8.1 - Cell Respiration

8.1 – Cell Respiration

8.1.1 - State that oxidation involves the loss of electrons from an element, whereas reduction involves a gain of electrons; and that oxidation frequently involves gaining oxygen or losing hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen

In the equation above, the glucose molecule is oxidised into CO2. The hydrogen atoms in the molecule are removed, and some of the oxygen atoms from the O2 are added.

The oxygen molecules are reduced to form the H2O molecules. Oxygen atoms are removed [separated], and then hydrogen atoms from the glucose molecule are added.

The reaction above shows ADP + Pi being converted into ATP. The ADP molecule is oxidised. In the reverse, when ATP is converted back into ADP, the ATP is reduced.

8.1.2 - Outline the process of glycosis, including phosphorylation, lysis, oxidation and ATP formation

Glycolysis takes place in the cytoplasm. It takes place in a series of steps, breaking down the glucose molecule into the pyruvate ions.

Phosphorylation

This is the first step, where the glucose molecule reacts with ATP to form glucose phosphate. It is the converted into fructose phosphate, which reacts with another ATP molecule. In total, two ATP molecules are converted into 2ADP.

Lysis

In this stage, the fructose biphosphate is split into two molecules of triose phosphate, a three-carbon molecule.

Oxidation

Hydrogen is removed from the triose phosphate molecules. An enzyme and a coenzyme allow for the reaction to take place. The coenzyme is called NAD [nicotinamide adenine dinucleotide] , and it is a hydrogen and electron acceptor. During the oxidation of triose phosphate, NAD is reduced to form NADH + H+

ATP Formation

When the triose phosphate is converted into pyruvate, ATP is released. This type of ATP formation is different, as it occurs at substrate level. Four molecules ...

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Lysis

In this stage, the fructose biphosphate is split into two molecules of triose phosphate, a three-carbon molecule.

Oxidation

ATP Formation

When the triose phosphate is converted into pyruvate, ATP is released. This type of ATP formation is different, as it occurs at substrate level. Four molecules of ATP are produced when two molecules of pyruvate are formed. Coupled with the loss of two ATP molecules in phosphorylation, the net gain of ATP in glycolysis is two.

The triose phosphate is oxidised to form pyruvic acid. The phosphate is donated to ADP to form the ATP. Pyruvic acid is also a three-carbon molecule. Under the conditions of the cytoplasm, the pyruvic acid immediately ionises to form the ion pyruvate.

The result of this entire process is:

The NADH + H+ will produce more ATP later. No oxygen is required for this process.

8.1.3 - Draw and label a diagram showing the structure of a mitochondrion as seen in electron micrographs

The mitochondrion is the organelle in which the rest of cellular respiration occurs.

All the enzymes necessary for these reactions are located here.

The matrix contains enzymes and metabolites.

The inner membrane folds in to form cristae, maximising the surface area.

8.1.4 - Explain aerobic respiration, including the link reaction, the Krebs cycle, the role NADH + H+, the electron transport chain and the role of oxygen

Link Reaction

Once the pyruvate has diffused through the membrane of the mitochondrion, it is metabolised. The reaction occurs in the matrix. The pyruvate has one carbon atom removed to form CO2 through decarboxylation. It is also oxidised through the removal of oxygen. Combined, this is referred to as oxidative decarboxylation. One of the products is an acetyl group, which joins to the coenzyme A [CoA] in the link reaction to form acetyl CoA.

It is called the link reaction because it essentially ‘connects’ glycolysis to the Krebs cycle.

Krebs Cycle

This is also called the citric acid cycle. After the link reaction, the acetyl CoA reacts with oxaloacetate [OAA], with the result of CoA and citrate.

Citrate then gives off two molecules of CO2 in separate decarboxylation reactions. A molecule of ATP is formed at substrate level. Three molecules of reduced NAD are produced along with one molecule of another hydrogen accepter. This accepter is called flavin adenine dinucleotide [FAD].

Two cycles of the Krebs cycle take place for each molecule of glucose, as there are two molecules of pyruvate formed.

Terminal Oxidation and Oxidative Phosphorylation

In the Krebs cycle and glycolysis, pairs of hydrogen atoms are removed from the respiratory substrates. Oxidised NAD is converted into reduced NAD, except in the Krebs cycle, where FAD is reduced instead.

Hydrogen atoms or their electrons are transported along a series of carriers in the final stage of respiration. They begin from reduced NAD or FAD, combine with oxygen and form water. Energy is released during the process, which is controlled and used by the cell in the form of ATP. For each molecules of NAD that is oxidised, 3 molecules of ATP are formed.

In total, aerobic respiration forms 38 molecules of ATP for each molecule of glucose.

8.1.5 - Explain the oxidative phosphorylation in terms of chemiosmosis

Chemiosmosis is the process where ATP synthesis is coupled with electron transport via the movement of protons (H+ ions).

Electron carrier proteins along the mitochondrial wall oxidise the reduced coenzymes. The energy from this is then used to pump the protons into the membrane space.

The protons accumulate in the space to form a gradient in hydrogen ion concentration and a lower pH. Potential energy is stored, and the ions will eventually flow back into the matrix through the channels in ATP synthase enzymes. The flow of protons causes ATP synthesis to occur.

8.1.6 - Explain the relationship between the structure of the mitochondrion and its function