Chemistry of Carbohydrates-Lipids-Nucleic Acid, Biology tutorial


Organic molecules are chemicals of life, compounds made up of more than one kind of element which are found in, and generated by, living organisms. Feature which differentiates the organic from inorganic molecule is that organic molecules have carbon-hydrogen bonds, while inorganic molecules do not. The 4 major classes of organic molecules comprise proteins, carbohydrates, nucleic acids and lipids.


The term carbohydrate is really a descriptor of what these molecules are made up of; carbon hydrates, in the ratio of one carbon molecule to one water molecule (CH2O)n. Word saccharide is handy synonym for carbohydrate, as it can be preceded with the prefix indicating size of molecule (mono-, di-, tri- poly-):

Monosaccharides: Simplest, single sugars. Examples: Glucose and fructose are monosaccharides.

Disaccharides: Double sugars which are a combination of two monosaccharides. E.g.: Sucrose (table sugar) is composed of glucose and fructose together.

Polysaccharides: These are polymers made up of several sugars. They can be one kind of monomer (many of same monosaccharide) or mixture of monomers. E.g.: Starch is a polysaccharide made up of several glucose molecules.

Carbohydrates are the most plentiful class of organic compounds found in living organisms. They begin as products of photosynthesis, an endothermic reductive condensation of carbon dioxide needing light energy and pigment chlorophyll.

Functions of Carbohydrates:

Carbohydrates provide numerous biochemical functions:

  • Monosaccharides are the fuel for cellular metabolism.
  • Monosaccharides are utilized in many biosynthesis reactions.
  • Monosaccharides may be converted in space-saving polysaccharides, like glyocogen and starch. These molecules give stored energy for plant and animal cells.
  • Carbohydrates are utilized to create structural elements, like chitin in animals and cellulose in plants.
  • Carbohydrates and altered carbohydrates are significant for the organism's fertilization, development, blood clotting and immune system function.


Lipids are molecules which are usually hydrophobic (not attracted to water) as non-polar covalent bonds linking their carbons and hydrogens are not attracted to polar bonds of water. Four main groups of lipids comprise phospholipids, fats, waxes and steroids.

1. Fats: These lipids are the fats and oils which we are familiar with as part of diet. They are composed from the combination of two types of molecules:

i) glycerol (a type of alcohol)

ii) three fatty acids (called as triglycerides)

2. Phospholipids: These lipids contain hydrophobic (water hating) hydrocarbon tails at one end and hydrophilic (water loving) phosphate group at other end. This signifies that they are soluble in both water and oil. Cell membranes are composed mostly of phospholipids arranged in the double layer, with tails from both layers facing inward and heads facing outward; arrangement called as lipid bilayer.

3. Waxes: Wax lipids are esters of alcohol, insoluble in water and hard to break down. Wax forms defensive and waterproof layers on various plants, animal fur, bacteria and integuments of insects.

4. Steroids: Cholesterol is one example of the steroid. Central core of the cholesterol molecule comprises of four fused rings, a chemical arrangement which is shared by all steroids. Cell membranes also have cholesterol that assists to keep membrane flexible and fluid even when cells are exposed to cooler temperatures.

Functions of Lipids:

Lipids are utilized by organisms for energy storage, as the signaling molecule (like, steroid hormones), and as structural component of cell membranes.

Nucleic Acids:

The genetic material is composed of DNA (deoxyribonucleic acid), molecule that has code for making operating your cells and your complete body. Nucleic acids are polymers composed of nucleotide monomers. Each monomer of nucleic acid is nucleotide, and comprises of three portions:

i) a pentose sugar

ii) one or more phosphate groups

iii) one of five cyclic nitrogenous bases (adenine, cytosine, guanine, thymine & uracil)

Nucleotides are connected by covalent bonds between phosphate of one nucleotide and sugar of next, creating a phosphate-sugar backbone. Nitrogenous bases extend from backbone like teeth of a comb. Ribonucleic acid (RNA) is single stranded molecule engaged in production of cellular proteins. On the contrary, DNA molecules are double stranded, having hydrogen bonds attracting complimentary bases which hold two phosphate-sugar strands together. Hydrogen bonds also twist phosphate-deoxyribose backbones in the double helix. Nucleic acids are slightly different from other Biomolecules in the structure and functions.

Building Blocks of Nucleic Acids:

Nucleic acids are bio polymers made up of monomer units known as nucleotides therefore they are building blocks of all nucleic acids. Every nucleotide has 3 components that are bonded together in the certain manner to create complete unit. These components are given below.

1) Nitrogen-containing base:

There are two kind of nitrogenous base present in nucleotides, pyrimidine (one ring) or purine (two rings) that are pretty vary from each other in there structures.

2. Five carbon sugar:

Two pentose sugars are there in nucleic acids, ribose or deoxyribose sugar. DNA has β-D-2-deoxyribose sugar where as RNA has β-D-ribose sugar. Both sugars are varying only in presence of one oxygen atom at C2 position.

3) Phosphate group:

The phosphate group serves as the linking chain between two sugar molecules to make the complete strand of nucleic acid. Oxygen part of phosphate group related with carbon atom of sugar to create nucleotide. The Nucleotide can also exist in activated forms with two or three phosphates, called as nucleotide diphosphates or triphosphates.

During creation of polynucleotide such as DNA or RNA, monomer units (nucleotides) are bonded with phospho diester bond in which the bond formed between 3' -OH group and 5' phosphate group through condensation reaction.

Functions of Nucleic Acids:

Various functions of nucleic acids are as follows:

  • The major functions is to store and transfer genetic information.
  • To employ genetic information to direct synthesis of new protein.
  • Deoxyribonucleic acid is storage for place for genetic information in cell.
  • DNA manages synthesis of RNA in cell.
  • Genetic information is transmitted from DNA to protein synthesizers in cell.
  • RNA also directs production of new protein by transmitting genetic information to protein building structures.

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