Lecture 14

Question 1

Define standard free energy and relate it to exergonic and endergonic reactions

Answer 1

Difference in free energy when 1 mole of each reactant is converted to 1 mole of each product at 1 atm pressure at 25 degrees C; negative in an exergonic reaction and positive in an endergonic reaction

Question 2

Relate free energy to ATP breakdown

Answer 2

Highly negative (exergonic)

Question 3

How does galactose and glucose enter glycolysis?

Answer 3

Galactose and glucose can be converted through a series of reactions into fructose-6-phosphate and then enter glycolysis

Question 4

Describe the uptake of glucose

Answer 4

Occurs via active sodium-glucose co-transport in GI tract and renal tubules; occurs via facilitated transport (higher to lower concentrations) in most tissues; presence of insulin increases glucose transport x10, phosphorylation of glucose prevents diffusion out of the cell, and phosphorylation can be reversed in liver, renal, and intestinal cells

Question 5

What are the end products of glycolysis?

Answer 5

2 molecules of pyruvic acid, 4 molecules of hydrogen ions, and 2 molecules of ATP

Question 6

What are the end products of the conversion of pyruvic acid to acetyl-CoA?

Answer 6

2 molecules of acetyl-CoA, 4 hydrogen ions, and 2 molecules of carbon dioxide

Question 7

What is the fate of pyruvic acid when oxygen is not present?

Answer 7

Converted into lactic acid

Question 8

What are the end products of the citric acid cycle?

Answer 8

16 hydrogen ions, 2 molecules of ATP, and 4 molecules of carbon dioxide

Question 9

Define oxidative phosphorylation and state where it occurs

Answer 9

Occurs on mitochondrial cristae;

Question 10

Define oxidative phosphorylation and state where it occurs

Answer 10

Occurs on mitochondrial cristae; think electron transport chain; per glucose molecule, we get 2 ATPs from glycolysis, 2 ATPs from the TCA cycle, and 34 ATPs from oxidative phosphorylation

Question 11

What is the fate of the hydrogen atoms and the electrons generated during glycolysis and the citric acid cycle? Name and compare the hydrogen ion carriers

Answer 11

Hydrogens are removed in pairs with one becoming an ion and the other pairing with NAD+ to become NADH

Question 12

List, in sequence, the components of the electron transport chain

Answer 12

Flavoprotein, several iron sulfide proteis, ubiquinone (Q), cytochrome A3 (cytochrome oxidase)

Question 13

Describe the pentose phosphate pathway and explain what it is primarily used for

Answer 13

Cyclical pathway in which one molecule of glucose is metabolized for each revolution of the cycle; mostly used for the synthesis of fats and other substances

Question 14

Describe the transport mechanism for hydrogen ions in the pentose phosphate pathway

Answer 14

Instead of using NAD+, hydrogens in this pathway are bound to NADP+, which can be used in the synthesis of fats from carbohydrates and NADPH participates in the conversion of acetyl-CoA into fatty acid chains

Question 15

Describe how trigylcerides are synthesized from glucose

Answer 15

Can be synthesized via alpha-glycerophosphate or made into fatty acids and then into triglycerides

Question 16

Explain how trigylcerides are absorbed from the intestinal lumen

Answer 16

Most triglycerides are digested into monoglycerides and fatty acids; intestinal epithelial cells resynthesize these into triglycerides that enter the lymph as chylomicrons

Question 17

Define chylomicrons and explain how they are transported and removed from the blood. What is the role of lipoprotein lipase?

Answer 17

Transported to the venous system via the thoracic duct and removed from the blood by various tissues (adipose, skeletal, heart); lipoprotein lipase is synthesized by these tissues, is transported to surface of capillary epithelial cells, and hydrolzes chylomicron trigylcerides, releasing fatty acids and glycerol

Question 18

Compare fat to carbohydrates as an energy source and explain under what conditions fat is used for energy

Answer 18

All normal energy requirements of the body can be provided by the oxidation of fatty acids without using carbohydrates or proteins as an energy source; starvation and diabetes mellitus increase the utilization of fat for energy

Question 19

Define lipoprotein and compare the various types of lipoproteins

Answer 19

Lipoproteins transport lipids in the blood; chylomicrons are synthesized by intestinal cells and VLDLs (very low density), LDLs (low density), and HDLs (high density) are synthesized by the liver

VLDLs: high concentrations of triglycerides and moderate amounts of cholesterol and phospholipids; transport lipids mainly from liver to adipose tissue

LDLs: high concentration of cholesterol and moderate concentration of phospholipids

HDLs: high concentration of proteins and low concentration of cholesterol and fatty acids

Question 20

How are triglycerides used as an energy source?

Answer 20

Hydrolyzed into fatty acids and glycerol, which are transported in blood to tissues; almost all cells except brain cells and rbcs use fatty acids for energy

Question 21

Describe the formation of acetoacetic acid

Answer 21

Fatty acids degraded in the liver release many acetyl-CoA’s not used for metabolism; 2 acetyl-CoA’s condense to form acetoacetic acid; some of this is converted to beta-hydroxybutyric acid or acetone

Question 22

Define ketone bodies and give examples. What is ketosis?

Answer 22

Ketone bodies are molecules that contain ketone groups and include beta-hydroxybutyric acid, acetoacetic acid, and acetone

Ketosis is the concentrations of ketone bodies increasing above normal in the blood

Question 23

List and describe the sequence of steps in the formation of an atherosclerotic plaque

Answer 23

1. Damage to vascular epithelium (increases the expression of adhesion molecules, decreases release of NO and other substances that prevent adhesion of macromolecules and cells)
2. Circulating monocytes and LDLs accumulate at injury site
3. Monocytes ( cross endothelium, enter intima, become macrophages)
4. Macrophages ( ingest lipoproteins, become foam cells, form visible fatty streaks)
5. Fatty streaks ( grow larger, coalesce)
6. Surrounding fibrous and smooth muscle tissues (proliferate, form large plaques)