Glycolysis Biochemistry

All organisms produce ATP by breaking down molecules and by releasing energy stored in glucose and other sugars.

Aerobic respiration - the process by which a cell uses O 2 to "burn" molecules and release energy The reaction: C 6 H 12 O 6 + 6O 2 >> 6CO 2 + 6H 2 O

Aerobic respiration - the process by which a cell uses O 2 to "burn" molecules and release energy The reaction: C 6 H 12 O 6 + 6O 2 >> 6CO 2 + 6H 2 O Note: this reaction is the opposite of photosynthesis

three major reaction pathways Glycolysis The Kreb's Cycle Electron Transport Phosphorylation (chemiosmosis)

glycolysis Glucose is metabolized to pyruvate by the pathway of glycolysis citric acid cycle CO2H2O oxidative phosphorylation Aerobic tissues metabolize pyruvate to acetyl-CoA, which can enter the citric acid cycle for complete oxidation to CO2 and H2O, linked to the formation of ATP in the process of oxidative phosphorylation

Glycolysis Glycolysis (glyco = sugar; lysis = breaking) Goal:Goal: break glucose down to form two pyruvates Who:Who: all life on earth performs glycolysis Where:Where: the cytoplasm

Glycolysis Glycolysis literally means "splitting sugars." glucose split two molecules three- carbon sugar. glucose (a six carbon sugar) is split into two molecules of a three- carbon sugar.

Glycolysis Is Regulated at Three Steps Involving Nonequilibrium Reactions reversible Although most of the reactions of glycolysis are reversible, exergonic three are markedly exergonic and must therefore irreversible be considered physiologically irreversible. These reactions, catalyzed by 1. hexokinase (and glucokinase) 2. Phosphofructokinase 3. pyruvate kinase, are the major sites of regulation of glycolysis.

The First Stage of Glycolysis 2Glucose (6C) is broken down into 2 (3C) This requires two ATP's

The Second Stage of Glycolysis 2 22 (3C) are converted to 2 pyruvates This creates 4 ATP's and 2 NADH's The net ATP production of Glycolysis is 2 ATP's

10 Steps of Glycolysis Glucose → Glucose 6-ph osphate Step 1 The enzyme hexokinase phosphorylates (adds a phosphate group to) glucose in the cell's cytoplasm. In the process, a phosphate group from ATP is transferred to glucose producing glucose 6-phosphate. Glucose (C 6 H 12 O 6 ) + hexokinase + ATP → ADP + Glucose 6-ph osphate (C 6 H 11 O 6 P 1 )

phosphoglucoisomerase Glucose 6-phosphate Fructose 6-phosphate Step 2 The enzyme phosphoglucoisomerase converts glucose 6- phosphate into its isomer fructose 6-phosphate. Isomers have the same molecular formula, but the atoms of each molecule are arranged differently. Glucose 6-phosphate (C 6 H 11 O 6 P 1 ) + Phosphoglucoisomerase → Fructose 6-phosphate (C 6 H 11 O 6 P 1 )

phosphofructokinase Fructose 6-phosphate Fructose 1, 6-diphosphate Step 3 The enzyme phosphofructokinase uses another ATP molecule to transfer a phosphate group to fructose 6-phosphate to form fructose 1, 6- diphosphate. Fructose 6-phosphate (C 6 H 11 O 6 P 1 ) + phosphofructokinase + ATP → ADP + Fructose 1, 6-diphosphate (C 6 H 10 O 6 P 2 )

aldolase Fructose 1, 6-bisphosphate → Dihydroxyacetone phosphate Glyceraldehyde phosphate Step 4 The enzyme aldolase splits fructose 1, 6- bisphosphate into two sugars that are isomers of each other. These two sugars are dihydroxyacetone phosphate and glyceraldehyde phosphate. Fructose 1, 6-bisphosphate (C 6 H 10 O 6 P 2 ) + aldolase → Dihydroxyacetone phosphate (C 3 H 5 O 3 P 1 ) + Glyceraldehyde phosphate (C 3 H 5 O 3 P 1 )

triose phosphate isomerase Dihydroxyacetone phosphate Glyceraldehyde phosphate Step 5 The enzyme triose phosphate isomerase rapidly inter- converts the molecules dihydroxyacetone phosphate and glyceraldehyde phosphate. Glyceraldehyde phosphate is removed as soon as it is formed to be used in the next step of glycolysis. Dihydroxyacetone phosphate (C 3 H 5 O 3 P 1 ) → Glyceraldehyde phosphate (C 3 H 5 O 3 P 1 ) Net result for steps 4 and 5: Fructose 1, 6-diphosphate (C 6 H 10 O 6 P 2 ) ↔ 2 molecules of Glyceraldehyde phosphate (C 3 H 5 O 3 P 1 )

triose phosphate isomerase Dihydroxyacetone phosphate Glyceraldehyde phosphate 2 molecules of Glyceraldehyde phosphate Step 5 The enzyme triose phosphate isomerase rapidly inter- converts the molecules dihydroxyacetone phosphate and glyceraldehyde phosphate. Glyceraldehyde phosphate is removed as soon as it is formed to be used in the next step of glycolysis. Dihydroxyacetone phosphate (C 3 H 5 O 3 P 1 ) → Glyceraldehyde phosphate (C 3 H 5 O 3 P 1 ) Net result for steps 4 and 5: Fructose 1, 6-diphosphate (C 6 H 10 O 6 P 2 ) ↔ 2 molecules of Glyceraldehyde phosphate (C 3 H 5 O 3 P 1 )

triose phosphate dehydrogenase First the enzyme transfers a hydrogen (H - ) adds a phosphate (P) + 2 glyceraldehyde phosphate 21,3-bisphoshoglyceric acid Step 6 The enzyme triose phosphate dehydrogenase serves two functions in this step. First the enzyme transfers a hydrogen (H - ) from glyceraldehyde phosphate to the oxidizing agent nicotinamide adenine dinucleotide (NAD + ) to form NADH. Next triose phosphate dehydrogenase adds a phosphate (P) from the cytosol to the oxidized glyceraldehyde phosphate to form 1, 3-bisphoshoglyceric acid. This occurs for both molecules of glyceraldehyde phosphate produced in step 5. A. Triose phosphate dehydrogenase + 2 H NAD + → 2 NADH + 2 H + B. Triose phosphate dehydrogenase + 2 P + 2 glyceraldehyde phosphate (C 3 H 5 O 3 P 1 ) → 2 molecules of 1,3-bisphoshoglyceric acid (C 3 H 4 O 4 P 2 )

phosphoglycerokinase transfers 21,3-diphoshoglyceric acid 2 3-phosphoglyceric acid 2 ATP Step 7 The enzyme phosphoglycerokinase transfers a P from 1,3-diphoshoglyceric acid to a molecule of ADP to form ATP. This happens for each molecule of 1,3- diphoshoglyceric acid. The process yields two 3- phosphoglyceric acid molecules and two ATP molecules. 2 molecules of 1,3-diphoshoglyceric acid (C 3 H 4 O 4 P 2 ) + phosphoglycerokinase + 2 ADP → 2 molecules of 3-phosphoglyceric acid (C 3 H 5 O 4 P 1 ) + 2 ATP

phosphoglyceromutase 2 3-Phosphoglyceric acid 22- Phosphoglyceric acid Step 8 The enzyme phosphoglyceromutase relocates the P from 3-phosphoglyceric acid from the third carbon to the second carbon to form 2- phosphoglyceric acid. 2 molecules of 3-Phosphoglyceric acid (C 3 H 5 O 4 P 1 ) + phosphoglyceromutase → 2 molecules of 2- Phosphoglyceric acid (C 3 H 5 O 4 P 1 )

enolase 22-Phosphoglyceric acid 2phosphoenolpyruvic acid Step 9 The enzyme enolase removes a molecule of water from 2-phosphoglyceric acid to form phosphoenolpyruvic acid (PEP). This happens for each molecule of 2-phosphoglyceric acid. 2 molecules of 2-Phosphoglyceric acid (C 3 H 5 O 4 P 1 ) + enolase → 2 molecules of phosphoenolpyruvic acid (PEP) (C 3 H 3 O 3 P 1 )

pyruvate kinase 2 PEP 2pyruvic acid 2 ATP Step 10 The enzyme pyruvate kinase transfers a P from PEP to ADP to form pyruvic acid and ATP. This happens for each molecule of PEP. This reaction yields 2 molecules of pyruvic acid and 2 ATP molecules. 2 molecules of PEP (C 3 H 3 O 3 P 1 ) + pyruvate kinase + 2 ADP → 2 molecules of pyruvic acid (C 3 H 4 O 3 ) + 2 ATP

Glycolysis produces 4 ATP's and 2 NADH, but uses 2 ATP's in the process a net of 2 ATP and 2 NADH a net of 2 ATP and 2 NADH NOTE: NOTE: this process does not require O 2 and does not yield much energy

usedsteps ATP are used in steps 1-3 generated step 7 2 ATP are generated in step 7 generatedstep 10 2 ATP are generated in step ATP molecules produced. - 2 ATP molecules used ATP 2 ATP molecules (Total)

Summary of Glycolysis a single glucose molecule in glycolysis produces a total of glycolysis pyruvic acid 2 molecules of pyruvic acid ATP 2 molecules of ATP NADH 2 molecules of NADH water 2 molecules of water

Kreb’s Cycle Citric Acid Cycle / Tricarboxylic Acid Cycle

What is Krebs Cycle? oxidize pyruvate Carbon Dioxide (CO 2 ) Water (H 2 O). Used to oxidize the pyruvate formed during the glycolytic breakdown of glucose into Carbon Dioxide (CO 2 ) and Water (H 2 O). oxidizes acetyl CoA It also oxidizes acetyl CoA which arises from breakdown of carbohydrate, lipid, and protein.

Metabolic pathways fall into three categories: endergonic. 1) Anabolic pathways are those involved in the synthesis of compounds. Anabolic pathways are endergonic. exergonic (2) Catabolic pathways are involved in the breakdown of larger molecules, commonly involving oxidative reactions; they are exergonic, producing reducing equivalents and, mainly via the respiratory chain, ATP. citric acid cycle (3) Amphibolic pathways occur at the “crossroads” of metabolism, acting as links between the anabolic and catabolic pathways, eg, the citric acid cycle.

GLUCOSEGLYCOLYSIS PYRUVATE KREB’S CYCLE CO2 & H20

beginsacetyl –CoA It begins when acetyl –CoA enters into a reaction to form citric Acid. This cycle was discovered by British biochemist Sir Hans Krebs.Sir Hans Krebs first product citric acid (citrate) citric acid cycle The first product of Krebs cycle is citric acid (citrate).Therefore, it is also known as citric acid cycle.

4C 6C THE OXIDATION OF PYRUVATE TO ACETYL-CoA IS THE IRREVERSIBLE ROUTE FROM GLYCOLYSIS TO THE CITRIC ACID CYCLE Pyruvate dehydrogenase

Pyruvate Dehydrogenase Is Regulated by End-Product Inhibition & Covalent Modification Pyruvate dehydrogenase is inhibited by its products 1.acetyl-CoA 2.NADH

All the products of digestion are metabolized to a common product, acetyl- CoA, which is then oxidized by the citric acid cycle

Steps of Krebs cycle cyclic oxidation process nine steps occur in overall Krebs cycle: 1. Condensation 1. Condensation 2. Isomerisation 2. Isomerisation 3. Dehydrogenation 3. Dehydrogenation 4. Decarboxylation 4. Decarboxylation 5. Oxidative Decarboxylation 5. Oxidative Decarboxylation 6. Substrate level ATP/GTP synthesis. 6. Substrate level ATP/GTP synthesis. 7. Dehydrogenation (oxidation) of Succinate 7. Dehydrogenation (oxidation) of Succinate 8. Hydration 8. Hydration 9. Dehydrogenation (Oxidation) of Malate 9. Dehydrogenation (Oxidation) of Malate

Step 1: Condensation In first step of Krebs cycle, Acetyl CoA combines with oxaloacetate in the presence of condensing enzymes citrate synthetase. CoA is released out. The product of condensation is citrate which is a tricarboxylic 6-carbon compound. CATALYTIC ROLE ROLE

Step 2: Isomerisation Citrate formed in first step is converted into its isomer isocitrate in a two – step reaction in the presence of iron containing enzyme aconitase. (i) Dehydration : A molecule of water is released and citric acid is changed into cis-aconitate.

Step 2: Isomerisation aconitase. Citrate formed in first step is converted into its isomer isocitrate in a two – step reaction in the presence of iron containing enzyme aconitase. (i) Dehydration : A molecule of water is released and citric acid is changed into cis-aconitate. (ii) Rehydration : Cis – aconitate combines with a molecule of water and form isocitrate.

Step 2: Isomerisation aconitase Citrate formed in first step is converted into its isomer isocitrate in a two – step reaction in the presence of iron containing enzyme aconitase. (i) Dehydration : A molecule of water is released and citric acid is changed into cis-aconitate. (ii) Rehydration : Cis – aconitate combines with a molecule of water and form isocitrate.

Step 3: Dehydrogenation isocitrate dehydrogenase Now isocitrate undergoes dehydrogenation in the presence of an enzyme isocitrate dehydrogenase. Mn 2 + ion is required for the functioning of enzyme. Hydrogen given out by isocitrate is picked up by NAD + (Nicotinamide adenine dinucleotide) to form NADH 2. After losing hydrogen, isocitrate is changed into oxalosuccinate (6C).

Step 4: Decarboxylation oxalosuccinate decarboxylase Oxalosuccinate in Step 4 undergoes decarboxylation. In the presence of oxalosuccinate decarboxylase enzyme, oxalosuccinate is changed into α-ketoglutarate.

Step 5: Oxidative Decarboxylation dehydrogenation decarboxylation In this step 5-carbon compound, α – Ketoglutarate undergoes simultaneous dehydrogenation and decarboxylation in the presence of enzyme α – ketoglutarate dehydrogenase complex. This enzyme complex contain Thiamine Pyrophosphate (TPP), Lipoic Acid, Mg 2 + and trans – succinylase. NAD + and CoA are required. The products formed are 4 – carbon compound succinyl CoA, NADH 2 and CO 2.

Step 6: Substrate level ATP/GTP Synthesis succinyl thiokinase In the presence of enzyme succinyl thiokinase, succinyl CoA is hydrolyzed. CoA and Succinate are formed. The energy liberated during the process is used in synthesis of ATP in Plants and GTP (Guanosine triphosphate) or ITP (Inosine triphosphate) in animals. CoA is released out.

Step 7: Dehydrogenation (Oxidation) succinate dehydrogenase 4 – Carbon compound Succinate is oxidized to another 4-carbon compound fumarate with the help of enzyme succinate dehydrogenase and hydrogen acceptor FAD (Flavin Adenine Dinucleotide). The enzyme is attached to inner mitochondrial membrane. It contains non haem iron (Fe–S) protein. This enables the enzyme to get directly linked to electron transport chain.

Step 8: Hydration fumarase Fumarate reacts with a molecule of water, in the presence of an enzyme fumarase forming another 4-carbon dicarboxylic acid called Malate.

Step 9: Dehydrogenation (Oxidation) malate dehydrogenase With the help of enzyme malate dehydrogenase, Malate formed in step 8 is oxidized to oxaloacetate. NAD + reduced to NADH 2. Malate + NAD + N oxaloacetate + NADH 2

oxaloacetate Back again to step 1 An oxaloacetate formed in this reaction becomes available to combine with acetyl CoA to start a new cycle all over again. Back again to step 1

Note : The overall equation of oxidative catabolism of pyruvate can be written as follows:- NADH 2 & FADH 2 electron transport system Oxidative Phosphorylation NADH 2 & FADH 2 are linked to electron transport system and formation of ATP by Oxidative Phosphorylation. 3 3

The Conversion of Pyruvate to Acetyl CoA for Entry Into the Kreb's Cycle 2 NADH's are generated 2 CO 2 are released

The Kreb's Cycle 6 NADH's are generated 2 FADH 2 is generated 2 ATP are generated 4 CO 2 's are released

Therefore, for each glucose molecule that enters into the Kreb's cycle (including the prepatory conversion to Acetyl CoA), the net production of products are:  8 NADH  2 FADH 2  2 ATP  6 CO 2

Stages of the TCA cycle The cycle can be divided into three stages according to the role of OAA: – Stage 1: The attachment of acetyl CoA to oxaloacetate carrier (reaction1) – Stage 2: Breaking of oxaloacetate carrier (reaction 2-5) – Stage 3: Regeneration of the carrier (reaction 6-8)

Functions of TCA cycle: Amphibolic Function: TCA cycle has both anabolic and catabolic functions a- Catabolic role: It is the final common pathway for oxidation of carbohydrate, lipids and proteins with energy production. B-Anabolic role: Source of the intermediates used in biosynthesis e.g. 1.Oxaloacetic acid is used in gluconeogenesis. 2.α- ketoglutarate is used for synthesis of some non essential amino a. 3.Succinyl CoA is used in heme synthesis

Besides Glycolysis and kreb’s, Is there anything more?

YES!E.T.P.

Electron Transport Phosphorylation (Chemiosmosis) Goal:Goal: to break down NADH and FADH 2, pumping H + into the outer compartment of the mitochondria Where: mitochondriaWhere: mitochondria

The figure is found at (December 2006)

The figure is found at (December 2006)

The figure is found at (December 2006) ATP synthase inner mitochondrial membrane

In this reaction, the ETS creates a gradient which is used to produce ATP, quite like in the chloroplast In this reaction, the ETS creates a gradient which is used to produce ATP, quite like in the chloroplast

Electron Transport Phosphorylation typically produces 32 ATP's

Aerobic Respiration Net Energy Production from Aerobic Respiration Glycolysis:Glycolysis: Kreb's CycleKreb's Cycle: Electron TransportElectron Transport Phosphorylation Phosphorylation: Net Energy ProductionNet Energy Production:

Aerobic Respiration Net Energy Production from Aerobic Respiration Glycolysis:Glycolysis: Kreb's CycleKreb's Cycle: Electron TransportElectron Transport Phosphorylation Phosphorylation: Net Energy ProductionNet Energy Production: LET’S COUNT THE ATP’S ONLY AND EXCLUDE NADH & FADH

Aerobic Respiration Net Energy Production from Aerobic Respiration Glycolysis:Glycolysis: Kreb's CycleKreb's Cycle: Electron TransportElectron Transport Phosphorylation Phosphorylation: Net Energy ProductionNet Energy Production:

Aerobic Respiration Net Energy Production from Aerobic Respiration Glycolysis: 2 ATPGlycolysis: 2 ATP Kreb's CycleKreb's Cycle: Electron TransportElectron Transport Phosphorylation Phosphorylation: Net Energy ProductionNet Energy Production:

Aerobic Respiration Net Energy Production from Aerobic Respiration Glycolysis: 2 ATPGlycolysis: 2 ATP Kreb's Cycle2 ATPKreb's Cycle: 2 ATP Electron TransportElectron Transport Phosphorylation Phosphorylation: Net Energy ProductionNet Energy Production:

Aerobic Respiration Net Energy Production from Aerobic Respiration Glycolysis: 2 ATPGlycolysis: 2 ATP Kreb's Cycle2 ATPKreb's Cycle: 2 ATP Electron TransportElectron Transport Phosphorylation32 ATP Phosphorylation: 32 ATP Net Energy ProductionNet Energy Production:

Aerobic Respiration Net Energy Production from Aerobic Respiration Glycolysis: 2 ATPGlycolysis: 2 ATP Kreb's Cycle2 ATPKreb's Cycle: 2 ATP Electron TransportElectron Transport Phosphorylation32 ATP Phosphorylation: 32 ATP Net Energy Production36 ATP!Net Energy Production: 36 ATP!