Nutrition, Metabolism, and Body Temperature Regulation Chapter 25 Nutrition, Metabolism, and Body Temperature Regulation Part A

Nutrition Nutrient – a substance that promotes normal growth, maintenance, and repair Major nutrients – carbohydrates, lipids, and proteins Other nutrients – vitamins and minerals (and technically speaking, water) Grains, fruits, vegetables, meats and fish, and milk products

Nutrition Figure 25.1

Carbohydrates Complex carbohydrates (starches) are found in bread, cereal, flour, pasta, nuts, and potatoes Simple carbohydrates (sugars) are found in soft drinks, candy, fruit, and ice cream Glucose is the molecule ultimately used by body cells to make ATP Neurons and RBCs rely almost entirely upon glucose to supply their energy needs Excess glucose is converted to glycogen or fat and stored

Carbohydrates The minimum amount of carbohydrates needed to maintain adequate blood glucose levels is 100 grams per day Starchy foods and milk have nutrients such as vitamins and minerals in addition to complex carbohydrates Refined carbohydrate foods (candy and soft drinks) provide energy sources only and are referred to as “empty calories”

Lipids The most abundant dietary lipids, triglycerides, are found in both animal and plant foods Essential fatty acids – linoleic and linolenic acid, found in most vegetables, must be ingested Dietary fats: Help the body to absorb vitamins Are a major energy fuel of hepatocytes and skeletal muscle Are a component of myelin sheaths and all cell membranes

Lipids Fatty deposits in adipose tissue provide: A protective cushion around body organs An insulating layer beneath the skin An easy-to-store concentrated source of energy Prostaglandins function in: Smooth muscle contraction Control of blood pressure Inflammation Cholesterol stabilizes membranes and is a precursor of bile salts and steroid hormones

Lipids: Dietary Requirements Higher for infants and children than for adults The American Heart Association suggests that: Fats should represent less than 30% of one’s total caloric intake Saturated fats should be limited to 10% or less of one’s total fat intake Daily cholesterol intake should not exceed 200 mg

Proteins Complete proteins that meet all the body’s amino acid needs are found in eggs, milk, milk products, meat, and fish Incomplete proteins are found in legumes, nuts, seeds, grains, and vegetables Proteins supply: Essential amino acids, the building blocks for nonessential amino acids Nitrogen for nonprotein nitrogen-containing substances Daily intake should be approximately 0.8g/kg of body weight

Proteins: Synthesis and Hydrolysis All-or-none rule All amino acids needed must be present at the same time for protein synthesis to occur Adequacy of caloric intake Protein will be used as fuel if there is insufficient carbohydrate or fat available

Proteins: Synthesis and Hydrolysis Nitrogen balance The rate of protein synthesis equals the rate of breakdown and loss Positive – synthesis exceeds breakdown (normal in children and tissue repair) Negative – breakdown exceeds synthesis (e.g., stress, burns, infection, or injury) Hormonal control Anabolic hormones accelerate protein synthesis

Vitamins Organic compounds needed for growth and good health They are crucial in helping the body use nutrients and often function as coenzymes Only vitamins D, K, and B are synthesized in the body; all others must be ingested Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract B12 additionally requires gastric intrinsic factor to be absorbed

Vitamins Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed with their digestion products Vitamins A, C, and E also act in an antioxidant cascade

Minerals Seven minerals are required in moderate amounts Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium Dozens are required in trace amounts Minerals work with nutrients to ensure proper body functioning Calcium, phosphorus, and magnesium salts harden bone

Minerals Sodium and chloride help maintain normal osmolarity, water balance, and are essential in nerve and muscle function Uptake and excretion must be balanced to prevent toxic overload

Metabolism Metabolism – all chemical reactions necessary to maintain life Cellular respiration – food fuels are broken down within cells and some of the energy is captured to produce ATP Anabolic reactions – synthesis of larger molecules from smaller ones Catabolic reactions – hydrolysis of complex structures into simpler ones

Metabolism Enzymes shift the high-energy phosphate groups of ATP to other molecules These phosphorylated molecules are activated to perform cellular functions

Stages of Metabolism Energy-containing nutrients are processed in three major stages Digestion – breakdown of food; nutrients are transported to tissues Anabolism and formation of catabolic intermediates where nutrients are: Built into lipids, proteins, and glycogen Broken down by catabolic pathways to pyruvic acid and acetyl CoA Oxidative breakdown – nutrients are catabolized to carbon dioxide, water, and ATP

Stages of Metabolism Figure 25.3

Oxidation-Reduction Reaction Oxidation occurs via the gain of oxygen or the loss of hydrogen Whenever one substance is oxidized, another substance is reduced Oxidized substances lose energy Reduced substances gain energy Coenzymes act as hydrogen (or electron) acceptors Two important coenzymes are nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD)

Mechanisms of ATP Synthesis: Substrate-Level Phosphorylation High-energy phosphate groups are transferred directly from phosphorylated substrates to ADP ATP is synthesized via substrate level phosphorylation in glycolysis and the Krebs cycle Figure 25.4a

Mechanisms of ATP Synthesis: Oxidative Phosphorylation Uses the chemiosmotic process whereby the movement of substances across a membrane is coupled to chemical reactions Is carried out by the electron transport proteins in the cristae of the mitochondria Nutrient energy is used to pump hydrogen ions into the intermembrane space A steep diffusion gradient across the membrane results When hydrogen ions flow back across the membrane through ATP synthase, energy is captured and attaches phosphate groups to ADP (to make ATP)

Mechanisms of ATP Synthesis: Oxidative Phosphorylation Figure 25.4b

Carbohydrate Metabolism Since all carbohydrates are transformed into glucose, it is essentially glucose metabolism Oxidation of glucose is shown by the overall reaction: C6H12O6 + 6O2  6H2O + 6CO2 + 36ATP + heat Occurs in three pathways Glycolysis Krebs cycle The electron transport chain and oxidative phosphorylation

Carbohydrate Metabolism Figure 25.5

Glycolysis A three-phase pathway in which: Pyruvic acid: Glucose is oxidized into pyruvic acid NAD+ is reduced to NADH + H+ ATP is synthesized by substrate-level phosphorylation Pyruvic acid: Moves on to the Krebs cycle in an aerobic pathway Is reduced to lactic acid in an anaerobic environment

Glycolysis Figure 25.6

Glycolysis: Phase 1 and 2 Sugar activation Sugar cleavage Two ATP molecules activate glucose into fructose-1,6-diphosphate Sugar cleavage Fructose-1,6-diphosphate is cleaved into two 3-carbon isomers Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate

Glycolysis: Phase 3 Oxidation and ATP formation The 3-carbon sugars are oxidized (reducing NAD+) Inorganic phosphate groups (Pi) are attached to each oxidized fragment The terminal phosphates are cleaved and captured by ADP to form four ATP molecules The final products are: Two pyruvic acid molecules Two reduced NAD+ (NADH + H+) molecules A net gain of two ATP molecules