B9 Respiration

B.9.1 Compare aerobic and anaerobic respiration of glucose in terms of oxidation/reduction and energy released.
Redox equations should be used as appropriate.

Aerobic - uses oxygen as the terminal electron acceptor
Anaerobic - uses terminal electron acceptors other than oxygen

Aerobic respiration
- glucose is converted into pyruvate, which, in presence of oxygen, changes to carbon dioxide and water. Overall, glucose undergoes oxidation and oxygen undergoes reduction.
- breaks down glucose, amino acids and fatty acids to release energy
- oxygen is the terminal electron acceptor

Glucose + Oxygen à  Carbon dioxide + Water + Energy

- high energy yielding process
- up to 38 ATP molecules produced for every glucose
- occurs in almost all living organisms
- excess carbon dioxide and water is excreted (the removal of the toxic waste products of metabolism) and maximum energy is released from the glucose

Anaerobic respiration
- happens in the absence of air
- pyruvate is converted to lactate in human beings, whereas yeast converts pyruvate into ethanol and carbon dioxide.
- not so much energy and more toxic waste produced.
- If oxygen is unavailable this process also occurs in humans.
E.g. intense exercise - lactic acid in muscle tissue is built up, resulting in muscle pain and cramping.
E.g. bacteria in milk also produces lactic acid (the optical isomer of the one produced in muscle cramping)
E.g. yeast produces alcohol (also toxic). In the end there is too much alcohol that the yeast cannot survive.
- Respiration that occurs without oxygen to produce ATP

Glucose à Energy (ATP) + Ethanol + Carbon dioxide

or

Glucose à Energy (ATP) + Lactic acid

- relatively less energy yield than aerobic
- in alcoholic fermentation 2 molecules of ATP are produced for every glucose in the reaction. The same for lactate fermentation
- Hence, in anaerobic respiration one glucose is broken down into 2 ATP.




B.9.2 Outline the role of copper ions in electron transport and iron ions in oxygen transport.
(Cytochromes and hemoglobin are suitable examples)

HEMOGLOBIN AND OXYGEN
- iron is essential in this process, because of its ability to form complexes.

Hemoglobin
- a complex protein
- has porphyrin rings at certain sites.
- A Fe2+ ion at the center of the ring attracts and transports oxygen.
- At high oxygen concentrations (like the lungs) the hemoglobin binds to the oxygen which is then carried around through the bloodstream to cells for respiration.
- At high carbon dioxide concentrations (like in cells) the hemoglobin binds to the carbon dioxide which are then transported back to the lungs where the carbon dioxide is exhaled.
- Carbon monoxide and cyanide are poisonous for hemoglobin. They attach rather permanently to the Fe2+ ion so it is unable to bind to any oxygen molecules rendering it useless.

In the mitochondria food is oxidised at the cellular level involving redox reactions and electron transport.
Cytochromes - enzymes that catalyse the oxidation processes; it incorporates porphyrin rings with either a Cu2+ or Fe2+at the center,
- contain Cu2+ or Fe3+ ions
- porphyrin ligand contains 4 nitrogen atoms, each dontaes 2 electrons
For each step of the oxidation of glucose:

Fe3+à Fe2+ + e-

or 

Cu2+à Cu+ + e-

Cytochrome structure heme group is from cytochrome oxidase.

Oxidation stage of glucose:

C6H12O6 + 6H2O à 6CO2+ 24H+ +24e-

Fe3+ + e- à  Fe2+   (Metal ion is reduced)

Reduction stage:

O2 + 4H+ +4e- à  2H2O

Fe2+ à  Fe3+ + e-   (Metal ion is oxidized)

Cu+  à Cu2+  + e-