An easy approach to controversial questions in Biochemistry

Jun 17 , 2020

There are a few questions that need to be solved with caution as these questions require you to know the underlying controversy in that particular topic. One has to carefully analyze the correct answer depending upon what is asked in the question and the available options.

Once you find out that there is a controversy, you will be able to solve the question.

Dr. Smily Pruthi, a leading Biochemistry faculty has helped us to create a list of a few examples of such questions along with a suitable approach. 

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Polarity of Amino Acid

Amino acids are classified as polar or non-polar on the basis of their side-chain polarity as shown below:

Two amino acid glycine and Tyrosine are generally classified as non-polar amino acids due to low or negligible charge on their side chains. So, they are in controversy.

For some questions, you need to mark them as polar after carefully analyzing other options.
For example:


Suitable Approach:

Now in the options, if glycine is given with other highly non-polar amino acids (Q1) then consider glycine as polar whereas if one of the other options include a highly polar amino acid (aspartate) (Q2) then consider glycine as non-polar.



Glucogenic and Ketogenic Amino Acids

Amino acids can be classified either as glucogenic or ketogenic or both based on whether their intermediary metabolites can be used for the formation of glucose or ketone bodies or both respectively.

Below is the table giving a classification of amino acid based on this property:


The above table shows that only 2 amino acids ‘ Leucine and Lysine’ are purely ketogenic which cannot form glucose but there is controversy regarding Lysine to be purely ketogenic.

For some questions, you need to mark lysine as glucogenic while for others you need to consider it as ketogenic.
For example:


a) Now for the kind of question given above, if Leucine is given with lysine as an option (Q1) then you can consider lysine as glucogenic here. This is because you are 100% sure about leucine as ketogenic but have a doubt about lysine.

However, if lysine is the only option with other glucogenic amino acids (Q2) then consider lysine as purely ketogenic.

b) PGI pattern (multiple options): Choose leucine and lysine if both are given (Q1)


Urea Cycle Energetics

Suitable Approach

If both 3ATP and 4ATP options are given (Q1) then choose 4 ATP as the best answer because 1 ATP can be considered equivalent to one high energy phosphate and total 4 high energy phosphates are equal to 4ATPs but if only 3ATP option is given (Q2) then go with it.


After going through this blog, we are pretty sure that now you’ll have a good idea on how to attempt the questions which have underlying ambiguity in their interpretation among the scientific community.


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