1. Chapter 27 Nutrition and Metabolism

2. Overview of Nutrition and Metabolism
Nutrition refers to the food (nutrients) humans eat
Malnutrition—a deficiency in the consumption of food, vitamins, and minerals
Categories of nutrients
Macronutrients—nutrients needed in large amounts (bulk nutrients)
Macromolecules such as carbohydrates, fats (lipids), and proteins
Water
Macrominerals - sodium, chloride, and calcium
Micronutrients—nutrients needed in very small amounts
Vitamins
Microminerals (trace elements) - iron, iodine, zinc,
Balance of nutrients is required for good health

3. Overview of Nutrition and Metabolism
Metabolism - the use of nutrients
Many chemical processes
Catabolism
Breaks food down into smaller molecular compounds
Releases two forms of energy—heat and chemical energy
Anabolism
A synthesis process
Both processes take place inside of cells continuously and concurrently
Chemical energy released by catabolism must be transferred to ATP, which supplies energy directly to the energy-using reactions of all cells

4. Carbohydrates Dietary sources of carbohydrates Complex carbohydrates
Polysaccharides—starches; found in vegetables and grains; glycogen is found in meat
Cellulose—a component of most plant tissue; passes through the digestive system without being broken down
Disaccharides—found in refined sugar; must be broken down before they can be absorbed
Monosaccharides—found in fruits; move directly into the internal environment without being processed directly
Glucose—carbohydrate most useful to the human cell; can be converted from other monosaccharides

6. Carbohydrates Carbohydrate metabolism (review pages 101-106, 321-322)
Glucose transport and phosphorylation
Glucose reacts with ATP to form glucose-6-phosphate
This step prepares glucose for further metabolic reactions
This step is irreversible except in the intestinal mucosa, the liver, and the kidney tubules
Glycolysis
The first process of carbohydrate catabolism
Consists of a series of chemical reactions
Glycolysis occurs in the cytoplasm of all human cells
An anaerobic process—the only process that provides cells with energy under conditions of inadequate oxygen
It breaks down chemical bonds in glucose molecules and releases about 5% of the energy stored in them
It prepares glucose for the second step in catabolism—the citric acid cycle

9. Carbohydrates Carbohydrate metabolism (cont.) Citric acid cycle
Two pyruvic acid molecules from glycolysis are converted to two acetyl molecules in a transition reaction
Releases two carbon dioxide molecules
Acetyl CoA is converted to a number of intermediates
Citrate (C6)
Isocitrate (C6)
Alph-ketoglutarate (C5)
Succinyl CoA (C4)
Succinate (C4)
Fumarate (C4)
Malate (C4)
Oxaloacetate (C4)

12. Carbohydrates Carbohydrate metabolism (cont.)
Electron transport system
High-energy electrons (along with their protons) removed during citric acid cycle enter a chain of molecules that are embedded in the inner membrane of the mitochondria
As electrons move down the chain, they release small bursts of energy to pump protons between the inner and the outer membrane of the mitochondrion
Protons move down their concentration gradient and across the inner membrane, driving ATP-synthase
Oxidative phosphorylation—the joining of a phosphate group to ADP to form ATP by the action of ATP synthase

16. Carbohydrates Carbohydrate metabolism (cont.) The anaerobic pathway
A pathway for the catabolism of glucose
Transfers energy to ATP using only glycolysis
Produces lactic acid
Glycogenesis
Glucose molecules are joined to form a strand of glucose beads
Operates when the blood glucose level increases above the midpoint of its normal range
Glycogenolysis
The reversal of glycogenesis
Gluconeogenesis
The formation of new glucose
Cccurs chiefly in liver

18. Carbohydrates Carbohydrate metabolism (cont.)
Control of glucose metabolism—hormonal and neural devices maintain homeostasis of blood glucose concentration
Insulin
secreted by beta cells to decrease blood glucose level
Glucagon
secreted by alpha cell to increases blood glucose level
Increases activity of enzyme phosphorylase
Epinephrine
Hormone secreted in times of stress
Increases phosphorylase activity
Adrenocorticotropic hormone
Stimulates adrenal cortex to increase its secretion of glucocorticoids
Glucocorticoids accelerate gluconeogenesis
Growth hormone
Increases blood glucose level by shifting from carbohydrate to fat catabolism
Thyroid-stimulating hormone has complex effects on metabolism

21. Carbohydrates Carbohydrate metabolism (cont.) Hyperglycemic
Hormones that cause the blood glucose level to rise
Glugacon GH
Epinephrine
Glucocorticoids
ACTH
Hypoglycemic
Hormones that cause the blood glucose level to decrease
Insulin