CELLULAR RESPIRATIONREVIEW ON AEROBIC RESPIRATION

CELLULAR RESPIRATIONAllows organisms to use energy

stored in the chemical bonds of glucose to produce ATP. Cells use ATP as a “currency unit” to supply their energy needs.

Cellular respiration is a process in which energy in glucose is

transferred to ATP. C6H12O6 (aq) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (l) + heat

ΔG = -2880 kJ per mole of C6H12O6

In respiration, glucose is oxidised to release energy and oxygen is reduced to form water.

The carbon atoms of sugar are released as Carbon Dioxide.

The complete breakdown of glucose to Carbon Dioxide and Water requires 2 MAJOR steps:

Glycolysis produces 2 ATPAerobic respiration produces 36 ATP

(Predicted Not Absolute!)

GLYCOLYSISThe glycolytic pathway is used by

all tissues for glucose breakdown to provide energy.

Pyruvate is the end product in cells with mitochondria with an adequate oxygen supply.

OXIDATION OF PYRUVATEOccurs in two stages:

Oxidation of pyruvate into acetyl-CoA- One carbon of three-carbon pyruvate is cleaved, leaves as Carbon Dioxide. This is a decarboxylation reaction that leaves a pair of electrons and associated H+ reduces NAD+

to NADH.Oxidation of acetyl-CoA- Enters into TCA cycle, oxidised to form Carbon Dioxide, Water and forms ARP both at substrate level and through the respiratory chain.

ATP GENERATION PER GLUCOSE MOLECULE THROUGH COMPLETE OXIDATION UNDER AEROBIC RESPIRATION Glycolysis

Hexokinase -1Phosphofructokinase -1Glyceraldehyde-3-P DH 2 NADH 61,3-BPG kinase 1x2 2Pyruvate kinase 1x2 2

Pyruvate to acetyl-CoA 2 NADH 6 TCA Cycle

Isocitrate DH 2 NADH 6a-k DH 2 NADH 6S. kinase 1x2 2S. DH 2 FADH2 2

M. DH 2 NADH 6

Net generation of ATP 38

WHY 38 ATP GENERATED IS PREDICTED NOT ABSOLUTE? Although there is a theoretical yield of 38 ATP molecules per

glucose during cellular respiration, such conditions are generally not realized due to losses such as the cost of moving pyruvate (from glycolysis), phosphate, and ADP (substrates for ATP synthesis) into the mitochondria. All are actively transported using carriers that utilise the stored energy in the proton electrochemical gradient.

Pyruvate is taken up by a specific, low km transporter to bring it into the mitochondrial matrix for oxidation by the pyruvate dehydrogenase complex.

The phosphate translocase is a symporter and the driving force for moving phosphate ions into the mitochondria is the proton motive force.

The adenine nucleotide carrier is an antiporter and exchanges ADP and ATP across the inner membrane. The driving force is due to the ATP (−4) having a more negative charge than the ADP (−3) and thus it dissipates some of the electrical component of the proton electrochemical gradient.

The outcome of these transport processes using the proton electrochemical gradient is that more than 3 H+ are needed to make 1 ATP. Obviously this reduces the theoretical efficiency of the whole process and the likely maximum is closer to 28–30 ATP molecules. In practice the efficiency may be even lower due to the inner membrane of the mitochondria being slightly leaky to protons.

Other factors may also dissipate the proton gradient creating an apparently leaky mitochondria.

KEYWORDSOxidative Phosphorylation - the

synthesis of ATP by phosphorylation of ADP for which energy is obtained by electron transport chain and which takes place in the mitochondria during aerobic respiration.

Subtrate-Level Phosphorylation - ATP formation in glycolysis is powered by the addition/removal of phosphate groups (phosphorylation) to molecules of glucose (the substrate).