Chapter 8 & 9 (Questions) Flashcards
The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____.
a catabolic pathway
Cellular respiration is a
catabolic pathway
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.
Bonds are a form of potential energy because the energy
arises from the relative positions of the atoms that form the bond.
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.
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 reactions 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.
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.
Catabolic pathways provide the energy needed to make ATP from ADP and Pi. The hydrolysis of
ATP to ADP + Pi releases the same amount of energy.
Enzymes are described as catalysts, which means that they _____.
increase the rate of a reaction without being consumed by the reaction.
This permits enzyme molecules to be used repeatedly.
Which of the following would be unlikely to contribute to the substrate specificity of an enzyme?
The enzyme has an allosteric regulatory site.
The allosteric site is distinct from the active site, and does not affect the substrate specificity of the enzyme.
Which of the following would be likely to contribute to the substrate specificity of an enzyme?
- A hydrophobic group on the substrate interacts with several hydrophobic amino acids on the enzyme.
- A similar shape exists between a pocket on the surface of the enzyme and a functional group on the substrate.
- A positive charge on the substrate is attracted to a negative charge in the active site of the enzyme.
- The enzyme has the ability to change its configuration in response to the substrate binding.
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.
Which of the following are ways in which an enzyme can speed up the reaction that it catalyzes?
- The enzyme binds a cofactor that interacts with the substrate to facilitate the reaction.
- The binding of two substrates in the active site provides the correct orientation for them to react to form a product.
- The active site of the enzyme can provide a microenvironment with a different pH that facilitates the reaction.
- Binding of the substrate to the active site can stretch bonds in the substrate that need to be broken.
An enzyme cannot extract heat from the environment to speed a reaction. It can only
lower the activation energy barrier so that more substrates have the energy to react.
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.
A competitive inhibitor slows down the enzyme by competing with the
substrate for binding at the active site. Increasing substrate concentrations will reduce the effectiveness of a competitive inhibitor.
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.
It is quite common that the end product of the pathway controls the overall rate of the pathway.
Which of these is exhibiting kinetic energy?
a space station orbiting Earth.
Kinetic energy is
energy of motion.
“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
Cellular respiration 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
The reaction A –> B + C + heat is released in 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.
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 reaction ADP + P –> ATP is a(n) _____ reaction.
endergonic.
Energy has been acquired from the surroundings.
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.
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.
What are the correct associations with each of these:
- kinetic energy …
- enzyme …
- exergonic …
- potential energy …
- motion
- protein
- spontaneous
- positional energy.
What is energy coupling?
the use of energy released from an exergonic reaction to drive an endergonic reaction
What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?
hydrolysis
Hydrolysis involves
breaking bonds with the addition of water.
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.
Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?
- y(looks like a y) phosphate (the terminal phosphate)
The y (looks like a y kind of) -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 - or -phosphate.
In general, enzymes are what kinds of molecules?
proteins
Enzymes work by _____.
reducing the energy of activation (EA)
An enzyme
is an organic catalyst.
Enzymes are proteins that
behave as catalysts.
What name is given to the reactants in an enzymatically catalyzed reaction?
substrate
As a result of its involvement in a reaction, an enzyme _____.
is unchanged.
Enzymes are not changed as a result of their participation in a reaction.
The energy of activation must be overcome in order for
a reaction to proceed.
Consider a situation in which the enzyme is operating at optimum temperature and , 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 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.
A competitive inhibitor has a
structure that is so similar to the substrate that it can bond to the enzyme just like the substrate.
A noncompetitive inhibitor
binds to a site on the enzyme that is not the active site.
Usually, an irreversible inhibitor forms a
covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity.
The competitive inhibitor competes with the
substrate for the active site on the enzyme.
When the noncompetitive inhibitor is bonded to the enzyme,
the shape of the enzyme is distorted.
Enzyme inhibitors disrupt normal interactions between an
enzyme and its substrate.
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.
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).
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.
An enzyme is denatured when
it loses its native conformation and its biological activity.
An enzyme is considered a catalyst because
it speeds up chemical reactions without being used up.
An enzyme is considered specific because
of its ability to recognize the shape of a particular molecule.
A cofactor, such as a vitamin, binds to
an enzyme and plays a role in catalysis.
When properly aligned, the
enzyme and substrate form an enzyme-substrate (ES) complex.
A substrate binds to an enzyme at the
active site, where the reaction occurs.
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.
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.
Which of the following best describes the main purpose of the combined processes of glycolysis and cellular respiration?
transforming the energy in glucose and related molecules in a chemical form that cells can use for work
The energy made available during cellular respiration is
coupled to a production of ATP, the basic energy currency that cells use for work.
In the combined processes of glycolysis and cellular respiration, what is consumed and what is produced?
Glucose is consumed, and carbon dioxide is produced.
The carbon in glucose is oxidized to
carbon dioxide during cellular respiration.
Which of the following describes the process of glycolysis?
It represents the first stage in the chemical oxidation of glucose by a cell.
Catabolism of glucose begins with
glycolysis.
A glucose molecule is completely broken down to carbon dioxide and water in glycolysis and the citric acid cycle, but together these two processes yield only a few molecules of ATP. What happened to most of the energy that the cell obtains from the oxidation of glucose?
It is stored in NADH and FADH2
The electrons obtained from the oxidation of glucose are temporarily stored in NADH and FADH2.
The energy derived from the oxidation of NADH and FADH2 is used to drive the electron transport chain and chemiosmotic synthesis of ATP.
Which statement about the citric acid cycle is correct?
The last reaction in the citric acid cycle produces a product that is a substrate for the first reaction of the citric acid cycle.
The electrons stripped from glucose in cellular respiration end up in which compound?
water.
At the end of the electron transport chain, the electrons and hydrogen atoms are added to
oxygen, forming water.
Which of the following statements about the chemiosmotic synthesis of ATP is correct?
The chemiosmotic synthesis of ATP requires that the electron transport in the inner mitochondrial membrane be coupled to proton transport across the same membrane.
Chemiosmosis uses the energy of a proton gradient to make ATP;
the proton gradient is formed by coupling the energy produced by electron transport with movement of protons across the membrane.
Which one of the following statements about the redox reactions of the electron transport chain is correct?
The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane.
The reduction and oxidation of electron carriers in the electron transport chain provide the energy to
move protons across a membrane against the chemical gradient of protons.
In the absence of oxygen, what is the net gain of ATP for each glucose molecule that enters glycolysis?
two ATP.
Four ATP are made, but two ATP are consumed to start the process of glycolysis.
In most cells, not all of the carbon compounds that participate in glycolysis and the citric acid cycle are converted to carbon dioxide by cellular respiration. What happens to the carbon in these compounds that does not end up as CO2?
The carbon compounds are removed from these processes to serve as building blocks for other complex molecules.
Glycolysis and the citric acid cycle provide many compounds that are
the starting point for the synthesis of amino acids and lipids.
Chloroplasts are the sites of
photosynthesis.
Photosynthesis produces
glucose and releases oxygen into the atmosphere.
Mitochondria are the sites of
cellular respiration.
Carbon dioxide and water are the by-products of
cellular respiration.
Glycolysis occurs in the
cytosol.
The citric acid cycle transfers electrons to
NADH and FADH2.
Oxygen is the final electron acceptor of
cellular respiration.
Which term describes the degree to which an element attracts electrons?
electronegativity
Electronegativity is the tendency of an atom to
attract electrons toward itself.
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.
Each atom will carry a charge from the transfer of electrons.
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.
Which of the following statements are true of most cellular redox reactions?
- Changes in potential energy can be released as heat.
- The reactant that is oxidized loses electrons.
- The electron acceptor is reduced.
- A hydrogen atom (proton, or H+) is often transferred to the atom that gains an electron
How many NADH are produced by glycolysis?
2.
Two NADH molecules are produced by
glycolysis.
In glycolysis, ATP molecules are produced by _____.
substrate-level phosphorylation.
A phosphate group is transferred from glyceraldehyde phosphate to ADP.
Which of these is NOT a product of glycolysis?
FADH2.
FADH2 is a product of the
citric acid cycle.
Which of these are products of glycolysis?
pyruvate
NADH
ATP
In glycolysis, what starts the process of glucose oxidation?
ATP.
Some ATP energy is used to start the process of glucose oxidation.
In glycolysis there is a net gain of _____ ATP.
2.
It takes 2 ATP to produce 4 ATP.
In glycolysis, as in all the stages of cellular respiration, the transfer of electrons from electron donors to electron acceptors plays a critical role in the overall conversion of the energy in foods to energy in ATP.
These reactions involving electron transfers are known as oxidation-reduction, or redox, reactions.
When a compound donates (loses) electrons, that compound becomes
oxidized. Such a compound is often referred to as an electron donor.
When a compound accepts (gains) electrons, that compound becomes
reduced. Such a compound is often referred to as an electron acceptor.
In glycolysis, the carbon-containing compound that functions as the electron donor is
glucose.
Once the electron donor in glycolysis gives up its electrons,
it is oxidized to a compound called pyruvate.
NAD+ is the compound that functions as the
electron acceptor in glycolysis.
The reduced form of the electron acceptor in glycolysis is
NADH.
In the net reaction for glycolysis, glucose (the electron donor) is oxidized to
pyruvate. The electrons removed from glucose are transferred to the electron acceptor, NAD+, creating NADH.
Which of these enters the citric acid cycle?
acetyl CoA.
Acetyl CoA is a reactant in the citric acid cycle
In the citric acid cycle, ATP molecules are produced by _____.
substrate-level phosphorylation.
A phosphate group is transferred from GTP to ADP.
Which of these is NOT a product of the citric acid cycle?
acetyl CoA.
Acetyl CoA enters the
citric acid cycle.
Which of these are products of the citric acid cycle?
ATP
NADH + H^+
FADH2
CO2
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.
The net result of this complex series of reactions in the citric acid cycle is the
complete oxidation of the two carbon atoms in the acetyl group of acetyl CoA to two molecules of CO2.
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.
Pyruvate is oxidized to
CO2
NAD+ is reduced to
NADH
FAD is reduced to
FADH2
As in glycolysis, the electrons removed from carbon-containing intermediates during acetyl CoA formation and the citric acid cycle are passed to the electron carrier NAD+, reducing it to NADH.
The citric acid cycle also uses a second electron carrier, FAD (flavin adenine dinucleotide), the oxidized form, and FADH2, the reduced form.
Why is the citric acid cycle a cyclic pathway rather than a linear pathway?
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.
Although it is possible to oxidize the two-carbon acetyl group of acetyl CoA to two molecules of CO2, it is much more difficult than adding the acetyl group to a four-carbon acid to form a six-carbon acid (citrate). Citrate can then be oxidized sequentially to release two molecules of CO2.
For each glucose that enters glycolysis, _____ acetyl CoA enter the citric acid cycle.
2
Each glucose produces two pyruvates,
each of which is converted into acetyl CoA.
For each glucose that enters glycolysis, _____ NADH + H+ are produced by the citric acid cycle.
6
3 NADH + H+ are produced per
each acetyl CoA that enters the citric acid cycle.
In cellular respiration, most ATP molecules are produced by _____.
oxidative phosphorylation.
This process utilizes energy released by electron transport.
The final electron acceptor of cellular respiration is _____.
oxygen.
Oxygen is combined with electrons and hydrogen to form water.
During electron transport, energy from _____ is used to pump hydrogen ions into the _____.
NADH and FADH2 … intermembrane space
The energy released as electrons, which have been donated by NADH and FADH2, is passed along the electron transport chain and
used to pump hydrogen ions into the intermembrane space.
ATP synthase phosphorylates
ADP.
The proximate (immediate) source of energy for oxidative phosphorylation is _____.
kinetic energy that is released as hydrogen ions diffuse down their concentration gradient
Concentration gradients are a form of
potential energy.
The reactions of cellular respiration can be broken down into four stages:
- glycolysis
- acetyl coenzyme A (acetyl CoA) formation
- citric acid cycle (also known as the Krebs cycle)
- oxidative phosphorylation (electron transport and chemiosmotic ATP synthesis)
Glycolysis occurs in the
cytosol
cytoplasm
acetyl CoA formation occurs in the
mitochondrial matrix
the citric acid cycle occurs in the
mitochondrial matrix
