AIEEE Chemistry UNIT 26 BIO MOLECULES

Syllabus 2008

General introduction and importance of biomolecules.
CARBOHYDRATES - Classification: aldoses and ketoses; monosaccharides (glucose and fructose), constituent monosaccharides of oligosacchorides (sucrose, lactose, maltose) and polysaccharides (starch, cellulose, glycogen).
PROTEINS - Elementary Idea of ? - amino acids, peptide bond, polypeptides; Proteins: primary, secondary, tertiary and quaternary structure (qualitative idea only), denaturation of proteins, enzymes.
VITAMINS - Classification and functions.
NUCLEIC ACIDS - Chemical constitution of DNA and RNA.
Biological functions of nucleic acids.
--------


CARBOHYDRATES - Classification: aldoses and ketoses; monosaccharides (glucose and fructose), constituent monosaccharides of oligosacchorides (sucrose, lactose, maltose) and polysaccharides (starch, cellulose, glycogen).



Carbohydrates are classified as:
Monosaccharides

Oligosaccharides

Polysaccharides

Monohydrates may be represented as follows
H
!
C=O
!
(H-C-OH)-n
!
CH-2OH

A polyhdroxy aldehyde

CH-2OH
!
C=O
!
(H-C-OH)-n
!
CH-2OH

A polyhdroxy ketone

Monosaccharides are named as follows.
1. The calss name of monosaccharides begins with the prefix 'aldo' for polyhydroxy aldehydes and "keto' for polyhydroxy ketones.
2. the name ends with suffix 'ose".
3. In between prefix and suffix, the number of carbon atoms (i.e. di, tri, tetr etc.) is inserted.

Examples

H
|
C=O
|
(H-C-OH)
|
CH-2OH

Aldotriose - (A polyhdroxy aldehyde)

CH-2OH
|
C=O
|
CH-2OH

Ketotriose - (A polyhdroxy ketone )

Reducing and Nonreducing Sugars

Reducing sugars are easily oxidized to give carboxylic acid.

They reduce
(i) Tollens reagent (an ammoniacal solution of silver nitrate) to shiny silver mirror.
(ii) Fehling's solution (an acqueous solution of cupric iron and tartrate salts) to red precipitate of cuprous oxide, and
(iii) Benedict's reagent (an alkaline solution containing a cupric citrate complex) to red precipitate of curous oxide)

All aldoses are reducing sugars, but some ketoses are reducing sugars as well. For example, fructose (a ketose) reduces Tollens reagent. This occurs because fructose is readily isomerized to an aldose in basic solution.

amino acids are organic compounds containing both an amino group (NH2) and carboxylic group (COOH). They are represented by the general formula:
R
|
C-COOH
|
NH2


Essential amino acids

These amino acids are required by the body but are not made by our bodies. hence they must be supplied in diets.

Valine
Leucine
Isoleucine
Phenylalanine
Methionine
Trptophan
threonine
Lysine
Agrinine


L-Family of Amino Acids
With the exception of glycine, all other α amino acids have chiral carbon atom and have two optically active isomers.

However all naturally occurring amino acids belong to L series which have -NH2 group on the left.



Structure of Amino acids

amino acids exist as dipolar ion called a zwitter ion.

i) when an acid is added to an amino acid-COO- accepts this proton and therefore the basic character is due to -COO-group.

ii) When an alkali is added to amino acid -NH3+ group releases the proton and therefore acidic character is due to -NH3+ group.

Peptide

peptides are compounds formed by the condensation of two or more same or different α amino acids. The condensation occurs between amino acids with the elimination of water. In this case,the carboxyl group of one amino acid and amine group of another amino acid gets condensed with the elimination of water molecule. The resulting C-N linkage is called peptide linkage. The bond of C with O becomes a double bond.

The formation of peptide can be between two amino acid molecules or the number can go on until a single molecule containing several hundred thousands of aminoacids is formed.


Proteins

Structurally, proteins are long polymers of amino acids linked by peptide bonds