Biol 1406 learning curve ch 8

The hydrolysis of one mole of ATP to ADP and inorganic phosphate is accompanied by the release of 7.3 kcal of energy. Some biological transformations are coupled to ATP hydrolysis. Reaction _______ is an example of a biological transformation that could be coupled to ATP hydrolysis.

2

Which two facts taken together support the claim that cells convert the chemical energy of ATP into other forms of energy?

3 and 5

How much energy is released when 1.0 mole of ATP is hydrolyzed?

7.3 kcal

A particular enzyme is used to convert substrate A into product B. If you wished to use this enzyme in another reaction with a different substrate, which of the following substrates could theoretically be acted on by the same enzyme?

A molecule with the same three-dimensional shape as A

The graph of enzyme activity versus substrate concentration for an enzyme has a sigmoidal (S-shaped) appearance. Such an activity curve indicates which type of enzyme?

A multisubunit allosteric enzyme

In solution, ATP is readily hydrolyzed into

ADP and one phosphate ion.

Which statement regarding ATP is not true?

ATP is chemically stable and can be stored easily for extensive periods of time.

The energy currency of cells is

ATP.

Which term refers to the location on the enzyme where the substrates are bound?

Active site

Which action could indicate whether a given reaction is endergonic? Assume that no other small molecules are present in the reaction solution.

Add ATP and see if the reaction creates more product.

Based on the graph, which statement best describes these chemical reactions?

Addition of a catalyst to a reaction does not affect the equilibrium position of the reaction, but only increases the rate of attainment of equilibrium.

Which is an example of an enzyme using substrate orientation as a mechanism for lowering the activation energy of a reaction?

Aligning the substrate atoms so they are brought into proximity with each other, favoring the chemical reaction

Phosphofructokinase catalyzes the first reaction in a pathway that commits the product to proceed through glycolysis, often called the first commitment step in glycolysis. Phosphofructokinase is also regulated so that the cell can quickly respond to its energy needs. Given this background information about phosphofructokinase, what is the most likely mode of inactivation of this enzyme when the cell needs to slow down or turn off glycolysis?

Allosteric inhibition

Which part of an enzyme molecule may function as a direct participant in the chemical reaction it catalyzes?

Amino acid side chains

This is an important equilibrium system in aquatic environments, particularly in the oceans. Which statement correctly describes a reaction of this system in response to an environmental change?

An increase in carbon dioxide shifts the equilibrium to the right.

Which is the correct general equation for an enzyme-catalyzed reaction? Enzyme is represented by "E," substrate by "S," and product by "P."

E + S → ES → E + P

Which word best fits into this figure where the question mark is located?

Energy

Which statement is not true about enzymes?

Enzymes can shift the position of equilibrium to favor products.

Which enzymes are most likely to not be affected by an increase in temperature?

Enzymes isolated from bacteria that colonize geothermal vents at the bottom of the ocean

Which statement best describes the mechanism by which enzymes catalyze a reaction?

Enzymes lower the energy barrier necessary to achieve the transition state of a reaction.

Which enzymes' catalytic activity is predicted to be most sensitive to changes in pH?

Enzymes with amino (-NH2) or carboxy (-COOH) side chains at the active site

If all that is required to drive a chemical reaction is heat, why can't we speed up biological chemical reactions by heating the cell?

Excess heat would indiscriminately speed up all chemical reactions, including desirable and undesirable reactions, as well as denature the biological compounds involved.

Which type of reaction is used to break down ATP into ADP and Pi?

Hydrolysis

In which sequence does the form of energy change as a person sees a friend and waves hello?

Light → chemical → electrical → mechanical

Measure the concentrations of A and B and see if they change.

Measure the concentrations of A and B and see if they change.

Which of the following can participate in an enzymatic reaction as an electron donor or acceptor?

Metal ion bound to amino acid side chains in the active site

The enzyme alcohol dehydrogenase was purified from yeast cells. It was then dialyzed against a buffer solution, which means that it was placed inside a bag consisting of a semipermeable membrane that allowed small molecules and ions to pass through, but not the enzyme. The enzyme was removed from the dialysis bag, incubated with the compound N-ethylmaleimide, and then dialyzed a second time. At each step, the enzyme's catalytic activity was measured and expressed as a percentage of its original activity shown in the table. Which statement expresses a valid conclusion that can be made based on these results?

N-ethylmaleimide is an irreversible inhibitor of alcohol dehydrogenase.

This figure shows an example of a biological molecule that can function as an enzyme. This type of enzyme is called a ribozyme because it consists of a molecule of _______. [Use abbreviation.]

RNA

A theoretical enzyme, anyase, catalyzes the same reaction using five different substrates. The dissociation constants for these substrates and the enzyme are listed below. Which substrate will produce the greatest concentration of anyase-substrate complex?

Substrate A, KD = 10-7 M

Where is the chemical energy that is used to drive endergonic reactions contained in a molecule of ATP?

The P-O bond of the third phosphate group

What features of an enzyme's active site allow it to recognize and bind a substrate?

The active site shape is specific for the substrate.

What explains the sharp drop-off in enzyme activity as the temperature is raised?

The enzyme's three-dimensional structure must be intact for catalysis to occur and becomes disrupted at very high temperatures.

Which statement regarding enzyme-substrate (ES) complexes is true?

The formation of an ES complex helps to achieve the transition state, favoring product formation.

During the metabolism of glucose, the conversion of glucose to glucose 6-phosphate cannot proceed without the hydrolysis of ATP. Which is a reason for this?

The reaction is endergonic.

This graph shows the change in free energy for the same reaction with and without a catalyst. Which tracing represents the catalyzed reaction and why?

The red tracing represents the catalyzed reaction because it has a smaller activation energy than the uncatalyzed reaction.

Living things use chemical reactions to live, grow, and reproduce. Chemical reactions are accompanied by energy changes. Which term refers to the topic of energy change in chemical reactions?

Thermodynamics

Which statement about enzymes is true?

They are not permanently altered by the reactions they catalyze.

Which of the following could we infer about a chemical reaction with a large positive change in entropy (ΔS) as the reaction proceeds and no corresponding change in enthalpy (ΔH)?

Total ΔG of the reaction will decrease.

Hexokinase is the enzyme that catalyzes the reaction shown below. (Click image to enlarge.) To which class of enzymes does hexokinase belong? Please choose the correct answer from the following choices, and then select the submit answer button.

Transferases

Which term describes the high-energy state that two substrates must form before the reaction can proceed?

Transition state

Which series best summarizes the relative energies of the different stages of an endergonic chemical reaction?

Transition state > products > reactants

Which series best summarizes the relative energies of the different stages of an exergonic chemical reaction?

Transition state > reactants > products

Does this figure illustrate both the first and second laws of thermodynamics?

Yes, the figure illustrates both laws of thermodynamics because it shows conservation of total energy and a decrease in usable energy during a transformation.

The creation of ATP from ADP requires the addition of

a phosphate ion.

All of the following are examples of potential energy

chemical bonds. concentration gradients. electrical potential difference. electrical charge imbalance.

Ascorbic acid, which is found in citrus fruits, acts as an inhibitor to catechol oxidase, the enzyme responsible for the browning reaction in fruits such as apples, peaches, and pears. One explanation for the inhibiting function of ascorbic acid could be its similarity, in terms of size and shape, to catechol, the substrate of the browning reaction. If this explanation is correct, then this inhibition is most likely an example of _______ inhibition.

competitive

The formation of covalent bonds between active site side chains and the substrate is an example of _______ catalysis, whereas the transfer of protons between active site side chains and the substrate is an example of _______ catalysis.

covalent; acid-base

ATP hydrolysis is an example of reaction A that is coupled to reaction B in order to provide it with sufficient _______ to allow the reaction to occur.

energy

The energy released by the hydrolysis of ATP to ADP and Pi is

equal to the energy needed by the reverse reaction of ADP + Pi → ATP.

Anabolic reactions

generally require an input of energy.

The hydrolysis of sucrose into glucose and fructose by the enzyme sucrase

increases entropy.

An inhibitor that binds through covalent bonds to the active site of an enzyme is known as a(n) _______ inhibitor.

irreversible

An enzyme

is a catalyst.

Enzymes are biological catalysts and function by

lowering the activation energy of a reaction.

In order to measure the standard free energy change, ΔG°, for the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate, you set up the reaction at 25°C with 1 M reactants and

maintain one atmosphere of pressure.

Information about two reactions is provided. From this information, it can be stated that reaction B is exergonic because its ΔG° is _______.

negative

Some enzymes cause chemical bonds in their substrates to become stretched as the substrate binds to the active site. This change is called

physical strain.

A reaction with a negative ΔG

releases energy.

The term referring to a reactant in an enzyme-catalyzed reaction is

substrate.

The ΔG of a reaction is dependent on all of the following except

the change in the activation energy.

Transition-state intermediates have higher energies than the reactants and/or products because

the chemical bonds of the reactants have been stretched and stressed to near breaking.

The ΔG of a reaction is dependent on all of the following

the free energy of the reactants. the change in entropy. the free energy of the products. the change in enthalpy.

The conversion of A to B, which is an endergonic reaction, can proceed if it is coupled

with the hydrolysis of ATP.

What would happen to the value of ΔG for the reaction in which phosphoenolpyruvate is converted to pyruvate (ΔG = -23 kJ/mol) when it reaches equilibrium?

ΔG would equal 0.