Chapter 8- Introduction to metabolism
Which of these is exhibiting kinetic energy?
a space station orbiting Earth
"Conservation of energy" refers to the fact that _____.
energy cannot be created or destroyed but can be converted from one form to another
Chemical energy is a form of _____ energy
potential. Chemical energy is a form of stored energy
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.
Which of these are by-products of cellular respiration?
heat, carbon dioxide, and water
Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy?
the covalent bonds of a sugar molecule: potential energy
The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____.
a catabolic pathway note: Cellular respiration is a catabolic pathway.
Which of the following statements about the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O) is correct?
The entropy of the products is greater than the entropy of the reactants. note: A large molecule (glucose) has been converted into several smaller molecules (water and carbon dioxide); thus, the products have more disorder (greater entropy) than the reactants.
Which of the following statements about equilibrium of chemical reactions is correct?
A reaction that is at equilibrium is not capable of doing any work.
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.
In this reaction _____.
the products have less potential energy than the reactants
In this reaction _____.
heat has been released to the environment. note: The potential energy of the products is less than that of the reactants.
The following reaction
A --> B + C + heat
is a(n) _____ reaction.
exergonic... energy is being released!
A(n) _____ reaction occurs spontaneously.
exergonic. In exergonic reactions the products have less potential energy than the reactants.
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
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.
The hydrolysis of ATP provides the energy needed for an endergonic reaction.
NOTE: Energy has been acquired from the surroundings.
The energy for an endergonic reaction comes from a(n) _____ reaction.
exergonic note: The energy released by an exergonic reaction can be used to drive an endergonic reaction.
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.
note: by acquiring the phosphate group the reactant acquires energy.
This graph illustrates a(n) _____ reaction.
Select the INCORRECT association.
enzyme ... protein
exergonic ... uphill
exergonic ... spontaneous
potential energy ... positional energy
kinetic energy ... motion
exergonic ... uphill
What is energy coupling?
the use of energy released from an exergonic reaction to drive an endergonic reaction
Which of these is ATP?
What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?
Hydrolysis: involves breaking bonds with the addition of water.
Which of the following statements about ATP (adenosine triphosphate) is correct?
The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways.
In which region does the reaction rate remain constant?
In region C of the graph, the reaction rate is independent of substrate concentration.
In which region is the enzyme saturated with substrate?
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 pH 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.
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.
look at item
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.
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.
The Haber process is typically carried out at a temperature of approximately 500∘C. What would happen to the rate of the forward reaction if the temperature were lowered to 100∘C?
The reaction rate would decrease. Most reactions double in rate for each 10∘C increase in temperature.
What would happen to the rate of the forward reaction if the concentration of nitrogen were decreased?
The reaction rate would decrease. As the concentration of nitrogen decreases, collisions between nitrogen and hydrogen are less likely to occur.
Which of the following would increase the rate of the reverse reaction?
increasing the concentration of ammonia. The concentration of NH3 affects how quickly N2 and H2 can be made.
What will happen to the rates of the forward and reverse reactions when a catalyst is added?
Both forward and reverse rates increase. The Haber process can be cheaply catalyzed using porous iron. A much more effective catalyst for the Haber process is osmium; however, it is very expensive and toxic.
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.
uncatalyzed reaction - a reaction catalyzed by enzyme a- reaction catalyzed by enzyme b
look at item 13
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.
In general, enzymes are what kinds of molecules?
Enzymes work by _____.
An enzyme _____.
is an organic catalyst
What name is given to the reactants in an enzymatically catalyzed reaction?
As a result of its involvement in a reaction, an enzyme _____.
What is the correct label for "A"?
energy of activation. The energy of activation must be overcome in order for a reaction to proceed.
Which of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes?
The active site can provide heat from the environment that raises the energy content of the substrate.
The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation?
The compound is a competitive inhibitor.
Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _______ is to _______.
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.
Which of the following statements about feedback regulation of a metabolic pathway is correct?
The final product of a metabolic pathway is usually the compound that regulates the pathway. note: It is quite common that the end product of the pathway controls the overall rate of the pathway.
Which of the following metabolic processes can occur without a net influx of energy from some other process?
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
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.
Some bacteria are metabolically active in hot springs because
their enzymes have high optimal temperatures.
If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur?
Nothing; the reaction will stay at equilibrium.
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.
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.