Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones.
The carbohydrates may be summarised as below.

(i) Sugar: They are sweet crystalline substance and soluble in water.
(a) Monosaccharides: They are polyhydroxy aldehydes (or) polyhydroxy ketones.
Aldoses - Carbohydrates containing aldehyde group. Eg: Glucose
Ketoses - Carbohydrates containing ketone group. Eg: Fructose.
(b) Oligosaccharides: They are sugars that yield two to ten monosaccharide molecules on hydrolysis.
Disaccharides: They are sugars which on hydrolysis give two molecules of same or different monosaccharides. Eg: Sucrose, maltose.
\(\underset { Sucrose }{ { C }_{ 12 }{ H }_{ 22 }{ O }_{ 11 } } +{ H }_{ 2 }O\longrightarrow \underset { Glucose }{ { C }_{ 6 }{ H }_{ 12 }{ C }_{ 6 } } +\underset { Frutose }{ { C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } } \)
Trisaccharides: They are sugars which gives three molecules of monosaccharides on hydrolysis
Eg: Raffinose
\(\underset { Raffinose }{ { C }_{ 18 }{ H }_{ 32 }{ O }_{ 16 } } +{ 2H }_{ 2 }O\longrightarrow \underset { Gialactose }{ { C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } } +\underset { Glucose }{ { C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } } +\underset { Frutose }{ { C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } } \)
(ii) Non-sugars (or) Polysaccharides:
They are non-sugars which involve a large number of monosaccharide units linked to each other by oxide bridges. These bridges are called glycosidic linkages. Eg: starch, cellulose.
\(\underset { Starch }{ \left( { C }_{ 6 }{ H }_{ 10 }{ O }_{ 5 } \right) _{ n } } +n{ H }_{ 2 }O\overset { { H }^{ + } }{ \longrightarrow } \underset { Glucose }{ { nC }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } } \)

Importance of proteins:
Proteins are the functional units of living things : play vital role in all biological processes
(i) All biochemical reactions occur in the living systems are catalysed by the catalytic proteins called enzymes.
(ii) Proteins such as keratin, collagen acts as structural back bones.
(iii) Proteins are used for transporting molecules (Haemoglobin), organelles (Kinesins) in the cell and control the movement of molecules in and out of the cells (Transporters).
(iv) Antibodies help the body to fight various diseases
(v) Proteins are used as messengers to coordinate many functions. Insulin & glucagon controls the glucose level in the blood.
(vi) Proteins act as receptors that detect presence of certain signal molecules and activate the proper response.
(vii) Proteins are also used to store metals such as iron (Ferritin) etc.

Structure of fructose: Fructose is the sweetest of all known sugars. It is readily soluble in water. Fresh solution of fructose has a specific rotation -1330 which changes to - 920 at equilibrium due to mutarotation. Similar to glucose, the structure of fructose is deduced from the following facts.
(i) Elemental analysis and molecular weight determination of fructose show that it has the molecular formula C₆H₁₂O₆.
(ii) Fructose on reduction with HI and red phosphorus gives a mixture of n - hexane (major product) and 2 - iodohexane (minor product). This reaction indicates that the six carbon atoms in fructose are in a straight chain.

(ii) Fructose reacts with NH₂OH and HCN. It shows the presence of carbonyl groups in the molecule of fructose.
(iv) Fructose reacts with acetic anhydride in the presence of pyridine to form penta acetate. This reaction indicates the presence of five hydroxyl groups in a fructose molecule. ,
(v) Fructose is not oxidized by bromine water. This rules out the possibility of presence of an aldehyde (-CHO) group.
(vi) Partial reduction of fructose with sodium amalgam and water produces mixtures of sorbitol and mannitol which are epimers at second carbon. New asymmetric carbon is formed at C-2. This confirms the presence of keto group.

(vii) On oxidation with nitric acid, it gives glycolic acid and tartaric acids which contain smaller number of carbon atoms than in fructose.

This shows that a keto group is present in C-2. It also shows the presence of 10 alcoholic groups at C- 1 and C- 6

Importance of carbohydrates:
(i) Carbohydrates, widely distributed in plants and animals, acts mainly as energy sources and structural polymers.
(ii) Carbohydrate is stored in the body as glycogen and in plant as starch.
(iii) Carbohydrates such as cellulose which is the primary components of plant cell wall, is used to make paper, furniture (wood) and cloths (cotton)
(iv) Simple sugar glucose serves as an instant source of energy.
(v) Ribose sugars are one of the components of nucleic acids.
(vi) Modified carbohydrates such as hyaluronate (glycosaminoglycans) act as shock absorber and lubricant.

(i) The amino acids are linked covalently by peptide bonds. The carboxyl group of the first amino acid react with the amino group of the second amino acid to give an amide linkage between these amino acids. This amide linkage is called peptide bond. The resulting compound is called a dipeptide. Addition an another amino acid to this dipeptide a second peptide bond results in tripeptide.

(ii) Thus we can generate tetra peptide, penta peptide etc... When you have more number of amino acids linked this way you get a polypeptide. If the number of amino acids are less it is called as a polypeptide, if it has large number of amino acids (and preferably has a function) then it is called a protein.
(iii) The amino end of the peptide is known as N - terminal or amino terminal while the carboxy end is called C-terminal or carboxy terminal. In general protein sequences are written from N-Terminal to C-Terminal.The atoms other than the side chains (R-groups) are called main chain or the back bone of the polypeptide.

Watson & Crick proposed a 3-dimensional secondary structure of DNA. In this DNA molecule, Monomners of DNA are held together by Phosphodiester linkage. This linkages are occured in 5' & 3' carbon atoms of Pentose sugar.

Vitamin K.

Lipids can be classified as simple lipids, compounds lipids and derived lipids.

Human blood contains about 100 mg/dL of glucose, hence it is also known as blood sugar.

The process by which one epimer is converted into other is called epimerisation and it requires the enzymes epimerase. Galactose is converted to glucose by this manner in our body.

The type of sugar that contains 4 carbon atoms and -CHO group is Aldotetrose. Example of Aldotetrose is Erythrose.

α - Helix:
In the a-helix sub-structure, the amino acids are arranged in a right handed helical (spiral) structure and are stabilised by the hydrogen bond between the carbonyl oxygen one amino acid (nth residue) with amino hydrogen of the fifth residue (n + 4^th residue).The side chains of the residues protrude, outside of the helix. Each turn of an a-helix contains about 3.6 residues and is about 5.4 Å long.The amino acid proline produces a kink in the helical structure and often called as a helix breaker due to its rigid cyclic structure.

∴ Two dipeptides structures are possible from glycine and alanine. They are glycyl alanine and Alanyl glycine.

Vitamins are classified into two groups based on their solubility in water or in fat.
(a) Fat soluble vitamins:
These vitamins absorbed best when taken with fatty food and are stored in fatty tissues and livers. These vitamins do not dissolve in water. Hence they are called fat soluble vitamins. Vitamin A, D, E & K are fatsoluble vitamins.
(b) Water soluble vitamins:
Vitamins B (B₁, B₂, B₃, B₅, B₆, B₇, B₉ & B12) and C are readily soluble in water. On the contrary to fat soluble vitamins, these can't be stored. The excess vitamins present will be excreted through urine and are not stored in our body. Hence, these two vitamins should be supplied regularly to our body.

i) Starch - Polysaccharide
ii) fructose - monosaccharide
iii) sucrose - oligosaccharides 
iv) lactose - oligosaccharides
iv) maltose - oligosaccharides

i) Rickets - Vitamin - D (Cholecalciferol - (D₃) Ergocalciferol - (D₂)
ii) Scurvy (bleeding gums) - vitamin - C (Ascorbic acid)

(i) Oligosaccharides are sugars that yield two to ten monosaccharide molecules on hydrolysis. Eg: Sucrose, Raffinose
(ii) Polysaccharides are carbohydrates which involve a large number of monosaccharide units linked to each other by oxide bridges. These linkages are called glycosidic linkages.
Eg: Starch, cellulose and inulin.

(i) Enzymes are biocatalysts that catalyse a specific biochemical reaction.
(ii) They generally activate the reaction by reducing the activation energy by stabilising the transition state.
(iii) In a typical reaction, enzyme E binds with the substrate molecule reversibly to produce an enzyme substrate complex.
(iv) During this stage,the substrate is converted into product and the enzyme becomes free and is ready to bind to another substrate molecule.
\(\underset { Enzyme }{ E } +\underset { Substance }{ S } \longrightarrow \underset { Enzyme-substratecomplex }{ [ES] } \) 
[ES]➝E+P

On oxidation with nitric acid, it gives glycolic acid and tartaric acids which contain smaller number of carbon atoms than in fructose.

This shows that a keto group is present in C-2.

(i) Oxidation of fructose yields a mixture of glycollic acid and tartaric acid.
(ii) When fructose is treated with HCN, it forms an addition product which upon hydrolysis and subsequent reduction with hydroiodic acid and red phosphorous gives 2-methyl-hexanoic acid.
This indicates that the ketone group is

i) Reducing sugars:
1. Sugars which reduce Tollen's reagent or Fehling's solution or Benedict's solution are called reducing sugars.
2. These contain either α - hydroxyl ketone or cyclical hemi acetal or hemi ketal or structures in equilibrium with open chain forms having a free- CHO or C=O group.
3. E.g. a) All monosaccharide's like D - glucose, D - fructose (aldoses and ketoses)
b) Sugars like Lactose and maltose except sucrose.
ii) Non - reducing sugars:
1. Sugars which do not reduce either Tollen's reagent, Fehling's solution or Benedict's solution are called non-reducing sugars.
2. They contain a stable acetal or ketal structures which cannot be opened into a free carbonyl group.
E.g. Sucrose, starch, cellulose, glycogen, dextrin etc.