Biochemical Energy Production

Metabolism– Sum of all the chemical activities taking place in

an organism– Catabolism

• Larger molecules broken down into smaller ones– Stages 1-4 (Digestion; Formation of Acetyl CoA; Citric Acid Cycle;

Electron Transport Chain & Oxidative Phosphorylation)

• Releases energy (may be stored temporarily as ATP)– Anabolism

• Complex molecules synthesized from simpler substances• Absorbs energy & stores it as chemical bonds

Enzymes play a key role in metabolic pathways

• Series of small reactions are run with help of enzymes• Free energy differences between reactants & products is

low• Concentration differences keep enzyme-run reactions

going in one direction• How? • Products are constantly removed so no build up at the end.

Concentration stays low for products

Enzymes catalyze oxidation via series of small steps – Free E transferred to carrier molecules (e.g. ATP & NADH). Enzymes (∆G) reduce activation energy barrier.

Total free energy released is the same in (A) and (B).

Eukaryotic cell with organelles

In eukaryotic cells, the mighty

mitochondrion is where the majority

of our energy is grabbed from our food molecules in a process called aerobic cellular

respiration

Anaerobic respiration•Fermentation•Does not require oxygen

All are exergonic (occur spontaneously)Use a lot of coupled reactions

Cellular respiration

Aerobic respiration•Requires molecular oxygen•Includes redox reactions

• A pyramid of production reveals the flow of energy from producers to primary consumers and to higher trophic levels

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Producers

10 kcal

100 kcal

1,000kcal

10,000 kcal

1,000,000 kcal of sunlight

Most biochemical pathways involve coupled reactions

• ATP is the most common “energy carrier”• This is why examinations of metabolic

products focus on ATP production• Other molecules can also act as exergonic

energy carriers to help drive an endergonic biochemical reaction– Examples: NADH and FADH2 will become

familiar to you as energy carriers– GTP, UTP, etc.

Reaction Coupling: released energy drives an endergonic reaction

1) ATP Hydrolysis reaction: Exergonic (spontaneous)

ATP + H2O ADP + Pi + H+ ∆G = ~ -30 kJ

2) Phosphorylation of Glucose reaction: Endergonic (nonspontaneous)

Glucose + Pi + H+ Glucose-Phosphate + H2O∆G = ~ +14 kJ

3) Coupled Reaction (showing just the key reactants & products): Glucose + ATP Glucose-Phosphate + ADPnet∆G = ~ -16 kJ

Coupled reaction has a net Exergonic effect,so will occur “spontaneously”

Structural relationships among AMP, ADP, and ATP molecules.

ATP links exergonic andendergonic reactions

High Energy Phosphate Compounds

• High energy compounds have greater free energies of hydrolysis than typical compounds

• They contain very reactive (strained) bonds - represented by a squiggle (~)

Redox reactions (oxidation/reduction)oxidized species can gain O or lose H. Substance that becomes oxidized gives up energy

reduced species can gain H or lose O. Substance

that becomes reduced receives energy

Essential part of cellular respiration

Many metabolic pathways use a series of small Redox reactions

to minimize energy loss.

Energy is transferred in the form of electrons (e-)

Summary of RedOx Reactions

• FAD + 2H+ + 2e- <==> FADH2

• NAD+ + 2H+ + 2e- <==> NADH + H+

energy transfer agent: In reduced state has more

free energy; less in its oxidized state.

Structural formula for coenzyme A

• The active portion of CoA is the sulfhydryl group• An acetyl group bonds to CoA through a thioester

bond

Classification of metabolic intermediate compounds according to function

Four stages of aerobic respiration

Note location of each stage & amount of ATP formedProduct of one stage becomes reactant of next stage

the Four Stages of

Biochemical Energy

Production

Stages 1 & 2

• Both stages are specific to the type of food

• Related to metabolism of:– Carbohydrates– Lipids– Proteins