Revision: Biomolecules Chemistry Science (English Medium) Class 12 CBSE

Carbohydrates that are crystalline solids, sweet in taste and soluble in water are called sugars.

Carbohydrates that are amorphous solids, tasteless and insoluble in water are catled non-sugars.

Carbohydrates are optically active polyhydroxy aldehydes or polyhydroxy ketones or compounds that can be hydrolysed to polyhydroxy aldehydes or polyhydroxy ketones.

The sugars that reduce the Tollen's reagent and Fehling's solution are called reducing sugars.

An aldose monosaccharide that has six carbon atoms (e.g., Glucose) is called an aldohexose.

A ketose with six carbon atoms is called a ketohexose.

A monosaccharide that contains one ketonic carbonyl group is called a ketose.

Monosaccharides that contains one aldehydic group is called aldose.

In the hydrolysis of sucrose, there occurs a change in the sign of optical rotation from dextro (+) to laevo (−). The product so obtained is referred to as invert sugar.

Carbohydrates that yield two to ten monosaccharide units, on hydrolysis, are called oligosaccharides.

Amino acids that cannot be synthesised in the human body and must be obtained through diet are known as essential amino acids.

An ∝-amino acid molecule contains both acidic carboxyl (-COOH) group as well as basic amino (-NH₂) group. Proton transfer from acidic group to basic group of amino acid forms a salt, which is a dipolar ion called zwitter ion.

Amino acids which are synthesised by the body itself are called non-essential amino acids.

Amino acids which contain more number of amino groups than carboxyl groups are called basic amino acids.

Proteins may have one or more polypeptide chains. Each polypeptide in a protein has amino acids linked with each other in a specific sequence and it is this sequence of amino acids that is said to be the primary structure of that protein. Any change in this primary structure, i.e., the sequence of amino acids, creates a different protein.

Amino acids which contain equal number of amino groups and carboxyl groups are called neutral amino acids.

Amino acids which contain more number of carboxyl groups than amino groups are called acidic amino acids.

Chemically, peptide linkage is an amide formed between the –COOH group and –NH₂ group. The reaction between two molecules of similar or different amino acids proceeds through the combination of the amino group of one molecule with the carboxyl group of the other. This results in the elimination of a water molecule and the formation of a peptide bond –CO–NH–. The product of the reaction is called a dipeptide because it is made up of two amino acids.

For example, when the carboxyl group of glycine combines with the amino group of alanine, we get a dipeptide, glycylalanine.

Denaturation is the process in which the secondary and tertiary structure of a protein is disrupted due to heat, a change in pH, or chemicals, while the primary structure remains unchanged. In denaturation, peptide bonds are not broken; only the weak bonds (like hydrogen bonds) are disturbed.

Bifunctional organic compounds containing a carboxylic and an amino group either at the same carbon atom or at nearby carbon atoms are called amino acids.

α-Amino acids are carboxylic acids having an amino (–NH₂) group bonded to the α-carbon, that is, the carbon next to the carboxyl (–COOH) group.

The bond that connects α-amino acids to each other is called a peptide bond.

Chemically proteins are polyamides which are high molecular weight polymers of the monomer units, i.e., α-amino acids. OR It can also be defined as proteins are the biopolymers of a large number of α-amino acids and they are naturally occurring polymeric nitrogenous organic compounds containing 16% nitrogen and peptide linkages (-CO-NH-)

Enzymes are biological catalysts that speed up chemical reactions in living cells without being consumed in the process.

Chemically, proteins are polyamides, which are high molecular weight polymers of the monomer units called \[\alpha\]-amino acids.

A nucleoside consists of a nitrogenous base linked to a pentose sugar without a phosphate group.

A nitrogenous base is an organic molecule (purine or pyrimidine) that carries genetic information in nucleic acids.

RNA is a single-stranded nucleic acid that helps in protein synthesis and information transfer.

DNA is a double-stranded nucleic acid that stores and transmits hereditary information and can replicate itself.

Nucleic acids are large biological macromolecules that store and transmit genetic information in living organisms.

The unit formed by joining the anomeric carbon of the furanose (sugar) with a nitrogen of a base is called nucleoside.

A nucleotide is the basic structural unit of nucleic acids, composed of a nitrogenous base, a pentose sugar, and a phosphate group.

Hormones are chemical messengers created by the endocrine glands and transported through the bloodstream to govern body functions such as development, metabolism, reproduction and mood by interacting with specific target cells.

Optically active polyhydroxy aldehydes or ketones or the compounds which yield such units on hydrolysis are called carbohydrates.

Carbohydrates which cannot be hydrolysed to simpler units are called monosaccharides.

Carbohydrates which yield two to ten monosaccharide units on hydrolysis are called oligosaccharides.

Carbohydrates which yield a large number of monosaccharide units on hydrolysis are called polysaccharides.

The linkage formed between two monosaccharide units through an oxygen atom is called glycosidic linkage.

Long chains of nucleotides joined by phosphodiester linkage are called nucleic acids.

The sequence of amino acids in a polypeptide chain is called primary structure of protein.

Biological catalysts which increase the rate of biochemical reactions are called enzymes.

Chemical messengers secreted by endocrine glands and transported through blood are called hormones.

Organic compounds required in small amounts in the diet to perform specific biological functions are called vitamins.

The unit formed when a nucleoside is linked to phosphoric acid is called nucleotide.

The cyclic hemiacetal forms of a sugar differing in configuration at the anomeric carbon are called anomers.

• Carbohydrates are organic biomolecules made of C, H and O, usually fitting the general formula Cx(H₂O)y and existing as aldoses or ketoses.
• They are classified into monosaccharides, disaccharides and polysaccharides; monosaccharides cannot be hydrolysed further, disaccharides are formed by two monosaccharides via glycosidic bonds, and polysaccharides are long polymers.
• Some sugars like digitoxose (C₆H₁₂O₄) and rhamnose (C₆H₁₂O₅) do not obey the typical Cx(H₂O)y formula.
• All monosaccharides are reducing sugars because they possess a free aldehyde or ketone group.
• Cellulose is a linear polymer of β‑D‑glucose, unlike starch and glycogen, which are polymers of α‑glucose and show branching.
• Biologically, carbohydrates supply energy for metabolism; glucose is the main substrate for ATP synthesis, and lactose provides energy to infants.
• Polysaccharides such as starch and glycogen act as storage products and also contribute to structural components of cell membranes and cell walls.

• Glucose is a monosaccharide, an aldohexose, and a reducing sugar, commonly found in fruits and also known as dextrose.
• It can be prepared by hydrolysis of sucrose (using dilute acid) or hydrolysis of starch under heat and pressure.
• Glucose confirms a straight-chain structure of six carbon atoms when reduced to n-hexane.
• Presence of functional groups is shown by reactions: –CHO (aldehyde), five –OH groups, and formation of derivatives like oxime and cyanohydrin.
• Oxidation reactions indicate the formation of gluconic acid (mild oxidation) and saccharic acid (strong oxidation), confirming functional groups in glucose.

• Glucose is an aldohexose with molecular formula \[C_{6}H_{12}O_{6},\mathrm{M.P.146^{\circ}C.}\]
• 'D' in D-(+)-Glucose = configuration; (+) = dextrorotatory nature; 'D'/'L' have no relation to optical activity.
• Glucose has five —OH groups (confirmed by glucose pentaacetate) and one aldehydic carbonyl group (confirmed by oxime & cyanohydrin formation).
• Glucose is soluble in water, sparingly soluble in alcohol, and insoluble in ether.
• The additional chiral centre in glucose ring structures is formed due to ring closure.

• Sucrose consists of one unit each of α-D-glucopyranose and β-D-fructofuranose.
• It contains an α, β-1,2-glycosidic linkage.
• Maltose is composed of two α-D-glucopyranose units joined by an α-1,4-glycosidic bond.
• Lactose consists of β-D-galactopyranose and β-D-glucopyranose units.
• It has a β-1,4-glycosidic linkage.

• The primary structure of proteins shows the sequence of amino acids in a polypeptide chain.
• Secondary structure is formed by hydrogen bonding and mainly includes α-helix and β-pleated sheet.
• In an α-helix, the chain coils into a right-handed spiral stabilised by hydrogen bonds.
• In a β-pleated sheet, chains are stretched and arranged side by side, held by intermolecular hydrogen bonds.
• Tertiary structure is the overall 3D folding of the chain due to interactions like hydrogen bonds, disulfide bonds, and van der Waals forces, while quaternary structure is the arrangement of multiple polypeptide chains.

1. Enzymes are biological (protein) catalysts that increase the rate of biochemical reactions without being consumed.

2. Most enzymes are globular proteins and show high specificity due to their unique 3D structure and active site.

3. Enzymes bind with substrate to form enzyme–substrate complex, then release product and remain unchanged.

4. Enzyme activity is affected by temperature and pH, and reactions are usually reversible.

5. Types of enzymes:

• Simple enzymes (only protein)
• Conjugated enzymes (protein + cofactor)

6. Examples of enzymes and their functions:

• Amylase: Starch → glucose
• Maltase: Maltose → glucose
• Lactase: Lactose → glucose + galactose
• Invertase: Sucrose → glucose + fructose
• Pepsin: Proteins → amino acids

• Origin of the name: The word "protein" is derived from the Greek word 'proteios', meaning "primary" or "of prime importance", reflecting proteins' essential role in living organisms.
• Chemical nature: Proteins are polyamides — high molecular weight polymers made up of monomer units called α-amino acids (general formula: RCH(NH₂)COOH).
• Nutritional sources: Key dietary sources of protein include milk, pulses, nuts, fish, and meat.
• Fibrous proteins have thread-like structures where polypeptide chains run parallel, held by hydrogen and disulphide bonds; they are insoluble in water — e.g., Keratin (hair, skin, nails) and Myosin (muscles).
• Globular proteins have a spherical shape where polypeptide chains coil around; they are soluble in water — e.g., Insulin, Egg albumin, and Legumelin.

• Nitrogenous bases in nucleic acids are of two types: purines and pyrimidines.
• Purine bases have a double-ring structure and include Adenine (A) and Guanine (G).
• Pyrimidine bases have a single-ring structure and include Cytosine (C), Thymine (T), and Uracil (U).
• Thymine is present in DNA, while Uracil is present in RNA instead of thymine.

• Chemical coordination is the process by which cells and organisms communicate using chemical signals.
• There are four types of chemical signaling: autocrine, paracrine, endocrine, and pheromones.
• Hormones are chemical messengers that regulate various body functions.
• Hormones are classified based on their chemical nature into amines, peptide/protein hormones, steroid hormones, fatty acid derivatives, and gases.
• Examples include epinephrine and thyroxine (amines), insulin and growth hormone (proteins), estrogen and testosterone (steroids), prostaglandins (fatty acids), and nitric oxide (gas).

• Proteins are classified into two types based on their molecular shape: fibrous proteins and globular proteins.
• Fibrous proteins consist of parallel polypeptide chains held together by hydrogen and disulphide bonds; they are generally insoluble in water and provide structural support.
• Globular proteins are formed when polypeptide chains coil into a spherical shape; they are usually soluble in water and perform functional roles such as enzymatic and hormonal activities.
• Protein structure is organized into four hierarchical levels: primary, secondary, tertiary, and quaternary, each representing increasing complexity of folding and organization.
• The stability of higher-level protein structures (secondary, tertiary, and quaternary) is maintained by hydrogen bonds, disulphide linkages, van der Waals forces, and electrostatic interactions.