Microbiology Chapter 6 - Exam #1
The enzymes of the tricarboxylic acid cycle are found in the ______ matrix in eukaryotes and in the _____ in prokaryotes.
mitochondrial; cytoplasm
Escherichia coli's electron transport chain (ETC) is ______.
modular, meaning that different components are used depending on the conditions
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
oxidative phosphorylation
The mechanism by which cellular respiration uses reducing power generated in glycolysis, the transition step, and the TCA cycle to synthesize ATP is _____
oxidative phosphorylation
Cells use three key metabolic pathways referred to as the central metabolic pathways. These collectively ______.
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; reduced
The form of energy that results from the electrochemical gradient established by the electron transport chain is the ______.
proton motive force
In the process called _____, cells break down glucose via glycolysis and then use pyruvate or a derivative as a terminal electron acceptor.
fermentation
Exergonic Reaction
Describes a chemical reaction that releases energy because the starting compounds have more free energy than the products
TCA cycle
oxidation Explanation: TCA completes the oxidation of glucose to CO2
The electron transport chain (ETC) components used by E. coli vary depending on all of the following conditions EXCEPT ______. - temperature - type of energy source available - level of O2
temperature
Which of the following forms of phosphorylation require an electron transport chain for ATP production?
- photophosphorylation - oxidative phosphorylation
During the transition step of central metabolism, all of the following occur EXCEPT ______. - 2 ATP are generated. - The 2-carbon acetyl group is joined to coenzyme A to form acetyl-CoA. - Electrons are transferred to NAD+, reducing it to NADH + H+. - CO2 is removed from pyruvate.
2 ATP are generated.
Two 3-carbon molecules enter the latter phase of glycolysis for each initial glucose molecule, meaning the steps of this phase occur twice for each glucose. During this second phase of glycolysis, what is the total number of NADH and ATP molecules produced from a single glucose molecule?
2 NADH and 4 ATP
The TCA cycle incorporates an acetyl group from the transition step and releases two different precursor metabolites, two molecules of _______, and two molecules of
CO2; ATP
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 _____
allosteric (noncompetitive) regulation
Endergonic Reaction
Describes a chemical reaction that requires a net input of energy because the products have more free energy than the starting compounds
Oxidative phosphorylation
Energy from exergonic reactions is used to create a proton motive force that drives the addition of P to ADP
Glycolysis can be viewed as having two phases. Why is the initial phase sometimes referred to as the investment phase or preparatory phase?
Energy is spent to add two high-energy phosphate groups to glucose, which is then split to yield two 3-carbon molecules.
Substrate-level phosphorylation
Energy released in an exergonic reaction is used to power the addition of P to ADP
True/False: The metabolism of photosynthetic organisms and chemoorganotrophs involves the creation of energy.
False Explanation: Energy cannot be created or destroyed; instead, the cells convert energy from one for to another
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
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 terms of reducing power, what are the products of the TCA cycle?
6 NADH and 2 FADH2
Anabolism (Biosynthesis)
Cellular processes that synthesize and assemble subunits of macromolecules, using the energy of ATP
The Chemiosmotic Theory, proposed by Peter Mitchell in 1961, explains ______.
how the electron transport chain is linked to ATP synthesis
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 biosynthetic pathways, feedback inhibition refers to ______.
the end product acting as an allosteric inhibitor of the pathway
The central metabolic pathways together produce ______.
water and carbon dioxide
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 accurately describe fermentation?
- Fermentation does not involve the tricarboxylic acid (TCA) cycle. - Glucose is broken down via glycolysis. - NAD+ is regenerated from NADH by the transfer of electrons to pyruvate or a derivative.
Transition step
- Links glycolysis to TCA cycle - Converts pyruvate to acetyl CoA
Which of the following are important electron carriers for a cell?
- NAD+/NADH - NADP+/NADPH - FAD/FADH2
What are the reduced forms of the electron carriers NAD+ and FAD?
- NADH - FADH2
When a single molecule of glucose is processed by glycolysis in an E. coli cell, which of the following make up the net gain of this process?
- Six precursor metabolites - 2 molecules of NADH - 2 molecules of ATP
Which of the three central metabolic pathways generate a modest amount of ATP via substrate-level phosphorylation?
- Tricarboxylic acid (TCA) cycle - Glycolysis
Allosteric & Active Site
....
ATP Formation & Breakdown
1. ATP 2. Energy released drives anabolic reactions 3. ADP 4. Energy used comes from catabolic reactions
Fermentation
A catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid.
Cells use ATP as the ready and immediate donor of free energy. ATP stands for
ATP = Adenosine Triphosphate
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.
Catabolism
Metabolic processes that harvest energy released during the breakdown of compounds such as glucose, using it to synthesize ATP
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.
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
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.
Theoretically, if a bacterial cell had no ATP and was given glucose, what would happen with glycolysis?
The cell would be unable to perform glycolysis, since it would lack the initial investment of high-energy phosphate groups.
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 electron
Glycolysis can be viewed as having two phases. The second phase is sometimes referred to as the pay-off phase. Why would that be?
The initial investment of two high-energy phosphate bonds is recovered, and net energy yielded.
Photophosphorylation
The sun's radiant energy and an electron transport chain create a proton motive force that drives the addition of P to ADP
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.
Cyclical Pathway
Type of Metabolic Pathway Others: - Linear - Branch
The critical site of an enzyme to which a substrate binds by weak forces is called the ____
active site
The energy released by ______ is captured by cells to make ATP; this ATP can then be used for biosynthesis, or ______.
catabolism; anabolism
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
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/electron; terminal
The central metabolic pathway that splits glucose and gradually oxidizes it to form two molecules of pyruvate is _____
glycolysis
Enzymes function as biological catalysts, accelerating the conversion of one substance, the ______ , into another, the _______
substrate/reactant; product
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 explain why a cell might undergo fermentation? Multiple select question.
- The cell has a limited number of electron carrier molecules that must be regenerated for glycolysis to continue. - The cell might not have the appropriate terminal electron acceptor available for respiration. - The cell might lack the pathways for respiration, so fermentation might be the only option.
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.
In contrast to an exergonic reaction, which of the following accurately describe an endergonic reaction?
- The products have more free energy than the starting compounds. - The reaction consumes energy.
Which of the following are reasons an organism might use fermentation?
- They lack an electron transport chain. - A suitable inorganic terminal electron acceptor is not available.
For each glucose molecule degraded, the net yield of glycolysis is ______.
2 ATP, 2 NADH, and 6 precursor metabolites
______ 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
Photosynthetic/ Photoautotrophic/ Phototrophic; Chemoorganotrophs/ Chemotrophs/ Heterotrophs
Proteins that function as biological catalysts are called ____
enzymes
Cells constantly produce ATP during _____ reactions of ______ and then use it to power ______ reactions of _______
exergonic; catabolism endergonic; anabolism
