CBSE Class 12 Chemistry Revision Notes Chapter 14

Class 12 Chemistry Chapter 14 Notes: Biomolecules

This chapter deals with Biomolecules, which comprise a biological living system that sustains and reproduces itself. Furthermore, a living system comprises non-living atoms and molecules. Biochemistry is the study of what goes on chemically within a particular living ecosystem. Most noteworthy, living organisms consist of various complex biomolecules, including nucleic acids, lipids, carbohydrates, proteins, etc.

Biomolecules describe the molecules living things require to build body parts and maintain the biochemical processes required for life functions. These biomolecules may be divided into either organic or inorganic compounds. Organic compounds are compounds containing carbon which are found in living things. Know more details about these in Class 12 Chemistry Chapter 14 Notes: Biomolecules, available at the Extramarks’ website. 

As stated in the Chemistry Class 12 Chapter 14 Notes, proteins and carbohydrates are essential elements of our food. Furthermore, these biomolecules interact with one another and are the molecular logic of life processes. Moreover, mineral salts and vitamins play a crucial role in various essential functions of organisms. 

Thus, biomolecules Class 12 Notes contain all the information you need. The complex organic substances, which combine in a specific manner to produce living systems and maintain them, are called biomolecules. Biomolecules are the branch of Chemistry that studies chemical reactions in living organisms.

Key Topics covered in Class 12 Chemistry Chapter 14 Notes

This unit will discuss the structure and functions of some biomolecules. The structure and function of biomolecules inside the living organism are studied in Biochemistry. Living systems comprise several complex biomolecules like carbohydrates, proteins, enzymes, lipids, vitamins, hormones, nucleic acids, and compounds for storing and exchanging energy like ATP.

Carbohydrates:

The term carbohydrate is a combination of the “hydrates of carbon”. They are also known as “Saccharides”, a derivation of the Greek word “Sakcharon”, which means sugar. The definition of carbohydrates in Chemistry is shown as follows:

“Optically active polyhydroxy aldehydes or ketones or substances formed during hydrolysis are known as carbohydrates”.

Few of the most common carbohydrates that we come across in our daily lives are in the form of sugars. These sugars can be in the form of Glucose, Sucrose, Fructose, Cellulose, Maltose etc.

The general formula for carbohydrates is Cx(H2O)y. Although, it must be considered that this is just a standard formula. Carbohydrates are also termed saccharides. Few of the carbohydrates which are sweet to taste are also called Sugars. There are several exceptions to this.

Let us take a look at acetic acid, which is CH3COOH. Although this will fit the standard formula of carbohydrates, i.e. Cx(H2O)y, we mention that acetic acid is not a carbohydrate.

Formaldehyde also falls under this category of this general formula but is also not a carbohydrate. And on the other hand, Rhamnose (C6H12O6) is a carbohydrate but does not follow the general formula. Students can refer to the Class 12 Chemistry Chapter 14 Notes to get more information on this topic.

Classification of Carbohydrates:

The main classification of carbohydrates is done based on hydrolysis. This classification is as follows:

1. Monosaccharides are the more straightforward form of carbohydrates that cannot be hydrolyzed into a more straightforward unit of polyhydroxy aldehyde or ketone called monosaccharides. Approximately twenty monosaccharides are known to occur in nature. For example, glucose and fructose. Their general formula is (CH2O)n. Some examples are glucose, Ribose, etc.
2. Oligosaccharides: Carbohydrates that, upon hydrolysis yield, two to ten smaller units or monosaccharides are called oligosaccharides. They are a large category and further divided into various subcategories.
3. Disaccharides: A further classification of oligosaccharides, gives two units of different or the same monosaccharides on hydrolysis. One example, sucrose on hydrolysis gives one molecule of glucose and fructose each. In contrast, maltose on hydrolysis gives two molecules of only glucose.
4. Trisaccharides: Carbohydrates that on hydrolysis give three molecules of monosaccharides, identical or different. An example is Raffinose.
5. Tetrasaccharides: As the name suggests, this carbohydrate on hydrolysis gives four molecules of monosaccharides. Stachyose is an example.
6. Polysaccharides: The last and final category of carbohydrates. These give a very large number of monosaccharides when they go through hydrolysis. These carbohydrates are not sweet and are also known as non-sugars. Some common examples are starch, glycogen etc.

Importance of Carbohydrates:

As discussed in Class 12 Chemistry Chapter 14 Notes, carbohydrates are essential for life on the planet. So lets take a more detailed look at the necessity of carbohydrates.

• They are responsible for storing chemical energy in living organisms. You must hear it all the time when athletes carbo-load before a game. This is to provide them with extra energy. They are also an essential constituent for supporting tissues in plants and even in some animals.
• Photosynthesis is a process by which plants use solar energy to produce food for themselves. . With this process, plants fix CO2 and synthesize carbohydrates. Let us take a look at the chemical reaction involved during photosynthesis.

x(CO2) + y(H2O) + Solar energy ⇒ Cx (H2O)y + O2

• So carbohydrates, due to photosynthesis, are plants’ repositories of solar energy. When plants or animals metabolize these carbohydrates, this energy is released. The metabolizing equation shown below is just the reverse of the photosynthesis equation.

Cx (H2O)y + O2 ⇒ x(CO2) + y(H2O) + Energy

Sugar and Non Sugars: 

Monosaccharides and oligosaccharides are crystalline solids that are soluble in water and sweet to taste, collectively known as sugars. The polysaccharides are amorphous, insoluble in water, tasteless, and are known as non-sugars.

Reducing and non-reducing carbohydrates: 

Tollen reagents are termed reducing carbohydrates. The carbohydrates containing free aldehyde or ketone group can reduce Fehling’s solution. Many monosaccharides, whether aldose or ketose, are reduced in behaviour. The carbohydrates in which the reducing part are not free can’t reduce Fehling’s solution, and tollens reagents are termed as non-reducing carbohydrates. Many polysaccharides like starch, cellulose, glycogen etc., are non-reducing carbohydrates.

Monosaccharides: 

These are the most straightforward carbohydrates that can’t be hydrolyzed into more minor compounds. They are called aldose or ketose, depending upon whether they have an aldehyde or ketone group. Based on the number of carbon atoms present, they are called triose, tetrose etc. All monosaccharides are sweet-smelling crystalline, water-soluble and can diffuse through cell membranes. Students are advised to refer to Class 12 Chemistry Chapter 14 Notes, available on the Extramarks’ website, for a more detailed explanation of the Monosaccharides.

Glucose:

It occurs in nature in free and in combination forms. Glucose is present in sweet fruits and honey. Ripe grapes contain approx 20% of glucose.

The most abundant monosaccharide in nature is, in fact, glucose. We can find glucose in fruits, honey, starch, and sugarcane. We obtain a large amount of the energy in our bodies from glucose through the foods we eat. It is aldohexose, which means it has a total of six carbon atoms in its molecule. Its chemical formula is C6H12O6.

We get glucose mostly from two sources –  starch and sucrose. Let us now look at how we can prepare glucose from these two sources. Students may refer to the Class 12 Chemistry Chapter 14 Notes to learn about glucose and its functions.

Preparation of Glucose:

• From Starch:

On a large commercial scale, glucose is mostly prepared from hydrolysis of starch by boiling it with dilute H2SO4 at 393 K under high pressure. This is the commercial way for the preparation of glucose. The chemical reaction is as follows:

(C6H10O5) + n (H2O) ————-> n C6H12O6

Starch                                               Glucose

• From Sucrose: 

Another way to prepare glucose, with fructose as a by-product, is to boil sucrose in diluted HCl or H2SO4 in an alcoholic solution. The chemical reaction for this is as below:

C12H22O11 + H2O ————> C6H12O6 + C6H12O6

Sucrose                            Glucose      +  Fructose

For example, glucose is considered to be an aldohexose while fructose is ketohexose. Both of them have six carbon atoms. The simplest monosaccharide is triose (n=3), such as Glyceraldehyde and Dihydroxyacetone. They are optically active and have one or more asymmetric carbon.

Structure of Glucose:

Glucose is an aldohexose that is the monomer of many more significant carbohydrates like starch, cellulose etc. 

 Configuration:

All naturally occurring monosaccharides belong to the D—series, the OH group at their penultimate C-atom.

The cyclic structure of glucose: 

It was proposed that glucose form a six-membered ring in which OH at C5 can add to the CHO group and form a cyclic hemiacetal structure. This explains the absence of the CHO group and also the existence of glucose in alpha and beta anomeric forms as:

The two cyclic hemiacetal forms of glucose vary only in the configuration of the hydroxyl group at C1, known as anomeric carbon. The corresponding alpha and beta forms are called anomers. It is observed that alpha and beta forms of glucose are not minor images of each other and hence are not enantiomers.

Fructose: 

Fructose is an important ketohexose. The hydrolysis of sucrose obtains it. Based on molecular weight determination, elemental analysis, and various reactions, its molecular formula is found to be C6H12O6, and its open-chain structure can be written as:

Fructose is a ketonic monosaccharide, primarily found in fructose in plants and their fruits, flowers and root vegetables, earning it the moniker of fruit sugar. It is also present abundantly in corn syrup and honey. Usually, fructose and glucose bonds to form a disaccharide called sucrose. Fructose was first discovered by French chemist Augustin – Pierre Debrunfaut.

The chemical formula of fructose is also C6H12O6, but the bonding of fructose is very different from the bonding of glucose. Fructose has a cyclic structure which is an intramolecular hemiacetal. Fructose has its carbonyl group at its number two carbon (a ketone function group). In its cyclic format, it (typically) forms a five-member ring which we call a Furanose ring with an analogy of the compound furan.

1. Oligosaccharides:

These carbohydrates, on hydrolysis, give 2 to 9 molecules of monosaccharides.

They are further of few types: 

Disaccharides (C12H22O11): 

On hydrolysis, they give two molecules of monosaccharides held together by Glycosidic linkage.

example: Sucrose.

Trisaccharides (C18H32O16):

On hydrolysis, they form three molecules of monosaccharides.

example: Raffinose.

Tetra-saccharides: (C24H42O21):

Such as stachyose which gives four monosaccharides on hydrolysis.

Polysaccharides:

These are the carbohydrates which, on hydrolysis, yield more than nine monosaccharides molecules.

example: Starch.

Mutarotation:

Glucose exists in two forms: i.e. alpha –D glucose with a specific rotation of 112 degrees and beta D-glucose with a specific rotation of +19 degrees. However, when either of these two forms is dissolved in water and allowed to stand, it gets converted into the same equilibrium mixture of alpha and beta forms with a small amount of open-chain form having a specific rotation of 52.7 degrees. As a result, equilibrium, the specific rotation of freshly prepared solution of alpha glucose, decreases from +112 degrees to 52.7 degrees while that for beta glucose increases from +19 to 52.7 degrees. This phenomenon of change in specific rotation of optically active compounds with time to an equilibrium value is known as Mutarotation.

The alpha D (+) glucose and beta (+) glucose differ in configuration at C-1 carbon, and the compounds differing in configuration at C-1 are called Anomers.

2. Disaccharide:

The disaccharides are the combination of two units of monosaccharides. They give the corresponding monomers on hydrolysis with dilute acids or specific enzymes.

C12H22O11 + H2O → C6H12O6 + C6H12O6

In disaccharides, the two monosaccharides’ units are connected by an oxide linkage formed by the loss of water molecules and the linkage is called glycosidic linkage. 

These topics are complex and many students find it difficult to understand. So students can refer to the step-by-step detailed chapter notes given in our  Class 12 Chemistry Chapter 14 Notes to get more clarity on these concepts.

Sucrose: 

A glycosidic linkage between C1 of α-glucose and C2 of β-fructose holds these two monosaccharides together. Sucrose is a non-reducing sugar due to the reducing groups of glucose and fructose involved in forming glycosidic bonds.

Maltose:

It is developed by the glycosidic linkage between the C1 of one glucose unit and the C4 of another. With acid or enzyme treatment, maltose is hydrolyzed into two molecules. That is alpha D-glucose. Since one of the glucose units exists in hemiacetal form, it is a reducing sugar.

Lactose: 

It is made up of any molecule and a molecule of galactose. The units are linked together. Lactose is found in milk, also termed milk sugar. It is developed by the glycosidic linkage between C1 of alpha D- galactose unit and C4 of beta D- glucose unit. Lactose is a reducing sugar.

The sweetness of sugars:

• All the monosaccharides and disaccharides are sweet and hence also known as sugars.
• Sucrose is given a sweet value of 100. The sweetness of other sugars is compared with the value of sucrose.
• The sweetness of fructose is -173, invert sugar 130, sucrose 100, glucose 74, galactose 32, maltose 32 and lactose 16.
• The monosaccharides and disaccharides are reducing agents due to hemiacetal and hemiketal forms, which quickly change into aldehydic in the alkaline medium.
• Although fructose doesn’t contain any aldehydic group yet, it gives Tollen’s reagent test and Fehling’s solution test because, under the primary conditions of the reagent, the fructose gets converted into the mixture of glucose and mannose, both of which contain the aldehydic group.
• This is called the Lobry De Bruyn Van Eikensten rearrangement.

Students may refer to the CBSE Class 12 Chemistry Chapter 14 Notes and other study materials available at the Extramarks’ website to learn more about the above phenomena.

• The alpha and beta glucose react with one ethanol molecule to form the corresponding methyl glucosides.
• When glucose is treated with methanol in the presence of HCl, the hemiacetal form changes to acetal form. 

3. Polysaccharides:

Polysaccharides are long-chain polymers composed of many monosaccharide units joined together by glycosidic linkages. They primarily show as food storage or structural materials. For example, starch, cellulose, glycogen etc.

Starch(C6H10O5)n: 

Plants’ primary storage polysaccharide is starch. It is the essential source of nutrition for a human being. Cereals, rice,  roots, tubers, and some vegetables have a high starch content. Starch is a polymer of alpha D+ glucose composed of two components, i.e. Amylose and Amylopectin. 

Amylose:

• Amylose is a water-soluble component which accounts for about 15-20% of starch. 
• Amylose is a long unbranched chain containing 15- 20% of starch. 
• It is a straight-chain polysaccharide containing α -D-(+)-glucose units held together by a C1-C4 glycosidic linkage. 

Amylopectin:

• Amylopectin is a branched chain of polysaccharides.
• It is insoluble in water. 
• It constitutes approximately 80-85% of starch. 
• It is a branched-chain polymer of α-D-glucose units with a chain formed by C1-C4 glycosidic linkage, whereas branching occurs by C1-C6 glycosidic linkage.

Cellulose:

• It is a straight-chain of polysaccharides composed of only a beta D glucose unit. 
• Cellulose is found mainly in all plants, constituting 50% of total organic matter in living beings. 
• Cotton is pure cellulose. 
• Cellulose is a linear polymer of beta D-glucose. The chains are arranged to form bundles and linked together by hydrogen bonds between glucose molecules of adjacent organic solvents. It slowly passes into the solution when treated with concentrated sulphuric acid in the cold.
• When diluted with water, this solution gives the starch-like substance amyloid, parchment paper.
• On boiling with water, it is hydrolyzed into D-glucose. Cellulose gives many useful products when treated with chemicals like rayon, gum, cotton etc. Cellulose is directly used in making cloth and paper.

Students should visit the Extramarks’ website to access the Class 12 Chemistry Chapter 14 Notes and get more in depth study notes on this chapter.

Glycogen:

• The structure of Glycogen is similar to amylopectin, with more branching than in amylopectin. 
• It is also called animal starch. 
• In the body, carbohydrates are stored as glycogen, and when the body needs glucose, enzymes break the glycogen down to glucose. 
• Glycogen is present in the liver, muscle and brain.
• In glycogen, there are about 25 glucose units. Its structure is the same as amylopectin, a condensation polymer of alpha glucose. 

Tests for carbohydrates:

For this, a Molisch test is performed. Molisch reagent, a 10% alcoholic solution of alpha naphthol, is added to an aqueous solution of carbohydrates, followed by concentrated sulphuric along the sides of the tube. As a result, a violet ring is formed at the junction of two layers.

Importance of carbohydrates: 

Carbohydrates are essential for life in plants and animals; carbohydrates are stored in plants as starch and in animals as glycogen. Carbohydrates are the primary source of energy (except cellulose). These carbohydrates store energy for the functioning of living organisms. They are used as raw materials in producing textiles, papers, lacquers, breweries, etc. 

Proteins:

Proteins are higher in molecular weight, complex bio-polymers of alpha-amino acids found in all living organisms. They occur in all parts of the body and form the fundamental basis of the structure and functions of life. The term ‘Protein’ is derived from the Greek word ‘Protein’, which means ‘Primary importance’. 

Proteins are the amplest biomolecules of the living cell. The primary sources of proteins are milk, cheese, pulses, peanuts, fish etc. All living systems comprise biomolecules with high molecular mass, called amino acids.

Amino acids: 

These acids are the building block units of proteins. These are the organic compounds which contain amino as well as carboxyl functional groups known as amino acids. Depending upon the relative position of the amino group concerning the COOH group, amino acids are Classified into alpha-beta, gamma delta and so on. Hydrolysis of proteins gives only alpha-amino acids represented as:

• The above unit may be connected to any carbon atom other than the -COOH group.
• The amino acids can also be classified based on their need and availability in the human body.

Essential Amino Acids: 

These acids cannot be synthesised in our bodies and are essential amino acids that must be taken through diet. We must depend on food sources to obtain these amino acids. Some of the primary essential Amino Acids are as below:

• Leucine.
• Isoleucine.
• Lysine.
• Threonine.
• Methionine.
• Phenylalanine.
• Valine.
• Tryptophan.
• Histidine (conditionally essential).

Non-Essential Amino acids: 

These acids are synthesised in our bodies by themselves. So we need not rely on external sources for them. They are produced in our bodies and also obtained from protein breakdowns.

Properties of Amino Acids:

We have seen the overall structure and types of amino acids. Based on this information, we can arrive at the properties of amino acids. 

• Each amino acid has an acidic and fundamental group, as seen from its structure. Because of this reason they behave similar to salts. 
• They exist as dipolar ions. 
• Any amino acid in the dry state exists in crystalline form. 
• The NH2 group exists as a cation, and the COOH group exists as an anion. This dipolar ion has a unique name, “Zwitterions’. 
• In an aqueous solution, alpha-amino acids exist in equilibrium between a cationic form, an anionic form and a dipolar ion. 
• The isoelectric point(IEP) is the pH point at which the concentration of zwitterions is the highest, and the concentration of cationic and anionic forms is equal. 
• This specific point is definite for every α-amino acid. 
• They are generally water-soluble and also have high melting points.

Structure of proteins:

• Amino acids exist as a zwitterion, which is dipolar.
• The fundamental nature of the zwitterion is due to the -COO– ion.
• The acidic character of the zwitterion is due to the -NH3+ group.

Peptide linkage:

When two or more amino acids are attached, the resulting -CO-NH- link is termed peptide linkage of the peptide bond.

Peptides: 

When amino acids are joined together by amides bonds, they form larger molecules called peptides and proteins.

Students are advised to visit the Extramarks’ website and access the Class 12 Chemistry Chapter 14 Notes, which are prepared by the subject experts team of Extramarks. These are most reliable study notes and lakhs of students have trusted our study solutions for their board exam preparation.

Polypeptides: 

A dipeptide contains two amino acids linked by one peptide linkage. A tripeptide contains three amino acids linked by two peptides linkage and so on. When the number of few amino acids is more than ten, the products are known as polypeptides. Students can visit the Extramarks’ website and access the NCERT solutions Class 12 Chemistry Chapter 14 Notes for a more detailed explanation of the Polypeptides.

Classification of amino acids:

Amino acids can be Classified as:

1. Neutral amino acids: These amino acids contain an equal number of amino and carboxyl groups. For example, glycine, alanine, valine, etc.
2. Acidic, neutral acids: These amino acids contain more carboxyl groups than amino groups, examples include aspartic acid, asparagine, and glutamic acid, which contain two carboxylic (-COOH ) groups and one -NH3 amine group.
3. Essential amino acids: These consist of more amino groups than carboxyl groups, examples are lysine, arginine, and histidine.

Classification of Proteins:

Based on molecular shape, proteins are classified into two types:

• Fibrous protein: When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, a fibre-like structure is formed, known as fibrous protein. Such proteins are insoluble in water. For example, keratin, myosin etc.
• Globular protein: Globular proteins form when the polypeptide chains coil around to give a spherical shape. Such proteins are usually soluble in water. For example., Insulin, albumin etc.  

Primary, Secondary, Tertiary and Quaternary Structure of Proteins:

Primary structure of proteins:

Proteins are linked in one or more polypeptide chains, known as the primary structure of proteins. Each polypeptide is a protein with amino acids linked with each in a specific sequence, and it is the sequence of amino acids. It is said to be the primary structure of that protein.

Secondary structure of proteins:

The secondary structure refers to the shape in which a long polypeptide chain can exist. The folding and rearrangement of polypeptide chains give the shape or conformation of the protein. Secondary structure can be of alpha-helix or beta-pleated sheet structure.

Tertiary structure:

This protein structure represents the overall folding of the polypeptide chains due to the folding, bending, and coiling, resulting in three-dimensional structures. It gives rise to two main molecular shapes, namely fibrous and globular.

Quaternary structure:

Many proteins exist by grouping two or more polypeptide chains referred to as sub-units. These polypeptide chains are called the sub-units, and the spatial arrangement of these subunits concerning each other is known as quaternary structure.

Denaturation of proteins:

The loss in the biological activity of a protein due to the unfolding of globules and uncoiling of helix is termed denaturation of protein. During denaturation, secondary and tertiary structures vanish, but primary structures remain intact. The coagulation of egg white on steaming is a typical example of denaturation. Proteins can be denatured (physical and biological changes), but there is no chemical variation in the protein structure. 

Denaturation can arise due to various factors, such as changes in temperature, pH, or specific chemical agents. Refer to Class 12 Chemistry Chapter 14 Notes and download the Extramarks’ app to learn more about this and other related concepts.

Enzymes:

A colloidal solution of protein which works as a biological catalyst is known as an enzyme. Many enzymes are globular proteins. Zymase, invertase, lactase, maltase emulsion, urease, pepsin trypsin alpha-amylase etc., are examples of enzymes.

Enzymes are biological catalysts which catalyse chemical reactions in living organisms. For example, hydrolysis of maltose is catalysed by maltase.

C12H22O11    →   2C6H12O6

Maltose           Glucose

Mechanism of enzyme action:

The mechanism is given as follows:

1. The enzyme (E) binds to the substrate(s)

E+S→ES

2. Product formation

ES→EP

3. Products released from the above complex.

EP→E+P

The enzymes process best at an optimum temperature range of 298 K to 313 K. Their activity decreases with a decrease or increase in temperature and stops at 273 K. 

To master Chemistry, students may refer to various study materials based on CBSE solutions and also check out our Class 12 Chemistry Chapter 14 Notes to ace their examinations, all available on Extramarks’ website. 

Vitamins:

Vitamins are organic compounds essential for the average growth of life for animals, some bacteria and microorganisms. These are the biomolecules which are not produced by the body and hence, need to be supplied in small amounts for necessary biological functions. Vitamins are an essential dietary factor.

A, B, C, D, E, & K vitamins are present in various food forms.

Classification of vitamins:

Vitamins are classified into two categories:

• Water-soluble vitamins: Water-soluble vitamins are vitamin B and C complex etc. These vitamins need to be transferred to the body from time to time.
• Fat-soluble vitamins: Vitamins only soluble in fat are called fat-soluble vitamins. A(Retinol), D(calciferol), E(Tocopherol), and K(Phylloquinone) vitamins are soluble in fat.

Particular vitamins are responsible for certain essential functions. Let us have a brief look at them.

• Vitamin A: Required to enable night vision in humans. Cells require Vitamin A for the transfusion of light.
• Vitamin B: Necessary for creating serotonin, myelin, dopamine and epinephrine. It also lowers cholesterol levels.
• Vitamin C:  Increases the immune system and helps fatigued muscles.
• Vitamin D: The formation of RNA needs Vitamin D. It also helps bones absorb calcium to stay healthy and strong and reduces the risk of fractures
• Vitamin E has antioxidant properties that help our bodies get rid of free radicals and assist in the formation of red blood cells.
• Vitamin K: Essential in creating some crucial proteins, Various important vitamins, their sources and their deficiency diseases.

Nucleic acids:

As described in the Class 12 Chemistry Chapter 14 Notes, the particles in the nucleus of the biological cell responsible for heredity are called chromosomes which are made up of proteins and other biomolecules called nucleic acids. Nucleic acids are polymers which are present in all human bodies.

• Nucleic acids play an essential role in the development and reproduction of every life form.
• Nucleic acid contains the elements carbon-oxygen, nitrogen and phosphorus.
• They have nucleotides as their repeating units.

Two types of nucleic acids:

• DNA (Deoxyribonucleic acid).
• RNA (Ribonucleic acid).

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two major types of nucleic acids. DNA and RNA are responsible for inheriting and transmitting specific characteristics from one generation to the other.

Deoxyribonucleic Acid (DNA):

• Chemically, DNA comprises a pentose sugar, phosphoric acid and a few cyclic bases containing nitrogen. 
• The sugar unit present in DNA molecules is β-D-2-deoxyribose. 
• The cyclic bases that have nitrogen-containing in them are Adenine (A), guanine (G), thymine (T)  and cytosine(C). 
• These bases and their configuration in the molecules of DNA play an essential role in storing information from one generation to the next. 
• DNA has a double-strand helical structure in which the strands complement each other.

Ribonucleic Acid (RNA):

• The RNA molecule is also composed of phosphoric acid, a pentose sugar and a few cyclic bases containing nitrogen. 
• RNA has β-D-ribose in it as the sugar unit. 
• The heterocyclic bases available in RNA are Adenine (A), guanine (G), cytosine(C) and uracil (U). 
• In RNA, the fourth base varies from that of DNA. 
• The RNA commonly consists of a single strand which sometimes folds back; that results in a double helix structure. 

There are three different types of RNA molecules, each having a specific function:

1. Messenger RNA (mRNA).
2. Ribosomal RNA (rRNA).
3. Transfer RNA (t-RNA).

To learn more about the above three RNA molecules, students are recommended to visit the Extramarks’ website and refer to the Class 12 Chemistry Chapter 14 Notes.

Chemical composition of nucleic acids:

Nucleotides contain three chemical components: 

• A heterocyclic base.
• A five-carbon sugar moiety.
• A phosphate group.

Structure of Nucleic acids:

1. Nitrogen-containing heterocyclic base: Purines and pyrimidines are two types of heterocyclic bases. For example, Adenine and guanine are purines. Cytosine, thymine, and uracil are pyrimidines.
2. Sugars: The two types of sugars are RNA and DNA.

iii. Phosphate group: Nucleotides are joined by these linkages.

1. Nucleoside: A nucleoside unit is produced when a nitrogen base is attached to a sugar molecule.

Base + sugar = nucleoside.

1. Nucleotide: When a nitrogen base is attached to a sugar molecule and phosphate, the unit forms a nucleotide. 

Base+Sugar+phosphate → nucleotide.

The primary structure is based on how sugar, phosphate, and bases are linked in nucleic acids.

Secondary structure: 

Watson and Crick described the double helix structure of DNA. The nucleotides in each strand are connected by phosphate ester bonds and the bases of one strand by hydrogen bonds. Adenine pairs with thymine through two double hydrogen bonds. In contrast, cytosine pairs with guanine through triple hydrogen bonds. 

The two strands of DNA are always complementary to each other; i.e., if on one side there is Purine, then on another side at the same position, Pyrimidine is present. For example, if the base sequence on the strand is ACTCGCCA, then on the other strand, the sequence will be complementary: TGAGCGGT.

The biological function of nucleic acids:

A few of the biological functions of nucleic acids, as per the Class 12 Chemistry Chapter 14 Notes, are:

• Nucleic acids are responsible for transmitting inherent characteristics from parent to offspring. They are also responsible for the synthesis of protein in our bodies.
• DNA fingerprinting is a method that is used by forensic experts to determine paternity. This method is also used for the identification of criminals. It has also played a significant role in biological evolution and genetics studies.
• Replication: It is the characteristics of a bio-molecule to synthesize different molecules. For example, DNA has a specific property to replicate itself.
• Protein synthesis: Genetic information collected in DNA in a specific base sequence is expressed in the form of a specific base sequence.
• Gene and genetic code: Every segment of DNA molecule that codes for a specific protein or a polypeptide, known as the relationship between nucleotides triplets and the amino acids, is called the genetic code. This is what forms gene and genetic code.
• Mutation: A chemical process in a DNA molecule leads to the synthesis of proteins with a changed amino acid sequence. Radiation, viruses or chemical agents cause these changes. Special enzymes replicate most changes in DNA in the cell, but if there is a failure to repair by the enzymes, then it can cause mutation.

Hormones:

Hormones are molecules which act as intracellular messengers. These are constructed by endocrine glands in the body and are poured directly into the bloodstream, which transports them to the site of action. 

Hormones have various functions in the body. They help to adjust the balance of biological activities in the body. Testosterone is the primary sex hormone developed in males and progesterone in females. 

Hormones are chemical compounds which are produced in ductless glands in the body. Because of their function, hormones are also termed chemical messengers. 

To understand more about the Hormones and its functions, students are advised to visit the Extramarks’ website and access the Class 12 Chemistry Chapter 14 Notes.

Key Features of Class 12 Chemistry Chapter 14 Notes

Extramarks is the best website for students to enhance their board preparation. The platform is trusted by lakhs of students and teachers across the country. CBSE Class 12 Chemistry Chapter 14 Notes can be used as study reference material and also as quick revision notes. These are beneficial for a quick revision for competitive examinations like board exams, JEE Mains, NEET, etc. Class 12 Chemistry Chapter 14  Notes can also be used for offline revision. 

Below are few of the important features for students to study from Extramarks study materials:

• The study materials at Extramarks are well prepared with comprehensive coverage of all topics from NCERT textbook and NCERT exemplar. 
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• The notes are prepared by subject experts with decades of teaching experience. The chapter notes cover all topics with detailed explanations and also include a set of important questions and formulas for quick reference.

Class 12 Chemistry Chapter 14 Notes: Exercise & Answer Solutions

Class 12 Chemistry Chapter 14 Notes includes questions and answer solutions which are based on NCERT books. Every exercise and solution is compiled to add more value for the students while revising the chapter. Students may refer to various study materials such as revision notes, past years’ questions papers, and essential questions and learn more about the chapter concepts from the Extramarks’ website. 

NCERT Exemplar Class 12 Chemistry

All solutions and problems are given to help students prepare for their final examinations. These NCERT Exemplar book questions are a little more complex and cover every concept introduced in Class 12 Chemistry chapters.

Students will fully understand the concepts covered in each chapter by practising this NCERT Exemplar for Class 12 Chemistry. Exemplars provide the best solutions to challenges that students might face in board exams. They cover all the topics taught in each class and provide the most outstanding practising materials or worksheets for students. These questions from exemplars strictly follow the latest CBSE guidelines and board examinations pattern.