1. 24
Nutrition, Metabolism, and Body Temperature
Regulation
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)
USDA Food Guide Pyramid
Nutrition
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
Carbohydrates
* 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

2. * 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
Lipids
* Prostaglandins function in:

3. * 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
* 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

4. * 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
Essential Amino Acids
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

5. * 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

6. * 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
Oxidation-Reduction (Redox) Reactions
* 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

7. * ATP is synthesized via substrate-level phosphorylation in glycolysis
and the Krebs cycle
Mechanisms of ATP Synthesis:
Oxidative Phosphorylation
* Uses the chemiosmotic process whereby the movement of substances
across a membrane is coupled to chemical reactions
Mechanisms of ATP Synthesis:
Oxidative Phosphorylation
* 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
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 + 36 ATP + heat
* Glucose is catabolized in three pathways
* Glycolysis
* Krebs cycle

8. * The electron transport chain and oxidative phosphorylation
Carbohydrate Catabolism
Glycolysis
* A three-phase pathway in which:
* 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
Glycolysis
Glycolysis
Glycolysis
Glycolysis
Glycolysis
Glycolysis
Glycolysis
Glycolysis: Phase 1 and 2
* Phase 1: Sugar activation
* Two ATP molecules activate glucose into
fructose-1,6-diphosphate
* Phase 2: Sugar cleavage

9. * Fructose-1,6-bisphosphate is cleaved into two
3-carbon isomers
* Bishydroxyacetone phosphate
* Glyceraldehyde 3-phosphate
Glycolysis: Phase 3
* 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
Glycolysis: Phase 3
* The final products are:
* Two pyruvic acid molecules
* Two NADH + H+ molecules (reduced NAD+)
* A net gain of two ATP molecules
Krebs Cycle: Preparatory Step
* Occurs in the mitochondrial matrix and is fueled by pyruvic acid and
fatty acids
Krebs Cycle: Preparatory Step
* Pyruvic acid is converted to acetyl CoA in three main steps:
* Decarboxylation
* Carbon is removed from pyruvic acid
* Carbon dioxide is released
Krebs Cycle: Preparatory Step

10. * Oxidation
* Hydrogen atoms are removed from pyruvic acid
* NAD+ is reduced to NADH + H+
* Formation of acetyl CoA – the resulting acetic acid is combined with
coenzyme A, a sulfur-containing coenzyme, to form acetyl CoA
Krebs Cycle
* An eight-step cycle in which each acetic acid is decarboxylated and
oxidized, generating:
* Three molecules of NADH + H+
* One molecule of FADH2
* Two molecules of CO2
* One molecule of ATP
* For each molecule of glucose entering glycolysis, two molecules of
acetyl CoA enter the Krebs cycle

11. Electron Transport Chain
* Food (glucose) is oxidized and the released hydrogens:
* Are transported by coenzymes NADH and FADH2
* Enter a chain of proteins bound to metal atoms (cofactors)
* Combine with molecular oxygen to form water
* Release energy
* The energy released is harnessed to attach inorganic phosphate groups
(Pi) to ADP, making ATP by oxidative phosphorylation
Mechanism of Oxidative Phosphorylation
* The hydrogens delivered to the chain are split into protons (H+) and
electrons
* The protons are pumped across the inner mitochondrial membrane by:
* NADH dehydrogenase (FMN, Fe-S)
* Cytochrome b-c1
* Cytochrome oxidase (a-a3)
* The electrons are shuttled from one acceptor to the next
Mechanism of Oxidative Phosphorylation
* Electrons are delivered to oxygen, forming oxygen ions
* Oxygen ions attract H+ to form water
* H+ pumped to the intermembrane space:
* Diffuses back to the matrix via ATP synthase
* Releases energy to make ATP

12. Electronic Energy Gradient
* The transfer of energy from NADH + H+ and FADH2 to oxygen
releases large amounts of energy
* This energy is released in a stepwise manner through the electron
transport chain
Electronic Energy Gradient
* The electrochemical proton gradient across the inner membrane:
* Creates a pH gradient
* Generates a voltage gradient
* These gradients cause H+ to flow back into the matrix via ATP
synthase
ATP Synthase
* The enzyme consists of three parts: a rotor, a knob, and a rod
* Current created by H+ causes the rotor and rod to rotate
* This rotation activates catalytic sites in the knob where ADP and Pi
are combined to make ATP
Structure of ATP Synthase

13. Summary of ATP Production
Glycogenesis and Glycogenolysis
* Glycogenesis – formation of glycogen when glucose supplies exceed
cellular need for ATP synthesis
* Glycogenolysis – breakdown of glycogen in response to low blood
glucose
Gluconeogenesis
* The process of forming sugar from noncarbohydrate molecules
* Takes place mainly in the liver
* Protects the body, especially the brain, from the damaging effects of
hypoglycemia by ensuring ATP synthesis can continue
Lipid Metabolism
*Most products of fat metabolism are transported in lymph as
chylomicrons
* Lipids in chylomicrons are hydrolyzed by plasma enzymes and
absorbed by cells
* Only neutral fats are routinely oxidized for energy
Lipid Metabolism
* Catabolism of fats involves two separate pathways
* Glycerol pathway
* Fatty acids pathway
Lipid Metabolism
* Glycerol is converted to glyceraldehyde phosphate
* Glyceraldehyde is ultimately converted into acetyl CoA

14. * Acetyl CoA enters the Krebs cycle
Lipid Metabolism
* Fatty acids undergo beta oxidation which produces:
* Two-carbon acetic acid fragments, which enter the Krebs cycle
* Reduced coenzymes, which enter the electron transport chain
Lipid Metabolism
Lipogenesis and Lipolysis
* Excess dietary glycerol and fatty acids undergo lipogenesis to form
triglycerides
* Glucose is easily converted into fat since acetyl CoA is:
* An intermediate in glucose catabolism
* The starting molecule for the synthesis of fatty acids
Lipogenesis and Lipolysis
* Lipolysis, the breakdown of stored fat, is essentially lipogenesis in
reverse
* Oxaloacetic acid is necessary for the complete oxidation of fat
* Without it, acetyl CoA is converted into ketones (ketogenesis)
Lipogenesis and Lipolysis
Lipid Metabolism:
Synthesis of Structural Materials
* Phospholipids are important components of myelin and cell
membranes
Lipid Metabolism:
Synthesis of Structural Materials

15. * The liver:
* Synthesizes lipoproteins for transport of cholesterol and fats
* Makes tissue factor, a clotting factor
* Synthesizes cholesterol for acetyl CoA
* Uses cholesterol to form bile salts
* Certain endocrine organs use cholesterol to synthesize steroid
hormones
Protein Metabolism
* Excess dietary protein results in amino acids being:
* Oxidized for energy
* Converted into fat for storage
* Amino acids must be deaminated prior to oxidation for energy
Protein Metabolism
* Deaminated amino acids are converted into:
* Pyruvic acid
* One of the keto acid intermediates of the Krebs cycle
* These events occur as transamination, oxidative deamination, and
keto acid modification
Amino Acid Oxidation