Question

Name one element invariably found in proteins but not in all carbohydrates and lipids.

Answer 1

Hint:-All living organisms are composed of the same chemicals i.e., elements and compounds. If we see and analyse a plant tissue, animal tissue or a microbial paste, we obtain elements like carbon, hydrogen, oxygen etc. in living organisms the relative percentage and composition of carbon and hydrogen with respect to other elements is more than in earth's crust.

Complete answer:
Living organisms are used to generate thousands of organic compounds (biomolecules) including amino acids, sugars, chlorophylls, haems etc. These are necessary for their basic metabolic processes like photosynthesis, respiration, protein and lipid metabolism etc.
Now let us see the different compounds.
Carbohydrates:
Carbohydrates are mainly composed and made up of carbon, hydrogen and oxygen. These are also termed as saccharides due to their basic components are sugars. They are of two types, small and large complex). Small carbohydrates (biomacromolecules) are further divided into monosaccharides, derived monosaccharides and oligosaccharides. Large carbohydrates (biomacromolecules) are called polysaccharides.
They are made up of carbon, hydrogen and oxygen uniquely.
Lipids:
Lipids are composed of carbon, hydrogen and some amount of oxygen and are water insoluble but get dissolved in organic solvents like ether, benzene, acetone etc. The lipids are not polymers but they are associated with smaller molecules by dehydration.
Lipids could be simple fatty acids or glycerol (which is trihydroxy propane). Many lipids have both glycerol and fatty acids. Some lipids have phosphorus and a phosphorylated organic compound in them. Some lipids have more complex structures.
Proteins:
Proteins are large-sized macromolecules having one or more polypeptides (chains or polymers of amino acids linked by peptide bonds). The term polypeptide is often used interchangeably with protein. However, a single polypeptide must be at least 50 amino acids long in order to qualify for the term.
As proteins are made up of amino acids, Amino acids are organic compounds, having amino group $\mathop {NH}\nolimits_2 $ and carboxyl group $ - COOH$ attached to the same carbon i.e., the a-carbon (a-carbon is the carbon to which functional groups are attached). The a-carbon also bears hydrogen and a variable R group. They are substituted methanes as there are four different types of groups occupying the four valency positions of carbon. Since both the functional groups are attached to the a-carbon so they are called a-amino acids.
So, nitrogen is only present in proteins and not in carbohydrates and lipids.



Note:- Amino acids which occur in proteins are only of twenty types. The R group in these amino acids that are used to perform could be a hydrogen (glycine), a methyl group (alanine), hydroxy methyl (serine), etc. Humans are incapable of synthesizing half of the 20 standard amino acids and these are known as essential amino acids.