Lecture 17: Energy Balance and Metabolism I

Question 1

Define Free energy and relate to exergonic and endergonic reactions

Answer 1

• Free energy
  
  • The amount of energy liberated by complete oxidation of a food is called the free energy of oxidation
• Exergonic-
  
  • negative change in G
• Endergonic
  
  • positive change in G

Question 2

Relate free energy to ATP breakdown

Answer 2

• The amount of free energy in each of the bonds of ATP is about 12,000 calories under the usual conditions of temperature and concentrations of the reactants in the body

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 and glucose can be converted to fructose-6-phosphate and enter the glycolytic pathway

Question 4

Describe the uptake of glucose

Answer 4

• via active sodium-glucose co-transport:
  
  • active transport of sodium provides energy for absorbing glucose against a concentration gradient
• via faciliated transport:
  
  • only transported form higher to lower concentrations
• (note the presence of insulin increases glucose transport x10)

Question 5

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

Answer 5

• Enzymes
  
  • Glucokinase
    
    • Transfers phosphate from ATP to glucose
  • Phosphatase
    
    • Removes phosphate to allow Glucose-6-phosphate to leave cell
  • Phosphorylase
    
    • Catalyzes production of glucose-1-phosphate from glycogen

Question 6

Know the end products of glycolysis

Answer 6

• Pyruvic acid (2 molecules)
• Hydrogen (4)
  
  • release is catlayzed by a dehydrogenase
• ATP (2 molecules)
  
  • 4 produced and two used means a net of 2

Question 7

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

Answer 7

• Acetyl-CoA (2 molecules)
• Hydrogens (4)
  
  • release is catalyzed by a dehydrogenase
• Carbon dioxide (2 molecules)

Question 8

Know the fate of pyruvic acid when oxygen is not present

Answer 8

Leads to the production of lactic acid

Question 9

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

Answer 9

Question 10

state where the citric acid cycle occurs in the cell

Answer 10

Occurs in the mitochondrial matrix

Question 11

List the end products of the citric acid cycle

Answer 11

• Hydrogen (16)
  
  • release is catalyzed by a dehydrogenase
• ATP (2 molecules)
• Carbon dioxide (4 molecules)

Question 12

Define oxidative phosphorylation

Answer 12

the synthesis of ATP by phosphorylation of ADP for which energy is obtained by electron transport and which takes place in the mitochondria during aerobic respiration

Question 13

• 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 13

• Hydrogens are removed in pairs
• one member of each pair becomes a hydrogen ion
• the other member of a pair combines with NAD+—-> NADH
• The fate of these electrons is that they enter the electron transport chain

Question 14

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

Answer 14

• Flavoprotein
• several iron sulfide proteins
• Ubiquinone (Q)
• Cytochrome A3 (cytochrome oxidase)
  
  • located on inner membrane
  • can give up two electrons to oxygen

Question 15

Describe the chemiosmotic mechanism

Answer 15

1. electrons pass through chain, releasing large amounts of energy
2. energy is used ot pump hydrogen 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+ 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
8. Note that the 2 pairs of hydrogens derived from the CAC enter the ETC at a later point and provide energy for 2 ATP molecules per hour.

Question 16

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

Answer 16

• Cyclical pathway in which one molecule of glucose is metabolized for each revolution of the cycle
  
  • for every six molecules of glucose that enter the pathway, five molecules of glucose of glucose are resynthesized
• This pathway is mostly used for synthesis of fats and other substances

Question 17

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

Answer 17

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

Question 18

Describe how triglycerides are synthesized from glucose

Answer 18

• Fatty acids are prodduced by glucose by the addition of Acetyl CoA and NADPH, which are both made from glucose
• fatty acids combine with alpha-glycerophosphate (which is the glycerol backbone)

Question 19

Explain how triglycerides are absorbed from the intestinal lumen

Answer 19

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

Question 20

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

Answer 20

• Three long-chain fatty acid molecules are bound to one molecule of glycerol.
• Three most common in the human body
  
  • stearic acid (tristearin)
  • oleic acid
  • palmitic acid

Question 21

* Define chylomicrons

• explain how they are transported and removed from the blood
• What is the role of lipoprotein lipase

Answer 21

• Chylomicrons
  
  • a droplet of fat present in the blood or lymph after absorption from the small intestine
• Chylomicrons are removed from the blood by various tissues, especially
  
  • Adipose tissue
  • skeletal tissue
  • heart
• These tissues synthesize lipoprotein lipase, which:
  
  • is transported to surface of capillary epithelial cells
  • hydrolyzes chylomicron triglycerides, releasing fatty acids and glycerol

Question 22

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

Answer 22

• 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
  
  • conditions that increase utilization of fat for energy:
    
    • Starvation
    • Diabetes Mellitus

Question 23

• Define lipoprotein
• Compare the Various types of lipoproteins

Answer 23

• Lipoprotein
  
  • small particles
  • contain:
    
    • triglycerides
    • cholesterol
    • phospholipids
    • protein
• Synthesized by intestinal cells
  
  • Chylomicrons
• Synthesized by liver
  
  • very low density lipoproteins (VLDLs)
    
    • High concentrations of triglycerides and moderate amounts of cholesterol and phospholipids
    • Transport lipids mainly from liver to adipose tissue
  • intermediate density lipoproteins (IDLs)
  • Low density lipoproteins (LDLs)
    
    • High concentration of cholesterol and moderate concentration of phospholipids
  • High density lipoproteins (HDLs)
    
    • High concentration of proteins and low concentration of cholesterol and fatty acids

Question 24

• how are triglycerides used as an energy source

Answer 24

They are hydrolyzed into fatty acids and glycerol. both ar transported in the blood to the active tissues, where they will be oxidized to give energy (glycerol goes through glycolysis and fatty acids go through beta-oxidation)

Question 25

Describe the formation of acetoacetic acid

Answer 25

• A large share of initial degradation of fatty acids occurs in the liver, especially when large amounts of lipids are being used for energy
• The liver uses only a small proportion of fatty acids for its own intrinsic metabolic processes.
• The fatty acids in the liver have been split into acetyl-CoA,
  
  • two molecules of acetyl-CoA condense to fomr one molecule of acetoacetic acid

Question 26

• Define ketone bodies and give examples
• What is ketosis?

Answer 26

• Ketone bodies
  
  • acetoacetic acid
  • beta-hydroxybutyric acid
  • acetone
• ketosis
  
  • ketone bodies rise to levels man times normal in the blood and interstitial fluids
  • conditions favoring ketosis
    
    • starvation
    • diet composed entirely of fat
    • DM

Question 27

Describe the synthesis of fatty acids

Answer 27

• The synthesis of fatty acids from acetyl-CoA is a two-step process using the following as principal intermediates in the polymerization process
  
  • Malonyl-CoA
  • NADPH

Question 28

What are principal functions of the liver in lipid metabolism

Answer 28

• a large share of the initial degradation of fatty acids occurs in the liver. it makes acetyl-CoA and turns it into acetoacetic acid which can be transported in the blood to be used as energy in the body

Question 29

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

Answer 29

• during the early stages of starvation
• Diabetes mellitus
• any other condition in which fat instead of carbohydrates is being used for energy

Question 30

Explain why fats are poorly synthesized during insulin insufficiency

Answer 30

• 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
• lack of glucose in the fat cells greatly reduces the availability of alpha-glycerophosphate
  
  • makes it diffucult for the tissues to form triglycerides

Question 31

Explain why carbohydrates are preferred over fats for energy

Answer 31

• When excess quantities of carbohydrates are available in the body, carbohydrates are used preferentially over triglycerides for energy.
• why?
  
  • fats in adipose tissue cells are present in two forms in constant equilibrium with each other
    
    • stored triglycerides
    • small quantities of free fatty acids
    • when excess quantities of alpha-glycerophosphate (important product of glucose metabolism) binds to free fatty acids. shifting the equilibrium toward stored triglycerides and leaving little free fatty acids available for energy
  • 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
  • increased carbohydrates leads to intrease intermediates and fatty synthesis
  • plus fatty acids can be produced by carbohyrates

Question 32

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

Answer 32

• Damage to vascular endothelium
  
  • Increases the expression of adhesion molecules
  • Decreases release of NO and other substances that prevent adhesion of macromolecules and cells
• Circulating monocytes and LDLs accumulate at injury site
• Monocytes
  
  • Corss endothelium
  • enter intima
  • become macrophages
• Macrophages
  
  • Ingest lipoproteins
  • become foam cells
  • form visible fatty streaks
• Fatty streaks
  
  • grow larger
  • Coalesce
• Surrounding fibrous and smooth muscle tissues
  
  • proliferate
  • form large plaques
• Large plaques:
  
  • may occlude lumen
  • may become sclerotic or fibrotic
  • may become calcified

Question 33

What are the basic causes of atherosclerosis

Answer 33

• Increased LDLs
• Familial hypercholesterolemia (defective LDL receptors)