Cellular Respiration

#biology/Chapter12

Respiration contains 4 stages:

• Glycolysis

• The Link Reaction

• Kerbs Cycle

• Oxidative Phosphorylation

Glycolysis

Takes place in the cytoplasm:

• Involves splitting the 6 carbon sugar into two molecules of pyruvate, each 3 carbon compounds

• At the end of this stage 4 ATP molecules are produced, 2 ATP molecules are used resulting in a net total of 2 ATP molecules.

• 2 molecules of NADH are also produced

Step 1

ATP is hydrolysed to produce ADP and a phosphate group. Glucose is then phosphorylated using this phosphate group. This produces a glucose phosphate compound. The phosphate group is added to the 6th carbon in the glucose molecule.

Step 2

Phosphoglucose isomerase is used to convert glucose into its isomer, fructose 6 phosphate.

Step 3

ATP is hydrolysed again to produce an extra phosphate group which is added to the fructose phosphate. This results in fructose 1,6 bisphosphate.

Step 4

Fructose is then converted into 2 molecules of Triose phosphate which are 3 carbon compounds each

Step 5

The triose phosphate is then dehydrogenated and is reduced to NAD, forming NADH

Step 6

Each triose phosphate is dephosphorylated and the 2 phosphate groups are then added to ADP to produce 2 ATP molecules each, total 4 ATP molecules. After dephosphorylation, pyruvate is produced. 2 molecules of NADH is produced.

The Link Reaction

Occurs in the Matrix

• Involves decarboxylating pyruvate, removing the CO2 from the compound, forming Acetyl Acetyl is a 2 carbon compound

Coenzyme A is then added to the Acetyl compound to from Acetyl CoA

• The function of the Co-enzyme A is to act as a carrier of acetyl groups to the Krebs cycle

Krebs Cycle

Occurs in the Matrix

Co-enzyme A does not enter the Krebs cycle instead it is recycled to facilitate the next Acetyl compound.

Stage 1

Acetyl combines with a 4C compound called oxaloacetate to form a 6C compound called citrate

Stage 2

Citrate is decarboxylated and dehydrogenated in a series of step to yield CO2 and hydrogen ions.

• CO2 is given off as waste gas while hydrogen ions are added to electron carriers such as NAD and FAD

For every turn of the Krebs cycle, one FADH is produced, 3 NADH is produced, two molecules of CO2 are given off, and one ATP is generated.

[image:C47DFEF0-DEB9-4D3B-A968-ED75F228141B-2257-00000011AE69F5AB/F09CD1E3-BF66-415E-BA0C-89509C28EB28.png]

Oxidative Phosphorylation and the Electron Transport Chain

Occurs in the inner mitochondrial membrane, also knowns as the cristae

Step 1

Hydrogen is removed from the NADH and FADH and is split into a proton and an electron. Electron carriers then transport the electron from hydrogen releasing energy as electron moves through the electron transport chain.

• The electrons move within the inner mitochondrial membrane until it finds the final electron acceptor — (See Below)

Step 2

Some of the energy moves protons from the matrix into the inner-membrane space of the mitochondrion, causing a concentration gradient.

Step 3

Protons flow back into the matrix through a protein channel down the concentration gradient. ATP Synthase is part of the protein and as protons pass through, their electrical energy from the protons is used to synthesize ATP (Chemiosmosis)

• After the proton enters the matrix, it combines with the electron. Water is then formed after the interacting with the final electron acceptor — (See Below)

Final Step

Oxygen is the final electron acceptor. In the mitochondrial matrix oxygen is reduced to water.

This forms the aerobic respiration equation: C6H12O6 + 6O2 ————> 6CO2 + 6H2O + ATP

• 6CO2 is formed during the Krebs cycle

• 6H2O is formed during Oxidative Phosphorylation and The Electron Transport Chain These steps yields 28 ATP [image:91C10A79-2FBB-4B7F-8586-6F83FB790A7D-2257-00000019C1EE6892/92F4AE88-6660-445F-8B5A-401270E61232.png]

Sites of the Different Stages of Respiration

[image:4E564C25-4AA1-4AA8-B9FE-C78D032E0BF1-2257-0000001CB620106D/14D46C1C-03DA-40A3-BBC9-7560AFE6E859.png]

ATP used vs. ATP produced

Glycolysis

ATP used: 2 ATP made: 4 Net Gain: 2

Link Reaction

ATP used: 0 ATP made: 0 Net Gain: 0

Krebs cycle (2 turns per glucose)

ATP used: 0 ATP made: 2 Net Gain: 2

Oxidative Phosphorylation

ATP used: 0 ATP made: 28 Net Gain: 28

Total ATP produced from one respiration cycle: 32