Carbohydrates
40-75% of energy intake
In terms of their physiological there are available and unavailable carbohydrates
Available carbohydrates are those that are hydrolyzed by enzymes of the human
Unavailable carbohydrates are not hydrolyzed by endogenous human enzymes
Carbohydrate Metabolism
Glycogenesis
is the synthesis of glycogen from glucose-6-phosphate
Glycogen is a highly branched glucose polymer used for carbohydrate storage in animals
Glycogen stores are used to keep the blood sugar level steady between meals
it occurs when high levels of glucose-6-phosphate are formed in the first reaction of glycolysis
it does not operate when glycogen stores are full, which means that additional glucose is converted to body fat
Glycogenolysis
is the breakdown of glycogen to glucose
The glucose is phosphorylated as it is cleaved from the glycogen to form glucose-1-phosphate
Glucose-1-phosphate can be converted to glucose-6-phosphate, which can enter glycolysis
Phosphorylated glucose can’t be absorbed into cells
- in the liver and kidneys, glucose-6-phosphate can be hydrolized to glucose
Glycogenolysis is activated by glucogon in the liver and epinephrine in muscles
Glycogenolysis is inhibited by insulin
GLUCONEOGENESIS
It is synthesis of glucose from non-carbohydrate sources
It occurs mainly in the liver cells and to lesser extent in kidneys
Cytoplasm except for the first step (carboxylation of pyruvate) occurs in the mitochondria.
Major pathway for Glucose oxidation
Glycolysis
means oxidation of glucose to give pyruvate or lactate
Location
in all cells
Citric Acid Cycle
Complete oxidation of acetyl-CoA to 2 molecules of CO2 and generating energy
Location
All cells that contain mitochondria
Functions
Energy production
Catabolic for glucose, fat &proteins
Anabolic Function
Minor Pathways for Glucose oxidation
HMP shunt
a pathway by which pentose phosphate is produced from glucose
Site
Cytoplasm
classified
sugars
Simple carbohydrates
Monosaccharides
Ribose
Deoxyribose
Glucose
Fructose
Galactose
Mannose
Disaccharides
Maltose
Lactose
Sucrose
oligosaccharides
Complex carbohydrates
Raffinose
Stachyoses
Verbascose
polysaccharides
Complex carbohydrates
Starch
glycogen
Cellulose
Absorption
movement of molecules across the gastrointestinal (GI) tract into the circulatory system
Most of the end-products of digestion are absorbed in the small intestinal by four mechanisms for absorption :
active transport
requires energy
passive diffusion
endocytosis, and
facilitative diffusion