RESPIRATION

Glucose is a hexose produced during photosynthesis.

It is a complex molecule containing energy absorbed from sunlight 'trapped' within its carbon-hydrogen bonds.

Carbon framework of glucose is broken down and the carbon-hydrogen bonds broken.

Energy released is then used in the synthesis of ATP by chemiosmosis

Respiration is a complex multi-step reaction pathway.

Occurs in the cytoplasm of the cell.

Does not require oxygen (anaerobic)

Glucose is split into 2 smaller, 3 carbon pyruvate molecules.

ATP and reduced nicotinamide adenine dinucleotide (NAD) are also produced.

1. Phosphorylation - requires 2 molecules of ATP. 2 phosphates, released from 2 ATP molecules, are attached to a glucose molecule forming hexose biphosphate.

2. Lysis - destabilises the molecule causing it to split into 2 triose phosphate molecules

3. Phosphorylation - another phosphate group is added to each triose phosphate forming 2 triose biphosphate (phosphate groups come from free inorganic phosphate ions present in the cytoplasm)

4. Dehydration and formation of ATP - 2 triose biphosphate molecules are oxidised by removal of hydrogen atoms (dehydrogenation) to form 2 pyruvate molecules. NAD coenzymes accept the removed hydrogens they're reduced forming 2 reduced NAD molecules

Four ATP molecules are produced using phosphates from the triose biphosphate molecules.

2 ATP used to prime the process and 4 are made

1st step in aerobic respiration

Links anaerobic glycolysis to the aerobic steps of respiration

Pyruvate enters the mitochondrial matrix by active transport and undergoes oxidative decarboxylation  (CO2 is removed along with hydrogen)

Hydrogen is accepted by NAD to form NADH.

Resulting 2 carbon acetyl group is bound by coenzyme A forming acetylcoenzyme A which delivers the acetyl group to the next stage of aerobic respiration (Krebs Cycle).

NAD is used in oxidative phosphorylation to synthesise ATP

CO2 will either diffuse away and be removed as metabolic waste or in autotrophic organisms used as raw materials in photosynthesis

Takes place in the mitochondrial matrix and each complete cycle results in the breakdown of an acetyl group that are all that remain of the glucose that entered glycolysis.

Involves decarboxylation, dehydrogenation and substrate level phosphorylation.

Hydrogen atoms released are picked up by the coenzymes NAD and flavin adenine dinucleotide (FAD).

CO2 is a by product and ATP produced is available for use by energy-requiring processes within the cell.

Reduced NAD and FAD produced are used in the final, oxygen-requiring step of aerobic respiration to produce large quantities of ATP.

1. Acetyl CoA delivers an acetyl group to the Krebs cycle. 2 carbon acetyl group combines with 4 carbon oxaloacetate to from six carbon sugar citrate.

2. Citrate molecule undergoes decarboxylation and dehydrogenation producing one reduced NAD and CO2. 5 carbon compound is formed.

3. 5 carbon compound undergoes further decarboxylation and dehydrogenation reactions regenerating oxaloacetate so the cycle continues.

More CO2, two more reduced NADs and one reduced FAD are produced. ATP is produced bysubstrate-levell phosphorylation

Coenzymes are required to transfer protons, electrons and functional groups between many of these enzyme-catalysed reactions.

Redox reactions have an important role and without coenzymes transferring electrons and protons between these reactions many respiratory enzymes would be unable to function.

NAD and FAD are both coenzymes that accept protons and electrons released during the breakdown of glucose in respiration

NAD takes place in all stages of cellular respiration, FAD only accepts hydrogens in the Krebs cycle

NAD accepts 1 hydrogen, FAD accepts 2

Reduced NAD is oxidised at the start of the electron chain releasing protons and electrons, FAD is further along the chain

reduced NAD results in the synthesis of 3 ATP molecules but reduced FAD is only 2

Hydrogen atoms that have been collected by the coenzymes NAD and FAD are delivered to electron transport chains present in the membranes of the mitochondria. 

Hydrogen atoms dissociate into hydrogen ions and electrons.

High energy electrons are used in the synthesis of ATP by chemiosmosis.

Energy is released during redox reactions as the electrons reduce and oxidise electron carriers as they flow along the electron transport chain.

Energy is used to create a proton gradient leading to the diffusion of protons through ATP synthase resulting in the synthesis of ATP.

At the end of the chain electrons combine with hydrogen ions and oxygen to form water.

Oxygen is the final electron acceptor, the chain cannot operate unless it is present.

Phosphorylation of ADP to form ATP is dependant on electrons moving along electron transport chains.

Hydrogen released from NAD and FAD could combine directly with oxygen, releasing energy from the formation of bonds during the production of water but the energy could not be used to synthesise ATP

Production of ATP involving the transfer of a phosphate group from a short-lived, highly reactive intermediate such as creatine phosphate.

Different from oxidative ph which couples the flow of protons down the electrochemical gradient through ATP synthase to the phosphorylation of ADP to produce ATP.

Results in the synthesis of smaller quantities of ATP

Temporary 'emergency' measure to keep vital processes functioning

Obligate anaerobes - cannot survive in the presence of oxygen (prokaryotes)

Facultative anaerobes - synthesise ATP by aerobic respiration if oxygen is present but can switch to anaerobic respiration

Obligate aerobes - can only synthesise ATP in the presence of oxygen

Complex organic compounds are broken down into simpler inorganic compounds without the use of oxygen or the involvement of an electron transport chain.

Glucose is not fully broken down so less ATP is produced. 

The small amount produced is synthesised by substrate-level phosphorylation alone.

Alcoholic fermentation occurs in yeast and some plant root cells.

When there is no oxygen to act as the final electron acceptor the flow of electrons stops so the synthesis of ATP by chemiosmosis also stops. Reduced NAD and FAD are no longer able to be oxidised as there is nowhere for the electrons to go. NAD and FAD cannot be regenerated so the decarboxylation of pyruvate and the Krebs cycle comes to a halt.

Glycolysis would also halt due to the lack of NAD.

Pyruvate can act as a hydrogen acceptor taking the hydrogen from reduced NAD, catalysed by the enzyme lactate dehydrogenase.

Pyruvate is converted to lactate and NAD is regenerated which can be used to keep glycolysis going so a small quantity of ATP is synthesised.

Lactic acid is converted back to glucose in the liver but requires oxygen which is the reason for oxygen debt after exercise.

Reduced quantities of ATP would not be enough to maintain vital processes

Accumulation of lactic acid causes a fall in pH causing proteins to denature

Not a reversible process like lactate fermentation.

Pyruvate is converted to ethanal catalysed by pyruvate decarboxylase.

Ethanal can accept a hydrogen atom from reduced NAD becoming ethanol 

Triglycerides are hydrolysed to fatty acids, which enter the Krebs Cycle via acetyl CoA and glycerol.

Glycerol is converted to pyruvate before undergoing oxidative decarboxylation producing an acetyl group which is picked up by coenzyme A forming acetyl CoA which can lead to the formation of as many as 50 acetyl CoA molecules resulting in the synthesis of up to 500 ATP molecules.

Proteins have to be hydrolysed to amino acids and then deaminated before entering the respiratory pathway.

It takes 6 oxygen molecules to completely respire one molecule of glucose resulting in the production of 6 molecules of CO2.

Lipids contain a greater proportion of carbon-hydrogen bonds than carbohydrates so produce more ATP