Respiration overview

Respiration requires organic molecules to be used as fuelThe starting molecule is usually glucoseIt is broken down in a series of stepsThis will give potential chemical energy

In the first step glucose is split

This stage is called glycolysis

In a series of enzyme controlled reactions two molecules of pyruvate are made

Pyruvate can stay in the cytoplasm and enter into the anaerobic pathway

This occurs in the absence of oxygen

If oxygen is present pyruvate enters the mitochondrionIt is converted to Acetyl CoA in the Link reaction

This molecule now enters the Krebs Cycle where NAD and FAD are reducedMost of the CO2 is made at this stage

The reduced molecules carry Hydrogen to the Electron transfer ChainThis generates ATP The final hydrogen acceptor is oxygen

Hydrogen Carrier Molecules

There are two of these in respiration

NADNicotinamide Adenine DinucleotideThis is a co-enzymeThis can accept electrons and hydrogen and become reduced

FADFlavin adenine dinucleotideIt is derived from Vitamin B2 (riboflavin)

NAD NADreduced

NAD is a hydrogen carrier moleculeWhen it picks up hydrogen it becomes reduced

FAD is more complex – all you need to know is it will carry hydrogen to the final stage of respiration

Glycolysis

This is the splitting of sugar or more specifically glucoseIt takes place in the cytoplasm

6 Carbon glucose is split into 3 Carbon Pyruvate in a series of steps

ATP is used in the first steps but generated in the last few steps

NAD is reduced

In the first steps of glycolysis glucose has 2 phosphates attached

We say glucose is phosphorylated These are transferred from ATPSo two ATP molecules are usedA hexose biphosphate is made

We will tally the NAD reduced made here

We will keep tally of ATP here

This hexose phosphate is split into TWO triose (3C) phosphates

So from her onwards everything must be X2 for each molecule of glucose

The 3 Carbon phosphates look like this in case you are interested

Each triose phosphate then have a hydrogen removedThis is attached to NAD which becomes NADreduced

This is an energy yielding step – ADP is phosphorylated to ATP

Another phosphate is lost to form Pyruvate and another ATP

Pyruvate looks like this

It is an acid

So the products of glycolysis of one molecule of glucose are:

2 x pyruvate

2 x NADreduced

2 x ATP (net)