Nutrition, Metabolism, and Body Temperature Regulation Nutrition, Metabolism, and Body Temperature Regulation Objectives: For each major nutrient (carbohydrates,

Nutrition, Metabolism, Nutrition, Metabolism, and Body Temperature and Body Temperature

RegulationRegulation

Objectives:For each major nutrient (carbohydrates, lipids and proteins) as well as

vitamins and minerals, provide a description of 1.basic structure (monomers), function in body and RDA

2.Description of mechanisms of digestion and unique requirements for absorption

3.Role of the nutrient, vitamin or mineral in production of ATP4.Diseases or syndromes associated with excess or deficits of a specific

nutrient, vitamin or mineral

NutritionNutrition

Nutrient: a substance in food that promotes normal growth, maintenance, and repair

Major nutrients◦Carbohydrates, lipids, and proteins

Other nutrients ◦Vitamins and minerals (and, technically

speaking, water)

Figure 23.1a

(a) USDA food guide pyramid

Grains

Vegetables

Fruits

Meat andbeans

Oils

Milk

Figure 23.1b

Red meat, butter:use sparingly

Vegetables inabundance

Whole-grainfoods atmost meals

Daily excercise and weight control

(b) Healthy eating pyramid

Dairy or calcium supplement: 1–2 servings

White rice, white bread,potatoes, pasta, sweets:

use sparingly

Fish, poultry, eggs:0–2 servings

Nuts, legumes:1–3 servings

Fruits:2–3 servings

Plant oilsat most

meals

Figure 23.5

Via oxidativephosphorylationVia substrate-level

phosphorylation

MitochondrionMitochondrialcristaeCytosol

KrebscycleGlucose

Glycolysis

Pyruvicacid

Electron transportchain and oxidativephosphorylation

Chemical energy (high-energy electrons)

1 During glycolysis, each glucose molecule is broken down into two molecules of pyruvic acid in the cytosol.

2 The pyruvic acid then enters the mitochondrial matrix, where the Krebs cycle decomposes it to CO2. During glycolysis and the Krebs cycle, small amounts of ATP are formed by substrate-level phosphorylation.

3 Energy-rich electrons picked up bycoenzymes are transferred to the elec-tron transport chain, built into the cristae membrane. The electron transport chain carries out oxidative phosphorylation, which accounts for most of the ATP generated by cellular respiration.

Chemical energy

Figure 23.6 (3 of 3)

To Krebscycle

(aerobicpathway)

2

2

4 ADP

2 Lactic acid

2 Pyruvic acid

Dihydroxyacetonephosphate

Glyceraldehyde3-phosphate

Phase 3Sugar oxidationand formationof ATPThe 3-carbon frag-ments are oxidized (by removal of hydrogen) and 4 ATP molecules are formed

Carbon atomPhosphate

2 NAD+

2 NAD+

NADH+H+

NADH+H+

Glycolysis Electron trans-port chain and oxidativephosphorylation

Krebscycle

Figure 23.7

Krebs cycle

NAD+

NAD+

GDP +

NAD+

FAD

NAD+

NADH+H+

Cytosol

Mitochondrion(matrix)

NADH+H+

FADH2

NADH+H+

Citric acid

(initial reactant)

Isocitric acid

Oxaloacetic acid

(pickup molecule)

Malic acid

Succinic acidSuccinyl-CoA

GTP

ADP

Carbon atom

Inorganic phosphate

Coenzyme A

Acetyl CoA

Pyruvic acid from glycolysis

Transitionalphase

Fumaric acid

NADH+H+

CO2

CO2

CO2

-Ketoglutaric acid

Electron trans-port chain and oxidativephosphorylation

Glycolysis Krebscycle

Figure 23.8

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

NADH + H+

NAD+

FAD

(carryingfrom food)

FADH2

Krebscycle

GlycolysisElectron transportchain and oxidativephosphorylation

Electron Transport Chain Chemiosmosis

ADP +

2 H+ +

Electrons are transferred from complex to complex and some of their energy is used to pump protons (H+) into the intermembrane space, creating a proton gradient.

ATP synthesis is powered by the flow of H+ back across the inner mitochondrial membrane through ATP synthase.

ATPsynthase

12

Figure 23.9

Glycolysis Krebscycle

Electron trans-port chain and oxidativephosphorylation

EnzymeComplex I

EnzymeComplex III

EnzymeComplex IV

EnzymeComplex II

NADH+H+

FADH2

Fre

e e

nerg

y r

ela

tive t

o O

2 (

kcal/

mol)

Figure 23.11

Mitochondrial matrix

Intermembrane space

ADP+

A stator anchored in the membrane holds the knob stationary.

As the rotor spins, a rod connecting the cylindrical rotor and knob also spins.

The protruding, stationary knob contains three catalytic sites that join inorganic phosphate to ADP to make ATP when the rod is spinning.

A rotor in the membrane spins clockwise when H+

flows through it down the H+ gradient.

CarbohydratesCarbohydrates

Dietary sources◦Starch (complex carbohydrates) in grains and

vegetables◦Sugars (simple carbohydrates) in fruits,

sugarcane, sugar beets, honey and milk◦Monosaccharides: ◦Insoluble fiber: cellulose in vegetables;

provides roughage◦Soluble fiber: pectin in apples and citrus fruits;

reduces blood cholesterol levels

CarbohydratesCarbohydrates

Complex Carbohydrates◦Polysaccharides◦Starch◦Cellulose◦glycogen

Simple Carbohydrates◦Sucrose / Lactose/ Maltose◦Disaccharides

Simple Sugars◦Glucose/ Galactose/ Fructose◦Monosaccharides

CarbohydratesCarbohydrates

Uses◦Glucose is the fuel used by cells to make ATP

Neurons and RBCs rely almost entirely upon glucose

Excess glucose is converted to glycogen or fat and stored

CarbohydratesCarbohydrates

Dietary requirements◦Minimum 100 g/day to maintain adequate

blood glucose levels◦Recommended minimum 130 g/day ◦Recommended intake: 45–65% of total calorie

intake; mostly complex carbohydrates◦Fiber 25-30 g/day

CarbohydratesCarbohydrates

Digestion◦Amylase in mouth◦Pancreatic amylase in duodenum◦Maltase, lactase in brush border of intestinal

villi cellsAbsorption

◦Glucose and galactose: cotransportation with sodium ions

◦Fructose: facilitated diffusion◦All monosaccharides enter capillaries through

facilitated diffusion and head to liver through hepatic portal vein.

CarbohydratesCarbohydrates

Metabolism◦Glucose provides 32 ATP in oxidative respiration

◦Glycogenesis: production of glycogen when ATP levels are high

◦Glycogenolysis: When blood glucose levels drop, glycogen is split. Liver glycogen produces glucose for other organs and skeletal muscle

◦Carbohydrate loading is used to increase glycogen before a major race or event

◦Gluconeogenesis: When too little glucose is available, glycerol and amino acids are converted to glucose/ this is “new” glucose from noncarbohydrate sources

Carbohydrate Carbohydrate and Sugar and Sugar structuresstructures

Figure 23.13

Cell exterior

Hexokinase(all tissue cells)

Cell interior

Mutase

GlycogenesisGlycogenolysis

Mutase

ADP

Glucose-6-phosphatase(present in liver,kidney, andintestinal cells)

Glycogensynthase

Glycogenphosphorylase

Pyrophosphorylase

2

Blood glucose

Glucose-6-phosphate

Glucose-1-phosphate

Glycogen

Uridine diphosphateglucose

When glucose supplies exceed demands, glycogenesis occurs and glucose is converted to glycogen

Falling blood glucose levels stimulate glycogenolysis or the breakdown of glycogen in order to release glucose

Which of these processes would be used in carb loading?

LipidsLipids

Dietary sources◦Triglycerides: primary form of “fat” carried in the blood

from the food we eat and stored as “fat” Saturated fats (meat, dairy foods, and tropical oils) Unsaturated fats (seeds, nuts, olive oil, and most

vegetable oils)◦Cholesterol (egg yolk, meats, organ meats, shellfish,

and milk products)/ not an energy sourceEssential fatty acids

◦Linoleic and linolenic acid, found in most vegetable oils

◦Must be ingested as liver cannot synthesize

Lipids: Triglyceride structureLipids: Triglyceride structure

LipidsLipids

Essential uses of lipids in the body◦Help absorb fat-soluble vitamins◦Major fuel of hepatocytes and skeletal muscle◦Phospholipids are essential in myelin sheaths

and all cell membranes

The structure shown here is a phospholipid

Synthesis of Structural MaterialsSynthesis of Structural Materials

Phospholipids for cell membranes and myelin

Cholesterol for cell membranes and steroid hormone synthesis

In the liver ◦Synthesis of transport lipoproteins for

cholesterol and fats◦Synthesis of cholesterol from acetyl CoA◦Use of cholesterol to form bile salts

Lipoproteins enable lipids to be Lipoproteins enable lipids to be carried in bloodstreamcarried in bloodstream

High Density Lipoproteins

Low Density Lipoproteins

Collect cholesterol from body tissues and carries it back to liver

Carry cholesterol from liver to cells of body

One is considered good and the other bad…both are needed, it’s the ratio of one to the other that is important. Look up correct blood levels of each.

LipidsLipids

Functions of fatty deposits (adipose tissue)◦Protective cushions around body organs◦Insulating layer beneath the skin◦Concentrated source of energy

LipidsLipids

Regulatory functions of regulatory molecules; prostaglandins◦Prostaglandins formed from linoleic acid◦Primarily act as paracrines

Smooth muscle contraction Control of blood pressure Inflammation

Functions of cholesterol◦Stabilizes membranes◦Precursor of bile salts

and steroid hormones

LipidsLipids

Dietary requirements suggested by the American Heart Association◦Fats should represent 30% or less of total

caloric intake◦Saturated fats should be limited to 10% or less

of total fat intake◦Daily cholesterol intake should be no more than

300 mg

LipidsLipids

Digestion◦Requires bileemulsion

◦Pancreatic lipases primarily in duodenum and jejunum

Absorption◦Assisted by bile to

become micelles; little “clumps” of fatty elements in intestinal lumen

◦Enter intestinal cells through diffusion

◦Chylomicrons are extruded into lacteals via exocytosis

LipidsLipids

Lipid Metabolism◦Fats are the body’s most concentrated source

of energy◦Yield 9 kcal per gram of fat◦Most fat is transported in lymph as

chylomicrons Hydrolyzed by enzymes in capillary endothelium Fatty acids and glycerol are taken up by cells

primarily through simple diffusion

Lipid MetabolismLipid Metabolism

Glycerol is converted to glyceraldehyde phosphate◦Enters the Krebs cycle◦Equivalent to 1/2 glucose

Lipogenesis Lipogenesis

Triglyceride synthesis occurs when cellular ATP and glucose levels are high

Glucose is easily converted into fat because acetyl CoA is ◦An intermediate in glucose catabolism ◦A starting point for fatty acid synthesis

LipolysisLipolysis

The reverse of lipogenesis: triglycerides are broken down or oxidized

Oxaloacetic acid is necessary for complete oxidation of fat◦Without it, acetyl CoA is converted by

ketogenesis in the liver into ketone bodies (ketones)

Figure 23.14

Krebscycle

Glycerol Fatty acids

Coenzyme A

Lipase

Oxidationin the mito-chondria

Cleavageenzymesnips off2C fragments

Glycolysis

Glyceraldehydephosphate

(a glycolysis intermediate)

Pyruvic acid

Lipids

Acetyl CoA

FAD

H2O

NAD+

NADH + H+

FADH2

Lipids (summary of metabolism)Lipids (summary of metabolism)

Lipogenesis: storage of excess glycerol and fatty acids as triglycerides in subcutaneous tissue◦Additional triglycerides can also be made from

acetyl CoA (an intermediate in glucose metabolism…feeds into the Krebs cycle). For this reason, glucose is easily converted to fat

Lipolysis: releasing fatty acids and glycerol into blood. ◦Can be used as fuel, feeding into Krebs cycle

LipidsLipids

Ketogenesis: if not enough carbohydrates for all components of Krebs, then acetyl CoA builds up◦Liver converts acetylCoA molecules to ketone

bodies or ketones, which are released into the blood

◦These ketones can be used for gluconeogenesis or put into Krebs cycle in cells

◦Excess ketones are broken down and excreted in urine

◦However, if excess builds up in blood (ketosis), causes drop in blood pH, (ketoacidosis)

LipidsLipids

Most ketone bodies can be metabolized in Krebs cycle… however excess ketones in blood indicates metabolic disease

Figure 23.15

ElectrontransportCholesterol

Stored fatsin adipose

tissue

Dietary fats

Glycerol

GlycolysisGlucose

Glyceraldehydephosphate

Pyruvic acid

Acetyl CoA

CO2 + H2O+

Steroids

Bile salts

Fatty acids

Ketonebodies

Triglycerides(neutral fats)

Certainaminoacids

Ketogenesis (in liver)

Catabolic reactions

Anabolic reactions

Lipogenesis

Krebscycle

ProteinsProteins

Dietary sources◦Eggs, milk, fish, and most meats contain complete proteins

◦Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids)

◦Legumes and grains (cereals) together contain all essential amino acids

Figure 23.2

Corn andother grains

Beansand otherlegumes

Tryptophan

Methionine

Valine

Threonine

Phenylalanine

Leucine

Isoleucine

Lysine

Vegetarian diets providing the eightessential amino acids for humans

(b)Essential amino acids(a)

Valine

Threonine

Phenylalanine(Tyrosine)

Leucine

Isoleucine

Lysine

Methionine(Cysteine)

Tryptophan

Histidine(Infants)Arginine(Infants)

Totalproteinneeds

ProteinsProteins

Uses◦Structural materials: keratin, collagen, elastin,

muscle proteins◦Most functional molecules: enzymes, some

hormones

ProteinsProteins

Use of amino acids in the body1. All-or-none rule

All amino acids needed must be present for protein synthesis to occur

2. Adequacy of caloric intake Protein will be used as fuel if there is

insufficient carbohydrate or fat available

ProteinsProteins

3. Nitrogen balance State where the rate of protein synthesis

equals the rate of breakdown and loss Positive if synthesis exceeds breakdown

(normal in children and tissue repair) Negative if breakdown exceeds synthesis (e.g.,

stress, burns, infection, or injury)4. Hormonal controls

Anabolic hormones (GH, sex hormones) accelerate protein synthesis

ProteinsProteins

Dietary requirements◦Rule of thumb: daily intake of 0.8 g per kg body

weight◦Amount of protein varies greatly◦Certain stages of life requiring more protein

Protein diet with exerciseused to lose weightprotein reduces hungerincreases fat lossimproves blood nutrient levelsmajor risk is related to kidney function

ProteinProteinStructureStructure

Amino Acid structureAmino Acid structure

ProteinsProteins

Digestion◦Pepsin in stomach◦Pancreatic enzymes:

trypsin, chymotrypsin, carboxypeptidase in duodenum and jejunum

◦Brush border enzymes; aminopeptidase, carboxypeptidase

Absorption◦Amino acids absorbed

by cotransport with sodium ions

◦Amino acids leave the epithelial cells by facilitated diffusion and transported to liver through hepatic portal vein

ProteinsProteins

Metabolism◦Your body replaces tissue proteins from ingested

amino acids at a rate of 100g/day (anabolic; protein synthesis)

◦If you have excess protein in diet, amino acids are oxidized for energy or converted to fat for future needs Before amino acids can be used for energy they

must be deaminated (amino acid removed) Then they can be oxidized in Krebs cycle or

converted to glucose End products: keto acid (former amino acid) and

urea made from amine/ ammonia

VitaminsVitamins

Organic compounds Crucial in helping the body use nutrients Most function as coenzymesVitamins D, some B, and K are

synthesized in the body

VitaminsVitamins

Two types, based on solubility1. Water-soluble vitamins

B complex and C are absorbed with water B12 absorption requires intrinsic factor Not stored in the body

2. Fat-soluble vitamins A, D, E, and K are absorbed with lipid digestion

products Stored in the body, except for vitamin K Vitamins A, C, and E act as antioxidants

MineralsMinerals

Seven required in moderate amounts:◦Calcium, phosphorus, potassium, sulfur,

sodium, chloride, and magnesiumOthers required in trace amountsWork with nutrients to ensure proper body

functioningUptake and excretion must be balanced to

prevent toxic overload

MineralsMinerals

Examples◦Calcium, phosphorus, and magnesium salts

harden bone◦Iron is essential for oxygen binding to

hemoglobin◦Iodine is necessary for thyroid hormone

synthesis◦Sodium and chloride are major electrolytes in

the blood

MetabolismMetabolism

Metabolism: biochemical reactions inside cells involving nutrients

Two types of reactions◦Anabolism: synthesis of large molecules from

small ones◦Catabolism: hydrolysis of complex structures to

simpler ones

MetabolismMetabolism

Cellular respiration: catabolism of food fuels and capture of energy to form ATP in cells

Enzymes shift high-energy phosphate groups of ATP to other molecules (phosphorylation)

Phosphorylated molecules are activated to perform cellular functions

Figure 23.3

Stage 1 Digestion in GI tract lumen to absorbable forms.Transport via blood totissue cells.

Stage 2 Anabolism (incorporation into molecules) and catabolism of nutrients to form intermediates within tissue cells.

Stage 3 Oxidative breakdown of products of stage 2 in mitochondria of tissue cells. CO2 is liberated, and H atoms removed are ultimately delivered to molecular oxygen, formingwater. Some energy released isused to form ATP.

Catabolic reactionsAnabolic reactions

Glycogen

PROTEINS

Proteins Fats

CARBOHYDRATES

Glucose

FATS

Amino acids Glucose and other sugars Glycerol Fatty acids

Pyruvic acid

Acetyl CoA

Infrequent CO2

NH3

H

Krebscycle

Oxidativephosphorylation

(in electron transport chain)

O2

H2O

Stages of MetabolismStages of Metabolism

Processing of nutrients1. Digestion, absorption and transport to tissues2. Cellular processing (in cytoplasm)

Synthesis of lipids, proteins, and glycogen, or Catabolism (glycolysis) into intermediates

3. Oxidative (mitochondrial) breakdown of intermediates into CO2, water, and ATP

Oxidation-Reduction (Redox) Oxidation-Reduction (Redox) ReactionsReactions

Oxidation; gain of oxygen or loss of hydrogen

Oxidation-reduction (redox) reactions◦Oxidized substances lose electrons and energy◦Reduced substances gain electrons and energy

Oxidation-Reduction (Redox) Oxidation-Reduction (Redox) ReactionsReactions

Coenzymes act as hydrogen (or electron) acceptors◦Nicotinamide adenine dinucleotide (NAD+) ◦Flavin adenine dinucleotide (FAD)

ATP Synthesis ATP Synthesis

Two mechanisms1. Substrate-level phosphorylation2. Oxidative phosphorylation

Substrate-Level PhosphorylationSubstrate-Level Phosphorylation

High-energy phosphate groups directly transferred from phosphorylated substrates to ADP

Occurs in glycolysis and the Krebs cycle

Figure 23.4a

Enzyme

Catalysis

Enzyme

(a) Substrate-level phosphorylation

Oxidative PhosphorylationOxidative Phosphorylation

Chemiosmotic process◦Couples the movement of substances across a

membrane to chemical reactions

Oxidative PhosphorylationOxidative Phosphorylation

In the mitochondria◦Carried out by electron transport proteins ◦Nutrient energy is used to create H+ gradient

across mitochondrial membrane ◦H+ flows through ATP synthase◦Energy is captured and attaches phosphate

groups to ADP

Figure 23.4b

ADP +

Membrane

High H+ concentration inintermembrane space

Low H+ concentration in mitochondrial matrix

Energyfrom food

Protonpumps

(electrontransport

chain)

ATPsynthase

(b) Oxidative phosphorylation

Carbohydrate MetabolismCarbohydrate Metabolism

Oxidation of glucose C6H12O6 + 6O2 6H2O + 6CO2 + 36 ATP +

heatGlucose is catabolized in three pathways

◦Glycolysis◦Krebs cycle◦Electron transport chain and oxidative

phosphorylation

GlycolysisGlycolysis

10-step pathway Anaerobic Occurs in the cytosol Glucose 2 pyruvic acid molecules Three major phases

1. Sugar activation :Glucose is phosphorylated by 2 ATP to form fructose-1,6-bisphosphate

2. Sugar cleavage:Fructose-1,6-bisphosphate is split into 3-carbon sugars

3. Sugar oxidation and ATP formation:3-carbon sugars are oxidized (reducing NAD+) 4 ATP are formed by substrate-level phosphorylation

Figure 23.6 (1 of 3)

Glucose

Phase 1SugarActivationGlucose is activated by phosphorylationand converted to fructose-1, 6-bisphosphate

Fructose-1,6-bisphosphate

2 ADP

Carbon atom

Phosphate

GlycolysisElectron trans-port chain and oxidativephosphorylation

Krebscycle

Figure 23.6 (2 of 3)

Fructose-1,6-bisphosphate

Dihydroxyacetonephosphate

Glyceraldehyde3-phosphate

Phase 2SugarCleavageFructose-1, 6-bisphosphate is cleaved into two 3-carbon fragments

Carbon atom

Phosphate

Glycolysis Electron trans-port chain and oxidativephosphorylation

Krebscycle

GlycolysisGlycolysis

Final products of glycolysis ◦2 pyruvic acid

Converted to lactic acid if O2 not readily available Enter aerobic pathways if O2 is readily available

◦2 NADH + H+ (reduced NAD+)◦Net gain of 2 ATP

Krebs CycleKrebs Cycle

Occurs in mitochondrial matrixFueled by pyruvic acid and fatty acids

Krebs CycleKrebs Cycle

Transitional phase◦ Each pyruvic acid is converted to acetyl CoA

1. Decarboxylation: removal of 1 C to produce acetic acid and CO2

2. Oxidation: H+ is removed from acetic acid and picked up by NAD+

3. Acetic acid + coenzyme A forms acetyl CoA

Krebs CycleKrebs Cycle

Coenzyme A shuttles acetic acid to an enzyme of the Krebs cycle

Each acetic acid is decarboxylated and oxidized, generating: ◦3 NADH + H+

◦1 FADH2

◦2 CO2

◦1 ATP

Krebs Cycle Krebs Cycle

Does not directly use O2

Breakdown products of fats and proteins can also enter the cycle

Cycle intermediates may be used as building materials for anabolic reactions

Electron Transport Chain and Electron Transport Chain and Oxidative PhosphorylationOxidative Phosphorylation

The part of metabolism that directly uses oxygen

Chain of proteins bound to metal atoms (cofactors) on inner mitochondrial membrane

Substrates NADH + H+ and FADH2 deliver hydrogen atoms

Electron Transport Chain and Electron Transport Chain and Oxidative PhosphorylationOxidative Phosphorylation

Hydrogen atoms are split into H+ and electrons

Electrons are shuttled along the inner mitochondrial membrane, losing energy at each step

Released energy is used to pump H+ into the intermembrane space

Electron Transport Chain and Electron Transport Chain and Oxidative PhosphorylationOxidative Phosphorylation

Respiratory enzyme complexes I, III, and IV pump H+ into the intermembrane space

H+ diffuses back to the matrix via ATP synthase

ATP synthase uses released energy to make ATP

Electron Transport Chain and Electron Transport Chain and Oxidative PhosphorylationOxidative Phosphorylation

Electrons are delivered to O, forming O–

O– attracts H+ to form H2O

Electronic Energy GradientElectronic Energy Gradient

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

ATP SynthaseATP Synthase

Two major parts connected by a rod 1. Rotor in the inner mitochondrial membrane2. Knob in the matrix

Works like an ion pump in reverse

Figure 23.12

MitochondrionCytosol

2AcetylCoA

Electron transportchain and oxidativephosphorylationGlucose

Glycolysis

Pyruvicacid

Net +2 ATPby substrate-levelphosphorylation

+ about 28 ATPby oxidativephosphorylation

+2 ATPby substrate-levelphosphorylation

Electronshuttle across mitochondrialmembrane

Krebscycle

(4 ATP–2 ATPused foractivationenergy)

2 NADH + H+

2 NADH + H+ 6 NADH + H+ 2 FADH2

About32 ATP

MaximumATP yieldper glucose

10 NADH + H+ x 2.5 ATP

2 FADH2 x 1.5 ATP