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 Metabolism = all of the chemical pathways in a living organism (or single cell) Catabolism (oxidation reaction) - The breakdown of larger molecules into smaller ones through the removal of electrons. e.g. digestion Anabolism (reduction reaction) - The synthesis of larger molecules from smaller ones through the addition of electrons (and accompanying protons or H+ ions). e.g. protein synthesis These metabolic pathways are able to occur at normal temperatures because of the catalytic interaction of a group of chemicals called enzymes. Enzymes help lower the activation energy needed for the reactions to occur.

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 – the controlled stepwise oxidation of sugar in a cell, compared with ordinary burning. In the cell, enzymes catalyze oxidation via a series of small steps in which free energy is transferred in conveniently sized packets to carrier molecules, most often ATP and NADH. At each step, an enzyme controls the reaction by reducing the activation energy barrier that has to be surmounted before the specific reaction can occur. The total free energy released is exactly the same in (A) and (B). 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

All are exergonic (occur spontaneously) Use a lot of coupled reactions Cellular respiration Anaerobic respiration Fermentation Does not require oxygen Aerobic respiration Requires molecular oxygen Includes redox reactions Cellular Respiration Cellular respiration - Process by which cells convert the energy of fuel molecules (eg. glucose) into usable bond energy in ATP. (Break the $100 dollar bill into small change) Anaerobic respiration - Cellular respiration in the absence of oxygen. Aerobic respiration - Cellular respiration which uses oxygen to completely oxidize fuel molecules. All are exergonic (occur spontaneously) Use a lot of coupled reactions

A pyramid of production reveals the flow of energy from producers to primary consumers and to higher trophic levels Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers 1,000 kcal Producers 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 + ADP net ∆G = ~ -16 kJ In cells, an exergonic reaction is “coupled” to an endergonic reaction to give it free energy to drive the reaction. Note: energy is measured in kilojoules (kJ) or kilocalories (kcal). Example of Reaction Coupling and ATP Hydrolysis 1) ATP Hydrolysis reaction: ATP + H2O ----- ADP + Pi + H+ DG = ~ -30 kJ Exergonic (spontaneous) 2) Phosphorylation of Glucose reaction: Glucose + Pi + H+ ----- Glucose Phosphate + H2O DG = ~ +14 kJ Endergonic (needs energy to be supplied) 3) Coupled Reaction: Glucose + ATP ----- Glucose Phosphate + ADP DG = ~ -16 kJ Coupled reaction has a net Exergonic effect, so will occur “spontaneously” Coupled reaction has a net Exergonic effect, so will occur “spontaneously”

Structural relationships among AMP, ADP, and ATP molecules.

ATP links exergonic and endergonic 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; Nicotinamide adenine dinucleotide. Notice the N becoming reduced in charge as it takes an electron, and the other H atom hooking to the carbon. Electrons and their energy eventually used to produce ATP. NADP+ turns into NADPH doesn’t make ATP but actually supplies energy directly for some reactions (photosyn). Flavin adenine dinucleotide (FAD) accepts H atoms and when reduced turns into FADH2. Cytochromes are another set of iron containing proteins that accept e- from H atoms and transfers them to some other compound. All of these together are called electron transfer agents. In their reduced state they have more free energy, and less in their oxidized state. 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 Reaction Types in Cellular Respiration 1. Dehydrogenation - Hydrogens transferred to a coenzyme. 2. Decarboxylations - Carboxyl groups removed from substrates as carbon dioxide. 3. Preparation reactions - Molecules are rearranged in preparation for dehydrogenation or decarboxylation. Note location of each stage & amount of ATP formed Product 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