Microbiology Ch. 6
1. Hydrogen is transported from other reactions to the electron transport chain by ______.
1. NADH and FADH2
3. During the electron transport chain, ATP will be made from
ADP + Pi.
All of the following are essential for an electron transport chain to function EXCEPT ______.
ATP
Non-competitive inhibition by regulatory molecules
Allosteric regulators Inhibitor reversibly changes the shape of the enzyme so that the substrate can no longer bind to the active site
1. ______ refers to energy-requiring metabolic processes that result in the biosynthesis of macromolecules and cellular structures.
Anabolism
Consider the biochemical pathway: A → B → C Enzyme 1 catalyzes A → B Enzyme 2 catalyzes B → C If enzyme 2 is inactive, which of the following compounds will accumulate?
B only
How does the oxidase test help in bacterial identification?
It detects the activity of cytochrome c oxidase, a component of the electron transport chain of some but not all bacteria.
3. What happens to carbon dioxide after it is released during reactions of the TCA cycle?
It diffuses out of the cell.
Until the optimal temperature is reached, raising the temperature has what effect on the speed of enzymatic reactions?
It increases their rate.
Quinones
Lipid-soluble organic molecules that move freely in the membrane; includes one that serves as a source of vitamin K for humans and other mammals
Non-competitive inhibition by enzyme poisons
Mercury Inhibitor permanently changes the shape of the enzyme, making the enzyme non-functional
4. The two 3-carbon molecules glucose is split into are converted through a series of steps into pyruvate. During these steps
NAD+ is converted to NADH.
The electron transport chain is a cluster of membrane-embedded electron carriers that accept electrons from the coenzymes ______ and ______ and then pass these electrons along the chain.
NADH FADH2
The lactic acid fermentation pathway is shown here. What statement best explains what is happening in the diagram?
NADH + H+ are donating 2 electrons and 2 protons to pyruvate, an organic terminal electron acceptor, reducing it to lactate.
In aerobic respiration, ______ serves as the terminal electron acceptor.
Oxygen
In the representation of an electron transport chain (shown), the terminal electron acceptor is
Oxygen
2. Which of the following is not a catabolic process?
Protein synthesis
Flavoproteins
Proteins that are synthesized from the vitamin riboflavin
Cytochromes
Proteins that contain heme, a molecule that holds an iron atom in its center
2. The two 3-carbon molecules that glucose is split into during glycolysis are converted through a series of steps ending in what 3-carbon molecule?
Pyruvate
Which of the following binds to the active site of an enzyme?
Substrate
Competitive inhibition
Sulfa drugs Inhibitor binds to the active site of the enzyme, blocking access of the substrate
24 ATP
TCA cycle
Consider the figure showing the relationship between catabolism and anabolism. Which side shows catabolism, and which side shows anabolism?
The left side shows catabolism, and the right side shows anabolism.
1. What is oxidation?
The loss of electrons from a molecule.
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.
allosteric
The figure illustrates a type of regulation used by cells to rapidly control certain key enzymes. The arrow labeled "1" points to the ______ site, and the arrow labeled "2" points to the ______ site.
allosteric active
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
Examples of electron carriers are proteins that contain heme, a molecule that holds an iron in its center. These are called
cytochromes
In oxidative phosphorylation, quinones, cytochromes, and flavoproteins are all ______ carriers.
electron
In addition to four protein complexes, the mitochondrial electron transport chain has two freely-moving ______, ubiquinone and cytochrome c, that serve to ______.
electron carriers; shuttle electrons between the complexes
The capacity to do work is the definition of
energy
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 electron transport chain of mitochondria has ______ different protein complexes.
four
2. Glycolysis is the central metabolic pathway that involves the breakdown of ______.
glucose
The three central metabolic pathways that gradually oxidize glucose to CO2 are ______ , the ______ ______ pathway, and the ______ cycle.
glycolysis pentose phosphate TCA
Atoms that are more electronegative than others ______.
have a higher affinity for electrons
What are the two main forms of energy?
kinetic potential
5. After glycolysis, pyruvate can be converted into ______ under anaerobic conditions.
lactic acid
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
2. Hydrogen consists of
one proton and one electron.
Consider the biochemical pathway: A → B → C Enzyme 1 catalyzes A → B Enzyme 2 catalyzes B → C Enzyme 1 can use
only A as a substrate.
The TCA cycle completes the ______ of glucose.
oxidation
The mechanism by which cellular respiration uses reducing power generated in glycolysis, the transition step, and the TCA cycle to synthesize ATP is ______ phosphorylation.
oxidative
Cells use three key metabolic pathways referred to as the central metabolic pathways. These collectively ______.
oxidize glucose to CO2
During cellular metabolism, three key metabolic pathways together gradually _______. These are collectively referred to as the central metabolic pathways.
oxidize glucose to CO2
1. The terminal electron acceptor in aerobic respiration is ______.
oxygen
The central metabolic pathway that generates reducing power in the form of NADPH is the ______ ______ pathway.
pentose phosphate
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
Cells use ATP as the ready and immediate donor of free energy. ATP stands for
Adenosine triphosphate
The electron transport chain consists of large protein-complexes embedded in a membrane. These pass electrons from one to the next, while simultaneously pumping ______ across the membrane,
protons
5. The enzyme ATP synthase uses energy from ______ to make ATP.
protons re-entering the cell.
Menaquinone is a quinone used in the electron transport chain of some prokaryotes. It plays an important role for humans and other mammals because it ______.
serves as a source of vitamin K, providing much of the host's requirement via absorption in the intestinal tract
Enzymes function as biological catalysts, accelerating the conversion of one substance, the ______, into another, the ______
substrate product
Metabolism is best defined as ______.
sum total of all chemical reactions in a cell
Energy is defined as ______.
the ability to do work
2. The TCA (Krebs) cycle takes place in the mitochondria of eukaryote cells. Where does it take place in prokaryote cells?
the cytoplasm
1. In bacteria, the electron transport chain is located in
the cytoplasmic membrane.
In the electron transport chain, protons are pumped across the cell membrane. This results in
the formation of a proton motive force.
In aerobic respiration, oxygen acts as
the terminal electron acceptor.
4. Cells prefer to use carbohydrates as energy sources because
they are such good donors of hydrogen and electrons.
This picture of a set of stairs best exemplifies the electron ______ ______.
transport chain
Oxidative phosphorylation, the mechanism by which cellular respiration uses the NADH and FADH2 generated in glycolysis, the transition step, and the TCA cycle to synthesize ATP, involves what two steps?
- ATP synthase uses the energy of the proton motive force to drive the synthesis of ATP. - The electron transport chain generates a proton motive force.
Which of the following are true about glycolysis?
- The pathway provides the cell with a small amount of ATP, some reducing power, and six precursor metabolites. - The pathway splits glucose and oxidizes it to form two molecules of pyruvate.
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
The diagram shows a type of metabolic pathway known as a(n) ______ pathway
cyclical
1. Glycolysis takes place in the ______.
cytoplasm
All of the following accurately describe enzymes EXCEPT ______.
enzymes provide energy to help reactions proceed more rapidly
An atom that has a lower affinity (attraction) for electrons than another is described as ______ than the other.
less electronegative
The enzymes of the tricarboxylic acid cycle are found in the ______ matrix in eukaryotes and in the ______ in prokaryotes.
mitochondrial cytoplasm
Cells obtain energy by ______ food molecules such as glucose.
oxidizing
3. The electron transport chain is part of ______.
respiration
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.
tricarboxylic
2. In aerobic respiration, the last carrier protein in the electron transport chain transfers
two electrons to oxygen.
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 are important electron carriers for a cell?
NADP+/NADPH NAD+/NADH FAD/FADH2
Escherichia coli and Pseudomonas aeruginosa both have an electron transport chain that uses O2 as a terminal electron acceptor, yet E. coli is oxidase negative. Based on this information, it is logical to assume that E. coli ______.
lacks cytochrome c
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 oxidation-reduction reactions, or redox reactions, the substance that loses electrons is , ______ and the substance that gains those electrons is ______.
oxidized reduced
The figure depicts oxidation-reduction reactions, which are also known as ______ reactions.
redox
Consider the representation of an electron transport chain. O2 is serving as the terminal electron acceptor. Is it being oxidized or reduced?
reduced
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.
resperation
The central metabolic pathways together produce ______.
water and carbon dioxide
A general group of electron carriers found in electron transport chains is quinones, that ______.
- are lipid-soluble organic molecules that move freely in the membrane, transferring electrons between different protein complexes - exist as several types, including ubiquinone and menaquinone
Which of the following are reasons an organism might use fermentation?
- A suitable inorganic terminal electron acceptor is not available. - They lack an electron transport chain.
3. For each glucose molecule broken down by glycolysis, how many net ATP molecules are produced?
2
5. How many ATP molecules are produced in the TCA cycle for each glucose molecule that enters glycolysis?
2
6. For each glucose molecule that enters glycolysis, how many times does the TCA cycle "turn"?
2
4. How many molecules of NADH are generated for each turn of the TCA cycle?
3
If the theoretical maximum ATP yield in prokaryotes from oxidative phosphorylation is 34 ATP for a single glucose molecule, what is the total ATP gain when substrate-level phosphorylation is included?
38 ATP
3. During glycolysis, a single 6-carbon molecule of glucose is converted to two 3-carbon pyruvate molecules. During the later steps in this process, how many molecules of ATP are generated?
4
Some enzymes require a cofactor or a coeznyme in order to be active. What is the difference between cofactors and coenzymes?
Cofactors are non-protein components that assist enzymes and are typically trace elements; coenzymes are organic cofactors that loosely carry molecules or electrons.
4. Which of the following contain a metal ion that can accept and donate electrons?
Cytochromes
4. Where does the TCA cycle take place in bacteria?
Cytoplasm
True or False: With respect to prokaryotic species such as E. coli, each individual cell will have an electron transport chain made up of the same components.
False
2. Where do NADH and FADH2 go after being produced in the TCA cycle?
Electron transport chain.
Oxidative phosphorylation
Energy from exergonic reactions is used to create a proton motive force that drives the addition of Pi to ADP.
Substrate-level phosphorylation
Energy released in an exergonic reaction is used to power the addition of Pi to ADP.
Consider the image you labeled showing a metabolic pathway under allosteric regulation. Which enzyme in this pathway is most likely under allosteric control?
Enzyme a
What are the reduced forms of the electron carriers NAD+ and FAD?
FADH2 NADH
3. True or false: In prokaryotes and eukaryotes, the TCA cycle takes place in the mitochondria.
False
4. True or False: In anaerobic respiration, the terminal electron acceptor would also be oxygen.
False
True or False: All biochemical pathways have the same number of enzymatic reactions.
False
True or False: An enzyme can only bind one substrate at a time.
False
True or False: An enzyme speeds up a chemical reaction in the cell, but can only be used once.
False
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
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.
Which of the following is an example of activation energy?
The energy of a small flame used to light the natural gas of a Bunsen burner.
Photophosphorylation
The sun's radiant energy and an electron transport chain create a proton motive force that drives the addition of Pi to ADP.
Why does anaerobic respiration yield less energy than aerobic respiration?
The terminal electron acceptors used in anaerobic respiration have lower electron affinities than O2.
What happens to the protons received from NADH in bacteria?
They are transported across the cytoplasmic membrane, setting up a proton motive force.
Other than generating some ATP via the substrate-level phosphorylation steps of glycolysis, what critical role do the additional steps of fermentation accomplish?
They consume excess reducing power in order to regenerate NAD+ so that it can accept electrons to keep glycolysis going.
Although the actual procedure is much more involved, the basic metabolism of wine-making involves inoculating grape juice with a special strain of the yeast Saccharomyces cerevisiae. S. cerevisiae will preferentially perform aerobic respiration on sugars in the juice but can also ferment those sugars to yield CO2 and alcohol, an important component of wine. Assume you inoculate a completely full container of juice and then close the lid. What will the yeast do?
They will grow aerobically, consume the O2 dissolved in the juice, and then switch to fermenting sugars to yield alcohol.
38 ATP
Total yield of aerobic respiration
6 ATP
Transition step
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.
Tricarboxylic
In the figure, Compound X donates electrons to Compound Y. Which of the following correctly describes this process?
X is oxidized by the reaction, and Y is reduced by the reaction.
A hydrogen atom consists of
a proton and an electron.
2. The electron carrier proteins in the electron transport chain shuttle electrons to
a terminal electron acceptor.
In this figure, the relative energy (y-axis) of a reaction is plotted over time (x-axis). One curve represents the reaction in the absence of an enzyme, and the other in the presence of an enzyme. In each case, A and B represent the ______ ______ of the reaction.
activation energy
The critical site of an enzyme to which a substrate binds by weak forces is called the ______ ______.
active site
3. The energy released during the reactions of glycolysis is used to form ______.
adenosine triphosphate
Although the pentose phosphate pathway is used by cells to break down glucose, it is particularly important because of its contribution to ______.
biosynthesis
Which of the following are true statements about what happens to glucose inside a cell?
- some glucose might enter glycolysis, only to be siphoned off as a precursor metabolite for biosynthesis- glucose can be used in catabolism to yield energy, or the precursor metabolites generated from its breakdown can be used in anabolism- some glucose might be oxidized to CO2, generating the maximum amount of ATP
Consider the figure of relative energy (y-axis) versus progress of reaction (x-axis). Which represents the activation energy of the reaction catalyzed by an enzyme?
A
The main energy currency of cells is the molecule called
ATP
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
This diagram depicts the production of ethanol from pyruvate via fermentation. What best explains the mechanism?
CO2 removal converts pyruvate to the terminal electron acceptor acetaldehyde, which receives 2 electrons and protons from NADH + H+, making ethanol.
In respiring bacteria, how does ATP synthase generate ATP?
It uses the energy released from allowing protons to flow back into the cell to add a phosphate group to ADP
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 prokaryotes, how does the energy yield of aerobic respiration compare to anaerobic respiration?
The energy yield of aerobic respiration is greater than anaerobic respiration.
Metabolic pathways can be linear, ______ or ______.
branched cyclical
2. Early in glycolysis, two phosphates are added to the glucose molecule. These phosphates come from
breaking down ATP.
1. The coenzyme NADH is generated by
by oxidation reactions in glycolysis and the Krebs cycle.
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
Consider the effect of temperature on enzyme activity. If the temperature is too high, proteins will ______ and no longer function.
denature
This figure shows one half of a redox reaction. Compound X is the electron ______ and Compound Y is the electron ______.
donor acceptor
1. Glycolysis makes products that feed into
electron transport chain, TCA cycle AND fermentation.
Which of the following forms of phosphorylation require an electron transport chain for ATP production?
photophosphorylation oxidative phosphorylation
In prokaryotes, the electron transport chain is located in the ______ membrane, whereas in eukaryotic cells it is in the ______ membrane of mitochondria.
plasma inner
Energy is the ability to do work and can exist as ______ energy (stored energy) and ______ energy (energy of motion).
potential kenetic
Consider the three key central metabolic pathways (glycolysis, pentose phosphate pathway, and the TCA cycle). What three beneficial products of these pathways?
precursor metabolites ATP reducing power
1. The main purpose of cellular respiration is to
produce energy.
Enzymes are usually ______.
proteins
Photophosphorylation is similar to oxidative phosphorylation except for the fact that the energy of light is used to create the ______ ______ force.
proton motive
The form of energy that results from the electrochemical gradient established by the electron transport chain is the ______.
proton motive force
The three main types of electron carriers in a typical electron transport chain are ______, ______, and flavoproteins.
quinones cytochromes
3. During the electron transport chain in bacteria, protons are
shuttled to the outside of the cell membrane.
The ATP generated by fermentation comes from ______.
substrate-level phosphorylation during glycolysis
As part of cellular respiration, a membrane-bound enzyme called ATP ______ uses energy from a proton-motive force to add a phosphate group to ADP.
synthase
Certain intermediates of catabolic pathways, called precursor metabolites, are important because ______.
they serve as carbon skeletons from which subunits of macromolecules can be made
Which of the following correctly describe respiration?
- Electrons extracted from glucose are transferred to the electron transport chain - The electron transport chain uses the electrons to generate a proton motive force that can be used to generate ATP
In an electron transport chain, electron carriers are found in what two general locations?
- Grouped into large protein complexes that function as proton pumps. - Freely moving in the membrane where they can shuttle electrons between protein complexes.
Which of the following correctly describe cytochromes found in an electron transport chain?
- Several different cytochromes exist. - Cytochromes are proteins that contain heme, a molecule that holds an iron atom in its center. Need help? Review these concept resources.
Consider the image you labeled showing a metabolic pathway under allosteric regulation. Imagine if the final enzyme in the pathway was under allosteric regulation instead of the first. What impacts would this have?
- There would be a buildup of intermediate b. - The reaction would be less efficient.
Which of the following statements accurately describe biochemical pathways? Choose all that apply.
- They convert an initial substrate through a series of steps into an end product - They are well-organized and structured - They can be linear, branched, or cyclical. - They are carefully regulated
Which of the following correctly describe the transition step and the tricarboxylic acid (TCA) cycle?
- Together they generate the most reducing power of all the central metabolic pathways. - The TCA cycle oxidizes a 2-carbon acetyl group to release two molecules of CO2. - The transition step converts the pyruvate from glycolysis into acetyl-CoA.
True or False: In a biochemical pathway, the product of the first reaction becomes the substrate in the second reaction.
True
True or False: The energy captured in the phosphorylation of ADP to ATP comes from the proton motive force created in respiration.
True
True or False: Whenever a molecule is oxidized, another molecule must be reduced.
True
True or False: With respect to the location of the electron transport chain, the inner membrane of mitochondria is analogous to the cytoplasmic membrane of bacterial cells.
True
For each six-carbon molecule of glucose that enters glycolysis, how many molecules of pyruvate are made, and how many carbon atoms does each pyruvate have?
Two molecules of pyruvate, each with three carbon atoms.
E. coli will preferentially use ______ respiration in the presence of O2, but when O2 is not available, it can switch to ______ respiration if a suitable electron acceptor such as nitrate is present.
aerobic anaerobic
The function of NAD+/NADH, NADP+/NADPH, and FAD/FADH2 in a cell is to carry
electrons
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 ______ reactions of ______ and then use it to power ______ reactions of ______."
exergonic catabolism endergonic anabolism
3. The Tricarboxylic Acid Cycle (TCA cycle) occurs after ______.
glycolysis
8 ATP
glycolysis
Proton motive force is ______.
the form of energy that results from the electrochemical gradient established by the electron transport chain
