[Reading Ganong chp 17 p282]

 

Energy

1 cal = energy needed to increase 1 gram of water by 1 degree celcius.

 

carbohydrate: 4.1 kcal/g

fat: 9.3 kcal/g

protein: 5.3 kcal/g in vitro.

 

Protein is incompletely oxidated. And caloric value of protein is only 4.1kcal/g in body.

 

Respiratory quotient

Respiratory quotient = ratio in the steady state of the volume of CO2 produced to the volume of O2 consumed per unit of time.

Respiratory exchange ratio = ratio of CO2 to O2 at any given time.

 

RQ for carbohyrate = 1

RQ for fat = 0.703 (thus more O2 is consumed that CO2 produced in the metabolism of fat)

RQ for protein = 0.82

 

Specific dynamic action

SDA of a food is the obligatory energy expenditure that occurs during its assimilation into the body.

 

100kcal of protein increases metabolic rate by 30kcal

Carbohydrate by 6kcal

Fat by 4 kcal.

 

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Basal metabolic rate (BMR)

BMR = 3.52 weight^0.67

OR

BMR = 3.52 weight^0.75

 

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Directional-flow valve - reactions that proceed in one direction under the influence of one enzyme or transport mechanism, and in the opposite direction under the influence of another.

e.g. glucose to glucose-6-phosphate catalyzed by hexokinase, reverse is catalyzed by glucose-6-phosphatase

e.g. glucose 1-phosphate to glycogen via glycogen synthase, reverse by phosphorylase

e.g. fructose 6-phosphate to fructose 1,6-diphosphate by phosphofructokinase, reverse by fructose 1,6-diphosphatase

 

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Glycogen -> glucose 1-phsphate (by phosphorylase a)

 

Phosphorylase a = active form of phosphorylase

Phosphorylase b (or dephosphophosphorylase) = inactive form.

 

Example:

epinephrine act on beta2-adrenergic receptor, increasing level of cAMP

cAMP activate protein kinase A

Protein kinase A activates phosphorylase kinase by catalyzing transfer for a phosphate group to it

Phosphorylase kinase activates phosphorylase.

Phosphorylase a catalyzes breakdown of glycogen into glucose-1-phosphate

 

Glucose-1-phosphate <-> Glucose-6-phosphate

 

Liver contains glucose 6-phosphatase.

In liver, because of the glucose-6-phosphatase, glucose is produced in released.

In skeletal muscles, these glucose-6-phosphatase is catabolized down the Embden-Meyerhof pathway and hexose monophosphate shunt pathway, producing lactate.

 

Thus, epinephrine cause activation of phosphorylase in liver and skeletal muscle.

=> both plasma glucose and lactate level increase.

Glucagon only cause activation of phosphorylase in liver

=> only glucose increase. Lactate is unchanged.

 

 

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Renal threshold for glucose = 180 mg/dL

 

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In the context of proteins

Primary structure - order of amino acids

Secondary structure - spatial arrangement produced by folding and twisting
e.g. alpha-helix, beta-sheet

Tertiary structure - spatial arrangement of helices/sheets into layers, etc.

Quaternary structure - arrangement of subunits

 

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Most of the sulfates in urine are in the form of oxidation of cysteine

 

Essential amino acids are:

• Valine (Val)
• Leucine (Leu)
• Isoleucine (IIe)
• Threonine (Thr)
• Methionine (Met)
• Phenylalanine (Phe)
• Arginine (Arg)
• Lysine (Lys)
• Histidine (His)

 

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Transamination - conversion of one amino acid to the corresponding keto acid with simultaneous conversion of another keto acid to an amino acid

Transaminase may be released from active cells when damage occurs.

=> e.g. plasma aspartate aminotransferase (AST) after MI

 

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Leucine, isoleucine, phenylalanine are ketogenic because they can be converted to ketone body acetoacetate.

Alanine and some other amino acids are glucogenic because they can be converted to glucose

 

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Most NH4+ formed by deamination of amino acid in liver are converted to urea, and excreted in urine.

Most of the urea is formed in liver.

In severe liver disease, blood urea nitrogen falls and blood NH3 rises.

 

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Creatine is synthesized in liver from methionine, glycine, and arginine.

In skeletal muscles, it is used to form phosphorylcreatine.

 

Creatinine in urine is converted from phosphorylcreatine.

 

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Uric acid - formed by breakdown of purine and by direct synthesis from 5-phosphoribosyl pyrophosphate (5-PRPP) and glutamine.

Excreted in urine.

 

Xanthine oxidase converts xanthine into uric acid (final step)

 

Allopurinol inhibits xanthine oxidase.

Colchicine doesn't affect uric acid metabolism, but inhibits the phagocytosis of uric acid crystal by leukocytes.

 

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stopped at p302