Dm Basics Metabolism Overview

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DR. RAJENDRAN’S INSTITUTE OF MEDICAL EDUCATION Phone 0470 – 2604199, 09388852220.

DM – Overview of metabolism Diet – Energy from carbohydrates, fats, and proteins. ATP is the ‘Energy currency’. ATP transfer free energy from substances of high energy to substances of low energy. Mitochondria is the powerhouse of the cell. Oxidative phosphorylation couples respiration to generation of ATP. Oxidation is loss of electrons. Reduction is gain of electrons. Both are always combined. Cyanide inhibits oxidative phosphorylation.

Carbohydrate metabolism Glucose is the most important carbohydrate. All carbohydrates are converted to glucose. Glucose absorbed from intestine enters portal vein and go to the liver. Glucose in liver 1

Used for liver metabolism

2

Stored as glycogen (Glycogen is storage form of glucose)

3

Released into blood as glucose

4

Excess glucose converted to fat and stored in adipose tissue as triglycerides.

Major source of carbohydrates is plants CHO, fat, protein – common metabolite is acetyl CoA. Acetyl CoA is the common metabolic product of metabolism of CHO, fat and protein. Contains pantothenic acid. It enters citric acid cycle and generates ATP.

Glycolysis Aerobic Glucose molecules of ATP

Pyruvate

Acetyl CoA

Citric acid cycle

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Page 2 of 6 Anaerobic - Glucose ATP molecules)

Lactate. Provides ATP in the absence of Oxygen (but only 2

Glucose in muscle Glycogen ↔ Glucose

CO2 + Lactate

Converted to glucose in liver

Citric acid cycle (Kreb’s cycle) Final common pathway for metabolism of CHO, fats and proteins. H2o + Acetyl CoA Co2 + (2H) Respiratory chain. Generates 12 high energy phosphate bonds per turn of the cycle. The 4 vitamins in citric acid cycle are riboflavin, niacin, thiamine, and pantothenic acid. Gluconeogenesis Convert non-carbohydrates into glucose. Substrates are amino acids (from breakdown of muscle proteins), lactate (from breakdown of glucose in muscle), and glycerol (from adipose tissue).

Lipid metabolism

Page 3 of 6 Fats have high energy value. Fat is stored in adipose tissue as triglycerides (FA + glycerol). Fats are insoluble in water. They are transported bound to proteins (lipoproteins = fats + proteins). Main substrate for synthesis is glucose.

Beta oxidation (inside mitochondria) FA

Acetyl CoA APT generated

ketone bodies Citric acid cycle ATP generated

Ketone bodies formed in the liver when there is high rate of beta oxidation. FFA cannot pass though inner mitochondrial membrane. Transported by carnitine palmitoyl transport system into the mitochondria for beta oxidation.

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Chylomicrons are formed by the lymphatic system draining the intestine. They transport all dietary lipids into the blood. 80% of chylomicrons are metabolized by adipose tissue, heart and muscles. 20% of chylomicrons are metabolized by the liver. Chylomicrons contain 88% triglycerides

VLDL (Pre-beta lipoproteins) are produced in the liver for export of triglycerides. LDL is the final stage of catabolism of VLDL. HDL is involved in metabolism of chylomicrons and LDL. The predominant lipid in HDL is phospholipid. Lipoprotein lipase present in endothelium of caplillaries (not active in blood and liver).

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Protein metabolism

Integration of metabolism When there is positive caloric balance, food is stored as glycogen and triglycerides. During starvation, fat is oxidized in preference to glucose. Brain and RBCs always need glucose.

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