Chapter 3

Bioenergetics

Objectives

Discuss the function of cell membrane, nucleus, & mitochondriaDefine: endergonic, exergonic, coupled reactions & bioenergeticsDescribe how enzymes workDiscuss nutrients used for energy Identify high-energy phosphates

Objectives

Discuss anaerobic & aerobic production of ATPDescribe how metabolic pathways are regulatedDiscuss the interaction of anaerobic & aerobic ATP production during exerciseIdentify the rate limiting enzymes

IntroductionMetabolism: total of all chemical reactions that occur in the body– Anabolic reactions - Synthesis of molecules– Catabolic reactions - Breakdown of molecules

Bioenergetics– Converting foodstuffs (fats, proteins, carbohydrates)

into energySubstrate – Substance used by body in metabolismMetabolite – Byproduct of metabolism

Energy Forms

Energy originates in the sun– Chemical– Light– Mechanical– Electrical– Heat– Nuclear

Photosynthesis

Energy from the sun– Solar energy from sun converted to chemical

energy in plants– Plants use energy + water and carbon dioxide– Byproduct is oxygen– Build food molecules

Thermodynamics

1st Law– Conservation of energy-energy cannot be

created or destroyed. – They can be interchanged– Our bodies transform energy into a form that

we can used.

Biological Energy Cycle

Food + O2 → CO2 + H2O + energy Chemical Mechanical

60-70% of this energy is heatThe rest is used for – Muscle contraction– Cellular operations (respiration)

Digestion and absorption Synthesis of new compoundsGlandular function

Biological Energy Cycle

Chemical energy transformation to mechanical energyFood (Chemical energy) is used for muscular contraction (Mechanical energy)

ElementsBasic chemical substances– Oxygen – Carbon– Hydrogen– Nitrogen

Minor elements – Sodium, Iron, Zinc, Potassium, Magnesium, Chloride,

CalciumOrganic substances – contain carbonInorganic substances - do not contain carbon

Cell Structure

Cell membrane– Protective barrier between interior of cell and

extracellular fluid– Maintains ion concentrations (unequal)

Nucleus– Contains genes that regulate protein

synthesis

Cell Structure

Cytoplasm– Fluid portion of cell– Contains organelles (mitochondria)– Glycolysis – enzymes– Mitochondria

Structure of a Typical Cell

Fig 3.1

Cellular Chemical Reactions

Endergonic reactions – Require energy to be added – Photosynthesis – solar energy to chemical

energyEnergy stored

Exergonic reactions– Release energy– Breakdown of cellular bonds

The Breakdown of Glucose: An Exergonic Reaction

Fig 3.3

Coupled Reactions

Fig 3.4

Cellular Chemical Reactions

Coupled reactions– Liberation of energy in an exergonic reaction

drives an endergonic reaction– Breakdown of glucose-exergonic– Formation of ATP-endergonic

Oxidation-Reduction Reactions

Oxidation: removing an electron – Removing a negative charge = + >– (oxygen not required)

Reduction: addition of an electron– Adding a negative charge = - >

Oxidation and reduction are always coupled reactions

Oxidation-Reduction Reactions

Reducing agent: molecule that donates an electronOxidizing agent: molecule that accepts an electron

Oxidation-Reduction Reactions

In cells often involve the transfer of hydrogen atoms rather than free electrons– Hydrogen atom contains one electron– A molecule that loses a hydrogen also loses

an electron, and therefore is oxidized

Transfer of H+ and e-

Major transport molecules in bioenergetics– Nicotinamide adenine dinucleotide – Niacin (B3) – NAD – oxidized form– NADH – reduced form

Transfer of H+ and e-

Major transport molecules in bioenergetics– Flavin adenine dinucleotide– Riboflavin (B2)– FAD – oxidized form– FADH – reduced form

Enzymes

Catalysts that regulate the speed of reactions– Lower the energy of activation

Energy required to initiate the reaction– Speed up the rate of the reaction– Increase the rate of product formation

Enzymes Lower the Energy of Activation

Fig 3.6

Enzymes

Factors that influence enzyme activity– Temperature

Optimum temperature – most activeSlight increase increases activity of most enzymesUseful for muscular contraction

– pH Optimum pHAltered pH reduces enzyme activityHigh intensity exercise (LA) - ↓ pHDecreases ability to produce energy (ATP)Extreme acidity is a limiting factor in exercise.

Enzymes

Structural characteristics – Large proteins with 3 D shape– Characteristic grooves and ridges

Active sites– Interact with specific substrates

Lock and key model

Enzyme-Substrate Interaction

Complex lowers energy of activationReaction proceeds

Fig 3.7

Fuels for Exercise

Carbohydrates – Glucose – C6H12O6 (4 kcal/gram)

Monosaccharide Stored as glycogen (C6H12O6)n

– DisaccharidesSucrose

– PolysaccharidesCellulose Starch

Fuels for Exercise

Fats– Carbon, hydrogen, oxygen – Groups

Fatty acids – energy source (9 kcal/gram)– Stored as triglycerides-fat cells, skeletal muscle– Lipolysis-fatty acids and glycerol

Phospholipids – not an energy source– Structural component-cell membranes, myelin sheath

Steroids – not an energy source– Structural component-cell membranes– Synthesis of hormones

Fuels for Exercise

Proteins– Not a primary energy source during exercise– Amino acids– Limited usage

Extreme exercise conditions

Adenosine Triphosphate

We convert food: – Fat, Carbohydrate (CHO), Protein (limited)

Into energy: – Adenosine TriPhosphate (ATP)

Adenosine is a complex structurePhosphates (3 simpler structures)

Adenosine (P) ≈ (P) ≈ (P)

Structure of ATP

Fig 3.8

Model of ATP as the Universal Energy Donor

Fig 3.9

ATP

Adenosine (P) ≈ (P) ≈ (P)

ATP + H2O → ADP + PiATPase

7,000 to 12,000 calories or7 to 12 kilocalories

Breakdown requires regenerationCoupled reaction

Coupled ReactionATP + H2O ←→ ADP + Pi

ATPase

ADP + C~P ←→ ATP + C Creatine kinase

Bioenergetics

Cells need constant supply of ATPMinimal amounts stored for cellular processesMuscular contraction-exercise– Constant, large supply

Formation of ATP (3 metabolic pathways)– 1. Phosphocreatine (PC) breakdown

ATP-PC system (phosphagen system)

– 2. Degradation of glucose and glycogen Glycolysis (Glycolytic system)

– 3. Oxidative phosphorylation Tricarboxylic cycle, Krebs cycle

Bioenergetics

Anaerobic pathways (do not involve O2)– 1. ATP-PC breakdown – 2. Anaerobic glycolysis

Aerobic pathway– Requires O2

– 3. Oxidative phosphorylation

1. ATP-PC (Phosphagens)

Characteristics – ATP and PC stored in the contracting mechanism of

the muscle– Simplest and fastest way to produce ATP

ATP + H2O → ADP + PiATPase

– Provides energy for short term, maximal exercise5 sec

– High intensity activity30 sec

1. ATP-PC (Phosphagens)

Characteristics (cont)– At onset of exercise-rapid breakdown followed

by rapid resynthesisADP + C~P ←→ ATP + C

Creatine kinase

– ATP replenishment by PC maintains ATP levels for awhile.

– PC replenishment continues activity about 30 sec

1. ATP-PC (Phosphagens)Characteristics (cont)– 3 times more CP than ATP stored in muscle– Fastest rate of energy production, lowest stores

(capacity)– Used during

Initial onset of exercise (oxygen deficit)Short term, high intensity exercise (< 5 sec)

– Resynthesis only during recovery

– Activities (examples)Sprints (< 30 sec)High jumpingWeight lifting

100%

% C

apacity of Energy System

10 sec 30 sec 2 m in 5 m in +

Energy Transfer System s and Exercise

Aerobic Energy System

Anaerobic G lycolysis

ATP - CP