BSC Exam I Lectures and Text Pages I. Intro to Biology (2-29) II. Chemistry of Life – Chemistry review (30-46) – Water (47-57) – Carbon (58-67) – Macromolecules (68-91) III. Cells and Membranes – Cell structure (92-123) – Membranes ( ) IV. Introductory Biochemistry – Energy and Metabolism ( ) – Cellular Respiration ( ) – Photosynthesis ( )

Cellular Respiration ALL energy ultimately comes from the SUN Catabolic pathways  Yield energy by oxidizing organic fuels All the primary organic molecules can be consumed as fuel We’ll only examine the most common fuel = sugar (C 6 H 12 O 6 ) Exergonic rxn: ∆G = -686 kcal/mol of Glucose (the energy will be used to generate ATP)

Energy ultimately comes from the Sun Energy – Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM CO 2 + H 2 O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O 2 ATP powers most cellular work Heat energy Figure 9.2

Catabolic Pathways and Production of ATP The breakdown of organic molecules is exergonic (releases energy) Catabolic pathways yield energy by oxidizing organic fuels

Catabolic Pathways One catabolic process, fermentation – Is a partial degradation of sugars that occurs without oxygen – Involves Glycolysis – Yields 2 ATP/Glucose molecule

Catabolic Pathways Cellular respiration – Is the most prevalent and efficient catabolic pathway – Consumes oxygen and organic molecules such as glucose – Involves Glycolysis – Yields up to 38 ATP/Glucose molecule To keep working – Cells must regenerate ATP

Cellular Respiration Redox rxns = oxidation-reduction rxns Transfer of electrons (e-) releases energy stored in organic molecules  this energy is ultimately used to generate ATP Oxidation = loss of e- from one substance Reduction = addition of e- to another substance Na + Cl  Na + + Cl - Na is the reducing agent (donates an e- to CL) Cl is the oxidizing agent (removes an e- from Na)

Cellular Respiration Respiration is a redox rxn: By oxidizing glucose, energy stored in glucose is liberated to make ATP – Happens in a series of enzyme-catalyzed steps – Coenzyme (NAD+) acts as e- shuttle Electron transport chains (ETC) - breaks the energetic fall of e- into several energy-releasing steps (not one big explosive rxn), fig 9.5 – Consists of mostly proteins embedded in the inner mitochondrial membrane Overview of Respiration: (fig 9.6)

Redox Reactions: Oxidation and Reduction Catabolic pathways yield energy – Due to the transfer of electrons

The Principle of Redox Redox reactions – Transfer electrons from one reactant to another by oxidation and reduction In oxidation – A substance loses electrons, or is oxidized In reduction – A substance gains electrons, or is reduced

Examples of redox reactions Na + Cl Na + + Cl – becomes oxidized (loses electron) becomes reduced (gains electron)

Some redox reactions Do not completely exchange electrons Change the degree of electron sharing in covalent bonds CH 4 H H H H C OO O O O C HH Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxideWater + 2O 2 CO 2 + Energy + 2 H 2 O becomes oxidized becomes reduced Reactants Products Figure 9.3

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidation of Organic Fuel Molecules During Cellular Respiration During cellular respiration – Glucose is oxidized and oxygen is reduced C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes oxidized becomes reduced

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest via NAD + and the Electron Transport Chain Cellular respiration – Oxidizes glucose in a series of steps – Allows the cell to use the energy harvested from sugar to power work rather than losing it in one explosive reaction.

Electrons from organic compounds Are usually first transferred to NAD +, a coenzyme NAD + H O O OO–O– O O O–O– O O O P P CH 2 HO OH H H HOOH HO H H N+N+ C NH 2 H N H N N Nicotinamide (oxidized form) NH 2 + 2[H] (from food) Dehydrogenase Reduction of NAD + Oxidation of NADH 2 e – + 2 H + 2 e – + H + NADH O H H N C + Nicotinamide (reduced form) N Figure 9.4

NADH, the reduced form of NAD + Passes the electrons to the electron transport chain So it is an electron shuttle and moves electrons to the ETC from both glycolysis and from the citric acid cycle.

If electron transfer is not stepwise – A large release of energy occurs – As in the reaction of hydrogen and oxygen to form water (a) Uncontrolled reaction Free energy, G H2OH2O Explosive release of heat and light energy Figure 9.5 A H / 2 O 2

The electron transport chain (ETC) Passes electrons in a series of steps instead of in one explosive reaction Uses the energy from the electron transfer to form ATP

Electron Transport Chain 2 H 1 / 2 O 2 (from food via NADH) 2 H e – 2 H + 2 e – H2OH2O 1 / 2 O 2 Controlled release of energy for synthesis of ATP ATP Electron transport chain Free energy, G (b) Cellular respiration + Figure 9.5 B

An overview of cellular respiration Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH 2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis ATP Substrate-level phosphorylation Oxidative phosphorylation Mitochondrion Cytosol

Three Stages of Cellular Respiration: A Preview Respiration is a cumulative function of three metabolic stages – Glycolysis – The citric acid cycle (Kreb’s Cycle) – Oxidative phosphorylation (driven by the ETC)

Stages of Cellular Respiration 1. Glycolysis – Breaks down glucose into two molecules of pyruvate – Produces net 2 ATP and 2 NADH Conversion of pyruvate to acetyl CoA yields 2NADH 2. The citric acid cycle – Completes the breakdown of glucose – Produces net 2 ATP, 6 NADH and 2 FADH 2 from 2 Acetyl CoA

Stages of Cellular Respiration 3. Oxidative phosphorylation – Is driven by the electron transport chain (receives electrons from NADH and FADH 2 ) – Generates 32 – 34 ATP

An overview of cellular respiration Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH 2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis ATP Substrate-level phosphorylation Oxidative phosphorylation Mitochondrion Cytosol

Cellular Respiration Glycolysis & Citric Acid Cycle = catabolic pathways that breakdown glucose Glycolysis  pyruvate + coenzymes + ATP CAC  coenzymes + ATP ATP formed by substrate-level phosphorylation (fig 9.7) = enzyme transfers a phosphate group from an organic substrate to ADP to make ATP Oxidative Phosphorylation = ATP synthesis powered by ETC. Makes 90% of the 38 ATPs

Both glycolysis and the citric acid cycle Can generate ATP by substrate-level phosphorylation Figure 9.7 Enzyme ATP ADP Product Substrate P +

Glycolysis Glycolysis harvests chemical E by oxidizing glucose to pyruvate Glucose  Two 3-C sugars  oxidized & rearranged  Two pyruvates Two Major Phases of Glycolysis 1. E-investment phase (fig 9.9) Rearrange glucose + add phosphate groups (uses 2 ATP) Split 6-C sugar  two 3-C sugar isomers Glyceraldehyde-3-phosphate form  next phase 2. E-payoff phase (fig 9.9) 2 NAD+  2 NADH & a phosphate group added to each of 2 3-C sugars 4 ATP produced by substrate-level phosphorylation Rearrangement of remaining phosphate group and the 3-C substrate Final Products from 1 Glucose = 2 ATP + 2 pyruvate + 2NADH

Glycolysis Glycolysis harvests energy by oxidizing glucose to pyruvate Glycolysis – Means “splitting of sugar” – Breaks down glucose into pyruvate – Occurs in the cytoplasm of the cell

Glycolysis Glycolysis consists of two major phases – Energy investment phase – Energy payoff phase Glycolysis Citric acid cycle Oxidative phosphorylation ATP 2 ATP 4 ATP used formed Glucose 2 ADP + 2 P 4 ADP + 4 P 2NAD e - + 4H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Energy investment phase Energy payoff phase Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed – 2 ATP used 2 ATP 2NAD + + 4e – + 4H + 2NADH + 2H + Figure 9.8

Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate H H H H H OH HO CH 2 OH H H H H O H OH HO OH P CH 2 O P H O H HO H CH 2 OH P O CH 2 O O P HO H H OH O P CH 2 C O CH 2 OH H C CHOH CH 2 O O P ATP ADP Hexokinase Glucose Glucose-6-phosphate Fructose-6-phosphate ATP ADP Phosphoglucoisomerase Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Glycolysis CH 2 OH Oxidative phosphorylation Citric acid cycle Figure 9.9 A A closer look at the energy investment phase Uses 2 ATP. Produces 2 Glyceraldehyde-3-phosphates to feed into energy payoff phase.

2 NAD + NADH H + Triose phosphate dehydrogenase 2 P i 2 P C CHOH O P O CH 2 O 2 O–O– 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase CH 2 OP 2 C CHOH 3-Phosphoglycerate Phosphoglyceromutase O–O– C C CH 2 OH H O P 2-Phosphoglycerate 2 H 2 O 2 O–O– Enolase C C O P O CH 2 Phosphoenolpyruvate 2 ADP 2 ATP Pyruvate kinase O–O– C C O O CH Pyruvate O Figure 9.8 B A closer look at the energy payoff phase Produces 4 ATP, 2 NADH (for ETC), and 2 pyruvates to be converted to Acetyl-CoA and fed into Citric Acid Cycle. So, net of glycolysis is 2 ATP, 2 NADH, and 2 pyruvate.

Citric acid cycle Citric acid cycle completes the E-yielding oxidation of organic molecules Pyruvate enters mitochondrion via active transport  converted to acetyl coenzyme A (acetyl CoA) – Happens in 3 rxns catalyzed by a multienzyme complex Citric acid cycle (also = Krebs cycle) Citrate (ionized form of citric acid) = 1st molecule produced Acetyl CoA brings two C atoms to cycle  recycles oxaloacetate  C atoms leave cycle as CO 2 (completely oxidized) Ultimately get CO 2, NADH, FADH 2, and ATP from the CAC.

Before the citric acid cycle can begin Pyruvate must first be converted to acetyl CoA, which links the citric acid cycle to glycolysis Happens in 3 rxns catalyzed by a multienzyme complex. CYTOSOLMITOCHONDRION NADH + H + NAD CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O–O– O O C C CH 3 Figure 9.10 Process yields 2 NADH (for ETC) from 2 pyruvate