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Chapter 3: Carbohydrates

Terms in this set (46)

Which of the following is true about the net chemical reaction of glucose catabolism?

A. Pyruvate is the final product
B. Oxygen is required for adenosine triphosphate (ATP) synthesis
C. Both water and carbon dioxide (CO2) are produced
D. CO2 is produced but water is not
E. Water is produced but CO2 is not
C. Both water and carbon dioxide (CO2) are produced
Which of the following incorrectly pairs a metabolic process with its site of occurrence?

A. Glycolysis and cytosol
B. Tricarboxylic acid (TCA) cycle and mitochondrial membrane
C. ATP phosphorylation and cytosol and mitochondria
D. Electron transport chain and mitochondrial membrane
E. Oxidative decarboxylation of pyruvate and mitochondria
B. TCA cycle and mitochondrial membrane

TCA occurs inside the eukaryotic mitochondrion, not on the mitochondrial membrane
Which of the following is least likely to occur during oxygen debt? Why? How does this lead to muscle fatigue?

A. Buildup of lactic acid
B. Buildup of pyruvate
C. Decrease in pH
D. Increased fatigue
E. Shortage of ATP
B. Build-up of pyruvate

In anaerobic conditions, pyruvate accepts a hydrogen atom from NADH, forming nicotinamide adenine dinucleotide NAD+ and lactic acid. At physiological pH lactic acid dissociated into lactate and protons, thus the local pH decreases. This pathway only generates 2 ATP. Shortage of ATP is possible leading to muscle fatigue.
How many calories due carbohydrates provide?
Oxidation of 1 gram carbohydrate yields 4 kcal
When carbohydrate is hydrated in solution as dextrose and oxidized 3.4 kcal/g results
What are the 2 types of fiber? How do they differ?
1. Soluble
2. Insoluble

Depends on the degree of dispersion in hot water. Soluble fibers can be partially digested in the large bowel, insoluble fibers are not.
Which type of fibers are fermented by bacteria in the colon to produce short-chain fatty acids (SCFAs)?

A. Dietary fiber
B. Insoluble fiber
C. Saturated fiber
D. Soluble fiber
D. Soluble fiber
What is first pass metabolism?

What carbohydrates are removed during this process?
In the bloodstream most absorbed compounds pass first through the liver.

Fed state the liver removes ⅔ of the glucose from the portal vein blood. Fructose and galactose are almost totally removed by the liver
How much energy is produced per mol of ATP?

A. 9 kcal/mol
B. 8 kcal/mol
C. 7.6 kcal/mol
D. 7 kcal/mol
D. 7 kcal/mol

Approximately 7 kcal are released per mol of ATP
What cells do not perform the TCA cycle?

A. Neurons
B. Erythrocytes
C. Myocytes
D. Enterocytes
B. Erythrocytes (red blood cells)

Mature erythrocytes do not possess mitochondria
Glucose is never oxidized to water and CO2
Pyruvate is reduced to lactate
Where can gluconeogenesis occur?

A. Liver only
B. Liver and kidney
C. Liver, kidney and small intestine
D. Liver and small intestine
C. Liver, kidney and small intestine

Occurs mainly in the liver, can also occur in the kidney and small intestine under some conditions
What 2 amino acids cannot be used for gluconeogenesis?

What is the preferred amino acid?
1. Lysine
2. Leucine

Alanine
What molecule from triacylglycerol is used for gluconeogenesis?

A. Glycerol
B. Fatty acid
C. Carboxyl group
D. Methyl group
A. Glycerol

Glycerol derived from hydrolysis of triacylglycerols in fat cells can also be used for gluconeogenesis because glycerol can be phosphorylated to glycerol-3-phosphate a glycolytic intermediate
In a 70 kg healthy person how would glycogen be distributed? How much energy does this provide?
70 kg healthy person:
Liver contains approximately 100 g glycogen potential to provide 390 kcal
Skeletal muscle contains about 300-400 g glycogen less than 1560 kcal

Suggests that an adult stores enough glycogen for about a day of normal activities
What is the main difference between liver glycogen and skeletal muscle glycogen? Explain why this occurs.
Liver glycogen can be catabolized to provide glucose for use by the whole body. Skeletal muscle glycogen can only provide glucose to the muscle cells themselves

Myocytes do not have glucose-6-phosphatase
Glucose-6-phosphate is the final product in the skeletal muscle and enters glycolysis inside the myocyte
In humans what are the 4 primary substrates to gluconeogenesis?
1. Lactate
2. Glutamine
3. Alanine
4. Glycerol
What is a normal plasma glucose level?

A. 140-180 mg/dL
B. 110-160 mg/dL
C. 70-120 mg/dL
D. 100-200 mg/dL
C. 70-120 mg/dL

Plasma glucose concentrations are normally maintained in the range of 70-120 mg/dL
After 14 days of fasting where does most of the daily energy requirements come from?

A. Gluconeogenesis
B. Products of protein breakdown
C. Triglycerides
D. Ketones
C. Triglycerides

After 14 days of fasting, adipose tissue can provide more than 90% of daily energy requirements. Glycerol is transported to hepatocytes and enters the gluconeogenic pathway
When fatty acid oxidation rates are elevated what metabolic consequence occurs?

A. Increased cholesterol
B. Hyperglycemia
C. Ketogenesis
D. Decreased HDL
C. Ketogenesis

When fatty acid oxidation rates are elevated, acetyl-CoA is generated in amounts that exceed the capacity of the TCA cycle, Acetyl-CoA is diverted into ketogenesis
What are the 3 ketones formed from ketogenesis?
1. Acetoacetate
2. 1-hydroxybutyrate
3. Acetone
In early fasting (< 1 week) what tissues use ketones for energy?

A. Heart, skeletal muscle, brain
B. Heart and skeletal muscle
C. Brain
D. Kidney and heart
B. Heart and skeletal muscle

Early phases of fasting, ketones fuel the heart and musculoskeletal system, available glucose fuels the brain. After 1-2 weeks of starvation the brain is able to adapt and use ketones as a source of energy, metabolic fuel switch helps preserve the protein mass in prolonged fasting. Fat stores can be used in preference to protein stores.
How does the insulin response to an oral glucose load compare to that of an IV glucose infusion?

A. Oral glucose increases the insulin response
B. IV glucose increases the insulin response
C. Oral and IV glucose have the same insulin response
A. Oral glucose increases the insulin response

Compared with the response to an equivalent IV glucose infusion, the insulin response to an oral glucose load is much greater because incretins such as glucose-dependent insulin tropic peptide, cholecystokinin and glucagon-like peptide 1 increase the direct effect of glucose on beta cells.
How does fiber impact the upper digestive tract?
Upper digestive tract, fiber increase satiety. High doses of fiber tend to delay gastric emptying. Gastric emptying may be delayed because of the increased viscosity of gastric contents which reduces pyloric flow. Lower doses of fiber do not show a significant effect
Which fiber type is most completely broken down?
Amount of resistance of fibers to digestion varies substantially. Soluble fibers undergoing the most complete breakdown
What is the end result of soluble fiber breakdown?
SCFAs (butyrate, propionate and acetate) result
What is the metabolic fate of SCFAs?
Absorbed by colonic epithelia, Butyrate may also be metabolized.
Putative health claims for the benefits of fiber in a variety of primarily bowel disorders remain unproven in large RCTs, what are the 6 areas of health claims
1. Tube feeding has been associated with less diarrhea, firmer stools
2. High fiber diet in ambulatory patients to relieve constipation
3. Improve glucose control in patients with diabetes
4. Whole grain and bran intake were associated with lowering of all-cause and cardiovascular mortality
5. Dietary fiber proposed as a protective factor against colorectal carcinoma as well as adenoma
6. Lowers CVD rates thought to related to favorable changes in plasma lipid profiles
What is the role of insoluble fiber?
Fibers that resist degradation and fermentation add bulk, as well as water, to the stool
What is the benefit of adding fiber to tube feedings?
Addition of fiber to tube feeding for ill patients has been associated with less diarrhea, firmer stools,
Not all studies have been concordant
What is the evidence for dietary fiber and colorectal carcinoma?
Dietary fiber proposed as a protective factor against colorectal carcinoma as well as adenoma. Some epidemiologic studies fiber consumption is inversely proportional to risk of colonic neoplasia incidence or recurrence. Other studies have reached different conclusions. Nurse's Health Study noted no relationship between fiber intake and the risk of colorectal tumors. Intervention studies using higher fiber diet do not confirm protection
What are the 3 mechanisms by which fiber could reduce lipids?
Fiber could reduce lipids by many possible mechanisms
1. Binding of fibers in the gut to compounds such as sterols might otherwise be included in cholesterol metabolism
2. Improvements in insulin sensitivity
3. Impact of hepatic metabolism of SCFAs on liver production of lipid particles
What is the DRI for fiber in adults? What is this based on?
DRI for fiber in adults is 14 g per 1000 kcal ingested (about 25 g/d for women and 38 g/d for men)

Based on epidemiologic and clinical data about the cardioprotective effects of fiber consumption
What does the RDA for CHO reflect?
RDA for CHO reflect the brain's need for glucose
What is the minimum amount of CHO required in a day to avoid ketone production?

A. 20 g CHO
B. 130 g CHO
C. 80 g CHO
D. 50 g CHO
D. 50 g CHO

Minimum of 50 g CHO per day is required to avoid ketone production
What is the endogenous glucose production of a healthy adult following an overnight fast (in mg/kg/min)?

How much glucose does this suggest they can generate in one day?
Healthy adult endogenous glucose production from glycogen or gluconeogenesis is approximately 2 mg/kg/min following an overnight fast

Suggesting that a 70 kg individual can endogenously provide approximately 200 g glucose per day
What is CHO loading?

A. Eating spaghetti the night before a big workout
B. Eating a specified number of carbohydrates per kg for 36-48 hours before an exercise event
C. Eating all carbohydrates for 24-48 hours
D. Eating a meat-free diet
B. Eating a specified number of carbohydrates per kg for 36-48 hours before an exercise event

Recommended 10-12 g CHO/kg of body mass/day in the 36-48 hours before exercise
List 3 possible advantages of CHO loading.
Possible advantages
1. Provide optimal stores of muscle glycogen
2. Improve performance
3. Reduce fatigue in individuals engaging in exercise for more than 90 minutes
Would carbohydrate loading be beneficial for moderate intensity cycling or going for a short run? (Y or N)
No
What CHO intake is suggested after exercise?
Ingest 50 to 100 g of CHO immediately after exercise
Eat a high CHO meal 2 hours later

After exercise individuals must consume adequate amounts of CHO to refill glycogen stores in muscle and liver
What is the advantage of eating a protein and CHO meal after exercise?
Protein and CHO are consumed together in the immediate postexercise phase, insulin responses are augmented, and glycogen storage is enhanced
To have enough CHO available before and during exercise and replenish CHO stores after exercise individuals who are very active may require how much CHO/kg/day?

A. 3-4 g/kg/d
B. 4-5 g/kg/d
C. 15-20 g/kg/d
D. 9-10 g/kg/d
D. 9-10 g/kg/d

Athletes may need up to 9 to 10 g cHO per kg of body mass per day
What 2 benefits did studies of consumption of 30-60 g CHO/hour during sustained intensive exercise show?
Attenuated the usual increase in
1. exercise-induced stress hormone release
2. exercise-induced immune depression
What should be considered the primary energy source for patients with illness and injury?

A. Carbohydrate
B. Fat
C. Ketones
D. Protein
A. Carbohydrate

CHO should be considered the primary energy source for these patients
What is the recommended glucose infusion rate for parenteral nutrition patients?
< 4-5 mg/kg/min


This comes from evidence in burn patients glucose oxidation rates slow significantly if dextrose is given IV at a rate > 5 mg/kg/min; Patients receiving PN who are fed glucose IV at > 4 mg/kg/min have a substantial incidence of hyperglycemia
Which of the following is true about the net chemical reaction of glucose catabolism?

A. Pyruvate is the final product
B. Oxygen is required for ATP synthesis
C. Both water and carbon dioxide are produced
D. CO2 is produced but water is not
E. Water is produced but CO2 is not
C. Both water and carbon dioxide are produced
Which of the following incorrectly pairs a metabolic process with its site of occurrence?

A. Glycolysis and cytosol
B. TCA cycle and mitochondrial membrane
C. ATP phosphorylation and cytosol and mitochondria
D. Electron transport chain and mitochondrial membrane
E. Oxidative decarboxylation of pyruvate and mitochondria
B. TCA cycle and mitochondrial membrane
Which of the following is least likely to occur during oxygen debt?

A. Buildup of lactic acid
B. Buildup of pyruvate
C. Decrease in pH
D. Increased fatigue
E. Shortage of ATP
B. buildup of pyruvate
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