HW 7
What name is given to the reactants in an enzymatically catalyzed reaction?
substrate
In glycolysis, ATP molecules are produced by _____.
substrate-level phosphorylation
Which of the following would increase the rate of the reverse reaction?
increasing the concentration of ammonia
The Haber process is typically carried out at a temperature of approximately 500∘C∘C. What would happen to the rate of the forward reaction if the temperature were lowered to 100∘C∘C?
rxn rate decrease
During acetyl CoA formation and the citric acid cycle, all of the carbon atoms that enter cellular respiration in the glucose molecule are released in the form of CO2. Use this diagram to track the carbon-containing compounds that play a role in these two stages. Drag the labels from the left (which represent numbers of carbon atoms) onto the diagram to identify the number of carbon atoms in each intermediate in acetyl CoA formation and the citric acid cycle. Labels may be used more than once.
(a)2C (b)6C (c)6C (d)5C (e)4C (f)4C (g)4C (h)4C (i)4C
Approximately how much more free energy is supplied to the electron transport chain by NADH than by FADH2?
8 kcal/mol
Which of the following statements is not true of most cellular redox reactions?
A hydrogen atom is transferred to the atom that loses an electron.
Select the INCORRECT association.
exergonic...uphill
In cells, what is usually the immediate source of energy for an endergonic reaction?
ATP
In glycolysis, what starts the process of glucose oxidation?
ATP
Which of these enters the citric acid cycle?
Acetyl CoA
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.
Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?
Anion and cation.
What will happen to the rates of the forward and reverse reactions when a catalyst is added?
Both forward and reverse rates increase.
The ATP that is generated in glycolysis is produced by substrate-level phosphorylation, a very different mechanism than the one used to produce ATP during 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-level phosphorylation in glycolysis.
Correct:-One of the substrates is a molecule derived from the breakdown of glucose-An enzyme is required in order for the reaction to occur-A bond must be broken between an organic molecule and phosphate before ATP can form. Incorrect:-The phosphate group added to ADP to make ATP comes from free inorganic phosphate ions.-The enzymes involved in ATP synthesis must be attached to a membrane to produce ATP.
Look at the graph of reaction rate versus substrate concentration for an enzyme. In which region does the reaction rate remain constant?
Region C
Refer again to the graph. In which region is the enzyme saturated with substrate?
Region C
Which of these is NOT a product of glycolysis?
FADH2
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
In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction. Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct.
It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA
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. 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
Lowest to Highest: uncatalyzed, Enzyme A, Enzyme B
What is the correct order of electron transport compounds from best electron donor to best electron acceptor?
NADH -- Fe-S of Complex I -- Q -- Fe-S of Complex III -- Cyt c-- Cyt a of Complex IV -- O2
From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of glycolysis. Drag each compound to the appropriate bin. If the compound is not involved in glycolysis, drag it to the "not input or output" bin.
Net Input: ADP, NAD⁺, Glucose Net Output: ATP, NADH and Pyruvate, not input or output: O₂, CO₂, coenzyme A and acetyl CoA
How does the phosphorylation of glutamic acid (Glu) provide energy for the rest of the reaction to occur?
The addition of phosphate to the Glu forms a phosphorylated intermediate with more free energy than Glu. The ammonia can thus displace the phosphate in an exergonic reaction.
What molecule is indicated by the letter D?
Oxygen
Which of the following statements is true of the bonds in a water molecule?
Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero.
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 the role of ATP in cell metabolism is true?
The energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule.
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
What would happen to the rate of the forward reaction if the concentration of nitrogen were decreased?
The reaction rate would decrease .
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
Which of these is NOT a product of the citric acid cycle?
acetyl CoA
What process occurs within Box B?
citric acid cycle
The reaction ADP + P --> ATP is a(n) _____ reaction.
endergonic
What process occurs in Box A?
glycolysis
In this reaction _____.
heat has been released to the environment
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?
hydrogen, polar
In general, enzymes are what kinds of molecules?
proteins
Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?
pyruvate, ATP, and NADH
Which term describes the degree to which an element attracts electrons?
electronegativity
This graph illustrates a(n) _____ reaction.
endergonic
Which of these reactions requires a net input of energy from its surroundings?
endergonic
A cell can only carry out an ______________ reaction by pairing it with an ________________ reaction, such as ATP hydrolysis.
endergonic; exergonic
What is the correct label for "A"?
energy of activation
A(n) _____ reaction occurs spontaneously.
exergonic
The energy for an endergonic reaction comes from a(n) _____ reaction.
exergonic
The following reactionA --> B + C + heatis a(n) _____ reaction
exergonic
In the citric acid cycle, ATP molecules are produced by _____.
substrate-level phosphorylation
In this reaction _____.
the products have less potential energy than the reactants
What is energy coupling?
the use of energy released from an exergonic reaction to drive an endergonic reaction
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
Of the following lists of electron transport compounds, which one lists them in order from the one containing electrons with the highest free energy to the one containing electrons with the lowest free energy? Note that not all electron transport compounds in the electron transport chain are listed.
FADH2 -- Fe-S of Complex II -- Q -- Fe-S of Complex III -- Cyt c -- Cyt a of Complex IV -- O2
If a mitochondrion ran out of molecular oxygen (O2), predict which of the following situations would occur in its electron transport chain.
FMN prosthetic groups would remain reduced and NADH would have nowhere to donate electrons.
Each of the four stages of cellular respiration occurs in a specific location inside or outside the mitochondria. These locations permit precise regulation and partitioning of cellular resources to optimize the utilization of cellular energy. Match each stage of cellular respiration with the cellular location in which it occurs. Labels may be used once, more than once, or not at all.
Glycolysis - Cytosol Acetyl CoA - Mitochondrial matrix Citric acid cycle - Mitochondrial matrix Oxidative phosphorylation - inner mitochondrial membrane
In the citric acid cycle (also known as the Krebs cycle), acetyl CoA is completely oxidized. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of the citric acid cycle. Drag each compound to the appropriate bin. If a compound is not involved in the citric acid cycle, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of the citric acid cycle are included.)
Net Input: Acetyl CoA, NAD⁺, ADP Net Output: Coenzyme A, CO₂, NADH, ATP Not Input or Output: Pyruvate, Glucose, O₂
In the last stage of cellular respiration, oxidative phosphorylation, all of the reduced electron carriers produced in the previous stages are oxidized by oxygen via the electron transport chain. The energy from this oxidation is stored in a form that is used by most other energy-requiring reactions in cells. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of oxidative phosphorylation. Drag each compound to the appropriate bin. If a compound is not involved in oxidative phosphorylation, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of oxidative phosphorylation are listed.)
Net Input: NADH, ADP, O₂ Net Output: NAD⁺, ATP, and Water Not Input or Output: Pyruvate, Glucose, Acetyl CoA, Coenzyme A and CO₂.
In acetyl CoA formation, the carbon-containing compound from glycolysis is oxidized to produce acetyl CoA. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of acetyl CoA formation. Drag each compound to the appropriate bin. If a compound is not involved in acetyl CoA formation, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of acetyl CoA formation are included.)
Net Input: NAD⁺, coenzyme A, pyruvate Net Output: NADH, acetyl CoA, CO₂ not input or output: O₂, ADP, glucose and AT
What kind of bond is formed when lithium and fluorine combine to form lithium fluoride?
ionic
An enzyme _____.
is an organic catalyst
As a result of its involvement in a reaction, an enzyme ____
is unchanged
In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the electrons produced from this oxidation are passed on to two types of electron acceptors. Drag the labels on the left to show the net redox reaction in acetyl CoA formation and the citric acid cycle. Note that two types of electron carriers are involved.
pyruvate is oxidized to (a) CO2NAD+ is reduced to (b) NADH(c) FAD is reduced to (d)FADH2
Enzymes work by _____.
reducing EA
How many NADH are produced by glycolysis?
two
In glycolysis there is a net gain of _____ ATP.
two
A chemical reaction occurs between the amino acids alanine (Ala) and glycine (Gly), forming the compound alanylglycine. The simple conversion reaction of alanine and glycine into this compound is endergonic, with a ΔΔG of 6.9 kcal/mol. Therefore, it requires ATP hydrolysis to drive the nonspontaneous reaction. Calculate the free energy change for the whole process, applying what you know about ATP hydrolysis.
ΔG = -0.4 kcal/mol