Carbohydrates Dr. Ameerah M. Zarzoor
What Are Carbohydrates? Carbohydrates are the most abundant biomolecules on Earth Produced by plants during photosynthesis Carbohydrates are polyhydroxyl aldehydes and ketones, or substances that yield such compounds on hydrolysis After eating plant foods, humans convert the carbohydrates into glucose Glucose Most abundant carbohydrate Preferred source of energy for the blood, brain, and nervous system Carbohydrate-rich plant foods make up the foundation of diets all over the world
Classification of Carbohydrates Simple carbohydrates Monosaccharide Disaccharide Perceived as sweeter than complex carbohydrates - Mixes with saliva and reacts with taste buds Oligosaccharides Complex carbohydrates Polysaccharides
Monosaccharides Three nutritionally important monosaccharaides Glucose Fructose Galactose Glucose Blood glucose and blood sugar in the body Most abundant monosaccharide in the body - Is the preferred and main source of energy for the brain and red blood cells Part of every disaccharide Only monosaccharide in starches
Carbohydrates Monosaccharides D-glucose D-galactose
Disaccharides Three Disaccharides Sucrose - Most common Lactose Maltose - Least common - Formed from digestion of starches
Monosaccharides Link to Form Disaccharides Figure 4.3
Oligosaccharides Similar in length to simple carbohydrates Similar in makeup to polysaccharides Humans lack the enzymes necessary to digest them Intestinal microflora digest and ferment them Cause bloating, discomfort, and flatulence Food sources Legumes, beans, cabbage, brussels sprouts, broccoli
Polysaccharides Starch Plants store glucose in chains of starch - Amylose - Straight chain - More resistant to digestion - Resistant starch May improve health of digestive tract May improve glucose tolerance May stimulate growth of beneficial intestinal bacteria - Amylopectin - Branched chains - Easier to digest
Polysaccharides Cellulose reducing end
Carbohydrate Digestion and Absorption Disaccharides and starches are digested to monosaccharaides Monosaccharaides are easily absorbed Once digested to monosaccharaides Absorbed through the intestinal cell mucosa Transported to the liver via the portal vein Metabolic needs direct fate of the monosaccharaides - Galactose and fructose Used by the liver for energy Converted to glucose - Glucose Used for energy Converted to glycogen through glycogenesis Converted to glycerol and fatty acids for storage in adipocytes
Glucose Is Stored in the Liver and Muscle Cells as Glycogen Figure 4.9
Digestion of carbohydrates begins in the mouth Most carbohydrate digestion takes place in the small intestine Carbohydrates are broken down to monosaccharaides for absorption Monosaccharaides are converted to glucose in the liver and Used as energy Stored as glycogen in the liver and muscle cells Stored as glycerol and fatty acids in the adipocytes Fiber travels to the colon undigested and most is eliminated from the body
How to Maintain Blood Glucose Levels Epinephrine and norepinephrine increases blood glucose Stimulate glycogenolysis and gluconeogenesis Cortisol increases blood glucose Stimulates gluconeogenesis Reduces uptake of glucose by the muscle cells Growth hormone increases blood glucose Stimulates fat breakdown for energy Reduces uptake of glucose by the muscles Increase glucose production in the liver
Glucose is the body s preferred source of energy Especially the brain and red blood cells Adequate carbohydrate intake Maintains blood glucose levels Spares protein Prevents ketosis Blood glucose levels are maintained by two hormones Insulin which lowers blood glucose levels Glucagon which raises blood glucose levels Epinephrine, norepinephrine, cortisol, and growth hormone raise blood glucose levels.
Regulation of blood glucose Glycogenesis: glucose glycogen (liver, muscle) Glycogenolysis: glycogen glucose Gluconeogenosis: non-cho sources glucose Glycolysis: glucose CO 2 + H 2 O + ATP
Glucose Production Glucose Consumption Blood glucose 125g CO 2 brain Glucose 50g Glycogen (75%) pyruvate lactate (10-15%) 50g rbc wbc certain amino acids (10-15%) CO 2 glycerol (2%) muscle fat cell
Diabetes Mellitus Consume Carbohydrate s Blood Glucose Rises No Insulin Available or Cells Resistant Blood Glucose Rises Liver Breaks Down Glycogen and Produces Glucose from Non- Carbohydrate Sources Ketoadicosis Cell Starves Body Uses Fat for Fuel
Change in Blood Glucose After Eating a High-Carbohydrate Meal Figure 4.17
arbohydrate metabolism Glycolysis:-the degradation of glucose to pyruvate or lactate with the production of ATP. it is anaerobic oxidation. Glucose fructose -6-P 2pyruvic acid Krebs cycle:- the final oxidation of food to CO2 &H2O occurs in the Krebs cycle, also called citric acid cycle or tricarboxylic acid cycle (TCA). That reactions including converts pyruvic acid to CO2 + H2O + ATP (Aerobic oxidation
In anaerobic oxidation Glucose G-6-P fructose-6-phosphate ATP ADP Pyruvic acid