Thursday, July 30, 2020

Biomolecules - Notes | Class 11 | Part 1: Bio-micromolecules

9. BIOMOLECULES

Biomolecules are chemical compounds found in living organisms. 
They include organic and inorganic compounds.

ANALYSIS OF CHEMICAL COMPOSITION IN A TISSUE

  • Grind a living tissue (vegetable or piece of liver etc.) in trichloroacetic acid (Cl3CCOOH) to get thick slurry.
  • Strain this through a cheesecloth or cotton to get 2 fractions such as filtrate (acid-soluble pool) and the retentate (acid-insoluble fraction).
  • The filtrate contains biomicromolecules (biomolecules having molecular weight less than 1000 Dalton).
  • The retentate contains biomacromolecules (biomolecules having molecular weight higher than 1000 Dalton).
Analysis of inorganic compounds
  • Weigh a living tissue (wet weight) and it is dried (dry weight) to evaporate water.
  • It is fully burnt to oxidize all carbon compounds to gaseous form (CO2 & water vapour). It forms ash.
  • The ash contains inorganic elements (Ca, Mg, Na, K etc.) & inorganic compounds (SO42-, PO43-, NaCl, CaCO3 etc.).

Comparison of Elements in Non-living & Living Matter

Element

% Weight of

Earth’s crust

Human body

Hydrogen (H)

0.14

0.5

Carbon (C)

0.03

18.5

Oxygen (O)

46.6

65.0

Nitrogen (N)

Very little

3.3

Sulphur (S)

0.03

0.3

Sodium (Na)

2.8

0.2

Calcium (Ca)

3.6

1.5

Magnesium (Mg)

2.1

0.1

Silicon (Si)

27.7

Negligible


BIOMICROMOLECULES (MICROMOLECULES OR BIOMOLECULES)


Molecular weight of micromolecules found in the acid soluble pool ranges from 18 to 800 Dalton (Da). The acid soluble pool represents the cytoplasmic composition.
They include amino acids, sugars, nitrogen bases, lipids etc.
 

1. AMINO ACIDS

  • They are the compounds formed of an amino group (-NH2), an acid group (-COOH), H & a variable group (R).
  • –NH2 & –COOH are attached to the same carbon atom (α-carbon). So, they are called α-amino acids.
  • They are substituted methanes.

20 types of amino acids are used for protein synthesis. They include
  • Acidic amino acids: e.g. Glutamic acid, Aspartic acid.
  • Basic amino acids: e.g. Lysine, Arginine.
  • Neutral amino acids: e.g. Valine.
Some amino acids are aromatic. E.g. tyrosine, phenyl alanine and tryptophan.
Amino acids are 2 types:
  • Essential amino acids: They cannot be synthesized by the body and should be supplied through diet. E.g. Lysine, leucine, isoleucine, tryptophan etc.
  • Non-essential amino acids: They can be synthesized by the body. E.g. Glycine, alanine, serine, arginine etc.
In amino acids, –NH2 & –COOH have ionizable nature. So, structure of amino acids changes in solutions of different pH.

If both –NH2 & –COOH are ionized, it is called Zwitterion.

2. LIPIDS


Water insoluble. 

Contain C, H & O but number of oxygen atoms is less.

Types of lipids


a. Simple lipids: 

  • These are formed of Fatty acids and alcohol such as glycerol.
  • Fatty acids are lipids with a hydrocarbon chain (R- group) ending in –COOH group. i.e. R-COOH.
  • E.g. Palmitic acid has 16 carbons (CH3 - (CH2)14 - COOH or C15H31-COOH) and Arachidonic acid has 20 Carbons.

Fatty acids are 2 types:
  • Saturated fatty acids: They have no double or triple bonds between carbon atoms. E.g. Palmitic acid, Stearic acid (C17H35COOH) etc.
  • Unsaturated Fatty acids: They have one or more C=C bonds. E.g. Oleic acid (C17H33COOH), Arachidonic acid (C19H31COOH) etc.
Structure of glycerol (trihydroxy propane):

CH2-OH
|
CH-OH
|
CH2-OH

Fatty acids are esterified with glycerol through ester bond forming monoglycerides, diglycerides & triglycerides.
  • 1 glycerol + 1 fatty acid → Monoglyceride
  • 1 glycerol + 2 fatty acid → Diglyceride
  • 1 glycerol + 3 fatty acid → Triglyceride

Based on melting point, lipids (triglycerides) are 2 types:
  • Fats: Higher melting point.
  • Oils: Lower melting point.
b.Compound lipids: 
  • These are the esters of fatty acids and alcohol with additional groups.
  • E.g. They are found in cell membranes. E.g. Lecithin.

c.Derived lipids: 
  • These are the products of hydrolysis of simple lipids and compound lipids. 
  • E.g. Cholesterol.

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


These are the nitrogen containing cyclic compounds found in nucleic acids. 
They are 2 types:
a. Purines: Includes Adenine (A) & Guanine (G).
b. Pyrimidines: Includes Cytosine (C), Thymine (T) & Uracil (U).


Nitrogen base + Sugar → Nucleoside
 
Adenine     +     Sugar         Adenosine
Guanine     +     Sugar         Guanosine
Cytosine     +     Sugar         Cytidine
Thymine     +     Sugar         Thymidine
Uracil         +     Sugar         Uridine
Nitrogen base + Sugar + Phosphate → Nucleotide
 
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.
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