Chapter 12: Bioenergetics And Regulation Of Metabolism

Question 1

ATP energy

Answer 1

About -30 kJ/mol

Energy turnover in all cell types

Question 2

CAMP

Answer 2

-50.4 kJ/mol

Second messenger

Question 3

Creatine phosphate

Answer 3

-43.3 kJ/mol

Direct phosphorylation in muscle

Question 4

Glucose-6-phosphate

Answer 4

-30.5 kJ/mol

Intermediate of glycolysis and gluconeogenesis

Question 5

AMP

Answer 5

-9.2 kJ/mol

ATP synthesis

Question 6

ATP cleavage

Answer 6

Transfer of a high-energy phosphate group from ATP to another molecule

Question 7

Phosphoryl group transfers

Answer 7

The overall free energy of the reaction will be determined by taking the sum of the free energies of the individual reactions

Question 8

Flavoproteins

Answer 8

Contain a modified vitamin B2, or riboflavin; either flavin adenosine mononucleotide (FMN) or flavin mononucleotide (FAD); most notable for their presence in the mitochondria and chloroplasts as electron carriers; involved in the modification of other B vitamins to active forms; function as cofactors for enzymes in the oxidation of fatty acids, the decarboxylation of pyruvate and the reduction of glutathione

Question 9

Postprandial (absorptive) state

Answer 9

Absorptive or well-fed state, occurs shortly after eating; marked by greater anabolism and fuel storage than catabolism; generally lasts three to five hours after eating a meal

Question 10

What are the three major target tissues for insulin?

Answer 10

Liver, muscle, and adipose tissue
Liver: glycogenesis, lipogenesis (fatty acids and triacylglycerols) - most energy needs are met by the oxidation of excess amino acids
Muscle: glycogenesis, protein synthesis, glucose uptake, amino acid uptake
Adipose: TAG synthesis, glucose and TAG uptake
Insulin increases lipoprotein lipase activity which clears VLDL and chylomicrons from the blood; insulin decreases TAG breakdown in adipose tissue and the formation of ketone bodies by the liver

Question 11

What tissues does insulin not work on?

Answer 11

Nervous tissue and red blood cells
Nervous tissue: derives energy from oxidizing glucose to CO2 and water in postprandial and postabsorptive states
RBC: anaerobic use of glucose

Question 12

Postabsorptive (fasting) state

Answer 12

Glucagon, cortisol, epinephrine, norepinephrine, and growth hormone oppose the actions of insulin AKA counterregulatory hormones because of their effects on skeletal muscle, adipose tissue, and the liver
Liver: glycogenolysis, gluconeogenesis (12 hours to reach max velocity)
Skeletal muscle: release of amino acids provide carbon skeleton and energy for gluconeogenesis (caused by decrease in insulin)
Adipose tissue: release of fatty acids provide the carbon skeleton and energy for gluconeogenesis (caused by decrease in insulin)

Question 13

Which tissue is least able to change its fuel source in periods of prolonged starvation?

Answer 13

Cells that depend on anaerobic mechanisms for energy (ex. RBC)

Question 14

In which tissues is glucose uptake not affected by insulin?

Answer 14

Nervous tissue, kidney tubules, intestinal mucosa, RBCs, and β-cells of the pancreas

Question 15

What is the most important controller of insulin?

Answer 15

Plasma glucose; above a threshold of 100 mg/dL or about 5.6 mM of glucose, insulin secretion is directly proportional to plasma glucose; glucose must enter the β-cells and be metabolized to ATP; ATP increase stimulates exocytosis of insulin via several ion and VG-channels; also affected by glucagon and somatostatin

Question 16

Glucagon

Answer 16

Increased liver glycogenolysis - activation of glycogen phosphatase and inhibition of glycogen synthase
Increased liver gluconeogenesis - promotes conversion of pyruvate to PEP via pyruvate carboxylase and PEPCK, increases conversion of F-1,6-BP to F-6-P by fructose-1,6-bisphosphatase
Increased liver ketogenesis and decreased lipogenesis
Increased lipolysis in the liver via activation of hormone-sensitive lipase in the liver (note glucagon is not considered a major fat-mobilizing hormone)

Question 17

What controls glucagon release?

Answer 17

Hypoglycemia (promoter) and hyperglycemia (inhibitor); (basic) amino acids (lysine, arginine and histidine) promote glucagon secretion; secreted in response to ingestion of a meal rich in proteins

Question 18

Cortisol

Answer 18

Promotes the mobilization of energy stores through the degradation and increased delivery of amino acids and increased lipolysis; elevates blood glucose levels, increasing glucose availability for nervous through inhibition of glucose uptake in muscle, lymphoid and fat tissue while increasing hepatic output of glucose via gluconeogenesis (from amino acids) and permissive function that enhances the activity of glucagon, epinephrine, and other catecholamines

Question 19

Side effects of long-term use of glucocorticoids?

Answer 19

Hyperglycemia which stimulates insulin; promotes fat storage rather than lipolysis

Question 20

Catecholamines

Answer 20

Secreted by the adrenal medulla and include epinephrine and norepinephrine; increase the activity of the liver and muscle glycogen phosphorylase, promoting glycogenolysis and increasing glucose output from the liver (not muscle - no glucose-6-phosphatase; increased lipolysis in adipose tissue via HSL; acts directly on heart to increase the basal metabolic rate through the SNS

Question 21

Thyroid hormones

Answer 21

T4 -thyroxine - increase in metabolic rate occurs after a latency of several hours but lasts for several days; converted to T3 by deiodinases
T3 - triiodothyronine - increase in metabolic rate occurs rapidly but is short-lasting

Question 22

What are the effects of thyroid hormones?

Answer 22

Lipid and carbohydrate metabolism; accelerate cholesterol clearance from the plasma and increase the rate of glucose absorption from the small intestine; epinephrine requires thyroid hormones to have significant metabolic effects

Question 23

Liver metabolism

Answer 23

Well-fed: glucose and amino acids
Fasting: fatty acids
1) Maintains a constant level of blood glucose under a wide range of conditions
2) Synthesizes ketones when excess fatty acids are being oxidized

Question 24

Well-fed state liver metabolism

Answer 24

The liver extracts excess glucose and uses it to replenish its glycogen stores; remaining glucose is used to synthesize fatty acids via acetyl-CoA; insulin increase after a meal stimulates both glycogen synthesis and fatty acid synthesis in the liver; fatty acids are converted to TAGs and released into the blood as VLDL; liver dervies most of its energy from the oxidation of excess amino acids

Question 25

Liver metabolism during fasting

Answer 25

Liver releases glucose into the blood; increase in glucagon during fasting promotes both glycogen degradation and gluconeogenesis; lactate from anaerobic metabolis,, glycerol from TAGs and amino acids provide carbon skeletons for glucose synthesis

Question 26

Adipose tissue metabolism

Answer 26

Well-fed: glucose
Fasting: fatty acids
Insulin triggers FA release from VLDL and chylomicrons; lipoprotein lipase (enzyme found in the capillary beds of adipose tissue) is induced by insulin; fatty acids released from lipoproteins are taken up by adipose tissue and re-esterified to TAGs for storage; glycerol phosphate comes from glucose; insulin suppresses the release of fatty acids from adipose tissue; during the fasting state, decreased levels of insulin and increased epinephrine activity rate from HSL

Question 27

Resting skeletal muscle

Answer 27

Glucose and fatty acids; major consumer of fuel; insulin promotes glucose uptake in skeletal muscle, which replenishes glycogen stores and amino acids used for protein synthesis; both excess glucose and amino acids can be oxidized for energy; in the fasting state, resting muscle uses fatty acids derived from FFA in the bloodstream as well as ketone bodies

Question 28

Active muscle metabolism

Answer 28

Creatine phosphate - a very short-lived source energy (2-7 seconds) which transfers a phosphate group to ADP to form ATP; skeletal muscle has stores of both glycogen and some triacylglycerols; blood glucose and FFA can also be used; short bursts of high intensity exercise are also supported by anaerobic glycolysis drawing on stored muscle glycogen; during moderately high-intensity continuous exercise, oxidation of glucose and fatty acids are both important, but after 1 to 3 hours, muscle glycogen stores are depleted and the intensity of exercise slows to a rate that can be supported by oxidation of fatty acids

Question 29

Cardiac muscle metabolism

Answer 29

Well-fed: fatty acids
Fasting: fatty acids, ketones
Mimics skeletal muscle after prolonged exercise
In a failing heart, glucose oxidation increases and β-oxidation falls

Question 30

Brain metabolism

Answer 30

Well-fed: glucose
Fasting: glucose (ketones for prolonged fasting - up to 2/3 of the brain’s energy supply)
Consumes ~25% of the total glucose despite comprising only ~2% of the total body weight
Tightly regulated blood glucose levels to maintain a sufficient glucose supply for the brain; normal function depends on a continuous glucose supply from the bloodstream; in hypoglycemic conditions (<70mg/dL), hypothalamic centers in the brain sense a fall in blood glucose level, and the release of glucagon and epinephrine is triggered; fatty acids cannot cross the BBB; relies on blood glucose from gluconeogenesis and glycogenolysis between meals

Question 31

Respiratory quotient (RQ)

Answer 31

RQ = CO2 produced/O2 consumed

Question 32

Basal metabolic rate (BMR)

Answer 32

Measured by calorimeters; based on heat exchange with the environment

Question 33

ghrelin

Answer 33

Secreted by the stomach in response to signals of an impending meal; sight, sound, taste, and especially smell all act as signals for its release; ghrelin increases appetite and stimulates secretion of orexin

Question 34

Orexin

Answer 34

Further increases appetite; involved in alertness and the sleep-wake cycle as well; triggered by ghrelin release and hypoglycemia

Question 35

Leptin

Answer 35

Hormone secreted by fat cells that decreases appetite by suppressing orexin production

Question 36

Respiratory quotient with carbohydrates? With lipids?

Answer 36

1; 0.7

Question 37

Threshold for uncompensated weight gain?

Answer 37

Lower than for weight loss —> easier to gain weight than lose it