Chemistry REVISION

Classification of carbohydrates

• color{green}("Monosaccharides ") : A carbohydrate that cannot be hydrolysed further to give simpler unit of polyhydroxy aldehyde or ketone is called a monosaccharide. About 20 monosaccharides are known to occur in nature. Some common examples are glucose, fructose, ribose, etc.

• color{green}("Oligosaccharides ") : Carbohydrates that yield two to ten monosaccharide units, on hydrolysis, are called oligosaccharides.

• color{green}("Polysaccharides ") : Carbohydrates which yield a large number of monosaccharide units on hydrolysis are called polysaccharides.

• color{green}("Non-reducing sugars ") : In disaccharides, if the reducing groups of monosaccharides i.e., aldehydic or ketonic groups are bonded, these are non-reducing sugars e.g. sucrose.

• color{green}("Reducing sugars ") :On the other hand, sugars in which these functional groups are free, are called reducing sugars, for example, maltose and lactose.

Glucose

(i) color{green}(["From sucrose (Cane sugar) "]) : If sucrose is boiled with dilute color{red}(HCl) or color{red}(H_2SO_4) in alcoholic solution, glucose and fructose are obtained in equal amounts.

color{red}(undersettext(Sucrose) (C_(12) H_(22)O_(11)) +H_2O overset(H^+)→ undersettext(Glucose)(C_6H_(12) O_6) +undersettext(Fructose)(C_6H_(12) O_6))

(ii) color{green}("From starch ") : Commercially glucose is obtained by hydrolysis of starch by boiling it with dilute color{red}(H_2SO_4) at 393 K under pressure.

color{red}(undersettext(Starch or cellulose ) ((C_6H_(10)O_5)_n) +nH_2O underset(393K ; 2-3 atm) overset(H^+) → undersettext(Glucose)(n C_6H_(12) O_6))

Cyclic Structure of Glucose :

•color{green}("Anomers ") : A pair of stereoisomers which differ in configuration only around C1 are called anomers and the C1 carbon is called anomeric carbon.

Dissacharides

● color{green}("Glycosidic linkage ") : The two monosaccharides are joined together by an oxide linkage formed by the loss of a water molecule. Such a linkage between two monosaccharide units through oxygen atom is called glycosidic linkage.

•color{green}("Sucrose ") : One of the common disaccharides is sucrose which on hydrolysis gives equimolar mixture of color{red}(D-(+))-glucose and color{red}(D-(-)) fructose.

•color{green}("Maltose ") : Another disaccharide, maltose is composed of two color{red}(α-D)-glucose units in which color{red}(C-1) of one glucose color{red}((I)) is linked to color{red}(C-4) of another glucose unit.

•color{green}("Lactose ") : It is more commonly known as color{green}("milk sugar") since this disaccharide is found in milk.

Amino acids

•color{green}(" α-amino acids ") : Chemically proteins are condensation polymers in which the monomeric units are called α-amino acids.

•color{green}(" Zwitter ion") : In aqueous solution, the carboxyl group can lose a proton and amino group can accept a proton, giving rise to a dipolar ion known as color{green}("zwitter ion"). This is neutral but contains both positive and negative charges.

Peptide bond

•color{green}(" Peptides ") :Peptides are amides formed by the condensation of amino group of one α amino acid with carbonyl group of another molecule of the same or different α amino acid with the elimination of water.

•color{green}(" Polypeptides "): If a large number of α amino acids are joined together by peptide bonds, the polyamide thus formed are called polypeptide

Structure of proteins

•color{green}(" Native protein "): A protein found in a biological system having a unique three dimensional structure and specific biological activity is called a native protein.

•color{green}(" Denatured protein "):If a native protein is subjected to physical or chemical treatment, which may disrupt its higher structures (conformations) without affecting its primary structure, the protein is said to be denatured.

Vitamins

•color{green}(" Vitamins "):Vitamins may be defined as a group of biomolecules most of which cannot be produced by the body and must be supplied in small amounts in diet to perform the specific biological functions for life, growth and health of human beings and animal organisms.

• color{green}("Fat Soluble Vitamins ") : Vitamins which are soluble in fat and oils but insoluble in water are kept in this group.

•color{green}("Water Soluble Vitamins ") : color{red}(B) group vitamins and vitamin color{red}(C) are soluble in water so they are grouped together.

Nucleic acids

• color{green}("Nucleic acids ") : Nucleic acids are biopolymers. They are also called polynucleotides since the repeating structural unit of nucleic acids is a nucleotide.

Structure of nucleic acids

• color{green}("DNA fingerprinting ") :A sequence of bases on DNA is also unique for a person and information regarding this is called DNA fingerprinting.