Cellular Pathways that Harvest Chemical Energy : Respiration

Cellular Pathways that Harvest Chemical Energy : Respiration

Energy flow and chemical recycling

Energy For Life

Photosynthesis stores chemical energy into chemical bonds and

Respiration releases the energy stored in the chemical bonds

ATP is the biological currency of Energy

Oxidation and Reduction

Gain of one or more electrons by an atom, ion or molecule is called Reduction

Oxidation and Reduction always occurs together, one material is oxidized (loss E) and other is Reduced (Gain E)

Oxidized and Reduced NAD

Coenzyme NAD is a key electron carrier in the redox Rxn

NAD+ as an electron shuttle

Energy Carrier

Oxidizing agent (NAD) accepts E in the process of oxidizing the reducing agent (AH2 to A). Oxidizing agent (NAD) becomes reduced (NADH).

Reducing agent donates E and becomes Oxidized as it reduces the Oxidizing agent (B to BH2)

Cellular Energy

Pathways

Overview of cellular respiration

Glycolysis and Fermentation

Changes in Free EnergyEach step in glycolysis changes the free energy available

Thus after the step 6 each following steps and metabolites or products will have less energy

First you invest energy then harvest it……

Glycolysis: Glucose to Pyruvate

The energy-investing reactions/phase of Glycolysis

Glycolysis: Glucose to Pyruvate

Energy-harvesting reactions/phase yields ATP and NADH

Pl note that step 5… each molecule is 2 units because 6C are splits into two 3C molecules

Step 6 to 7 is a substrate-level phosphorylation

Substrate-level

phosphorylation

Glu to Pyr

Step 9 to 10 is also a SLP

Glycolysis nets two Molecules of ATP and two Molecules of NADH

4ATP-2ATP=2ATP

In fermentation the net yield is only 2 ATP

Pyruvate Oxidation (Mito)

PDC is a large complex, Pyruvate DH converts Pyruvate to Acetyl CoA, releasing first Carbon dioxide

Pyruvate is Oxidized to acetyl group, E conserved in NADH and some energy is conserved by comining acetyl group to CoA

Pyruvate to acetyl CoA

Citric Acid or TCA Cycle

Acetyl CoA enters the TCA cycle, and CoA regenerated

TCA Cycle

Closer look at TCA cycle

Summary of TCA cycle

Free EnergyTCA cycle releases more energy than Glycolysis or pyruvate reduction

Oxidation of NADH + H+

Resp Chain

Chemiosmotic Mechanism

ATP SynthesisATP synthesis is a reversible reaction and ATP synthase can also act as an ATPase hydrolyzing ATP to ADP

Exergoic Rxn from Et drive the Electrogenic pumping of protons out of Mitochondria into IM space

Pot E of proton gradient has two role, act as channel for protons to diffuse back and it uses E of diffusion to make ATP

Chemi-osmotic

Mechanism

Chemi-osmotic

MechanismCouples ET to the ATP synthesis using ATP synthase using a Proton Gradient

Lactic Acid Fermentation

Alcoholic Fermentation

Cellular Respiration

Theoretical Net ATP yield from the complete oxidation each glucose molecule is 36 ATP, but never in a living system

Cellular Respiration

Cellular Respiration

ATP molecules during cellular respiration

Relationship among the other major Metabolic Pathways

Catabolism of various food molecules

Coupling Metabolic Pathways

OAA and Asp interconverts, is called Transamination

Regul by Negative

and Positive

FeedbackExcess accumulation of some products can shut down their synthesis or stimulate synthesis of other products

Feedback Regulation

Citrate and ATP inhibits PFK thus Glycolysis

ADP and AMP stimulates Glycolysis

Feedback Regulation

ATP and NADH inhibits TCA cycle

Citrate stimulates FA-CoA Rxn

NAD and ADP activated ICDH

ATP and NADH inhibits KGADH

Control of cellular respiration

Energy flow and chemical recycling

SummaryPhotosynthesis places energy into chemical bonds and respiration releases it

Glycolysis, TCA cycle,and ET chain and ATP synthesis

Fermentation of pyruvate to lactate or ethanol

Oxidation reduction reactions

Chemiosmotic synthesis of ATP using a proton gradient

Regulation of Metabolic pathways by positive and negative feedback

Various metabolic pathways inter-communicate with each other

Pl read pages 134-135 for a detailed summary