Download Answers - U of L Class Index

23
Answers and Solutions to Text Problems
23.1
The digestion of polysaccharides takes place in stage 1.
23.2
In stage 3, small molecules are converted to CO2, H2O, and energy for ATP synthesis.
23.3
A catabolic reaction breaks down larger molecules to smaller molecules accompanied by the
release of energy.
23.4
An anabolic reaction uses energy in the cell to build large molecules needed by the cell.
23.5
a. (3) Smooth endoplasmic reticulum is the site for the synthesis of fats and steroids.
b. (1) Lysosomes contain hydrolytic enzymes.
c. (2) The Golgi complex modifies products from the rough endoplasmic reticulum.
23.6
a. (3) The plasma membrane separates cell contents from surroundings.
b. (1) The mitochondria are the sites of energy production.
c. (2) The rough endoplasmic reticulum synthesizes proteins for secretion.
23.7
The phosphoric anhydride bonds (POP) in ATP release energy that is sufficient for energyrequiring processes in the cell.
23.8
The energy released by the hydrolysis of ATP is linked with an energy-requiring reaction
(anabolic) and used to “drive” that reaction.
23.9
a. PEP + H2O → pyruvate + Pi + 14.8 kcal /mole
b. ADP + Pi + 7.3 kcal/mole → ATP + H2O
c. Coupled: PEP + ADP → ATP + pyruvate + 7.5 kcal /mole
23.10
a. ATP + H2O → ADP + Pi + 7.3 kcal/mole
b. glycerol + Pi + 2.2 kcal /mole → glycerol-3-phosphate
c. Coupled: glycerol + ATP → glycerol-3-phosphate + ADP + 5.1 kcal /mole
23.11
a. Pantothenic acid is a component in coenzyme A.
b. Niacin is the vitamin component of NAD+.
c. Ribitol is the alcohol sugar that makes up riboflavin in FAD.
23.12
a. FAD
23.13
In biochemical systems, oxidation is usually accompanied by gain of oxygen or loss of
hydrogen. Loss of oxygen or gain of hydrogen usually accompanies reduction.
a. The reduced form of NAD+ is abbreviated NADH.
b. The oxidized form of FADH2 is abbreviated FAD.
23.14
a. FADH2
23.15
The coenzyme FAD accepts hydrogen when a dehydrogenase forms a carbon-carbon double
bond.
24.16
When a carbon-oxygen bond is formed, the coenzyme is NAD+.
b. NAD+
c. Coenzyme A
b. NAD+
Metabolic Pathways for Carbohydrates
23.17
23.18
Digestion breaks down the large molecules in food into smaller compounds that can be absorbed
by the body. Hydrolysis is the main reaction involved in the digestion of carbohydrates.
The _-amylase is produced by the salivary glands to begin the hydrolysis of the _-glycosidic
bonds in the polysaccharide amylose. The hydrolysis of the smaller sections of amylose
(dextrins) continues in the small intestine with _-amylase produced by the pancreas.
23.19
a. The disaccharide lactose is digested in the small intestine to yield galactose and glucose.
b. The disaccharide sucrose is digested in the small intestine to yield glucose and fructose.
c. The disaccharide maltose is digested in the small intestine to yield two glucose molecules.
23.20
a. small intestine; lactase
b. small intestine; sucrase
c. small intestine; maltase
23.21
Glucose is the starting reactant for glycolysis.
23.22
The end product of glycolysis is two molecules of pyruvate.
23.23
In the initial reactions of glycolysis, ATP molecules are required to add phosphate groups
to glucose.
23.24
Two ATP molecules are used for the initial steps in gylcolysis.
23.25
When fructose-1, 6-bisphosphate splits, glyceraldehyde-3-phosphate and dihydroxyacetone
phosphate are formed. The dihydroxyacetone phosphate is converted to glyceraldehyde-3phosphate for subsequent reactions.
23.26
One of the triose molecules is a ketose that cannot be oxidized further. The isomerization of the
ketose to a second molecule of glyceraldehyde-3-phosphate provides a compound that can be
oxidized later in the glycolysis pathway.
23.27
ATP is produced directly in glycolysis in two places. In reaction 7, phosphate from 1,3bisphosphoglycerate is transferred to ADP and yield ATP. In reaction 10, phosphate from
phosphoenolpyruvate is transferred directly to ADP.
23.28
The oxidation of a glucose molecule utilizes two ATP molecules. Later the two triose products
of glycolysis produce four ATP by direct phosphorylation to give a net yield of two ATP.
23.29
a. In glycolysis, phosphorylation is catalyzed by the enzyme hexokinase.
b. In glycolysis, direct transfer of a phosphate group is catalyzed by the enzyme phosphokinase.
23.30
a. isomerase
23.31
a. In the phosphorylation of glucose to glucose-6-phosphate 1 ATP is required.
b. One ATP is required for the conversion of glyceraldehyde-3-phosphate to
1,3-bisphosphoglycerate.
c. When glucose is converted to pyruvate, two ATP and two NADH are produced.
23.32
a. One ATP is produced for each triose molecule.
b. One ATP is required.
c. One ATP is produced for each phosphoenolpyruvate.
23.33
a. The first ATP is hydrolyzed in the first reaction in glycolysis; the change of glucose to
glucose-6-phosphate.
b. aldolase
Chapter 23 Answers and Solutions
b. Direct substrate phosphorylation occurs in reaction 7 of glycolysis when the transfer of
phosphate from 1,3-bisphosphoglycerate to ADP generates ATP. In reaction 10 of glycolysis,
phosphate is transferred from phosphoenolpyruvate directly to ADP.
c. In reaction 4 of glycolysis, the six-carbon fructose-1, 6-bisphosphate is converted to two
three-carbon molecules.
23.34
a. Step 2, conversion of glucose-6-phosphate to fructose-6-phosphate and step 5, conversion of
diydroxyacetone phosphate to glyceraldehyde-3-phosphate, both involve isomerization.
b. NAD+ is reduced in step 6, when two glyceraldehyde-3-phosphate are converted to
1,3-diphosphoglycerate.
c. The second ATP is synthesized in step 10, when phosphoenolpyruvate is changed to pyruvate
23.35
Galactose reacts with ATP to yield galactose-1-phosphate, which is converted to glucose
phosphate, an intermediate in glycolysis. Fructose reacts with ATP to yield fructose-1phosphate, which is cleaved to give dihydroxyacetone phosphate and glyceraldehyde.
Dihydroxyacetone phosphate isomerizes to glyceraldehyde-3-phosphate, and glyceraldehyde is
phosphorylated to glyceraldehyde-3-phosphate, which is an intermediate in glycolysis.
23.37
a. Low levels of ATP activate phosphofructokinase to increase the rate of glycolysis.
b. When ATP levels are high, ATP inhibits phosphofructokinase and slows or prevents
glycolysis.
23.38
a. Low levels of ATP will activate pyruvate kinase and increase the rate of glycolysis.
b. High levels of fructose-1,6-bisphosphate will inhibit pyruvate kinase and slow or stop
glycolysis.
23.39
A cell converts pyruvate to acetyl CoA only under aerobic conditions; there must be sufficient
oxygen available.
23.40
The change of pyruvate to acetyl CoA is catalyzed by the enzyme pyruvate dehydrogenase; the
coenzyme NAD+ is required as well. .
23.41 The overall reaction for the conversion of pyruvate to acetyl CoA is:
O
O
||
||
CH3CCOO− + NAD+ + HSCoA → CH3CSCoA + CO2 + NADH + H+
pyruvate
acetyl CoA
23.42
Under anaerobic conditions, pyruvate maybe converted to lactate or ethanol.
23.43
The reduction of pyruvate to lactate regenerates NAD+, which allows glycolysis to proceed and
produce two ATP.
23.44
After strenuous exercise, the oxygen in the cells is rapidly depleted and lactate accumulates. The
presence of the lactate causes the muscles to tire and become sore.
23.45
During fermentation the three-carbon compound pyruvate is reduced to ethanol while
decarboxylation removes one carbon as CO2.
23.46
When fermentation takes place, the products are ethanol and carbon dioxide gas. The production
of the carbon dioxide gas could cause the pressure to build up and the container may explode.
23.47
In glycogenesis, glycogen is synthesized from glucose molecules.
Metabolic Pathways for Carbohydrates
23.48
Glycogenolysis is the breakdown of glycogen to produce glucose.
23.49
Muscle cells break down glycogen to glucose 6-phosphate, which enters glycolysis.
23.50
Glucagon activates the breakdown of glycogen in the liver.
23.51
Glycogen phosphorylase cleaves the glycosidic bonds at the ends of glycogen chains to remove
glucose monomers as glucose 1-phosphate.
Phosphoglucomutase catalyzes the reversible reactions of glucose-1-phosphate to glucose-6phosphate in glycogenolysis and glucose-6-phosphate to glucose-1-phosphate in glycogenesis.
23.52
23.53
When there are no glycogen stores remaining in the liver, gluconeogenesis synthesizes glucose
from noncarbohydrate compounds such as pyruvate and lactate.
23.54
The three enzymes in glycolysis that are not used in gluconeogenesis are pyruvate kinase,
phosphofructokinase, and hexokinase.
23.55
The enzymes in glycolysis that are also used in their reverse directions for gluconeogenesis are
phosphoglucoisomerase, aldolase, triosephosphate isomerase, glyceraldehyde 3-phosphate
dehydrogenase, phosphoglycerokinase, phosphoglyceromutase, and enolase.
23.56
In gluconeogenesis, two lactate units in the skeletal muscle are converted to two pyruvate and
used to produce glucose.
23.57
a. Low glucose levels activate glucose synthesis.
b. Glucagon produced when glucose levels are low activates gluconeogenesis.
c. Insulin produced when glucose levels are high inhibits gluconeogenesis.
23.58
a. Low glucose levels inhibit glycolysis.
b. Insulin activates glycolysis
c. Glucagon inhibits glycolysis
23.59
Metabolism includes all the reactions in cells that provide energy and material for cell growth.
23.60
Catabolic reactions break down complex molecules and anabolic reactions build large molecules
from simple ones. Catabolic reactions provide energy, whereas anabolic reactions are energy
requiring.
23.61
Stage 1 involves the degradation of large molecules such as polysaccharides.
23.62
State 2 degrades monomers such as glucose to two- and three-carbon molecules.
23.63
A eukaryotic cell has a nucleus, whereas a prokaryotic cell does not.
23.64
The organelles are specialized structures that perform the specific functions in the cell.
23.65
ATP is the abbreviation for adenosine triphosphate.
23.66
Adenosine diphosphate
23.67
ATP + H2O → ADP + Pi + 7.3 kcal (31kJ)/mole
23.68
300 kcal ✕ 1 mole ATP/7.3 kcal = 41 moles ATP required
23.69
FAD is the abbreviation for flavin adenine dinucleotide.
23.70
FAD is used in oxidation reactions that produce a carbon-carbon (C=C) double bond.
23.71
NAD+ is the abbreviation for nicotinamide adenine dinucleotide.
23.72
NAD+ is used in oxidation reactions that produce a carbon-oxygen (C=O) double bond.
Chapter 23 Answers and Solutions
23.73
The reduced forms of these coenzymes include hydrogen obtained from an oxidation reaction.
a. FADH2
b. NADH + H+
23.74
a. riboflavin (vitamin B2)
23.75
Lactose undergoes digestion in the mucosal cells of the small intestine to yield galactose and
glucose.
23.76
When sucrose is digested in the small intestine, the products are glucose and fructose.
23.77
Galactose and fructose are converted in the liver to glucose phosphate compounds that can enter
the glycolysis pathway.
23.78
Hydrolysis
23.79
Glucose is the reactant and pyruvate is the product of glycolysis.
23.80
NAD+
23.81
Reactions 1 and 3 involve phosphorylation of hexoses with ATP, and reactions 7 and 10 involve
direct substrate phosphorylation that generates ATP.
23.82
When ATP levels are high, enzymes such as phosphofructokinase and pyruvate kinase are
inhibited. When ATP levels are low (ADP is high), the enzymes are activated.
23.83
Reaction 4 catalyzed by aldolase converts fructose 1,6-bisphosphate into two triose phosphates.
23.84
In reactions 1-5 of glycolysis 2 ATP are utilized, whereas reaction 6-10 produce 4 ATP. Thus a
net of 2 ATP are produced for every glucose molecule that undergoes glycolysis.
23.85
Phosphoglucoisomerase converts glucose-6-phosphate to the isomer fructose-6-phosphate.
23.86
1,3-bisphophoglycerate
23.87
Pyruvate is converted to lactate when oxygen is not present in the cell (anaerobic) to regenerate
NAD+ for glycolysis.
23.88
One carbon atom of pyruvate is removed as CO2.
23.89
Phosphofructokinase is an allosteric enzyme that is activated by high levels of AMP and ADP
because the cell needs to produce more ATP. When ATP levels are high, ATP inhibits
phosphofructokinase, which reduces its catalysis of fructose-6-phosphate.
23.90
Pyruvate kinase is inhibited at ATP, which causes glucose-6-phosphate to accumulate and inhibit
the phosphorylation of glucose. Thus, when ATP levels are high, glucose cannot enter the
glycolysis pathway.
23.91
The rate of glycogenolysis increases when blood glucose levels are low and glucagon has been
secreted, which accelerate the breakdown of glycogen.
23.92
Glucose-1-phosphate from glycogenolysis is converted to glucose-6-phosphate, which can then
enter glycolysis.
23.93
The breakdown of glycogen in the liver produces glucose.
23.94
glucose-6-phosphate
b. niacin
c. pantothenic acid (vitamin B3)
Metabolic Pathways for Carbohydrates
23.95
The cells in the liver, but not skeletal muscle, contain a phosphatase enzyme needed to convert
glucose--phosphate to free glucose that can diffuse through cell membranes into the blood
stream. Glucose-6-phosphate, which is the end product of glycogenolysis in muscle cells, cannot
diffuse easily across cell membranes.
23.96
The rate of glycogenesis increases when glucose levels are high. Insulin produced in the
pancreas enters the bloodstream and accelerates the synthesis of glycogen.
23.97
Insulin increases the rate of glycogenolysis and glycolysis, and decreases the rate of
glycogenesis. Glucagon decreases the rate of glycogenolysis and glycolysis, and increases the
rate of glycogenesis.
23.98
When glycogen stores are depleted, glucose is synthesized from noncarbohydrate compounds
such as lactate, amino acids, and glycerol.
23.99
The Cori cycle is a cyclic process that involves the transfer of lactate from muscle to the liver
where glucose is synthesized, which can be used again by the muscle.
23.100 a. glycogenolysis
c. glycolysis
b. gluconeogenesis
d. glycogenesis
23.101 a. Low glucose increases the breakdown of glycogen.
b. Insulin produced when glucose levels are high decreases the rate of glycogenolysis in the
liver.
c. Glucagon secreted when glucose levels are low increases the breakdown of glycogen.
d. High levels of ATP decrease the breakdown of glycogen.
23.102 a. decrease
23.103 a.
b.
c.
d.
b. increase
c. decrease
d. increase
High glucose levels decrease the synthesis of glucose (gluconeogenesis).
Insulin produced when glucose levels are high decreases glucose synthesis.
Glucagon secreted when glucose levels are low increases glucose synthesis.
High levels of ATP decrease glucose synthesis (gluconeogenesis).
23.104 a. increase
b. increase
c. decrease
d. decrease