Lecture 14: Energy Balance and Metabolism I

Question 1

Define free energy and relate 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
Negative = exergonic reaction
Positive = endergonic reaction

Question 2

Relate free energy to ATP breakdown.

Answer 2

Free energy is negative when ATP is broken down

Question 3

Trace basic pathway for glycolysis; know where ATP and ADP is involved in the pathway. Know how galactose and glucose enter the pathway.

Answer 3

Galactose uses ATP to become Galactose-1-phosphate
Glucose uses ATP to become Glucose-6-phosphate
Fructose uses ATP to become Fructose-6-phosphate
Galactose and glucose can be converted to fructose-6-phosphate and enter glycolytic pathway

Question 4

Describe the uptake of glucose.

Answer 4

Glucose is transported into the tissue cells by active sodium-glucose cotransport and facilitated transport

Question 5

Be able to trace the major steps involved in glycogenesis and glycogenolysis and the enzymes involved.

Answer 5

Glucokinase: transfers phosphate from ATP
Phosphatase: removes phosphate
Phosphorylase: catalyzes production of glucose-1-phosphate from glycogen

Question 6

Know the end products of glycolysis.

Answer 6

Pyruvic acid - 2
Hydrogens - 4
ATP - 2

Question 7

Know the end products of the conversion of pyruvic acid to acetyl-CoA.

Answer 7

Acetyl-CoA - 2
Hydrogens - 4
Carbon dioxide - 2

Question 8

Know the fate of pyruvic acid when oxygen is not present.

Answer 8

It converts to lactic acid

Question 9

Be able to trace the citric acid cycle and give the major intermediates.

Answer 9

Net reaction: 2 Acetyl-CoA + 6H2O + 2 ADP -> 4 CO2 + 16 H + 2 CoA + 2 ATP

Question 10

State where the citric acid cycle occurs in the cell.

Answer 10

Mitochondrial matrix

Question 11

List the end products of the citric acid cycle.

Answer 11

Hydrogens - 16
ATP- 2
Carbon dioxide - 4

Question 12

Define oxidative phosphorylation.

Answer 12

The oxidation of hydrogen to form more ATP

Question 13

State where oxidative phosphorylation occurs.

Answer 13

On mitochondrial cristae

Question 14

Describe 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 14

Fate of hydrogens -
Hydrogens are removed in pairs
One member of each pair becomes a hydrogen ion
The other member of a pair combines with NAD+ - NADH

Fate of electrons -
Enter electron transport chain

Question 15

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

Answer 15

Flavoprotein
Several ion sulfide proteins
Ubiquinone
Cytochrome A3

Question 16

Describe the chemiosmotic mechanism.

Answer 16

Electrons pass through chain, releasing large amounts of energy
Energy is used to pump hydrogen ions from inner matrix into outer chamber between inner and outer membranes
High concentration of H+ is created in chamber
Strong negative potential created in inner matrix
H+ ions flow from high to low concentration through ATP synthetase
Energy derived from H+ flow is used by ATPase to convert ADP to ATP

Question 17

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

Answer 17

`The pentose phosphate pathway is a cyclical pathway in which one molecule of glucose is metabolized for each revolution of the cycle
This pathway is mostly used for the synthesis of fats and other substances

Question 18

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

Answer 18

Hydrogens generated from this pathway are bound to NADP+ instead of NAD+

Question 19

Describe how triglycerides are synthesized from glucose.

Answer 19

Glucose either undergoes the glycolytic pathway or the pentose phosphate pathway.
The glycolytic pathway directly synthesizes triglycerides.
The pentose phosphate pathway synthesizes fatty acids which are then formed into triglycerides

Question 20

Review the basic chemical structure of triglycerides and identify the three most common fatty acids in the human body.

Answer 20

Stearic acid
Oleic acid
Palmitic acid

Question 21

Explain how triglycerides are absorbed from the intestinal lumen.

Answer 21

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

Question 22

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

Answer 22

Resynthesized triglycerides that enter the lymph

Lipoprotein lipase hydrolyzes chylomicron triglycerides, releasing fatty acids and glycerol

Question 23

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

Answer 23

Fatty acids can be used for fuel or again synthesized into triglycerides
All normal energy requirements of the body can be provided by the oxidation of fatty acids without using carbohydrates r proteins as an energy source
Conditions that increase utilization of fat for energy
-Starvation
-Diabetes mellitus

Question 24

Define lipoprotein and compare the various types of lipoproteins.

Answer 24

Lipoproteins transport lipids in the blood

Question 25

define VDL

Answer 25

high concentrations of triglycerides and moderate amounts of cholesterol and phospholipids

Question 26

define LDL

Answer 26

high concentration of cholesterol and moderate concentration of phospholipids

Question 27

define HDL

Answer 27

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

Question 28

What are triglycerides and how are triglycerides used as an energy source?

Answer 28

Triglycerides are hydrolyzed into fatty acids and glycerol

The fatty acids are used for energy

Question 29

Describe the formation of acetoacetic acid.

Answer 29

2 acetyl-CoAs condense to form acetoacetic acid

Question 30

Define ketone bodies and give examples. What is ketosis?

Answer 30

Ketosis occurs if concentrations of ketone bodies increase about normal in blood

Question 31

Describe the synthesis of fatty acids.

Answer 31

Made from the hydrolysis of triglycerides

It is a 2 step process that involves malonyl-CoA and NADPH

Question 32

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

Answer 32

Degrade fatty acids
Synthesize triglycerides
Synthesize other lipid from fatty acids

Question 33

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

Answer 33

During early stages of starvation
Diabetes mellitus
Any other condition in which fats instead of carbs are used for energy

Question 34

Explain why fats are poorly synthesized during insulin insufficiency.

Answer 34

When insulin is insufficient, fats are poorly synthesized because glucose does not enter the fat and liver cells satisfactorily and lack of glucose greatly reduces the availability of alpha-glycerophosphate

Question 35

Explain why carbohydrates are preferred over fats for energy.

Answer 35

It acts as a fat sparer and increases fat stores