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.
\(\underset { Starch }{ \left( { C }_{ 6 }{ H }_{ 10 }{ O }_{ 5 } \right) _{ n } } +n{ H }_{ 2 }O\overset { { H }^{ + } }{ \longrightarrow } \underset { Glucose }{ { nC }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } } \)

(i) Hormones are classified according to the distance over which they act as, endocrine, paracrine and autocrine hormones.
(ii) Endocrine hormones act on cells distant from the site of their release. Example: insulin and epinephrine are synthesized and released in the bloodstream by specialized ductless endocrine glands.
(iii) Paracrine hormones (alternatively, local mediators) act only on cells close to the cell that released them. For example, interleukin -1 (IL-1) Autocrine hormones act on the same cell that released them. For example, protein growth factor interleukin-2 (IL-2).

Primary structure of Proteins:
Proteins are polypeptide chains, made up of amino acids are connected through peptide bonds. The relative arrangement of the amino acids in the polypeptide chain is called the primary structure of the protein. Knowledge of this is essential as even small changes have potential to alter the overall structure and function of a protein.
\(\mathrm{H}_{2} \mathrm{~N}-\mathrm{Gly}-\mathrm{Met}-\mathrm{Phe}-\mathrm{Cys}-\mathrm{Arg}-\mathrm{Asp}-\mathrm{COOH}\)
α - Helix:
In the α-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 of one amino acid (n 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 α-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.

1. Linear sequence of aminoacids
2. Linear
3. Composed of peptide bonds formed between amino acids.
Secondary structure of Proteins:
The amino acids in the polypeptide chain forms highly regular shapes (sub-structures) through the hydrogen bond between the carbonyl oxygen (-C=O) and the neighbouring amine hydrogen (-NH) of the main chain. α-Helix and β-strands or sheets are two most common substructures formed by proteins.

β-Strand:
β-Strands are extended peptide chain rather than coiled. The hydrogen bonds occur between main chain carbonyl group one such strand and the amino group of the adjacent strand resulting in the formation of a sheet like structure. This arrangement is called β-sheets.

Anomers are cyclic monosaccharide differing from each other in the configuration of C₁ if they are aldoses or in the configuration of C₂ if they are ketoses.
E.g. α and βD - glucose.

Photosynthesis.

Lactose is a dissaccharide so on hydrolysis gives I two monosaccharides.
\(\underset { Lactose }{ { C }_{ 12 }{ H }_{ 22 }{ O }_{ 11 }+{ H }_{ 2 }O } \overset { + }{ \longrightarrow } \underset { D(+)G1ucoseD(+)Galactose }{ { C }_{ 6 }{ { H }_{ 12 }{ O }_{ 6 } }+{ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } } \)

(i) Enzymes are naturally occurring simple or conjugated proteins which act as biological catalysts in living systems.
(ii) E.g. Carbonic anhydrase, Lactase, Sucrose

(i) Hormone is an organic substance (e.g. a peptide or a steroid) that is secreted by one tissue. It limits the blood stream and induces a physiological response (e.g. growth and metabolism) in other tissues. It is an intercellular signalling molecule.
(ii) e.g. Testosterone, Thyroxine, Estrogen, Insulin, Oxytocin etc.

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.

On hydrolysis, sucrose yields equal amount of glucose and fructose units.
\(Sucrose\overset { Invertase }{ \longrightarrow } Glucose+Frutose\)
Sucrose (+66.6°) and glucose (+52.5^o) are dextrorotatory compounds while fructose is levo rotatory (-92.4°). During hydrolysis of sucrose, the optical rotation of the reaction mixture changes from dextro to levo. Hence, sucrose is called as invert sugar.

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) Ribonucleic acids are similar to DNA. Cells contain up to eight times high quantity of RNA than DNA. RNA is found in large amount in the cytoplasm and a lesser amount in the nucleus. In the cytoplasm it is mainly found in ribosomes and in the nucleus, it is found in nucleolus.
(ii) RNA molecules are classified according to their structure and function into three major types
i. Ribosomal RNA (rRNA)
ii. Messenger RNA (mRNA)
iii. Transfer RNA (tRNA)
rRNA:
rRNA is mainly found in cytoplasm and in ribosomes, which contain 60% RNA and 40% protein. Ribosomes are the sites at which protein synthesis takes place.
tRNA:
tRNA molecules have lowest molecular weight of all nucleic acids. They consist of 73 - 94 nucleotides in a single chain. The function of tRNA is to carry amino acids to the sites of protein synthesis on ribosomes.
mRNA:
mRNA is present in small quantity and very short lived. They are single stranded, and their synthesis takes place on DNA. The synthesis of mRNA from DNA strand is called transcription. mRNA carries genetic information from DNA to the ribosomes for protein synthesis. This process is known as translation.

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.