Chapter 13 - How Cells Obtain Energy from Food Flashcards
In cells that cannot carry out fermentation, which products derived from glycolysis will accumulate under anaerobic conditions?
- glucose and NADH
- pyruvate and NAD+
- pyruvate and NADH
- lactate and NAD+
- glucose 6-phosphate and NADH
Pyruvate and NADH
(Without oxygen, NADH would be unable to donate its electrons to the electron transport chain and the pyruvate produced by glycolysis would not be removed by fermentation.)
Most of the energy released by oxidizing glucose is saved in the high-energy bonds of what molecules?
- ATP and other activated carriers
- O2
- H2O and CO2
- GDP and other activated carriers
- ADP and other activated carriers
ATP and other activated carriers
(Much of the energy released by the oxidative breakdown of glucose is saved in the high-energy bonds of ATP and the high-energy electrons of NADH.)
Useful energy is obtained by cells when sugars derived from food are broken down by which processes?
- glycolysis, the citric acid cycle, and oxidative phosphorylation
- glycolysis, the Calvin cycle, and oxidative phosphorylation
- gluconeogenesis, fermentation, and oxidative phosphorylation
- glycolysis, the citric acid cycle, and gluconeogenesis
- gluconeogenesis, the citric acid cycle, and oxidative phosphorylation
Glycolysis, the citric acid cycle, and oxidative phosphorylation
(Together, these processes capture the energy released from the oxidative breakdown of sugars.)
Where does the oxidative (oxygen-dependent) stage of the breakdown of food molecules occur in a eukaryotic cell?
- mitochondrion
- Golgi apparatus
- endoplasmic reticulum
- cytosol
Mitochondrion
(The oxidative stage of the breakdown of food molecules takes place entirely in the mitochondrion.
The citric acid cycle, which requires oxygen to proceed, occurs in the mitochondrial matrix. And oxidative phosphorylation, which consumes a large amount of oxygen, takes place on the inner mitochondrial membrane.)
Which of the following processes generates the largest number of ATP molecules?
- gluconeogenesis
- fermentation
- electron transport chain
- glycolysis
- citric acid cycle
Electron transport chain
(The electron transport chain in the inner mitochondrial membrane generates large amounts of ATP from electrons donated by the active carriers produced during glycolysis and the citric acid cycle.)
Under anaerobic conditions, which metabolic pathway regenerates the supply of NAD+ needed for glycolysis?
- citric acid cycle
- fermentation
- breakdown of amino acids
- breakdown of fats
- formation of acetyl CoA
Fermentation
(Fermentation reactions convert the pyruvate produced during glycolysis into lactate or ethanol. In the process, NADH gives up its electrons, thereby producing NAD+.
Without replenishing NAD+, glycolysis could not continue.)
Although the citric acid cycle itself does not use O2, it requires a functioning electron transport chain (which uses O2) in order to regenerate which molecule for further use in the citric acid cycle?
- NADH
- ADP
- ATP
- NAD+
- FADH2
NAD+
(Like glycolysis, the citric acid cycle uses NAD+ as an electron acceptor. This molecule—along with FAD—must be regenerated for the citric acid cycle to continue. Generating NAD+ requires oxygen (or an ability to carry out fermentation reactions). Oxygen allows NADH to hand off its high-energy electrons, regenerating the NAD+ needed to keep the citric acid cycle going.)
The NADH generated during glycolysis and the citric acid cycle feeds its high-energy electrons to which of the following?
- FAD
- the electron transport chain
- ADP
- H2O
- the citric acid cycle
The electron transport chain
(The NADH generated during glycolysis (and the NADH and FADH2 produced by the citric acid cycle) feeds its high-energy electrons to the electron transport chain.)
In eukaryotic cells, what is the final electron acceptor in the electron transport chain?
- O2
- CO2
- ATP
- FADH2
- NAD+
O2
(High-energy electrons, donated to the electron transport chain by NADH and FADH2, are ultimately passed on to O2, which serves as the final electron acceptor in the chain.)
In the electron transport chain, the oxygen atoms in O2 become part of which of the following molecules?
- glucose (C6H12O6)
- NADH
- H2O
- ATP
- CO2
H2O
The electron transport chain donates electrons to O2, producing H2O.
Which two-carbon molecule enters the citric acid cycle?
- oxaloacetate
- citrate
- pyruvate
- acetyl CoA
- carbon dioxide
Acetyl CoA
(In the first step of the citric acid cycle, acetyl CoA donates a two-carbon acetyl group to oxaloacetate to form citrate. These carbons are then oxidized to produce CO2.)
What occurs in the first step of the citric acid cycle?
- ATP is consumed.
- A two-carbon molecule is combined with a four-carbon molecule to form citrate.
- CO2 is released.
- NADH is produced.
- Two molecules of acetyl CoA combine to form oxaloacetate.
A two-carbon molecule is combined with a four-carbon molecule to form citrate.
(In the initial reaction of the citric acid cycle, a two-carbon acetyl group combines with a four-carbon oxaloacetate molecule to form the six-carbon citrate after which the cycle is named.)
CO2 is released in which steps of the citric acid cycle, as shown below?
- Steps 1 and 8
- Steps 2, 3, and 4
- Steps 1 and 5
- Steps 3 and 4
- Steps 2 and 4
Steps 3 and 4
(The steps of the citric acid cycle that release CO2 are those in which an intermediate loses a carbon.
In step 3, a six-carbon substrate (isocitrate) is converted into a five-carbon product (α-ketoglutarate). The lost carbon is released as CO2. In step 4, the five-carbon α-ketoglutarate reacts with a molecule of coenzyme A to yield the four-carbon succinyl CoA. Again, the missing carbon is accounted for by CO2, which is released in this step.)
The ethanol in wine and beer is produced from metabolic reactions carried out by the yeast Saccharomyces cerevisiae. Since it is of great commercial value, researchers have studied factors that influence ethanol production. To maximize ethanol yield, which environmental factor should be limiting?
- sunlight
- carbon dioxide
- glucose
- oxygen
Oxygen
(In the absence of oxygen, yeast cannot perform aerobic respiration and instead switch to fermentation. Fermentation products in yeast include CO2 and ethanol.)
How do enzymes maximize the energy harvested from the oxidation of food molecules?
- They allow the stepwise oxidation of food molecules, which releases energy in small amounts.
- They guarantee that each reaction involved in the oxidation of food molecules proceeds in just one direction.
- They allow a larger amount of energy to be released from food molecules such as glucose.
- They allow oxidation reactions to take place without an input of activation energy.
- They allow what would otherwise be an energetically unfavorable oxidation reaction to occur.
They allow the stepwise oxidation of food molecules, which releases energy in small amounts.
(Enzymes allow cells to carry out the oxidation of sugars in a tightly controlled stepwise series of reactions. These reactions pay out energy in small packets to activated carriers, which allows cells to capture much of the energy released by the oxidative breakdown of glucose in the high-energy bonds of ATP and other activated carriers.)
What happens to the energy captured during glycolysis and the citric acid cycle by the activated carriers NADH and FADH2.
- It is passed to an electron transport chain that uses it to generate a proton gradient across the inner mitochondrial membrane.
- It is passed to an electron transport chain that uses it to oxidize food molecules.
- It is used to drive biosynthetic reactions.
- It is passed to ADP to form ATP.
- It is passed to an electron transport chain that uses it to produce oxygen.
It is passed to an electron transport chain that uses it to generate a proton gradient across the inner mitochondrial membrane.
(This proton gradient then serves as a source of energy (like a battery) that can be tapped to drive a variety of energy-requiring reactions, including the phosphorylation of ADP to generate ATP on the matrix side of the inner membrane.)
What does the term “gluconeogenesis” refer to?
- the transport of glucose across a cell membrane
- the breakdown of glucose during glycolysis
- the synthesis of glucose from small organic molecules such as pyruvate
- the breakdown of glucose during fermentation
- the release of glucose from molecules such as glycogen
The synthesis of glucose from small organic molecules such as pyruvate
(These reactions sometimes occur during periods of fasting, when glucose reserves are consumed faster than they can be replenished.)
When food is plentiful, animals can store glucose as what?
- starch
- acetyl CoA
- glucose 6-phosphate
- glycogen
- glycogen or starch
Glycogen
Glycogen and starch are both branched polysaccharides made of glucose, but only glycogen is made by animal cells.
When nutrients are plentiful, plants can store glucose as what?
- glucose 6-phosphate
- starch
- glycogen and starch
- fats
- glycogen
Starch
(This energy-rich material serves as a major food source for plants—and for the many animals that eat them, including humans.)
In what form do plant and animal cells store fat?
- triacylglycerol
- glycogen
- phospholipids
- starch
- nitroglycerin
Triaclyglycerol
(The triacylglycerol in plants and animals differs only in the types of fatty acids that predominate: plant oils contain unsaturated fatty acids (with one or more double bonds) and animal fats are saturated.)
You are packing for a hiking trip during which you’ll be burning a lot of calories with physical activity. You want to pack as efficiently as possible since you need to carry a tent and all your food. You can get the most calories out of 5kg of food if it is in the form of ______.
- starch
- glycogen
- fat
- glucose
Fat
Carbohydrates provide 4 calories per gram, and fat provides 9 calories per gram.
In the absence of oxygen, in cells that cannot carry out fermentation, glycolysis would halt at which step?
- the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate
- the phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate
- the transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to form ATP
- the reversible rearrangement of glucose 6-phosphate to fructose 6-phosphate
The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate
In the absence of oxygen, in cells that cannot carry out fermentation, glycolysis would halt at which step?
- the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate
- the phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate
- the transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to form ATP
- the reversible rearrangement of glucose 6-phosphate to fructose 6-phosphate
The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate
(Cells that cannot carry out fermentation will run out of NAD+ under anaerobic conditions. The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate is the only reaction in glycolysis that requires NAD+. Oxidation of glyceraldehyde 3-phosphate involves the transfer of a hydrogen atom, along with an electron, to NAD+.)
Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA?
- ATP
- GTP
- oxaloacetate
- NAD+
- GDP
- O2
- oxaloacetate
- NAD+
- GDP
- O2
(At the start of the citric acid cycle, a molecule of oxaloacetate accepts a two-carbon acetyl group from acetyl CoA to form citrate.
Oxidation of citrate yields energy that is used to produce GTP, NADH, and FADH2. Therefore, GDP and NAD+ (as well as FAD) are also needed for the cycle to continue.
Although molecular oxygen does not participate in the citric acid cycle directly, it is required for the reactions to continue as O2 is the ultimate acceptor for electrons donated by NADH and FADH2 to the electron transport chain. This electron transfer regenerates the NAD+ and FAD needed for the cycle to continue.)