Substrates for respiration.
Starch and glycogen, other sugar molecules, amino acids and fats.
Starch and glycogen are broken down to glucose for use as a respiratory substrate.
Other sugar molecules can be converted to glucose or glycolysis intermediates for use as respiratory
substrates.
Respiratory substrates
Carbohydrates
Starch (storage carbohydrate in plants) and glycogen (storage
carbohydrate in animals) are both complex molecules
composed of glucose sub-units.
They act as respiratory substrates since they can be broken
down to glucose which is then used in respiration.
Starch
Maltose
Glycogen
Glucose
Sucrose
Fructose
Other sugars like maltose and sucrose can be
converted to glucose or intermediates in glycolysis
and used as respiratory substrates
Pyruvate
Proteins can be broken down to amino acids and converted to intermediates of glycolysis and the citric
acid cycle for use as respiratory substrates.
Proteins
Proteins in the diet are digested to their component amino acids.
Excess amino acids undergo deamination in the liver.
Deamination forms the waste product urea and also forms intermediates in the respiration reactions.
These intermediates act as respiratory substrates in the pathway
Glucose
Diagram illustrates
how some amino
acid products enter
the respiratory
pathway and need
not be memorised
Amino acids
e.g. alanine
Protein
urea
Amino acids
Pyruvate
Acetyl coenzyme A
e.g. leucine
urea
Amino acids e.g.
aspartic acid
intermediate
urea
Citric
acid
cycle
Fats can also be broken down to intermediates of glycolysis and the citric acid cycle.
Fats
Fat is digested to glycerol and fatty acids.
When used in respiration, glycerol is converted to an intermediate in the glycolysis pathway.
Fatty acids are changed into acetyl coenzyme A
Glucose
Glycerol
Diagram illustrates
where glycerol and
fatty acids enter the
respiratory pathway
and need not be
memorised
intermediate
Fat
Pyruvate
Fatty acids
Acetyl coenzyme A
Citric
acid
cycle