CARBOHYDRATE CARBOHYDRATE METABOLISMMETABOLISM

BYBYDR. GAMAL GABRDR. GAMAL GABR

Dr. Gamal Gabr, College of Pharmacy

Dr. Gamal Gabr, College of Pharmacy

Carbohydrate MetabolismCarbohydrate Metabolism Starch and the major disaccharides are broken down by

digestive processes to glucose, fructose, and galactose monosaccharrides.

Fructose and galactose are readily converted by enzyme action to glucose.

Glucose is converted to the glucose 1-phosphate. For the production of energy, the glucose 1-phosphate

enters the catabolic process through glycolysis.

Carbohydrate MetabolismCarbohydrate Metabolism During glycolysis, an ancient pathway found in almost all

organisms, a small amount of energy is captured as a glucose molecule is converted to two molecules of pyruvate.

Glycogen, a storage form of glucose in vertebrates, is synthesized by glycogenesis when glucose levels are high and degraded by glycogenolysis when glucose is in short supply.

Glucose can also be synthesized from noncarbohydrate precursors by reactions referred to as gluconeogenesis.

The pentose phosphate pathway enables cells to convert glucose-6-phosphate, to ribose-5-phosphate(the sugar used to synthesize nucleotides and nucleic acids)

GLYCOLYSISGLYCOLYSIS

In glycolysis, also referred to as the Embden-Meyerhof-Parnas pathway, each glucose molecule is split and converted to two three-carbon units (pyruvate).

The small amount of energy captured during glycolytic reactions (about 5% of the total available) is stored temporarily in two molecules each of ATP and NADH.

GLYCOLYSISGLYCOLYSIS Glycolysis consists of 10 reactions, occurs in two stage

(1) Glucose is phosphorylated twice and cleaved to form two molecules of glyceraldehyde-3- phosphate (G-3-P).

(2) Glyceraldehyde-3-phosphate is converted to pyruvate. Four ATP and two NADH molecules are produced.

The glycolytic pathway can be summed up in the following equation:

D-Glucose + 2 ADP + 2 Pi + 2 NAD+ →

2 pyruvate + 2 ATP + 2 NADH + 2H+ + 2H2O

GLYCOLYSISGLYCOLYSIS

GLYCOLYSISGLYCOLYSIS

The Fates of PyruvateThe Fates of Pyruvate

When oxygen is available (left), aerobic organisms completely oxidize pyruvate to CO2 and H2O.

In the absence of oxygen, pyruvate can be converted to several types of reduced molecules. In some cells (e.g., yeast), ethanol and CO2 are produced (middle). In others (e.g., muscle cells), homolactic fermentation occurs in which lactate is the only organic product (right).

Entry of Other Monosaccharides into GlycolysisEntry of Other Monosaccharides into Glycolysis

Diseases incorporated with Diseases incorporated with Carbohydrates MetabolismCarbohydrates Metabolism

(1) Fructose intolerance: results from a deficiency in fructose 1-phosphate aldolase. Leads to an accumulation in fructose 1-phosphate and a depletion of ATP and Pi. Pi depletion makes it impossible to generate more ATP lowering levels even further. Causes cell damage.

(2) Fructosuria: results from a deficiency in fructokinase. Fructose appears in blood and urine. Relatively causes metabolic abnormality.