Lecture 14

Question 1

What is free energy regarding metabolism?

Answer 1

When a cell or enzyme is capable of doing work

Question 2

What is the relationship between free energy and endergonic and exergonic reactions?

Answer 2

-deltaG = exergonic 
\+deltaG = endergonic

Question 3

Relate free energy to ATP breakdown.

Answer 3

ATP → ADP + Pi (deltaG = -7300 cal/mole)

ATP → ADP + Pi (deltaG = -12000 cal/mole)

Question 4

Which pathway becomes the final common pathway for the transport of almost all the carbohydrates to the tissue cells?

Answer 4

Glucose

Question 5

Galactose, glucose, and fructose are all ___.

Answer 5

Interconvertible

Question 6

What can galactose and glucose be converted to and enter the glycolytic pathway?

Answer 6

Fructose-6-phosphate

Question 7

List the ways glucose can be uptaken.

Answer 7

Via active sodium-glucose co-transport, via facilitated transport

Question 8

Describe glucose uptake via active sodium-glucose co-transport.

Answer 8

Active transport of sodium provides energy for absorbing glucose against a concentration gradient

Question 9

Describe glucose uptake via facilitated transport.

Answer 9

Only transported from higher to lower concentrations

Question 10

How does the presence of insulin affect glucose transport?

Answer 10

Increases glucose transport 10x

Question 11

What type of modification on glucose prevents diffusion out of the cell?

Answer 11

Phosphorylation

Question 12

Where can the phosphorylation of glucose be reversed?

Answer 12

In liver, renal, and intestinal cells

Question 13

Where does the transport of glucose into tissue cells via active sodium-glucose co-transport occur?

Answer 13

In GI tract and renal tubules

Question 14

Where does the transport of glucose into tissue cells via facilitated transport occur?

Answer 14

In most tissues

Question 15

What is the role of glucokinase?

Answer 15

Transfers phosphate from ATP

Question 16

What is the role of phosphatase?

Answer 16

Removes phosphate

Question 17

What is the role of phosphorylase?

Answer 17

Catalyzes production of glucose-1-phosphate from glycogen

Question 18

What are the end products of glycolysis?

Answer 18

2 molecules of ATP, 2 molecules of NADH, 2 ATP, 4 H+

Question 19

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

Answer 19

2 acetyl CoA, 4 H+, 2 molecules of CO2

Question 20

What are factors that can activate phosphorylase?

Answer 20

Epinephrine (from adrenal medulla), glucagon (from alpha cells)

Question 21

Why is phosphorylase important?

Answer 21

Promotes conversion of glycogen to glucose so glucose can then be release into the blood

Question 22

In the conversion of pyruvic acid to acetyl-CoA, what catalyzes the release of the hydrogens?

Answer 22

Dehydrogenase

Question 23

Where does the citric acid cycle occur?

Answer 23

Mitochondrial matrix

Question 24

What are the end products of the citric acid cycle?

Answer 24

16 H+, 2 ATP, 4 CO2

Question 25

What is the net reaction of the citric acid cycle, excluding glycolysis?

Answer 25

2 acetyl CoA + 6 H2O + 2 ADP → 4 CO2 + 16 H + 2 CoA + 2 ATP

Question 26

Where does oxphos occur?

Answer 26

On mitochondrial cristae

Question 27

Describe the fate of the hydrogen atoms and the electrons generated during glycolysis and the citric acid cycle.

Answer 27

Hydrogens are removed in pairs. One member of each pair becomes a H ion, and the other member combines with NAD+ to form NADH. The electrons removed from hydrogen ions enter the ETC.

Question 28

List the major components of the ETC.

Answer 28

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

Question 29

Where is cytochrome oxidase located?

Answer 29

Inner membrane

Question 30

T or F: Cytochrome oxidase can give up 3 electrons to oxygen.

Answer 30

False. Cytochrome oxidase can give up 2 electrons to oxygen.

Question 31

Describe the chemiosmotic mechanism.

Answer 31

1. Electrons pass through chain, releasing large amounts of energy. 2. Energy is used to pump H ions from inner matrix into outer chamber between inner and outer membranes. 3. High concentration of H+ created in chamber. 4. Strong negative potential created in inner matrix. 5. H+ ions flow from high to low concentration through ATP synthetase. 6. Energy derived from H+ flow is used by ATPase to convert ADP to ATP. 7. For each 2 electrons that pass through electron transport chain, up to 3 ATP molecules are synthesized.

Question 32

Describe the pentose phosphate pathway.

Answer 32

Cyclical pathway where one molecule of glucose is metabolized for each revolution of the cycle (for every 6 molecules of glucose that enter, 5 molecules of glucose are resynthesized)

Question 33

What is the pentose phosphate pathway primarily used for?

Answer 33

Synthesis of fats and other substances

Question 34

When summarizing oxphos, how many ATP are formed per glucose molecule?

Answer 34

2 from glycolysis 2 from CAC 34 from oxphos

Question 35

T or F: The maximum number of ATP per glucose molecule is 38.

Answer 35

True.

Question 36

How efficient is oxphos?

Answer 36

66% efficiency

Question 37

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

Answer 37

Bound to NADP+ instead of NAD

Question 38

Explain how triglycerides are absorbed from the intestinal lumen.

Answer 38

Most are digested into monoglycerides and fatty acids; Intestinal epithelial cells resynthesize these into triglycerides that enter the lymph as chylomicrons; Apoprotein B is adsorbed to the chylomicron surfaces

Question 39

What are chylomicrons?

Answer 39

Lipoproteins synthesized by intestinal cells

Question 40

List the lipoproteins that are synthesized by the liver.

Answer 40

VLDLs, IDLs, LDLs, HDLs

Question 41

What is the purpose of a lipoprotein?

Answer 41

Transports lipids in the blood

Question 42

Describe VLDLs.

Answer 42

High concentration of triglycerides and moderate amount of cholesterol and phospholipids; transport lipids mainly from liver to adipose tissue

Question 43

How are chylomicrons transported?

Answer 43

Transported to venous system via thoracic duct; Removed from blood by various tissues (adipose tissue, skeletal muscle, heart)

Question 44

What is the role of lipoprotein lipase?

Answer 44

Hydrolyzes chylomicron triglycerides, releasing fatty acids and glycerol

Question 45

List the conditions that increase the utilization of fat for energy.

Answer 45

Starvation, diabetes mellitus

Question 46

Describe LDLs.

Answer 46

High concentration of cholesterol and moderate concentration of phospholipids

Question 47

Describe HDLs.

Answer 47

High concentration of proteins and low concentration of cholesterol and fatty acids

Question 48

What are the 3 most common fatty acids in the human body?

Answer 48

Stearic acid = 18-carbon chain and is fully saturated with hydrogen atoms Oleic acid = 18-carbon chain but has one double bond in the middle of the chain Palmitic acid = 16 carbon atoms, fully saturated

Question 49

How are triglycerides used as an energy source?

Answer 49

Hydrolyzed into fatty acids and glycerol, which are transported in blood to the tissues (glycerol is converted to glycerol-3-phosphate)

Question 50

What are the principal functions of the liver in lipid metabolism?

Answer 50

1. Degrade fatty acids into small compounds that can be used for energy 2. Synthesize triglycerides, mainly from carbohydrates, but to a lesser extent from proteins as well 3. Synthesize other lipids from fatty acids, especially cholesterol and phospholipids.

Question 51

Under what conditions do large quantities of triglycerides appear in the liver?

Answer 51

During the early stages of starvation, in diabetes mellitus, in any other condition in which fat instead of carbohydrates is being used for energy

Question 52

Explain why fats are poorly synthesized during insulin insufficiency.

Answer 52

First, when insulin is not available, glucose does not enter the fat and liver cells satisfactorily, so little of the acetyl-CoA and NADPH needed for fat synthesis can be derived from glucose. Second, lack of glucose in the fat cells greatly reduces the availability of α-glycerophosphate, which also makes it difficult for the tissues to form triglycerides

Question 53

Explain why carbohydrates are preferred over fats for energy.

Answer 53

First, fats in adipose tissue cells are present in two forms: stored triglycerides and small quantities of free fatty acids. They are in constant equilibrium with each other. When excess quantities of α-glycerophosphate are present (which occurs when excess carbohydrates are available), the excess α-glycerophosphate binds the free fatty acids in the form of stored triglycerides. As a result, the equilibrium between free fatty acids and triglycerides shifts toward the stored triglycerides; consequently, only minute quantities of fatty acids are available to be used for energy. Because α-glycerophosphate is an important product of glucose metabolism, the availability of large amounts of glucose automatically inhibits the use of fatty acids for energy. Second, when carbohydrates are available in excess, fatty acids are synthesized more rapidly than they are degraded. This effect is caused partially by the large quantities of acetyl-CoA formed from the carbohydrates and by the low concentration of free fatty acids in the adipose tissue, thus creating conditions appropriate for the conversion of acetyl-CoA into fatty acids. An excess of carbohydrates in the diet not only acts as a fat-sparer but also increases fat stores

Question 54

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

Answer 54

Attachment of a monocyte to an adhesion molecule on a damaged endothelial cell of an artery. The monocyte then migrates through the endo­thelium into the intimal layer of the arterial wall and is transformed into a macrophage. The macrophage then ingests and oxidizes lipoprotein molecules, becoming a macrophage foam cell. The foam cells release substances that cause inflammation and growth of the intimal layer. Additional accumulation of macrophages and growth of the intima cause the plaque to grow larger and accumulate lipids. Eventually, the plaque may occlude the vessel or rupture, causing the blood in the artery to coagulate and form a thrombus.