Also referred to as ketones or polyhydroxy aldehydes, carbohydrates are macromolecules. According to a layman's theory, carbohydrates are sweet-tasting substances or sugars. They are composed of hydrogen, carbon and oxygen, hence called carbohydrates. They are collectively referred to as saccharides.

According to the units of sugar present, they are divided into

           ● Monosaccharides, which consists of one unit of sugar

           ● Oligosaccharides, which consists of two to ten units of sugar

           ● Polysaccharides consist of more than ten units of sugar

Carbohydrates are the most abundant source of energy for living organisms and a very important structural component as well.

 

Nucleic acids are also essential to living organisms. These are genetic materials seen in cells that carry hereditary information from an organism to its offspring. Nucleic acids have two main functions - synthesis of protein (Transcription) and the transfer of genetic details (Translation).

Nucleic Acids are further divided into two major types

● DNA or Deoxyribonucleic Acid has four nitrogenous bases called guanine, adenine, thymine, and cytosine.

● RNA or Ribonucleic Acid consists of guanine, adenine, uracil, and cytosine.

 

 

Proteins are another type of important biomolecules. They are known for making up 50% of the total cellular dry weight. Proteins are nothing but polymers of amino acids arranged in a polypeptide chain. They play a major role in producing enzymes, hormones, metabolic chemicals and repairing tissues. 

Based on the complexity of structure and folding, Proteins are divided into

● Primary Structure

● Secondary Structure

● Tertiary Structure

● Quaternary Structure

 

 

Lipids are organic biomolecules that are insoluble in water. However, they are soluble in organic solvents. These oily and nonpolar molecules are considered a great source of energy and help in the formation of cellular structure. Examples of lipids are fats, fat-soluble vitamins, waxes etc.

There are many divisions of Lipids based on different categories.

Simple Lipids

● Fat

● Waxes

Complex Lipids

● Phospholipids

● Glycolipids

NCERT Class 12 chemistry has a detailed mention of the components of various biomolecules.

 

Question 1: The DNA strands are not similar or identical, but instead, they are complementary. Explain how

Question 2: What are essential and non-essential amino acids? Give examples for each.

Question 3: Why are vitamin A and vitamin C considered a significant source and essential for the human body?

Question 4: Differentiate between globular and fibrous proteins.

Question 5: What do you understand by the term glycogen? What makes glycogen different from starch?

Question 6: What are the structural and functional differences between DNA and RNA?

Question 7: What is Denaturation?

Question 8: What is Nucleic Acid? Discuss two important features of it.

Question 9: What are Enzymes?

Question 10: What are Monosaccharides?

Answer 1: If we see the helical structure of DNA, the two strands are held in place by hydrogen bonds between certain pairs of bases.

Cytosine forms a hydrogen bond with guanine, whereas adenine forms a hydrogen bond with thymine. As a result of this, the two strands are complementary to each other but not identical.

Answer 2: Essential amino acids are required by the human body, but they cannot be synthesised in the body. They must be taken through food. For example, valine and leucine.

Non-essential amino acids are also required by the human body, but they can be synthesised in the body. For example, glycine and alanine.

Answer 3: The deficiency or lack of vitamin A in the body often leads to xerophthalmia, also known as the hardening of the cornea present in the eye and also night blindness. At the same time, the deficiency of vitamin C leads to scurvy or bleeding gums.

Some sources of vitamin A are carrot, liver oil, fish and others. The sources of vitamin C are amla, citrus fruits such as orange and green leafy vegetables.

Answer 4: 

Globular proteins: They are proteins with a spherical structure that are usually soluble in water.

Fibrous proteins: They are held together by strong hydrogen bonds. They are not soluble in water.

Answer 5: Glycogen is a carbohydrate (polysaccharide). Animals store carbohydrates as Glycogen. 

Starch is also a carbohydrate that consists of two components - amylose ( 15 - 20%) and amylopectin ( 80 - 85%). 

However, Glycogen consists of only one component whose structure is similar to amylopectin. Also, Glycogen is more branched than amylopectin.

Answer 6:

Structural differences: DNA is double-stranded while RNA is single-stranded. 

DNA has a long chain of nucleotides while RNA has a shorter tide of nucleotides. 

Functional differences: DNA is responsible for the transmission of hereditary information while RNA is responsible for the transmission of the genetic code that is required to create important proteins.

Answer 7: Denaturation is the process through which proteins or nucleic acids lose their quaternary, tertiary or secondary structures. When this happens, globules get unfolded, and helices get easily uncoiled. While the secondary and tertiary structures of proteins get destroyed, the primary structure remains unchanged or unaltered. It can be therefore said that during the process of denaturation, secondary as well as tertiary structure proteins get changed into primary structure protein.

Answer 8: Nucleic acids are nothing but biomolecules generally found in the nuclei of almost all living cells as a constituent of chromosomes.

Nucleic Acid is also called polynucleotides because they appear to be long-chain polymers of nucleotides.

Two main functions are as follows:

• DNA is known to be responsible for the transmission of the inherent characters from one generation to another.
• Nucleic Acid, including both DNA as well as RNA are responsible for the synthesis of protein in cells.

Answer 9: Enzymes act as proteins that help in catalysing biological reactions. They can only catalyse a certain reaction for a single substrate. This is because they are very specific in nature. They are usually called after any particular substrate or a new class of substrate and sometimes even after a particular reaction.

For example, the enzyme which is used for catalysing the reaction of hydrolysis of maltose into glucose is known as maltase. Therefore, the enzymes which are used to catalyse the oxidation of one substrate with the further simultaneous reduction of other substrates are named oxidoreductase enzymes.

Answer 10: The carbohydrates that cannot be hydrolysed into further simpler units of polyhydroxy aldehyde or ketone are called Monosaccharides.

Monosaccharides are hence categorised according to the number of carbon atoms as well as the functional group present in them. Monosaccharides that contain an aldehyde group are referred to as aldoses, whereas the ones containing one or more keto groups are referred to as ketoses.

Monosaccharides are thus further categorised as trioses or tetroses or pentoses or hexoses and heptoses based on the number of carbon atoms they have. For instance, if we consider a ketose, which contains three carbon atoms, it is called ketotriose. At the same time, an aldose containing three carbon atoms is known as aldotriose.

 

Question 1: 

Choose the best answer.

All lipids are:

1) Composed of Fatty Acid

2) Triglycerides

3) Insoluble in water

4) All the above

Answer: 3

Question 2:

A higher nucleotide is a nucleotide having:

1) Higher molecular weight

2) More than one phosphate reticle

3) More than one nitrogen base

4) More than one sugar residue

Answer: 2

Question 3:

The sweetest among the naturally occurring sugars are:

(1) Glucose

(2) Fructose

(3) Sucrose

(4) Saccharine

Answer: 2

Question 4:

Which substance is most abundant in cells?

1) Carbohydrates

2) Protein

3) Water

4) Fats

Answer: 3

Question 5:

Nails, horns and hoofs contain which protein?

1) Chitin

2) Keratin

3) Both

4) None

Answer: 2

Question 6:

What is a sugar with a five-membered ring called?

1) Pyranose

2) Furanose

3) Dextrorotatory

4) Laevorotatory

Answer: 2

Question 7:

In which form is extra sugar stored in your body?

1) Glucose monosaccharide

2) Sucrose Disaccharide

3) Glycogen polysaccharide

4) Fatty acid and glycerol

Answer: 3

Question 8:

Glycogen can be termed as what?

1) Polymer of amino acids

2) Polymer of fatty acids

3) Unsaturated fats

4) Polymer of glucose

Answer: 4

Learn all about biomolecules with easily understandable class notes from MSVgo champs. You can share your notes with friends and make learning a fun exercise. Download for free.

Biomolecules are an essential chapter in class 12 chemistry. Students tend to be wary of this chapter due to the complex names and equations.