AC Lecture 60: Introduction to Metabolism

Question 1

What is catabolism?

Answer 1

oxidative degradation of large nutrient macromolecules into smaller, simpler compounds
usually accompanied by the release of free energy (conserved as ATP)

Question 2

What is anabolism?

Answer 2

the enzyme synthesis of larger molecular components of the cell from simple precursors
usually requires input of energy, often ATP

Question 3

What are amphibolic pathways?

Answer 3

pathways that contain both catabolic and anabolic components

e.g Krebs citric acid cycle

Question 4

How is metabolism regulated?

Answer 4

availability and concentration of substrates and cofactors
availability and need for energy/ATP
regulatory enzymes (allosteric effectors of some enzymes, end product feedback inhibition, etc.)
genetic control of rate of enzyme synthesis (e.g. by an enzyme substrate or a drug) determining the amount of active enzyme (constituative vs adaptive enzymes)
hormonal regulation (can act on regulatory enzymes or activate or repress gene expression)

Question 5

Describe how insulin regulates metabolism of glucose.

Answer 5

regulates glucose and fatty acid metabolism in many tissues
produced in the beta cells of the pancreas (in response to high glucose levels)
promotes utilization of glucose in teh body

Question 6

Describe how epinephrine regulates metabolism of glucose.

Answer 6

regulates glucose and fatty acid metabolism in many tissues

epi is produced in the adrenal glands in response to stress

Question 7

Describe how glucagon regulates metabolism of glucose.

Answer 7

regulates glucose and fatty acid metabolism in the liver and adipose tissue
produced in the alpha cells of the pancreas (in response to low glucose levels)
promotes production of glucose by the liver

Question 8

What is Type I DM?

Answer 8

associated with lack of insulin production due to destruction of pancreatic beta cells due to autoimmune attack

Question 9

What is Type II DM?

Answer 9

increased resistance to the actions of insulin

insulin is produced but its effectiveness in enhancing utilization of glucose is decreased

Question 10

What metabolic problems are caused by DM?

Answer 10

energy production from glucose is impaired
fat metabolism is elevated to provide energy
much of the fat is oxidized to ketone bodies (causing ketosis)
high levels of circulating glucose react improperly and result in modified proteins with altered functions
results in aldose reductase to sorbitol (results in increased osmotic pressure)

Question 11

How does glucagon promote glucose production in the liver?

Answer 11

1. stimulation of glucose synthesis (gluconeogenesis)

2. stimulation of glycogen breakdown

Question 12

What functions does glucagon perform?

Answer 12

promote glucose production in the liver

increase fatty acid release from triglycerides stored in adipose tissue

Question 13

How does glucagon perform its functions?

Answer 13

1. stimulating the activities of critical enzymes involved in synthesis of glucose and breakdown of glycogen
2. transcriptionally activating the genes for such critical enzymes

Question 14

How does insulin promote the utilization of glucose?

Answer 14

stimulating glycolysis
stimulating glucose uptake into some tissues (muscle, adipose)
stimulating glycogen formation
stimulating fatty acid synthesis from glucose
stimulating protein synthesis (several amino acids can be produced from glucose)

Question 15

What is the general rule regarding epi, glucagon, and insulin and phosphorylation.

Answer 15

glucagon: promotes phosphorylation of enzymes by activating cAMP-dependent PKA
epi: promotes phosphorylation of enzymes by activating cAMP-dependent PKA
insulin: promotes dephosphorylatin of enzymes by activating certain phosphatases

Question 16

How are glucagon (or epi) signals turned off?

Answer 16

hydrolysis of GTP by GTPase activity of alpha-GTP subunit resultin gin reassociation of the beta-gamma subunit with the alpha-beta (inactive GDP-bound G protein)

Question 17

Through what mechanism do epi, glucagon, and insulin act?

Answer 17

G-protein coupled receptor

Question 18

How is glucose transported into cells?

Answer 18

Liver, RBC, brain, pancreas, and most cells: pssive carrier-mediated glucose transport via glucose carriers (GLUT1 and GLUT3; liver and pancreas also have GLUT2)
Muscles: GLUT4
GI and Kidney: GLUT5 (catalyzes active transport of fructose; weak glucose uptake activity); SGLUT1 and SGLUT2 (active uptake of glucose linked to NA+ transport)

Question 19

How does insulin affect glucose carriers?

Answer 19

no effect on GLUT 1, 2, or 3

increases the number of GLUT 4 carriers on plasma membrane of muscle and fat cells (increases glucose uptake)