Macromolecules: Types, Practice Problems and FAQs

We all have varieties of food items, right?. It includes biryanis, naan, pulao, french fries, burgers etc. You know that these food items contain fibres, proteins, lipids, carbohydrates, nucleic acids etc.

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Fig: Burger

It provides us with the energy we require to perform life processes. So can you tell me what you call these substances? Yes, macromolecules. So the food we have contains macromolecules and micromolecules. In this article we are going to discuss in depth about macromolecules.

Macromolecules
Types of macromolecules
Importance of macromolecules
Practice Problems
FAQs

Macromolecules

Macromolecules are large sized, complex chemicals that have higher molecular weight, that means usually 10,000 daltons and above with lower solubility. Common examples include proteins, carbohydrates, lipids, and nucleic acids.

Formation of macromolecules

They are formed by the polymerisation of smaller subunits known as monomers and play a major role in the proper functioning of an organism. They possess chains with various lengths. For example, the monosaccharides are linked with glycosidic bonds in a polysaccharide.

Fig: Polysaccharide

Types of Macromolecules

There are mainly four types of macromolecules present in the body of an organism and they are as follows:

Carbohydrates
Lipids
Proteins
Nucleic acids

Carbohydrates

The word carbohydrates is derived from the French word ‘hydrate de carbone’ meaning hydrates of carbon. They are represented as C_n(H₂O)_n. These are macromolecules formed of carbon, hydrogen, and oxygen. These are found in milk, fruits, vegetables, and sugars. Chemically they are polyhydroxy aldehydes or ketones. They constitute a major part of the human diet. Carbohydrates are divided into three types as follows:

Fig: Carbohydrates

Monosaccharides

They are simple monomers of carbohydrates and have the general formula C_nH_2nO_n. They have only 3 to 7 carbon atoms per molecule. They include trioses (C₃H₆O₃), tetroses (C₄H₈O₄), pentoses (C₅H₁₀O₅), hexoses (C₆H₁₂O₆) and heptoses. The most common monosaccharides are galactose, glucose and fructose. Glucose is one of the most common monosaccharides and a significant source of energy. During cellular respiration, energy is derived from glucose; this energy is utilised to make ATP (adenosine triphosphate).

Fig: Monosaccharides

Disaccharides

These are formed by the condensation of two monosaccharide molecules with the elimination of a water molecule. They include sucrose, lactose, and maltose. The monosaccharide monomers are either the same molecule or two different molecules in them. These are called the digestible disaccharides present in food.

Common examples of disaccharides

Lactose → Glucose + Galactose
Maltose → Glucose + Glucose
Sucrose → Glucose + Fructose

GIF: Formation of disaccharide

Oligosaccharides

These are compounds formed by the condensation of 3 - 10 monosaccharide molecules. They are soluble in water and are commonly sweet in taste. Common examples include stachyose (Glucose + Galactose + Galactose + Fructose), and raffinose (Glucose + Galactose + Fructose).

Polysaccharides

They are complex carbohydrates formed by the polymerisation of a large number of monosaccharide monomers. They are represented as (C₆H₁₀O₅)_n. They are of two types as follows:

Homopolysaccharides

It is a polymer of one type of monosaccharide unit. Examples include glycan (made of glucose units) and fructan (composed of fructose units).

Heteropolysaccharides

It is a polymer of more than one type of monosaccharide monomer units. Examples include agar, hemicellulose and chitin.

Fig: Polysaccharides

Lipids

Lipids are fatty acid esters of alcohols and related substances. They are hydrophobic in nature and are insoluble in water. They can be dissolved in non-polar organic solvents like ether, chloroform, benzene etc. Lipids are used in the formation of cell membranes, production of hormones and can also be stored and used as fuel. The common lipids are steroids, phospholipids, carotenoids and triglycerides. Fatty acids and glycerol are the basic components of all lipids.

Fig: Lipids

Glycerol

The chemical formula for Glycerol is C₃H₈O₃. It contains three hydroxyl groups (-OH groups) in its chemical structure which are bound to the carbon atoms. It possesses three carbon atoms, 3 oxygen atoms, and eight hydrogen atoms.

Fig: Glycerol

Fatty acids

They are organic acids with a hydrocarbon chain ending in a carboxylic group. They possess straight or ring structure and are of two types as follows:

Unsaturated fatty acids

These fatty acids contain one or more double bonds in their carbon chain. They can take up additional hydrogen and hence are called unsaturated. Examples include oleic acid, linoleic acid, linolenic acid etc.

Fig: Unsaturated fatty acids

Saturated fatty acids

These types of fatty acids do not have double bonds in their carbon chains and cannot take up hydrogen. They possess straight-chains and are solid at room temperature. Animal fats are usually saturated. Examples include palmitic acid, stearic acid etc.

Fig: Saturated fatty acids

Proteins

These are the most abundant molecules in the cell. They are made up of carbon, hydrogen, oxygen, nitrogen and sulphur. The polymerisation of amino acids leads to the formation of proteins. In a polypeptide, the amino acids remain serially linked by peptide bonds (-CO-NH-). The various combinations of 20 amino acids results in the formation of a large number of proteins. Proteins play an important role in the production of carbohydrates and lipids as the enzymes used in the synthesis of carbohydrates and lipids are proteins. Examples include keratin proteins.

Fig: Formation of protein

Nucleic acids

These are the largest macromolecules in the living world. They are polymers of purine and pyrimidine nucleotides. The nucleotides are joined by phosphate groups. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two major types of nucleic acids.

Fig: Nucleic acids

Nucleotides

These are made up of a phosphate group, a pentose sugar, and a nitrogenous base. The nitrogenous bases present in DNA include Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). But in RNA instead of Cytosine, Uracil (U) is present. All the genetic information of a cell can be found in DNA.

Fig: Nucleotides

Importance of macromolecules

The following are the importance of macromolecules:

Carbohydrates and lipids act as the major sources of energy in the human body.
Proteins are mainly involved in the repair, growth and development of the body.
Cellulose provides structural integrity to the plant cell.
The storage forms of energy include glycogen (animal starch) in animals and starch in plant cells.
DNA and RNA act as genetic materials and help in the transmission of characteristics from one generation to the other.

Practice Problems

Which structure is a necessity to perform the biological activities of a protein?

(A) Primary structure

(B) Tertiary structure

(D) Secondary structure

Solution: The proteins possess 4 types of structures as follows:

Primary structure
Secondary structure
Tertiary structure
Quaternary structure

The tertiary structure is formed when a long protein chain folds in on itself like a hollow woollen ball. This creates a three-dimensional image of a protein. Tertiary structure of protein is required for many of their biological functions. Hence the correct option is B.

Fig: Tertiary structure

Identify the true macromolecule(s) of the cell?

(A) Polysaccharides

(B) Polynucleotides

(D) All of the above

Solution: Macromolecules or biomacromolecules are acid insoluble fractions which have molecular weight ranging from ten thousand daltons and above. The true macromolecules are formed by the acid insoluble polysaccharides, polypeptides and polynucleotides. Polysaccharides are macromolecules made up of long chains of sugars. They are made up of smaller units called monosaccharides. Polypeptides are proteins which are made up of long chains of amino acids bound together by the peptide bonds. Polynucleotides are nucleic acids which are formed by the building blocks known as nucleotides. The nucleotides are made up of nitrogenous base, sugar molecule and phosphate group. Hence the correct option is D.

Glycosidic bond is formed between ________________.

(A) Carbon and oxygen atoms of two adjacent monosaccharides

(B) Carbon and hydrogen atoms of two adjacent monosaccharides

(D) Two carbon atoms of two adjacent monosaccharides

Solution: A glycosidic bond is formed between two carbon atoms of two monosaccharides lying adjacent to each other. This results in the formation of polysaccharides by giving out a water molecule. Hence, it is a dehydration reaction. So the correct option is D.

GIF: Formation of disaccharide

FAQs

What are the major roles of macromolecules?

Answer: The following are the major roles of macromolecules:

They provide structural support. For example, Cellulose.
They act as a source of stored fuel. For example, starch.
They have the ability to store and retrieve genetic information. For example RNA and DNA.
They have the ability to speed up biochemical reactions. For example, proteins like enzymes.
Proteins, nucleic acids, carbohydrates, and lipids are the major macromolecules. They play important roles in the life of a cell.

Which is considered as the largest macromolecule?

Answer: DNA or deoxy ribonucleic acid is considered as the largest macromolecule in the living world.

Fig: DNA

Which is the largest polymer?

Answer: Polyethylene (PE) with the simplest basic structure, a repetition of CH₂ units, is the largest polymer.

Can we call cotton a polymer?

Answer: Cotton fibres are the purest form of cellulose. It is the most abundant polymer in nature. Nearly 90% of the cotton fibres are cellulose.

Which is considered as good cholesterol?

Answer: HDL (high-density lipoprotein) is considered as the good cholesterol. It absorbs cholesterol and carries it back to the liver from there it is flushed out. High levels of HDL cholesterol can reduce the risk for heart diseases.