Introduction to Metabolism

Nutrients=any substance in food that is used by the body to promote normal growth, maintenance, and repair.

Essential nutrients must be consumed in the diet.

There are six classes of nutrients.

OverviewClasses of nutrients: Carbohydrates, Lipids,

Proteins, Water, Vitamins, Minerals

RDA - recommended dietary amounts

Energy value of foods - kilocalorie - amount of heat energy to raise the temperature of 1 kilogram of water 1 degree Celsius

Composed of C, H, OProvide a major

source of fuel for the body

Basic unit is glucose Simple versus

Complex Energy yielding (4

kcal /gm)

CarbohydratesDivided into simple carbohydrates and

complex carbohydrates

Used in the process of ATP synthesis

Simple carbohydrates examples: soft drinks, candy, fruit, ice cream, pudding

Complex carbohydrates: bread, cereal, crackers, flour, pasta, nuts, rice, potatoes

RDA - 125-175 grams = 55-60% of total caloric intake

LipidsClasses: triglycerides, phospholipids, sterolsUsed in cell membrane synthesis, energy

production, vitamin storageAnimal sources: lard, meat, poultry, eggs,

milk, milk productsPlants sources: chocolate, corn soy,

cottonseed, olive oils, coconut, peanutsCholesterol sources: organ meats and egg

yolksRDA - 80-100 grams = 30% or less of total

caloric intake

Proteins20 amino acids 9 essential and 11 non-essentialUsed in synthesis of enzymes, antibodies,

hemoglobin, muscle, etc...Complete or incomplete depending if the source

has all amino acids needed by the bodyComplete protein sources: eggs, milk meat (fish,

poultry, pork, beef, lamb)Incomplete protein sources: legumes, nuts and

seeds, grains and cerealsRDA - 0.8g/kg of body weight = 10-15% of total

caloric intake

VitaminsTwo classes

Fat soluble - A, D, E, KWater soluble - C (ascorbic acid) and BB1: thiamine B2: riboflavin B3: nicotinamide (niacin)B5: pantothenic acidB6: pyridoxineBiotinB12 cyanocobalaminFolic acid

Uses Antioxidants (A,C&E), Hormone synthesis (D)Required for clotting proteins (K)Coenzymes (B vitamins)

RDA varies with each vitamin

MineralsSeven required (calcium, phosphorus,

potassium, sulfur, sodium. chloride, and magnesium)

Trace minerals needed (fluorine, cobalt, chromium, copper, iodine, iron, manganese, selenium, zinc)

Uses in bone formation, nerve transmission, cofactors of enzymes, protein synthesis, etc....

Metabolismsum of all the reactions occurring in the body at any

given time; a balance between catabolic and anabolic reactions

Catabolism – breakdown of complex organic compounds into simpler ones; reactions and are considered exergonic (gives off energy) and produces more energy than they consume

Anabolism – combining small organic compounds into larger ones; reactions are endergonic (requires energy) and consume more energy than they produce

Chemical reactions of living systems depend on efficiently transforming energy from one molecule to another. ATP (adenosine triphosphate) accomplishes this task.

ATP ADP + P + ENERGY

Composed of three pathways: Glycolysis, Krebs cycle, and Electron transport chain

ii. Glucose actively transported in GI tract then insulin-mediated facilitated diffusion in body cells

iii. Glycolysis Occurs in the cytosolOne six carbon glucose is split into two three

carbon pyruvate 2 ATPs are used but 4 are created2 nicotinamide adenine dinucleotide (NAD)

are hydrogenated

Krebs Cycle Pyruvate from glycolysis is converted into

Acetyl CoA in cytosol (NAD is hydrogenated and carbon dioxide is released)

Acetyl CoA is shuttled into the mitochondriaSeries of reactions takes placeOne ATP is created (per Acetyl CoA)2 carbon dioxides are released3 NADs are hydrogenatedOne flavin adenine dinucleotide (FAD) is

hydrogenated

Electron Transport Chain Occurs in the inner mitochondrial membraneElectrons and hydrogens are released from

NADs and FADsOxygen is the final electron acceptor -- if no

oxygen present lactic acid produced from pyruvate and krebs does not occur -- referred to as anaerobic carbohydrate metabolism

Hydrogen ions form a concentration gradient

A total of 36 ATP are produced from the complete breakdown of a glucose molecule.

Water and carbon dioxide are released as by products.

Chemical Equation for the entire reaction: C6H12O6 + 6O2 6H20 + 6CO2 + 36 ATP +

heat

Lipogenesis= triglyceride synthesis

Lipolysis=“fat splitting”

Metabolic rate=the body’s rate of energy output

Basal metabolic rate=the minimum energy expended in a fasting state (12 hours) to keep a resting, awake body alive in a warm, quiet environment.