1. Chapter 22 Metabolic Pathways for Carbohydrates
22.1 Metabolism and Cell Structure
22.2 ATP and Energy
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2. Metabolism Metabolism involves
Catabolic reactions that break down large, complex molecules to provide energy and smaller molecules.
Anabolic reactions that use ATP energy to build larger molecules.

3. Stages of Metabolism Catabolic reactions are organized as
Stage 1: Digestion and hydrolysis break down
large molecules to smaller ones that
enter the bloodstream.
Stage 2: Degradation breaks down molecules to
two- and three-carbon compounds.
Stage 3: Oxidation of small molecules in the citric
acid cycle and electron transport
provide ATP energy.

4. Stages of Metabolism Catabolic reactions:
Stage 1: Digestion and hydrolysis
break down large molecules to smaller ones that enter the bloodstream.
Stage 2: Degradation
Further breaking and some oxidation of molecules to 2 & 3-carbon compounds.
Stage 3: Oxidation
of small molecules to CO2 & H2O in the citric acid cycle and electron transport provides energy for ATP synthesis.

5. Cell Structure
Metabolic reactions occur in specific sites within cells.

6. Cell Components and Function

7. ATP and Energy Adenosine triphosphate (ATP)
Is the energy form stored in cells.
Is obtained from the oxidation of food.
Consists of adenine (nitrogen base), a ribose sugar, and three phosphate groups.
Requires 7.3 (31 kJ) per mole to convert ADP + Pi
to ATP.

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9. Hydrolysis of ATP
The hydrolysis of ATP to ADP releases 7.3 kcal (31 kJ/mole).
ATP ADP + Pi kcal (31 kJ/mole)
The hydrolysis of ADP to AMP releases 7.3 kcal (31 kJ/mole).
ADP AMP + Pi kcal (31 kJ/mole)

10. Hydrolysis of ATP to ADP and ADP to AMP
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11. ATP and Muscle Contraction
Muscle fibers
Contain the protein fibers actin and myosin.
Contract (slide closer together) when a nerve impulse increases Ca2+.
Obtain the energy for contraction from the hydrolysis of ATP.
Return to the relaxed position as Ca2+ and ATP decrease.

12. ATP and Muscle Contraction
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13. Learning Check Match the following: 1) ATP 2) ADP + Pi
A. Used in anabolic reactions.
B. The energy-storage molecule.
C. Coupled with energy-requiring reactions.
D. Hydrolysis products.

14. Solution Match the following: 1) ATP 2) ADP + Pi
A. 1 Used in anabolic reactions
B. 1 The energy-storage molecule.
C. 1 Coupled with energy-requiring reactions.
D. 2 Hydrolysis products.

15. Chapter 22 Metabolic Pathways for Carbohydrates
22.3 Important Coenzymes in
Metabolic Pathways
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16. Coenzyme NAD+ NAD+ (nicotinamide adenine dinucleotide)
Participates in reactions that produce a carbon-oxygen double bond (C=O).
Is reduced when an oxidation provides 2H+ and 2e-.
Oxidation O ||
CH3—CH2—OH CH3—C—H + 2H+ + 2e-
Reduction
NAD H+ + 2e NADH + H+

17. Structure of Coenzyme NAD+
Is nicotinamide adenine dinucleotide.
Contains ADP, ribose, and nicotinamide.
Reduces to NADH when the nicotinamide group accepts H+ and 2e-.
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18. Coenzyme FAD FAD (flavin adenine dinucleotide)
Participates in reactions that produce a carbon-carbon double bond (C=C).
Is reduced to FADH2.
Oxidation
—CH2—CH2— —CH=CH— + 2H+ + 2e-
Reduction
FAD + 2H+ + 2e- FADH2

19. Structure of Coenzyme FAD
Is flavin adenine dinucleotide.
Contains ADP and riboflavin (vitamin B2).

20. Coenzyme A
Coenzyme A.
Consists of vitamins B3, pantothenic acid, and ADP.
Activates acyl groups such as the two-carbon acetyl group for transfer.
O O
|| ||
CH3—C— + HS—CoA CH3—C—S—CoA
acetyl group acetyl CoA

21. Structure of Coenzyme A
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22. Learning Check Match the following: 1) NAD+ 2) FAD 3) NADH + H+
4) FADH2 5) Coenzyme A
A. Coenzyme used in oxidation of carbon-oxygen
bonds.
B. Reduced form of flavin adenine dinucleotide.
C. Used to transfer acetyl groups.
D. Contains riboflavin.
E. The coenzyme after C=O bond formation.

23. Solution Match the following: 1) NAD+ 2) FAD 3) NADH + H+
4) FADH2 5) Coenzyme A
A. 1 Coenzyme used in oxidation of carbon-oxygen
bonds.
B. 4 Reduced form of flavin adenine dinucleotide.
C. 5 Used to transfer acetyl groups.
D. 2 Contains riboflavin.
E. 3 The coenzyme after C=O bond formation.

24. Chapter 22 Metabolic Pathways for Carbohydrates
22.4
Digestion of Carbohydrates
22.5
Glycolysis: Oxidation of Glucose
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25. Stage 1: Digestion of Carbohydrates
In Stage 1, the digestion of carbohydrates
Begins in the mouth where salivary amylase breaks down polysaccharides to smaller polysaccharides (dextrins), maltose, and some glucose.
Continues in the small intestine where pancreatic amylase hydrolyzes dextrins to maltose and glucose.
Hydrolyzes maltose, lactose, and sucrose to monosaccharides, mostly glucose, which enter the bloodstream for transport to the cells.

26. Digestion of Carbohydrates
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27. Stage 2: Glycolysis Stage 2: Glycolysis
Is a metabolic pathway that uses glucose, a digestion product.
Degrades six-carbon glucose molecules to three-carbon. pyruvate molecules.
Is an anaerobic (no oxygen) process.
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28. Glycolysis: Energy-Investment
In reactions 1-5 of glycolysis,
Energy is required to add phosphate groups to glucose.
Glucose is converted to two three-carbon molecules.

29. Glycolysis: Energy Investment4 1 3 5 5 2
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30. Glycolysis: Energy-Production
In reactions 6-10 of glycolysis, energy is generated as
Sugar phosphates are cleaved to triose phosphates.
Four ATP molecules are produced.
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31. Glycolysis: Reactions 6-109 6 10 8 7
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32. Glycolysis: Overall Reaction
In glycolysis,
Two ATP add phosphate to glucose and fructose-6-phosphate.
Four ATP are formed in energy-generation by direct transfers of phosphate groups to four ADP.
There is a net gain of 2 ATP and 2 NADH.
C6H12O6 + 2ADP + 2Pi + 2NAD+
Glucose
2C3H3O3- + 2ATP + 2NADH + 4H+
Pyruvate

33. Regulation of Glycolysis
Glycolysis is regulated by three enzymes,
Reaction 1 Hexokinase is inhibited by high levels of glucose-6-phosphate, which prevents the phosphorylation of glucose.
Reaction 3 Phosphofructokinase, an allosteric enzyme, is inhibited by high levels of ATP and activated by high levels of ADP and AMP.
Reaction 10 Pyruvate kinase, another allosteric enzyme is inhibited by high levels of ATP or acetyl CoA.

34. Learning Check In glycolysis, what compounds provide phosphate
groups for the production of ATP?

35. Solution
In glycolysis, what compounds provide phosphate groups for the production of ATP?
In reaction 7, phosphate groups from two
1,3-bisphosphoglycerate molecules are transferred to ADP to form two ATP.
In reaction 10, phosphate groups from two phosphoenolpyruvate molecules are used to form two more ATP.

36. Chapter 22 Metabolic Pathways for Carbohydrates
22.6
Pathways for Pyruvate
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37. Pyruvate: Aerobic Conditions
Under aerobic conditions (oxygen present),
Three-carbon pyruvate is decarboxylated.
Two-carbon acetyl CoA and CO2 are produced.
O O pyruvate
|| || dehydrogenase
CH3—C—C—O- + HS—CoA + NAD+
pyruvate O ||
CH3—C—S—CoA + CO2 + NADH
acetyl CoA

38. Pyruvate: Anaerobic Conditions
Under anaerobic conditions (without oxygen),
Pyruvate is reduced to lactate.
NADH oxidizes to NAD+ allowing glycolysis to continue.
O O lactate
|| || dehydrogenase
CH3—C—C—O- + NADH + H+
pyruvate
OH O
| ||
CH3—CH—C—O- + NAD+
lactate

39. Lactate in Muscles During strenuous exercise,
Oxygen in the muscles is depleted.
Anaerobic conditions are produced.
Lactate accumulates OH │
C6H12O ADP + 2Pi CH3–CH–COO- + 2ATP
glucose lactate
Muscles tire and become painful.
After exercise, a person breathes heavily to repay the
oxygen debt and reform pyruvate in the liver.

40. Fermentation Fermentation
Occurs in anaerobic microorganisms such as yeast.
Decarboxylates pyruvate to acetaldehyde, which is reduced to ethanol.
Regenerates NAD+ to continue glycolysis.
O OH || |
CH3—C—COO- + NADH + H CH3—CH2 + NAD+ + CO2
pyruvate ethanol

41. Pathways for Pyruvate
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42. Learning Check Match the following terms with the descriptions
1) Catabolic reactions 2) Coenzymes
3) Glycolysis 4) Lactate
A. Produced during anaerobic conditions.
B. Reaction series that converts glucose to pyruvate.
C. Metabolic reactions that break down large molecules to smaller molecules + energy.
D. Substances that remove or add H atoms in oxidation and reduction reactions.

43. Solution Match the following terms with the descriptions:
1) Catabolic reactions 2) Coenzymes
3) Glycolysis 4) Lactate
A. 4 Produced during anaerobic conditions.
B. 3 Reaction series that converts glucose to pyruvate.
C. 1 Metabolic reactions that break down large
molecules to smaller molecules + energy.
D. 2 Substances that remove or add H atoms in
oxidation and reduction reactions.

44. Chapter 22 Metabolic Pathways for Carbohydrates
22.7
Glycogen Metabolism
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45. Glycogenesis Glycogenesis
Stores glucose by converting glucose to glycogen.
Operates when high levels of glucose-6-phosphate are formed in the first reaction of glycolysis.
Does not operate when energy stores (glycogen) are full, which means that additional glucose is converted to body fat.

46. Diagram of Glycogenesis
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47. Formation of Glucose-6-Phosphate
In glycogenesis
Glucose is initially converted to glucose-6-phosphate using ATP.
glucose-6-phosphate
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48. Formation of Glucose-1-Phosphate
Glucose-6-phosphate is converted
to glucose-1-phosphate.
glucose-6-phosphate glucose-1-phosphate

49. UDP-Glucose
UTP activates glucose-1-phosphate to form UDP-glucose and pyrophosphate (PPi).
UDP-glucose
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50. Glycogenesis: Glycogen
The glucose in UDP-glucose adds to glycogen.
UDP-Glucose + glycogen glycogen-glucose + UDP
The UDP reacts with ATP to regenerate UTP.
UDP + ATP UTP + ADP
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51. Glycogenolysis In glycogenolysis Glycogen is broken down to glucose.
Glucose molecules are removed one by one from the end of the glycogen chain to yield glucose-1-phosphate.
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52. Glycogenolysis Glycogenolysis
Is activated by glucagon (low blood glucose).
Bonds glucose to phosphate to form glucose-1-phosphate.
glycogen-glucose + Pi
glycogen + glucose-1-phosphate
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53. Isomerization of Glucose-1-phosphate
The glucose-1-phosphate isomerizes to glucose-6-phosphate, which enters glycolysis for energy production.

54. Glucose-6-phosphate Glucose-6-phosphate
Is not utilized by brain and skeletal muscle because they lack glucose-6-phosphatase.
Hydrolyzes to glucose in the liver and kidney, where glucose-6-phosphatase is available providing free glucose for the brain and skeletal muscle.
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55. Learning Check Match each description with
1) Glycogenesis 2) Glycogenolysis
A. Activated by low levels of blood glucose.
B. Converts glucose-1-phosphate to glucose-6-
phosphate.
C. Activated by high levels of glucose-6-phosphate.
D. Glucose UTP UDP-glucose + PPi

56. Solution Match each description with:
1) Glycogenesis 2) Glycogenolysis
A. 2 Activated by low levels of blood glucose.
B. 2 Converts glucose-1-phosphate to glucose-6-
phosphate.
C. 1 Activated by high levels of glucose-6-phosphate.
D. 1 Glucose + UTP UDP-glucose + PPi

57. Chapter 22 Metabolic Pathways for Carbohydrates
22.8
Gluconeogenesis: Glucose Synthesis
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58. Utilization of Glucose
Is the primary energy source for the brain, skeletal muscle, and red blood cells.
Deficiency can impair the brain and nervous system.
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59. Gluconeogenesis: Glucose Synthesis
Gluconeogenesis is
The synthesis of glucose from carbon atoms of noncarbohydrate compounds.
Required when glycogen stores are depleted.

60. Gluconeogenesis: Glucose Synthesis
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61. Gluconeogenesis: Glucose Synthesis
In gluconeogenesis,
Glucose is synthesized from noncarbohydrates such as lactate, some amino acids, and glycerol after they are converted to pyruvate or other intermediates.
Seven reactions are the reverse of glycolysis and use the same enzymes.
Three reactions are not reversible.
Reaction 1 Hexokinase
Reaction 3 Phosphofructokinase
Reaction 10 Pyruvate kinase

62. Gluconeogenesis: Pyruvate to Phosphoenolpyruvate
Pyruvate adds a carbon to form oxaloacetate by two reactions that replace the reverse of reaction 10 of glycolysis.
Then a carbon is removed and a phosphate added to form phosphoenolpyruvate.

63. Phosphoenolpyruvate to Fructose-1,6-bisphosphate
Phosphoenolpyruvate is converted to fructose-1,6-bisphosphate using the same enzymes in glycolysis.

64. Glucose Formation Glucose forms when
A loss of a phosphate from fructose-1,6-bisphosphate forms fructose-6-phosphate and Pi.
A reversible reaction converts fructose-6-phosphate to glucose-6-phosphate.
A phosphate is removed from glucose-6-phosphate.
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65. Cori Cycle The Cori cycle
Is the flow of lactate and glucose between the muscles and the liver.
Occurs when anaerobic conditions occur in active muscle and glycolysis produces lactate.
Operates when lactate moves through the blood stream to the liver, where it is oxidized back to pyruvate.
Converts pyruvate to glucose, which is carried back to the muscles.

66. Pathways for Glucose are derived from
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67. Regulation of Glycolysis and Gluconeogenesis
Regulation occurs as
High glucose levels and insulin promote glycolysis.
Low glucose levels and glucagon promote gluconeogenesis.

68. Regulation of Glycolysis and Gluconeogenesis
TABLE 22.2
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69. Learning Check Identify each process as: 1) glycolysis 2) glycogenesis
3) glycogenolysis 4) gluconeogenesis
A. The synthesis of glucose from noncarbohydrates.
B. The breakdown of glycogen into glucose.
C. The oxidation of glucose to two pyruvate.
D. The synthesis of glycogen from glucose.

70. Solution Identify each process as: 1) glycolysis 2) glycogenesis
3) glycogenolysis 4) gluconeogenesis
A. 4 The synthesis of glucose from
noncarbohydrates.
B. 3 The breakdown of glycogen into glucose.
C. 1 The oxidation of glucose to two pyruvate.
D. 2 The synthesis of glycogen from glucose.