Biomolecules class 12th notes- Free ncert class 12 Chemistry

Chapter 14 Notes- Download PDF

Updated on Apr 23, 2022 - 11:36 a.m. IST by Sumit Saini

NCERT Class 12 Chemistry chapter 14 notes help to establish a relationship between inorganic
molecules that makes a living organism. Biomolecules Class 12 notes cover a brief outline of topics
such as carbohydrates, proteins, vitamins, enzymes, nucleic acids, hormones, etc.

The NCERT Class 12 chapter 14 notes discuss all the main topics of NCERT chapter 14 of Class 12.
Some of the topics discussed in biomolecules Class 12 notes consist of carbohydrates such as
monosaccharides, disaccharides, polysaccharides, amino acids, mechanism of enzyme action, nucleic
acids, and hormones. Biomolecules are organic substances that build up the living organism and the
same biomolecules are also important for three-dimensional growth and maintenance. The branch
of science which deals with the study of biomolecules is known as biochemistry. Many of the
biomolecules are polymers. For example, protein is a polymer made up of amino acids as the
monomer unit.

All the topics in cbse class 12 chemistry chapter 14 notes are discussed in depth. CBSE Class 12
Chemistry chapter 14 notes also include quick points to remember from the exam point of view. All
the topics mentioned below can be easily downloaded by the student by Class 12 Chemistry chapter
14 notes pdf download.

Also, students can refer,

• NCERT Notes Class 12 Chemistry

• NCERT Solutions for Class 12 Chemistry Chapter 14 Biomolecules
• NCERT Exemplar Class 12 Chemistry Chapter 14 Solutions Biomolecules

NCERT Class 12 Chapter 14 Notes-

Biomolecules Class 12 Notes – Topic 1:

Biomolecules-

-Biomolecules are organic substances that form a basis for the growth and maintenance of the
human body.
-Biomolecules discussed here are carbohydrates, proteins, enzymes, vitamins, nucleic acids, and
hormones.

• Carbohydrates-

-Manufactured in plants by performing photosynthesis.

-optically active polyhydroxy aldehydes/ polyhydroxy ketones.

- Food, clothing, and shelter.

Classi昀椀cation of carbohydrates

1. Monosaccharides

Monosaccharides are the simplest carbohydrates that cannot be hydrolyzed into simpler
compounds.

Examples- glucose, fructose and, ribose.

General formula- (CH2O)5

1. Glucose-

-present in honey and fruits.

-belongs to D-family.

• Preparation of glucose-

From sucrose-

From starch-

• Structure of glucose-
Here are a few reactions to 昀椀nd the structure of glucose-

Straight chain structure-

Presence of 昀椀ve hydroxyl groups-

Presence of an aldehyde group-

Oxidation of glucose-

Oxidation of glucose indicates the presence of primary alcoholic group.

Open chain structure of Glucose-

D-(+)-Glucose

• The cyclic structure of glucose-

Limitations of open chain structure of glucose-

-Glucose does not undergo some of the characteristic reactions of aldehydes.

-no reaction with ammonia

-no reaction with hydroxylamine.

(+)-Glucose exists in two stereoisomeric forms i.e., α-D-glucose and β-D-Glucose.

Mutarotation-the two forms of glucose, convert into each other at equilibrium when glucose is
dissolved in water and allowed to stand.

Anomers-

Cyclization in the structure of glucose has been observed by the formation of hemiacetal between -
CHO group and -OH group. On C5 carbon.
Optical isomers exist when con昀椀guration around only one of the carbons C 1 takes place. These are

known as anomers.

α-D-glucose β-D-Glucose

2. Fructose-

Fructose is obtained when disaccharides are hydrolyzed. Fructose has six- member hemiacetal ring
structure.

Structure of fructose-

α-D-fructose β-D-fructose

Haworth structure of fructose-

α-D-fructose β-D-fructose

2. Disaccharides-

These are the type of carbohydrates that give more than one (can be the same or not)
monosaccharides.

Examples-

3. Polysaccharides-

These are polymer compounds that are formed by many numbers of monosaccharide units which
are joined together by glycosidic linkages.

Starch-

Found in plants.

Found in wheat, rice, maize, potatoes, barley, etc.

Starch reacts with iodine solution to give blue color.

It is a non-reducing saccharide.
Does not reduce Fehling’s solution.

Amylose-

Linear polymer

It contains 200-300 α-D-glucose units linked together by glycosidic linkages.

Molecular mass (10,000-500,000)

Amylopectin-

It is a highly branched polymer.

Do not react with iodine solution to give blue color.

Cellulose-

It is the most abundant organic polymer found on earth.

It is a straight-chain polymer joined by β-glycosidic linkages.

Used in the manufacturing of paper, textiles, and plastic industries.

Glycogen-

It is a polysaccharide found in animal cells occurring in muscles, and the liver.

It is known as animal starch.

It is a polymer made up of thousand glucose units.

4. Importance of carbohydrates-

• Plays a major role for both plants as well as animals.

• Carbohydrates are the major source of energy (except cellulose)

• Carbohydrates store energy for the functioning of living organisms.

• Carbohydrates are used as raw materials in the production of textiles, papers, lacquers, breweries,
etc.

• Proteins-

All the living cells are made up of biomolecules having high molecular mass known as amino acids.

1. Amino acids-
Amino acids are the building block units of proteins. These are the organic compounds that contain
amino as well as a carboxyl group.

The above unit may be attached to any other carbon atom other than that of -COOH group.

2. Classi昀椀cation of Amino Acids-

Amino acids can be broadly classi昀椀ed as – acidic, basic, or neutral.

Neutral amino acids- These are the amino acids that contain an equal number of amino and carboxyl
groups. Examples- glycine, alanine, valine, etc.

Acidic neutral acids- These are amino acids that contain more carboxyl groups than amino groups.
Examples- aspartic acid, asparagine acid, glutamic acid which contain two -COOH groups and one -
NH3 group.

Basic amino acids- These contain more amino groups than carboxyl groups. Examples- lysine,
arginine, and histidine.

3. Structure of Proteins-

-Amino acids exist as zwitterion which is dipolar.

-basic nature of zwitterion is due to -COO- ion.

-Acidic character of zwitterion is due to the -NH3+ group.

Peptide linkage- When two or more amino acids condense, the resulting -CO-NH- link is called
peptide linkage of the peptide bond.

Primary structure of proteins- amino acids are linked in one or more polypeptide chains which are
known as the primary structure of proteins.

Secondary structure of proteins- the folding and arrangement of polypeptide chains give the shape
or conformation of the protein.

Secondary structure can be of α- Helix structure type or β- pleated sheet structure.

Tertiary structure- the tertiary structure of the protein arise due to the folding, bending, and coiling
which results in three- dimensional structures.

Quaternary structure- many of the proteins exist as the grouping of two or more polypeptide chains.
These polypeptide chains are called the sub-units.

4. Denaturation of Proteins-

Proteins can be denatured (physical changes and biological changes) but there is no chemical change
in the protein structure.
Denaturation can arise due to many factors such as changes in temperature, pH, or certain chemical
agents.

• Enzymes- Enzymes are biological catalysts that catalyze biochemical reactions in living organisms.
For example- hydrolysis of maltose is catalyzed by maltase.

Mechanism of enzyme action-

The mechanism is given as-

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

E+S→ES

2. Product formation

ES→EP

3. Products releases from the above complex.

EP→E+P

• Vitamins-

These are the biomolecules that are not produced by the body and hence, need to be supplied in
small amounts for necessary biological functions of the body.

There are A, B, C, D, E, and K vitamins.

• Classi昀椀cation of Vitamins-

Water-soluble vitamins- water-soluble vitamins are vitamin B, vitamin C, etc.

These vitamins need to be supplied to the body from time to time.

Fat-soluble vitamins- vitamins that are only soluble in fat are called fat-soluble vitamins. A, D, E, and,
K vitamins are soluble in fat.

• Nucleic acids-

Nucleic acids are polymers that are present in all human bodies.

Nucleic acids play an important role in the development and reproduction of all life forms.

Nucleic acids have nucleotides as their repeating units.

There are two types of nucleic acids-

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

1. Chemical composition of nucleic acids-

Nucleotides consist of three chemical components such as a heterocyclic base, a 昀椀ve-carbon sugar,
and a phosphate group.

2. Structure of Nucleic acids-

a) Nitrogen-containing heterocyclic base- Purines and pyrimidines are two types of heterocyclic
bases. Example- Adenine, and guanine are purine. Cytosine, thymine, and uracil are pyrimidines.

b) Sugars- the two types of sugars are RNA and DNA.

c) phosphate group- nucleotides are joined by these linkages.

d)Nucleoside- When a nitrogen base is attached to a sugar molecule a nucleoside unit is produced.
 e) Nucleotide-

Base+Sugar+phosphate →nucleotide

1. The biological function of nucleic acids-

Some of the biological functions of nucleic acids are-

• Replication- It is the property of a biomolecule to synthesize another molecule.

Example- DNA has a unique property to replicate itself.

• Protein synthesis- genetic information stored in DNA in a speci昀椀c base sequence is expressed in
the form of a speci昀椀c base sequence.

• Hormones-

Hormones are chemical compounds that are produced in ductless glands in the body. Because of
their function hormones are also known as chemical messengers.

Signi昀椀cance of NCERT Class 12 Chemistry Chapter 14 Notes

Biomolecules Class 12 notes contain step vise step headings and subheadings as per mentioned in
the chapter 14 of Class 12 NCERT. NCERT Class 12 Chemistry chapter 14 notes are very helpful for a
quick revision for competitive exams like VITEEE, BITSAT, JEE Core, NEET, etc. Class 12 Chemistry
chapter 3 notes pdf download can be used for o昀툀ine revision.

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