chapter 6
Consider the three central metabolic pathways that gradually oxidize glucose to CO2. Why are these amphibolic pathways?
"Amphi" means "both kinds," which reflects the dual role of these central metabolic pathways. Although they are catabolic, the precursor metabolites and reducing power they generate can be diverted for biosynthesis (anabolism).
An organism that uses hydrogen sulfide as an energy source is called a _______ and is most likely _______.
chemolithotroph; prokaryotic
The capacity to do work is the definition of
energy
Proteins that function as biological catalysts are called
enzyme
Use the following four words to correctly complete the sentence: endergonic, exergonic, anabolism, catabolism."Cells constantly produce ATP during ______ reaction of _______ and then use it to power ______ reaction of ________.
exergonic catabolism endergonic anabolism
Photophosphorylation is similar to oxidative phosphorylation except for the fact that the energy of light is used to create the _________ _________ force
proton motive
What are the two main forms of energy?
kinetic and potential
In competitive inhibition such as occurs with sulfa drugs, as the concentration of the _____ increases relative to the _____, the more likely the active site of the enzyme will be occupied, thereby blocking the regular function of the enzyme.
inhibitor substrate
The series of sequential chemical reactions in a cell that converts a starting compound to an end product is called a ______ pathway.
metabolic
The sum total of all chemical reactions in a cell is called
metabolism
When an inhibitor binds to a site other than the active site, the type of inhibition is called ______ _______ inhibition
non competitive
Cells can quickly alter the activity of certain key enzymes, using other molecules that bind reversibly and distort them. This control of enzymes is called ______ regulation
noncompetitive
In _______, the inhibitor changes the enzyme shape so that it is no longer functional. Indeed, the inhibitor is said to "poison" the enzyme.
noncompetitive inhibition
Although a modest amount of ATP is generated via substrate-level phosphorylation by the central metabolic pathways, these pathways produce a large amount of reducing power that can be used to generate a much larger quantity of ATP via ______ phosphorylation.
oxidative
Which of the following forms of phosphorylation require an electron transport chain for ATP production? 1. oxidative phosphorylation 2. substrate level phosphorylation 3. photophosphorylation
oxidative phosphorylation photophosphorylation
Cells use three key metabolic pathways referred to as the central metabolic pathways. These collectively ______.
oxidize glucose to CO2
Each type of the major electron carriers is referred to by two different abbreviations (NAD+/NADH, NADP+/NADPH, and FAD/FADH2).The first of each pair refers to the ______ form and the second of each pair refers to the _____ form.
oxidized reduced
In aerobic respiration, _____ serves as the terminal electron acceptor.
oxygen
Photosynthetic organisms can generate ATP by _____ , a process that uses the sun's radiant energy and an electron transport chain to create a proton motive force.
photophosphorylation
Unlike chemoorganotrophs, photosynthetic organisms generate ATP by ______.
photophosphorylation
Energy is the ability to do work and can exist as _____ energy (stored energy) and _____ energy (energy of motion).
potential, kinetic
The removal of an electron from a biological molecule is typically followed by the loss of a ____. The end result would be a removal of a hydrogen atom.
proton
The form of energy that results from the electrochemical gradient established by the electron transport chain is the ______.
proton motive force
Consider the three key central metabolic pathways (glycolysis, pentose phosphate pathway, and the TCA cycle). What three beneficial products of these pathways?
reducing power ATP precursor metabolites
During cellular ______ , electrons extracted from glucose via the central metabolic pathways are transferred to the electron transport chain, where they are used to generate a proton motive force that can be harvested to make ATP via oxidative phosphorylation.
respiration
Which of the following is a true statement regarding forms of energy? 1. The total amount of energy in the universe changes continuously as some is created and some is destroyed. 2. Energy can be created when it is changed from one form to another, for example, a hydroelectric dam generating electricity. 3. Energy can be changed from one form to another. 4. When the form of energy is changed, some is lost forever.
3. Energy can be changed from one form to another.
Which of the following is an example of activation energy? 1. The energy present in the water stored behind a dam. 2. The energy present in the carbon bonds of glucose. 3. The energy in photons of sunlight. 4. The energy present in the battery of your cell phone. 5. The energy of a small flame used to light the natural gas of a Bunsen burner.
5. The energy of a small flame used to light the natural gas of a Bunsen burner.
The three central metabolic pathways break down glucose, but also generate precursor metabolites and reducing power that can be diverted for use in anabolic pathways. To reflect this dual role, these pathways are sometimes called ______ pathways
amphibolic
When a molecule other than O2 serves as the terminal electron acceptor for the electron transport chain, the organism is utilizing _____ respiration
anaerobic
Suppose you are investigating a metabolic pathway in a bacterial species, and you hypothesize that it is regulated by feedback inhibition. The pathway involves the steps: A → B → C → D → E. To evaluate this hypothesis, you could test whether _______ inhibits the enzyme catalyzing the reaction of _______.
E; A → B
Glycolysis can be viewed as having two phases. Why is the initial phase sometimes referred to as the investment phase or preparatory phase? 1. The cell prepares for glycolysis by shutting down other pathways, so that it can ramp up production of glycolysis. 2. Energy is spent to add two high-energy phosphate groups to glucose, which is then split to yield two 3-carbon molecules. 3. The cell must first synthesize enzymes in glycolysis; this corresponds to the lag phase of growth following the introduction of glucose. 4. The skeletal structure of the 6-carbon glucose is rearranged from its linear to circular form.
Energy is spent to add two high-energy phosphate groups to glucose, which is then split to yield two 3-carbon molecules.
True or false: The sole function of glucose for cells growing in a glucose-salts medium is as an energy source.
False
_____ organisms harvest the energy of sunlight, using it to power the synthesis of organic compounds from CO2, whereas _____ obtain energy by degrading organic compounds made by others.
Photosynthetic, chemotrophs
Prokaryotes are remarkably diverse in their metabolism. Many are _____ anaerobes which use O2 if it is available, but they can use an alternative if it is not.
facultative
True or false: Enzymes are changed by the reaction as they lower the activation energy.
false
True or false: The metabolism of photosynthetic organisms and chemoorganotrophs involves the creation of energy.
false
Consider the pathway that converts the amino acid threonine to the amino acid isoleucine. Isoleucine is an allosteric inhibitor of the first enzyme of the pathway. This is an example of the mechanism called ______.
feedback inhibition
A cell has only a limited number of electron carrier molecules. During glycolysis, if electrons are not removed from NADH, the cell soon runs out of available NAD+, and the breakdown of glucose ends. This presents a problem for cells that lack a suitable terminal electron acceptor for the electron transport chain or that cannot respire. The solution to this problem is a process called
fermentation
Atoms that are more electronegative than others ______.
have a higher affinity for electrons
The amino acid isoleucine is an allosteric inhibitor of the first enzyme of the pathway that converts threonine to isoleucine. Given this, the pathway is likely shut down then the level of isoleucine is ______, and active when the level of isoleucine is ______.
high low
Electron carriers can also be considered hydrogen carriers. This is because, along with electrons, they carry
hydrogen or protons
Consider how cells obtain energy to make ATP. The chemical that serves as the electron donor is the _____ source, and the one that ultimately accepts those electrons is the _____ electron acceptor.
energy terminal
The mutual interaction of substrate and enzyme is best described as a(n) ______.
induced fit
In a biosynthetic pathway, the end product generally acts as the allosteric inhibitor, allowing the cell to shut down the pathway when the product begins accumulating. This mechanism of control is called ____ feedback
inhibition
An atom that has a lower affinity (attraction) for electrons than another is described as ______ than the other.
less electronegative
During cellular metabolism, three key metabolic pathways together gradually _______. These are collectively referred to as the central metabolic pathways.
oxidize glucose to CO2
In oxidation-reduction reactions, or redox reactions, the substance that loses electrons is _____ , and the substance that gains those electrons is ______.
oxidized reduce
In addition to yielding energy, catabolic pathways generate carbon intermediates that can be used in anabolic pathways for the biosynthesis of macromolecules. These carbon skeletons are called ____ ______
precursor metabolites
Which of the following are true about glycolysis? 1. The pathway splits glucose and oxidizes it to form two molecules of pyruvate. 2. The pathway provides the cell with a small amount of ATP, some reducing power, and six precursor metabolites. 3. The pathway provides the cell with a large amount of ATP, reducing power, and a number of precursor metabolites. 4. The pathway splits glucose and reduces it to form two molecules of pyruvate.
1 and 2
Which of the following are important electron carriers for a cell? 1. NADP+/NADPH 2. FAD/FADH2 3. ADP/ATP 4. NAD+/NADH
1, 2, 4
All of the following accurately describe enzymes EXCEPT ______. 1. the name of an enzyme typically reflects its function and ends in -ase 2. enzymes provide energy to help reactions proceed more rapidly 3. enzymes are not used up in the process of catalyzing reactions 4. enzymes are very specific, usually acting on only one or a few substrates 5. enzymes are biological catalysts
2. enzymes provide energy to help reactions proceed more rapidly
The main energy currency of cells is the molecule called
ATP
Recall that E. coli can grow in glucose-salts medium, which contains only glucose and a few inorganic salts. This means the glucose is serving what two purposes in the cell?
Starting point from which all cell components are made energy source
In aerobic respiration, _______ serves as the terminal electron acceptor.
fermentation
Energy is defined as
the ability to do work
Which of the following are true statements about what happens to glucose inside a cell? 1. Glucose can be used in catabolism to yield energy, or the precursor metabolites generated from its breakdown can be used in anabolism. 2. All the glucose molecules are oxidized to CO2, generating ATP and reducing power in the process. 3. Some glucose might be oxidized to CO2, generating the maximum amount of ATP. 4. Some glucose might enter glycolysis, only to be siphoned off as a precursor metabolite for biosynthesis.
1. Glucose can be used in catabolism to yield energy, or the precursor metabolites generated from its breakdown can be used in anabolism. 2. Some glucose might be oxidized to CO2, generating the maximum amount of ATP. 3. Some glucose might enter glycolysis, only to be siphoned off as a precursor metabolite for biosynthesis.
Which of the following accurately describe fermentation? 1. Glucose is broken down via glycolysis. 2. It generates more ATP than either glycolysis or respiration. 3. Fermentation does not involve the tricarboxylic acid (TCA) cycle. 4. All cells are able to ferment certain substances. 5. NAD+ is regenerated from NADH by the transfer of electrons to pyruvate or a derivative.
1. Glucose is broken down via glycolysis. 3. Fermentation does not involve the tricarboxylic acid (TCA) cycle. 5. NAD+ is regenerated from NADH by the transfer of electrons to pyruvate or a derivative.
In contrast to an exergonic reaction, which of the following accurately describe an endergonic reaction? 1. The reaction consumes energy. 2. The reaction releases energy as it proceeds. 3. The products have more free energy than the starting compounds. 4. The starting compounds have more free energy than the products.
1. The reaction consumes energy. 4. The products have more free energy than the starting compounds.
When a cell processes glucose or other organic molecules through its central metabolic pathways, it does so to generate what three critical things?
ATP, reducing power, precursor metabolites
When discussing electron carriers in the context of biological reactions, why do we often ignore the location of protons?
In aqueous solutions, protons do not require carriers.
Until the optimal temperature is reached, raising the temperature has what effect on the speed of enzymatic reactions?
It increases their rate.
A dehydrogenation reaction is a(n) _______, while a hydrogenation reaction is a(n) _______.
Oxidation Reduction
What are the reduced forms of the electron carriers NAD+ and FAD?
NADH FADH2
Which of the three central metabolic pathways generate a modest amount of ATP via substrate-level phosphorylation?
TCA and glycolysis
Consider the following linear metabolic pathway of a bacterial cell: Starting compound → Intermediate-a → Intermediate-b → End Product. The first two reactions are catalyzed by enzymes A and B, respectively. If a mutant cell arose that was unable to produce enzyme B, what would be the impact on the other components of the pathway?
The cell could still produce intermediate-a but would be unable to produce intermediate-b or the end product.
What is the active site of an enzyme?
The critical site to which a substrate binds by weak forces.
In order for cells to obtain energy, they remove electrons from an energy source and ultimately donate them to the terminal electron acceptor. What does this tell us about the electron affinity of the energy source and the terminal electron acceptor?
The energy source has a lower affinity for electrons, and the terminal electron acceptor has a higher affinity for electrons.
In competitive inhibition, why is the inhibitor able to bind to the active site, thereby blocking access of the substrate?
The inhibitor has a chemical structure similar to the normal substrate.
Consider the following biosynthetic pathway: W → X → Y → Z. Which compound is most likely to serve as an allosteric inhibitor?
Z
the _____ energy is the energy it takes to start a reaction.
activation
The critical site of an enzyme to which a substrate binds by weak forces is called the
active site
Cells use ATP as the ready and immediate donor of free energy. ATP stands for ____
adenosine triphosphate
Metabolic pathways can be linear, ____ or _____
branched, cyclical
The central metabolic pathways together produce ______.
carbon dioxide and water
The energy released by ______ is captured by cells to make ATP; this ATP can then be used for biosynthesis, or ______.
catabolism, anabolism
Enzymes are biological ______ that are typically _______.
catalysts; protein
Glucose catabolism encompasses two key processes: (1) oxidizing glucose molecules to generate ATP, reducing power, and precursor metabolites; and (2) transferring the electrons carried by NADH and FADH2 to the terminal electron acceptor. The second process, transfer of electrons, is accomplished as part of which of the following?
cellular respiration fermentation
The metabolic pathway that oxidizes a 2-carbon acetyl group to release two molecules of CO2 and generates the most reducing power of all the central metabolic pathways is called the _____ acid cycle
citric
An organic cofactor that functions as a loosely bound carrier of molecules or electrons to assist an enzyme is called a
coenzyme
Some enzymes can only function in the presence of an attached non-protein component. This component is termed a(n)
cofactor
Some enzymes act with the assistance of a non-protein component. This component is called a ______ ; if that component is an organic molecule it can be called a _______
cofactor coenzyme
Identify each of the following by the most precise descriptive term as either a cofactor or coenzyme: magnesium: ______ ; NADP+: _______; zinc: ________
cofactor coenzyme cofactor
Magnesium, zinc, and copper often function as _______ for enzymes.
cofactors
When a compound binds to the active site of an enzyme, blocking access of the substrate to that site, the process is called ______ inhibition
competitive
Consider the effect of temperature on enzyme activity. If the temperature is too high, proteins will _____ and no longer function.
denature
All of the following are true statements regarding coenzymes EXCEPT ______. 1. coenzymes transfer substances from one compound to another 2. coenzymes are needed only in very small quantities 3. coenzymes function in different ways; some remain bound to the enzyme, and others separate from the enzyme 4. each coenzyme is specific to a single enzyme
each coenzyme is specific to a single enzyme
The function of NAD+/NADH, NADP+/NADPH, and FAD/FADH2 in a cell is to carry
electrons
A chemical reaction that requires an input of energy in order to proceed is termed _____, whereas one that releases energy is called _____
endergonic, exergonic
The energy released when a chemical bond is broken that is available to do work is called ______.
free energy
The central metabolic pathway that splits glucose and gradually oxidizes it to form two molecules of pyruvate is
glycolysis
The primary pathway used by many organisms to convert glucose to pyruvate is
glycolysis
The three central metabolic pathways that gradually oxidize glucose to CO2 are ______, the _______ _______ pathway, and the ______ cycle.
glycolysis pentose phosphate TCA
Enzymes function as biological catalysts, accelerating the conversion of one substance, the ____, into another, the
substrate, product
In biosynthetic pathways, feedback inhibition refers to ______.
the end product acting as an allosteric inhibitor of the pathway
Free energy is best defined as ______.
the energy available to do work
Proton motive force is ______.
the form of energy that results from the electrochemical gradient established by the electron transport chain
Metabolism is best defined as ______.
the sum total of all chemical reactions in a cell
Certain intermediates of catabolic pathways, called precursor metabolites, are important because ______.
they serve as carbon skeletons from which subunits of macromolecules can be made
Oxidative phosphorylation and photophosphorylation are similar in that both processes ______.
use an electron transport chain to set up a proton motive force used to generate ATP
Which of the following explain why a cell might undergo fermentation? 1. The cell might not have the appropriate terminal electron acceptor available for respiration. 2. The cell has a limited number of electron carrier molecules that must be regenerated for glycolysis to continue. 3. The cell might lack the pathways for respiration, so fermentation might be the only option. 4. The cell can obtain more ATP from this pathway than via respiration. 5. This allows the cell to grow in the presence of O2, which otherwise it would be unable to do.
1. The cell might not have the appropriate terminal electron acceptor available for respiration. 2. The cell has a limited number of electron carrier molecules that must be regenerated for glycolysis to continue. 3. The cell might lack the pathways for respiration, so fermentation might be the only option.
Which of the following correctly describe respiration? 1. The electron transport chain uses the electrons to generate a proton motive force that can be used to generate ATP. 2. It is only present in aerobic organisms. 3. Electrons extracted from glucose are transferred to the electron transport chain. 4. All organisms that grow in the presence of O2 must use respiration for their energy needs.
1. The electron transport chain uses the electrons to generate a proton motive force that can be used to generate ATP. 3. Electrons extracted from glucose are transferred to the electron transport chain.
Which of the following correctly describe the transition step and the tricarboxylic acid (TCA) cycle? 1. The transition step converts the pyruvate from glycolysis into acetyl-CoA. 2. Together they generate the most reducing power of all the central metabolic pathways. 3. The TCA cycle generates most of the ATP for the cell. 4. The TCA cycle oxidizes a 2-carbon acetyl group to release two molecules of CO2. 5. The TCA cycle reduces a 2-carbon acetyl group to release two molecules of CO2.
1. The transition step converts the pyruvate from glycolysis into acetyl-CoA. 2. Together they generate the most reducing power of all the central metabolic pathways. 4. The TCA cycle oxidizes a 2-carbon acetyl group to release two molecules of CO2.