Biomolecules are chemical compounds found in living organisms. They include organic and inorganic compounds.
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 Å (i.e. 3.4 Å 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.
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