From Food to ATP

Chemical Reaction

• rearrange atoms to form new substances

• existing bonds may be broken and new bonds may form

• atoms are conserved not created or destroyed

How Chemical Reactions Start

• molecules in our cells are constantly moving and colliding

• molecules have to collide appropriately and with enough energy to overcome an energy barrier

• increased temp leads to increased molecular kinetic energy which leads to more collisions

Activation Energy

the minimum energy reqired to overcome the barrier and initiate a chemical reaction

influences reaction rate, while ^G describes the overall free energy change

Enzymes Lower Activation Energy Barrier characteristics

• biological catalysts to convert substrates to products

• break and reform covalent bonds

• increase rate of reaction

Enzymes Provide an….

alternate pathway with a lower activation energy but do not change the overall energy released or required by the action

Metabolic Pathway

• a series of linked, enzyme-catalyzed reactions

• the equation is the overall result

Exergonic Reactions

• releases free energy

• ^G < 0 - products that have less free energy than reactants

Endergonic Reactions

• - requires energy input

• ^G > 0 - products have more free energy than reactants

1st Law of Thermodynamics

energy cannot be created or destroyed, only transferred or transformed

2nd Law of Thermodynamics

• energy transformations are not 100% efficient

• every energy transfer increases the dispersal of energy

Reaction Coupling

• exergonic and endergonic reactions can be coupled

• the energy released by an exergonic reaction is transferred to drive an endergonic reaction

• often occurs through ATP

ATP =

• adenosine triphosphate

• a high energy molecule that helps transfer energy in the cell

ATP Parts

• adenine - a nitrogen-containing base

• ribose - a 5-carbon sugar

• three phosphate groups - linked in a chain

ATP + H20 —> ADP + Pi + energy available for cellular network - explain this

• this reaction is catalyzed by the enzyme ATPase

• free energy released by ATP hydrolysis can be coupled to cellular network

ATP Hydrolysis is ______

exergonic

ATP Requirements of Muscle Activity

• cross bridge cycling

• Ca2+ reuptake

• maintaining ion gradients

Energy

the capacity to due work

Biological Work

mechanical, chemical, transport

ATP Resynthesis is ______

endergonic

ADP + Pi + energy —> ATP - explain

• ATP is continually recycled as an energy transfer intermediary between energy releasing metabolism and energy requiring cellular work

Catabolism (degradative)

break down of organic nutrients into end products, with release of energy stored as ATP and electron carriers

Anabolism (biosynthetic)

simple precursors are built into larger complex molecules using ATP energy or reducing power

ATP Resynthesis

• regeneration of ATP can be divided into three pathways

• phosphagen system

• glycolysis

• oxidative metabolism

The Fastest Way to Resynthesize ATP

• PCr rapidly transfers a phosphate group to ADP to regenerate ATP

• muscle PCr stores are limited — its relative contribution falls rapidly during sustained exercise

ATP Resynthesis is best for…

• brief, high-intensity movements

• ex: jump, heavy lift, acceleration

Phosphagen Pathway

• main source: PCr

• relative rate: fastest

• relative capacity: lowest

Glycolytic Pathway

• main source: glucose

• relative rate: fast

• relative size: moderate

Oxidative Pathway

• main source: glucose/fat + O2

• relative rate: slower

• relative capacity: highest

Glycolysis

• sugar splitting

• occurs in the cytosol

• does not directly require O2

• some energy must first be invested

• energy is captured as ATP and NADH

Glycolytic Pathway - Embden Meyerhof

• energy investment: glucose —> phosphorylated intermediates (2 ATP used)

• splitting: 6c —> 2 × 3c molecules

• energy payoff: 4 ATP + 2 NADH produced

Glycolytic Pathway Net from glucose

• 2 ATP

• 2 NADH

• 2 pyruvate

How does glycolysis capture some of glucose’s energy?

• 2 ATP - directly by substrate-level phosphorylation

• 2 NADH - indirectly by electron/energy carrier

NADH

• NAD+ (lost electrons) accepts high-energy electrons (and H+) —> NADH

• NADH carries electrons and their energy to other reactions

• reduced form (gained electrons)

NAD+ must be regenerated for _____ to continue

glycolysis

Pyruvate —> Lactate

• pyruvate + NADH + H+ —> lactate + NAD+

• regenerate NAD+

• allows glycolysis to continue

NADH —> mitochondrial electron transfer process

• NADH oxidized in ETC; NAD+ regenerated

• electrons can ultimately contribute to much greater ATP production

Pyruvate —> Mitochondria

• pyruvate contains considerable chemical energy

• pyruvate transported into mitochondrion

• converted into acetyl-CoA

• enters krebs cycle

Oxidative Phosphorylation

• more glucose’s chemical energy is transferred to NADH before acetyl-CoA enters the krebs cycle

• pyruvate + NAD+ + CoA —> acetyl-CoA + CO2 + NADH + H+

• NADH and NAD+ enters mitochondrion

• H+ from NADH + H+ passed to FAD

Krebs Cycle

• takes place in mitochondrial matrix

• called a cycle because oxaloacetate is regenerated after oxidation of acetyl-CoA

Krebs Cycle Products

• NAD+ and FAD+ are both reduced to become NADH + H+ and FADH2

• ATP via substrate-level phosphorylation

Krebs Cycle - per glucose/ 2 molecules acetyl-CoA

• 6 NADH + H+

• 2 FADH2

• 2 ATP

• 4 CO2

ETC + H+ Gradient

• electrochemical H+ gradient

• NADH donates high energy electrons

• electrons move through proteins in inner mitochondrial membrane

• energy released drives H+ pumping

• H+ accumulates in intermembrane space

Oxidative Phosphorylation

• high H+ intermembrane space

• H+ move down electrical gradient, used to drive ATP synthesis through ATP synthase

• ADP + Pi —> ATP

• oxygen is the final electron acceptor —> H2O

• oxidative - electron-transfer/redox reactions provide the energy

• phosphorylation - ADP = Pi —> ATP

Energy Continuum

• relative contribution of anaerobic vs aerobic energy

Energy Systems Approach

• ATP-PC: predominates in activities of 10 seconds

• glycolytic: lactic, lasts for 1-2 minutes

• aerobic: activities greater than 2 minutes

General Rule of Fuel Use during Exercise

• lower intensity, longer duration exercise relies more on fat as fuel

• higher intensity, shorter duration exercise relies more on CHO as a fuel