H2 Biology Core 3 - Cellular Respiration: ATP Production from Glucose

Step 1 - Why cells need ATP and the overview of respiration

Every living cell needs a continuous supply of A T P to drive active transport, biosynthesis, and movement.

Step 1 - Why cells need ATP and the overview of respiration

Cellular respiration is the process that converts the chemical energy in glucose into A T P.

Step 1 - Why cells need ATP and the overview of respiration

The overall equation is glucose plus six oxygen molecules yields six carbon dioxide, six water, and a large amount of A T P.

Step 1 - Why cells need ATP and the overview of respiration

Respiration has four main stages: glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation.

Step 2 - Glycolysis in the cytoplasm

Glycolysis takes place in the cytoplasm and does not require oxygen.

Step 2 - Glycolysis in the cytoplasm

One molecule of glucose, a six carbon sugar, is phosphorylated using two A T P and then split into two molecules of triose phosphate, each with three carbons.

Step 2 - Glycolysis in the cytoplasm

Each triose phosphate is oxidised to pyruvate, generating two A T P by substrate level phosphorylation and one reduced N A D.

Step 2 - Glycolysis in the cytoplasm

The net yield from glycolysis is therefore two A T P and two reduced N A D per glucose molecule.

Step 3 - Link reaction and the Krebs cycle in the mitochondrial matrix

Pyruvate enters the mitochondrial matrix and undergoes the link reaction.

Step 3 - Link reaction and the Krebs cycle in the mitochondrial matrix

Each pyruvate loses one carbon as carbon dioxide, and the remaining two carbon fragment combines with coenzyme A to form acetyl co A.

Step 3 - Link reaction and the Krebs cycle in the mitochondrial matrix

One reduced N A D is produced per pyruvate.

Step 3 - Link reaction and the Krebs cycle in the mitochondrial matrix

Acetyl co A then enters the Krebs cycle by combining with the four carbon compound oxaloacetate to form the six carbon compound citrate.

Step 3 - Link reaction and the Krebs cycle in the mitochondrial matrix

Through a series of decarboxylation and oxidation reactions, the cycle regenerates oxaloacetate and produces one A T P, three reduced N A D, and one reduced F A D per turn.

Step 4 - Oxidative phosphorylation on the inner mitochondrial membrane

This is where most A T P is made.

Step 4 - Oxidative phosphorylation on the inner mitochondrial membrane

Reduced N A D and reduced F A D donate electrons to the electron transport chain, which is a series of carrier proteins embedded in the inner mitochondrial membrane.

Step 4 - Oxidative phosphorylation on the inner mitochondrial membrane

As electrons pass along the chain, energy is released and used to pump hydrogen ions from the matrix into the intermembrane space, creating a proton gradient.

Step 4 - Oxidative phosphorylation on the inner mitochondrial membrane

Hydrogen ions flow back through A T P synthase by chemiosmosis, and this drives the synthesis of A T P from A D P and inorganic phosphate.

Step 4 - Oxidative phosphorylation on the inner mitochondrial membrane

Oxygen is the final electron acceptor, combining with electrons and hydrogen ions to form water.

Step 5 - Total ATP yield and the role of oxygen

Adding up all stages, one molecule of glucose yields a theoretical maximum of about thirty to thirty two A T P in aerobic respiration.

Step 5 - Total ATP yield and the role of oxygen

Glycolysis contributes two, the Krebs cycle contributes two more by substrate level phosphorylation, and oxidative phosphorylation generates approximately twenty six to twenty eight from the reduced coenzymes.

Step 5 - Total ATP yield and the role of oxygen

Without oxygen, the electron transport chain stops, reduced N A D accumulates, and the cell must rely on anaerobic respiration.

Step 5 - Total ATP yield and the role of oxygen

In anaerobic conditions, pyruvate is converted to either ethanol and carbon dioxide in yeast, or lactate in mammalian muscle, regenerating N A D so glycolysis can continue with a net yield of only two A T P per glucose.