Biomolecules are chemical compounds found in living
organisms. They include organic and inorganic compounds.
Include amino acids, sugars, nitrogen bases, lipids etc.
1. Amino acids
Sugars are sweet and water soluble carbohydrates. They are formed of C, H and O in the ratio of 1:2:1.
Includes Purines (Adenine & Guanine) and Pyrimidines (Cytosine, Thymine & Uracil)
BIOMACROMOLECULES
Acid
insoluble fraction includes
Average composition of cells
These are polymers of sugars (monosaccharides). E.g.
BIOMICROMOLECULES
Include amino acids, sugars, nitrogen bases, lipids etc.
1. Amino acids
A typical amino acid is formed of an amino group (-NH2), an acid group (-COOH), H & a variable group (R). –NH2 and –COOH are attached to the same carbon atom (α-carbon).
20 amino acids are
used for protein synthesis. They include
· Acidic amino acids
(e.g. glutamic acid)
· Basic amino acids
(e.g. Lysine)
· Neutral amino acids
(e.g. Valine)
Some amino acids are
aromatic (e.g. tyrosine, phenyl alanine, and tryptophan).
Amino acids have
ionizable nature of –NH2 & –COOH groups.
2. Lipids
- Water insoluble.
Contains fatty acids and glycerol.
- A fatty acid has –COOH
group attached to an R- group.
- Palmitic acid has 16
carbons (CH3-(CH2)14-COOH) and Arachidonic
acid has 20 Carbons.
- Fatty acids are 2
types:
o Saturated fatty acids: No double or triple
bonds between 2 carbon atoms.
o Unsaturated Fatty acids: One or more C=C
bonds.
- Structure
of glycerol (trihydroxy propane):
CH2-OH
|
CH-OH
|
CH2-OH
- Many lipids have both
glycerol and fatty acids to form fats. (Fatty acids are esterified with
glycerol).
- It includes monoglycerides,
diglycerides & triglycerides.
-
Based on melting point lipids are 2 types: fats
and oils.
3. Sugars (Carbohydrates)
Sugars are sweet and water soluble carbohydrates. They are formed of C, H and O in the ratio of 1:2:1.
4. Nitrogen Bases
Includes Purines (Adenine & Guanine) and Pyrimidines (Cytosine, Thymine & Uracil)
•
Nucleoside: Nitrogen base + Sugar.
Adenine
+ sugar = Adenosine
Guanine
+ sugar = Guanosine
Cytosine
+ sugar = Cytidine
Thymine
+ sugar = Thymidine
Uracil
+ sugar = Uridine
•
Nucleotide: Nitrogen base + Sugar + phosphate.
Adenine + sugar + phosphate = Adenylic
acid
Guanine + sugar + phosphate = Guanylic
acid
Cytosine + sugar + phosphate = Cytidylic
acid
Thymine + sugar + phosphate = Thymidylic
acid
Uracil + sugar + phosphate = Uridylic
acid
Nucleotides are
heterocyclic compounds.
Nucleic acids (DNA & RNA) are made up of nucleotides.
BIOMACROMOLECULES
- Molecules having
molecular weight greater than 1000 Dalton (Da) is called biomacromolecules.
- Molecules having
molecular weight less than 1000 Da are called micromolecules.
- Molecular weight of
compounds found in the acid soluble pool ranges from 18 to 800 Da. The
acid soluble pool represents the cytoplasmic composition.
- Biomacromolecules are
found in acid insoluble fraction.
-
Molecular weight
is 10,000 Da and above except lipids.
|
o Proteins
o Nucleic acids
o Polysaccharides
o Lipids
- Molecular weight of
lipids does not exceed 800 Da. But it comes under acid insoluble fraction because
lipids are arranged into structures like cell membranes. When a tissue is grinded,
these membranes are broken and form vesicles which are water insoluble, i.e.
lipids are not strictly macromolecules.
- Acid insoluble fraction: Includes macromolecules
from cytoplasm and organelles.
Average composition of cells
Water : 70-90 %
Protein : 10-15%
Carbohydrates : 3%
Lipids : 2%
Nucleic
acids : 5-7%
Ions :
1%
2. Polysaccharides
These are polymers of sugars (monosaccharides). E.g.
§ Starch (polymer of glucose)
§ Cellulose (polymer of glucose)
§ Inulin (polymer of fructose)
§ Glycogen
§ Glucosamine
§ N-acetyl galactosamine
§ Chitin (Exoskeleton of arthropods)
§ Glycosidic bond in polysaccharides: It is the bond formed
when individual monosaccharides are linked between 2 carbon atoms by
dehydration.
§
Starch
forms helical secondary structure. Starch holds I2 molecules in the
helical portion giving blue colour.
§
Cellulose
has no complex helices and so cannot hold I2.
§ Diagrammatic
representation of a portion of glycogen is given below:
3. Nucleic acids (DNA and RNA)
Secondary
structure of DNA (Watson - Crick Model)
- DNA exists as a double
helix. The 2 polynucleotide strands are arranged antiparallely.
- One full turn of
helical strand have 10 steps (10 base pairs).
- Length of one full
turn = 34 Ã… (i.e. 3.4 Ã… for each step).
-
At each step the strand turns 360
(3600 for a full turn).
- A polynucleotide chain
is heteropolymer of nucleotides.
- A nucleotide consists
of nitrogen bases, deoxyribose sugar and phosphate group.
- The backbone of DNA is
formed by the sugar-phosphate-sugar chain. Nitrogen base
pairs form the steps of DNA.
- Nitrogen bases include
Adenine (A), Guanine (G), Thymine (T) and Cytosine (C).
- A pairs with T (A=T)
by 2 hydrogen bonds.
- G pairs with C (G≡C)
by 3 hydrogen bonds.
- A phosphate molecule
links the 3’-carbon atom of one sugar of one nucleotide to the 5’-carbon
of the sugar of the succeeding nucleotide.
- There is an ester
bond between PO43- and –OH group of sugar.
As there is one such ester bond on either side, it is called phosphodiester
bond.