _____ reaction.

exergonic; Energy has been released.

A(n) _____ reaction occurs spontaneously.

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

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

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

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

exergonic; endergonic

In this reaction _____.

heat has been released to the environment; The potential energy of the products is less than that of the reactants.

Which of these are by-products of cellular respiration?

heat, carbon dioxide, and water; These are the by-products of cellular respiration.

An enzyme _____.

is an organic catalyst; Enzymes are proteins that behave as catalysts.

Chemical energy is a form of _____ energy.

potential; Chemical energy is a form of stored energy.

In general, enzymes are what kinds of molecules?

proteins (Enzymes are proteins.)

Enzymes work by _____.

reducing EA; Enzymes work by reducing the energy of activation.

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

region C

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

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

Most cells cannot harness heat to perform work because

temperature is usually uniform throughout a cell.

In this reaction _____.

the products have less potential energy than the reactants; This is what is shown by the graph.

What is energy coupling?

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

Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?

γ-phosphate (the terminal phosphate); The γ-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 α- or β-phosphate.

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.

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. (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.)

Which of the following statements about equilibrium of chemical reactions is correct? See Concept 8.2

A reaction that is at equilibrium is not capable of doing any work; The ΔG for a reaction at equilibrium is zero, which means that there is no free energy available to do any work.

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

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

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again?

Add more substrate; it will outcompete the inhibitor and increase the reaction rate; Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor. Many drugs used to treat different medical conditions, including hypertension, are competitive inhibitors. It is fairly easy to make a molecule that is similar in structure to a particular substrate because 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 noncompetitive inhibitor because it is less obvious what the noncompetitive inhibitor's shape and structure should be.

Select the highest energy form of adenosine from the following images.

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.

How does an enzyme increase the rate of the chemical reaction it catalyzes?

An enzyme reduces the free energy of activation (EA) of the reaction it catalyzes; An enzyme catalyzes a reaction by lowering EA, enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures. Read about enzymes and activation energy.

As a result of its involvement in a reaction, an enzyme _____.

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

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.

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. https://docs.google.com/document/d/1UkKgW01NpcQhUKCtO5gb0qc88BOcW0n_qvoUHvEP8F8/edit?usp=sharing

FUN FACT:

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. As the concentration of substrate increases, the reaction rate increases, until the point where the active site is saturated with substrate. When the enzyme is saturated, the rate of the reaction will not increase with the concentration of substrates.

Consider a situation in which the enzyme is operating at optimum temperature and pH, and has been saturated with substrate. What is your best option for increasing the rate of the reaction?

Increase the enzyme concentration.; If an enzyme is saturated with substrate, and it is operating at optimum pHpH 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.

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

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

Select the correct statement about chemical energy, a term used by biologists to refer to potential energy available for release in a chemical reaction.

Light energy is converted to chemical energy during photosynthesis; Photosynthetic cells capture light energy and transform some of it to chemical energy as they synthesize glucose from CO2 and H2O. Read about the laws of energy transformation.

FUN FACT^

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.

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

P4 binds E1 and deactivates it; 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.

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

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

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?

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity; Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive. Some drugs are irreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).

Which of the following statements about feedback regulation of a metabolic pathway is correct? See Concept 8.5

The final product of a metabolic pathway is usually the compound that regulates the pathway; It is quite common that the end product of the pathway controls the overall rate of the pathway.

Which of the following is a chemical reaction?

The formation of a covalent bond between two amino acids; If you had trouble with this question, review the following material: Chemical reactions involve the making and breaking of chemical bonds, leading to changes in the composition of matter. Ice melting changes the state of water rather than the composition of water, and hydrogen bonds do not change the composition of the molecules involved. Chemical reactions cannot create or destroy atoms but can only rearrange (redistribute) the electrons among them.

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

When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape; As the substrate enters the active site, the enzyme changes shape slightly due to interactions between the substrate's chemical groups and chemical groups on the side chains of the amino acids that form the active site. This shape change makes the active site fit even more snugly around the substrate. This induced fit is like a clasping handshake.

Which of these is exhibiting kinetic energy?

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

If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to

add more of the enzyme

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

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