Investigation of dehydrogenase activity at different temperatures
Introduction to the practical
Dehydrogenase enzymes carry hydrogen atoms from substrates such as glucose and
transfer them to co-enzymes such as NAD and FAD in the mitochondria, they REDUCE the
coenzymes by adding a hydrogen atom.
The hydrogen atoms are then released from NAD and FAD (the co-enzymes are oxidised)
and split into one proton and one electron.
Methylene blue is an artificial hydrogen acceptor i.e. it can bind to hydrogen atoms
therefore preventing them from being able to reduce NAD and FAD. Methylene blue has a
higher REDUCTION POTENTIAL than NAD and FAD so when they are both present,
methylene blue is reduced in preference to NAD and FAD.
When oxidised methylene blue is dark blue in colour and it loses its colour as it is reduced
(gains hydrogen atoms). The time taken for the methylene blue to lose its colour is a
measure of the rate of dehydrogenase activity. A short period of time for methylene blue to
change colour indicates a high rate of dehydrogenase activity as dehydrogenase is
responsible for carrying the hydrogen atoms.
Practical exam
This is your first attempt in A2 biology at a ‘full’ practical write up. As this is your first
attempt you have been provided with some questions to guide your write up. Make sure
you keep the answers/ write up safe as they will prove to be excellent revision tools and
contribute evidence towards your lab book.
In your Unit 5 practical exam you will be asked to complete a practical and then answer
similar questions to this under exam conditions. This will be completed under timed
conditions; you will have 2 hours to complete the practical and answer the questions (I
have added a couple of extra questions here so don’t panic!)
Questions – to be answered in lab book
1. Write a prediction for this experiment with an explanation (3)
Introduction to the practical
Dehydrogenase enzymes carry hydrogen atoms from substrates such as glucose and
transfer them to co-enzymes such as NAD and FAD in the mitochondria, they REDUCE the
coenzymes by adding a hydrogen atom.
The hydrogen atoms are then released from NAD and FAD (the co-enzymes are oxidised)
and split into one proton and one electron.
Methylene blue is an artificial hydrogen acceptor i.e. it can bind to hydrogen atoms
therefore preventing them from being able to reduce NAD and FAD. Methylene blue has a
higher REDUCTION POTENTIAL than NAD and FAD so when they are both present,
methylene blue is reduced in preference to NAD and FAD.
When oxidised methylene blue is dark blue in colour and it loses its colour as it is reduced
(gains hydrogen atoms). The time taken for the methylene blue to lose its colour is a
measure of the rate of dehydrogenase activity. A short period of time for methylene blue to
change colour indicates a high rate of dehydrogenase activity as dehydrogenase is
responsible for carrying the hydrogen atoms.
Practical exam
This is your first attempt in A2 biology at a ‘full’ practical write up. As this is your first
attempt you have been provided with some questions to guide your write up. Make sure
you keep the answers/ write up safe as they will prove to be excellent revision tools and
contribute evidence towards your lab book.
In your Unit 5 practical exam you will be asked to complete a practical and then answer
similar questions to this under exam conditions. This will be completed under timed
conditions; you will have 2 hours to complete the practical and answer the questions (I
have added a couple of extra questions here so don’t panic!)
Questions – to be answered in lab book
1. Write a prediction for this experiment with an explanation (3)
