Metabolism, Nutrition, and Energetics

Key Concepts of Metabolism, Nutrition, and Energetics

• Nutrients are described as essential elements and molecules required by the body.
• Metabolic activity involves breaking down organic molecules to obtain energy, which is stored as ATP.
• ATP can also be used to construct new organic molecules.
• Energetics involves how the body balances heat gains and losses.

Requirements for Cellular Reactions

• Cells require oxygen to carry out reactions.
• Water is a needed nutrient.
• Vitamins are necessary for cell processes.
• Mineral ions are crucial for cellular function.
• Cells need organic substrates to carry out reactions.

Metabolism Overview

• Metabolism sums chemical and physical changes in body tissues.
• It consists of catabolism and anabolism.
• Catabolism is the breakdown of large molecules into smaller ones (catabolic reactions).
• Anabolism involves the synthesis of larger molecules from smaller ones (anabolic reactions).
• The nutrient pool contains available nutrient molecules distributed in the blood.

Catabolism

• Catabolism converts large molecules into smaller ones.
• Organic substrate breakdown releases energy, which synthesizes ATP.

Anabolism

• Anabolism converts small molecules into larger ones.
• Anabolism synthesizes organic compounds, is an "uphill" process, and forms chemical bonds.

Anabolism Functions

• Anabolism performs structural maintenance or repairs.
• Anabolism supports growth.
• Anabolism produces secretions.
• Anabolism stores nutrient reserves.

Nutrient Reserves

• Triglycerides are the most abundant storage lipids, primarily consisting of fatty acids.
• Glycogen is abundant in storage carbohydrates, found as a branched chain of glucose molecules.
• Proteins are the body's most abundant organic components and perform vital cellular functions.

Energetics Explained

• Energetics studies the flow of energy and its change from one form to another.
• Oxidation and reduction reactions are always paired.
• Oxidation involves loss of hydrogen or electrons, where the electron donor is oxidized.
• Reduction involves gain of hydrogen or electrons, where the electron recipient is reduced.

Oxidation and Reduction Reactions

• Electrons carry chemical energy.
• In a redox reaction, a reduced atom or molecule gains energy.
• In a redox reaction, an oxidized atom or molecule loses energy.
• Some energy is always released as heat in oxidation and reduction reactions.
• The remaining energy can perform physical or chemical work like forming ATP.

Electron Transport Chain (ETC)

• The electron transport chain occurs via a series of protein complexes in mitochondria.
• Electrons pass through a series of oxidation-reduction reactions.
• Electrons are transferred to oxygen, forming water as electrons combine with oxygen atoms and hydrogen ions.

Coenzymes

• Coenzymes play a role in the flow of energy within a cell.
• Coenzymes act as intermediaries by accepting electrons from one molecule and transferring them to another.
• NAD and FAD are examples of coenzymes.
• Coenzymes remove hydrogen atoms from organic molecules.
• A hydrogen atom consists of an electron and a proton.
• Accepting a hydrogen atom reduces the coenzyme.

Coenzyme FAD Details

• Coenzyme FAD accepts 2 hydrogen atoms, gaining 2 electrons.
• Forming FADH2 is the result of FAD accepting hydrogen atoms.

Coenzyme NAD Details

• The oxidized form of coenzyme NAD has a positive charge (NAD+).
• Coenzyme NAD accepts 2 hydrogen atoms, gaining 2 electrons.
• 1 proton is released when NAD accepts hydrogen atoms.
• Forming NADH is the result of the actions of coenzyme NAD.

Carbohydrate Catabolism

• Carbohydrate catabolism generates ATP and other high-energy compounds.
• Cellular respiration includes glucose plus oxygen to produce carbon dioxide plus water.
• Cellular respiration involves glycolysis, citric acid cycle, and the electron transport chain.
• A molecule of glucose yields a net gain of 30–32 ATP molecules.

Glycolysis

• Glycolysis breaks down glucose in the cytosol into smaller molecules used by mitochondria.
• Glycolysis does not require oxygen (anaerobic reaction).
• Glycolysis breaks a 6-carbon glucose molecule into two 3-carbon molecules of pyruvic acid.
• Pyruvic acid's ionized form is called pyruvate.
• Glycolysis begins when an enzyme phosphorylates a glucose molecule, creating glucose-6-phosphate.

Glycolysis Requirements

• Glycolysis requires glucose molecules.
• Cytosolic enzymes are needed for glycolysis.
• ATP and ADP are needed for glycolysis.
• Inorganic phosphate groups are needed for glycolysis.
• NAD (coenzyme) is needed for glycolysis.

Aerobic Metabolism Characteristics

• Aerobic metabolism occurs within mitochondria.
• Aerobic metabolism requires oxygen.
• Energy, when released from breakdown of pyruvate, is used to produce a large amount of ATP.
• Aerobic metabolism involves the citric acid cycle and the electron transport chain.

Mitochondrial Membranes

• The outer mitochondrial membrane has large pores.
• The outer mitochondrial membrane is permeable to pyruvate and other ions/ small organic molecules.
• The inner mitochondrial membrane has a carrier protein that moves pyruvate into the mitochondrial matrix.
• The intermembrane space separates the outer and inner mitochondrial membranes.

Citric Acid Cycle

• H atoms of pyruvate are removed by coenzymes in the citric acid cycle.
• Hydrogen removal is a primary source of energy gain.
• C and O atoms are removed and released as CO2 in decarboxylation.
• Pyruvate interacts with NAD and coenzyme A (CoA) in the mitochondrion.
• The interaction of pyruvate, NAD, and CoA produces 1 CO2, 1 NADH, and 1 acetyl-CoA (acetyl group bound to CoA).

Citric Acid Cycle Details

• Acetyl group transfers from acetyl-CoA to a 4-carbon oxaloacetate molecule.
• Producing 6-carbon citric acid is an action in the Citric Acid Cycle.
• CoA releases to bind another acetyl group.
• One citric acid cycle removes two carbon atoms and regenerating the 4-carbon chain.
• Multiple steps involve more than one reaction or enzyme.
• H2O molecules bind in two steps.

Products of the Citric Acid Cycle

• One citric acid cycle produces one molecule of GTP (guanosine triphosphate).
• GTP production happens through substrate-level phosphorylation.

Citric Acid Cycle Summary

• CH3CO - CoA + 3NAD + FAD + GDP + P; + 2H2O produces CoA + 2CO2 + 3NADH + FADH2 + 2H+ + GTP

Oxidative Phosphorylation Details

• Oxidative phosphorylation generates ATP through the transfer of electrons from NADH and FADH2 to oxygen.
• That transfer can occurr via a sequence of electron carriers within mitochondria.
• Over 90 percent of ATP used by the body is from oxidative phosphorylation.
• Formation of water is the basis of oxidative phosphorylation (2H2 + O2 → 2H2O).

Electron Transport Chain (ETC) Specifics

• Protein complexes in the inner mitochondrial membrane make up the electron transport chain.
• Key reactions of oxidative phosphorylation occur at the ETC.
• Four respiratory protein complexes, coenzyme Q, and electron carriers (cytochrome molecules) are included in the ETC.
• Each cytochrome has two parts: a pigment (contains a metal ion) and a protein (surrounds the pigment).

Oxidative Phosphorylation

• Oxidative phosphorylation provides about 95 percent of the cells' ATP.
• Oxygen and electrons are needed, and availability limits the rate of ATP generation.
• Cells obtain oxygen by diffusion from extracellular fluid.

Energy production

• Generating ATP is the main method when starting with glucose and ending with carbon dioxide and water.

Glycolysis

• 1 glucose molecule will break down anaerobically, resulting in 2 pyruvate molecules.
• The cell gains a net 2 molecules of ATP in glycolysis.
• 2 molecules of NADH pass electrons to FAD, doing so via an intermediate electron carrier in intermembrane space and then to the ETC.

Citric Acid Cycle Numbers

• Two revolutions are required to break down the 2 pyruvate molecules.
• Each revolution yields 1 ATP by way of GTP.
• An additional gain of 2 molecules of ATP are produced.
• H atoms are transferred to NADH and FADH2.
• Coenzymes provide electrons to the electron transport chain.

Electron Transport Chain Outcome

• For each glucose molecule, deliver electrons to the electron transport chain including 10 NADH and 2 FADH2.
• Each NADH yields 2.5 ATP.
• Each of the 8 NADH from the citric acid cycle yields 2.5 ATP and 1 water molecule.
• Each FADH2 yields 1.5 ATP.
• 2 FADH2 from glycolysis yields 3 ATP and 2 water molecules/
• The total ATP yield from the electron transport chain is 23.

Summary of ATP Production

• For each glucose molecule processed, the cell gains 30–32 ATP molecules. • 2 from glycolysis • 3–5 from NADH generated in glycolysis • 2 from citric acid cycle (by means of GTP) • 23 from ETC
• All but 2 ATP is produced in mitochondria.

Gluconeogenesis

• Gluconeogenesis synthesizes glucose from noncarbohydrate molecules.
• These molecules include 3-carbon molecules other than pyruvate.
• Glucose is stored as glycogen in liver and skeletal muscle.

Glycogenesis

• Glycogenesis is the process of glycogen formation from excess glucose.
• Glycogenesis involves several steps and requires uridine triphosphate (UTP), a high-energy compound.

Glycogenolysis

• Glycogenolysis is the breakdown of glycogen to glucose monomers.
• Glycogenolysis happens quickly and only uses a single enzymatic step.

Lipids

• Lipids contain carbon, hydrogen, and oxygen.
• Lipids are in different proportions versus carbohydrates.
• Triglycerides are the most abundant lipid in the body.

Lipid Catabolism (Lipolysis)

• Lipolysis breaks lipids into pieces to be converted to pyruvate or channeled directly into citric acid cycle (hydrolysis).
• Hydrolysis splits triglyceride, resulting in 1 glycerol and 3 fatty acid molecules.
• The enzymes in the cytosol convert glycerol to pyruvate.
• Converted pyruvate becomes acetyl-CoA and enters citric acid cycle.

Lipids and Energy Output of the Cell

• A cell can gain 120 ATP from the breakdown of one 18-carbon fatty acid molecule.
• This is almost 1.3 times the energy from the breakdown of three 6-carbon glucose molecules.

Lipogenesis

• Lipogenesis can use almost any organic substrate.
• This is possible because lipids, amino acids, and carbohydrates can be converted to acetyl-CoA.
• Glycerol is synthesized from dihydroxyacetone phosphate.
• Dihydroxyacetone phosphate is an intermediate product of glycolysis and gluconeogenesis.

Types of Lipid Synthesis

• Nonessential fatty acids and steroids are synthesized from acetyl-CoA.
• Essential fatty acids cannot be synthesized in the body and must be consumed.
• Linoleic acid and linolenic acid are 18-carbon unsaturated fatty acids in plants.

Lipid Storage

• Lipids are important energy reserves and provide large amounts of ATP.
• Difficult for water-soluble enzymes to reach for break down.

Lipid Transport and Distribution Important Because

• Cells require lipids to maintain plasma membranes.
• Steroid hormones must reach target cells in different tissues.

Lipid Transport Details

• Lipids are not soluble in water, therefore special transport mechanisms carry lipids.
• Lipids circulate through bloodstream as lipoproteins.
• Free fatty acids make up a small percentage of total circulating lipids.

Free Fatty Acids (FFAs)

• FFAs can diffuse easily across plasma membranes.
• In blood, FFAs generally bind to albumin (the most abundant plasma protein).
• Sources of FFAs in blood include those not used to synthesize triglycerides and those diffused from intestinal epithelium
• Triglycerides, when broken down, also diffuse out of lipid reserves.

Free Fatty Acids as Energy

• FFAs are particularly important during periods of starvation or when glucose supplies are limited.
• Cells in liver, cardiac muscle, and skeletal muscle, can metabolize free fatty acids.

Lipoproteins

• Lipoproteins are lipid-protein complexes.
• Lipoproteins contain large insoluble glycerides and cholesterol.
• Four groups of lipoproteins: chylomicrons, very low-density lipoproteins (VLDLs), low-density lipoproteins (LDLs)—“bad cholesterol", high-density lipoproteins (HDLs)—“good cholesterol.”

Definition of Chylomicrons

• Chylomicrons are the largest lipoproteins.
• Intestinal epithelial cells produce chylomicrons from fats in food.
• Chylomicrons carry absorbed lipids into lymph and then into bloodstream.

Protein Metabolism

• The body synthesizes 100,000 to 140,000 different proteins.
• Each protein has different structures and functions.
• All proteins are built from the same 20 amino acids.
• Proteins function as enzymes, hormones, structural elements, and neurotransmitters.
• Very little protein is used as an energy source.

Amino Acid Catabolism

• Proteins must convert into substances that can enter the citric acid cycle before being used for energy.
• This conversion involves transamination, deamination, and the urea cycle.
• Removal of the amino group requires a coenzyme derivative of vitamin B6.

Transamination

• Transamination attaches an amino acid's amino group to a keto acid.
• Transamination converts a keto acid into an amino acid.
• This occurs by leaving mitochondrion and entering cytosol.
• The amino acids are available for protein synthesis.

Deamination

• Deamination prepares an amino acid for breakdown in the citric acid cycle.
• During deamination, the amino group and hydrogen atom are removed, generating a toxic ammonium ion.

Deamination Details

• Deamination generates ammonium ions primarily in liver cells.
• Liver cells have enzymes that remove toxic ammonium ions by synthesizing urea through the urea cycle.
• Urea is a harmless water-soluble compound excreted in urine.

Amino Acids and ATP Production

• When glucose and lipid reserves are inadequate, liver cells break down internal proteins.
• The liver then absorbs additional amino acids from the blood.
• Amino acids are deaminated, and then carbon chains are sent to mitochondria.
• As not all amino acids enter the cycle at the same point, ATP benefits vary.

Protein Catabolism Impractical Because

• Proteins are more difficult to break apart than are complex carbohydrates or lipids.
• Ammonium ions are toxic.
• Proteins form essential structural and functional components of cells.

Protein Synthesis

• The body synthesizes half of the amino acids needed to build proteins.
• There are ten essential amino acids, including eight that are not synthesized and two that are insufficiently synthesized.
• Nonessential amino acids are made by the body on demand, requiring amination (addition of an amino group).

Absorptive and Postabsorptive States are Characterized by

• Nutrient requirements of each tissue vary with types and quantities of enzymes.

Five Key Metabolic Tissues

• Liver
• Adipose tissue
• Skeletal muscle
• Nervous tissue
• Other peripheral tissues

Role of the Liver

• A focal point of metabolic regulation and control, with great diversity of enzymes.
• Carbohydrates, lipids, and amino acids are broken down or synthesized there.
• Hepatocytes have an extensive blood supply and monitor and adjust nutrient composition of circulating blood.
• There are significant energy reserves, such as glycogen deposits.

Adipose Tissue Details

• Adipose tissue stores lipids (primarily triglycerides).
• Adipocytes are located in areolar tissue, mesenteries, red and yellow bone marrows, epicardium, and around the eyes and kidneys.

Skeletal Muscle

• Skeletal muscle maintains substantial glycogen reserves.
• Contractile proteins can be broken down or amino acids can be used as an energy source if other nutrients are unavailable.

Nervous Tissue

• Nervous tissue cannot maintain reserves of carbohydrates, lipids, or proteins.
• A reliable glucose supply is required because it cannot metabolize other molecules.
• The CNS cannot function in low glucose conditions, leading to unconsciousness.

Other Peripheral Tissues

• Some tissues do not maintain large metabolic reserves.
• Some tissues can metabolize glucose, fatty acids, and other substrates.
• The substrate use depends on instructions from the endocrine system.

Two Metabolic States

• The absorptive state happens for around 4 hours after eating and nutrient absorption occurs.
• Normal blood glucose levels are maintained in the postabsorptive state, where the body relies on internal energy reserves.
• Most cells break down lipids or amino acids, reserving glucose for nervous tissue.

Lipid and Amino Acid Catabolism

• Lipid and amino acid catabolism generates acetyl-CoA.
• An increased concentration of acetyl-CoA causes ketone bodies to form.
• A ketone body is an organic compound produced by fatty acid metabolism and dissociates in solution, releasing a hydrogen ion.

Ketone Bodies

• The three types of ketone bodies are acetoacetate, acetone, and betahydroxybutyrate
• Liver cells cannot catabolize ketone bodies.
• Peripheral cells absorb ketone bodies from blood, reconverting them to acetyl-CoA for the citric acid cycle.
• Fasting produces ketosis, including high concentration of ketone bodies in body fluids.

Ketonomia

• Ketonemia is the appearance of ketone bodies in the bloodstream.
• It lowers blood pH, which must be controlled by buffers.
• Prolonged starvation leads to ketoacidosis.
• Ketoacidosis endangers through acidification of blood by ketone bodies.
• Ketoacidosis may cause coma, cardiac arrhythmias, and death.

What Do We Eat?

• Digestion must allow absorption of fluids, organic nutrients, minerals, and vitamins to maintain homeostasis.

Nutrition

• The absorption of nutrients.
• Body's requirement for each separate nutrient varies

Balanced Diet

• All ingredients are needed for homeostasis

Malnutrition

• Unhealthy state resulting from nutrient imbalance

Complete Proteins

• Provides all needed amino acids
• Beef, fish, poultry, eggs, and milk provide complete proteins.

Incomplete Proteins

• Has 1 or more lacking amino acids
• Found in plants

Minerals are Important Because

• Ions such as sodium and chloride determine osmotic concentrations of body fluids
• Ions play major roles in physiological processes
• Ions are essential cofactors in many enzymatic reactions

Bulk Minerals

• Sodium, potassium, chloride, calcium, phosphorus, and magnesium

Trace Minerals

• Iron, zinc, copper, manganese, cobalt, selenium, and chromium.

Vitamins:

• Vitamins are organic nutrients that aid in vital reactions
• Divided into:
• Fat-soluble vitamins
• Water-soluble vitamins

Fat-Soluble Vitamins

• Vitamins A, D, E, and K
• Absorbed primarily in the small intestine along with lipids of micelles
• Vitamin D produced when exposed to sunlight/UV
• Vitamin K is produced by the body through intestinal bacteria.

Vitamins and the Body

• Vitamin A aids in maintaining epithelia and required for synthesis of visual pigments
• Vitamin D is converted to calcitriol and required for normal bone growth
• Vitamin E prevents the breakdown of vitamin A and fatty acids
• Vitamin K is essential for the synthesis of clotting factors

Vitamin Reserves

• The body has an abundance of fat-soluble vitamins: normal metabolism will continue without any extra dietary sources
• Hypovitaminosis: rare, fat-soluble deficiencies.
• Hypervitaminosis: Body is less capable of storing, excreting, and using the vitamin

Water-Soluble Vitamins

• Water-soluble vitamins include components of coenzymes.
• They are exchanged between fluid in the digestive tract and the blood.
• Excesses are excreted by the body through urination
• Less common to overdose due to how the body handles them

Intestinal Vitamins

• Intestines produce 5 of 9 water-soluble vitamins, and fat-soluble vitamin K

Absorption

• Intestinal epithelium easily absorbs all water-soluble vitamins except B12
• The B12 molecule is large; therefore, it must bind to an intrinsic factor first for absorption

Metabolic Rate, How is it Found?

• Energy to average caloric expenditure
• Daily energy expenditures vary widely with activity

Energy Gains and Losses

• Energy is released when broken
• Energy is used to synthesize ATP
• Some energy is also lost as heat.

Measuring Energy

• Energy to needed to heat 1 g of water

• 1℃ is one cal

• Energy needed to heat 1 kg of water

• 1℃ is about one kcal or one Calorie

Energy Content of What You're Eating?

• Use Calorimetry
• Measure amount of energy released when you eat organic molecules
• Burning with oxygen and water

What does Each Type Release?

9.46 kcal per gram

• Carbs: 4.18 kcal per gram
• Proteins: 4.32 kcal per gram

Metabolic Rate Numbers

• Results can be from calories expended by a clinician
• Per hour
• Per Day
• Per Weight
• Affected by other factors.
• Exercise
• Climate
• Gender/Sex
• Hormones

Basal Metabolic Rate (BMR)

• Rate to expend energy while resting -Maintains your functions
• Energy Expendent: alert, awake

Measuring Energy Intake

• Thyroxine: the metabolism's "control" hormone
• Suppressing Appetite
• Adrenocorticotropic hormone (ACTH)
• Cholecystokinin (CCK)
• Leptin: Adipose tissues produce (Absorptive)
• Binds to the CNS, appetite suppressant
• Ghrelin: From the empty stomach, appetite "booster"

Obesity

• 20% + to ideal body mass
• Body is more susceptible to:
• Cardiovascular Disease
• Cancer
• Diabetes