Biology 1AA3 - Textbook Notes - Chapter 3
Idea of Chemical Evolution first introduced by Alexander Oparin in 1923 and then again by JBS Haldane.
o Can now be considered as an official scientific theory.
The theory consists of two components:
Pattern: Increasingly complex carbon-containing molecules formed in the atmosphere and ocean of
Process responsible for Pattern: Conversion of energy, from sunlight and other sources , into chemical
energy in the bonds of large, complex molecules.
This theory has been modified as well since more research has been conducted and new information has been
It can be broken down into four parts essentially:
o Chemical evolution: Started with the production of small organic compounds such as formaldehyde and
hydrogen cyanide -> REACTANTS WERE H , 2O , 3H a4d NH . 3
o Small organic compounds combined to form mid sized molecular compounds such as AMINO ACIDS, SUGARS
AND NITROGENOUS BASES.
o These molecules accumulated in shallow waters of ancient ocean --> complex solution formed called
MID SIZED MOLECULES joined to form large molecules found in cells today such as PROTEINS, NUCLEIC
ACIDS AND COMPLEX CARBOHYDRATES.
o These large molecules are made up of distinctive chemical subunits (monomers).
Proteins - Made up of Amino Acids
Nucleic Acids - Made up of Nucleotides
Complex Carbs - Made up of Sugars
o Origin of life was possible when one of these large molecules gained the ability to replicate itself.
Self replicating molecule began to multiply by means of chemical reactions that it controlled.
Chemical evolution led to Biological Evolution.
PROTEINS: STRUCTURE, FUNCTION AND SIGNIFICANCE
Structure – Proteins are basically made up of Amino acids
o As Miller proposed later research also found that amino acids and other compounds of the prebiotic soup
are formed readily under conditions that accurately simulate the atmosphere and the oceans ancient Earth.
o Amino acids are basically building blocks of proteins Most of the proteins in the humans body are
composed of just 21 amino acids.
o All amino acids have similar backbone structure
o It contains carbon atoms that 3 similar bonds:
The first bond is with N2 which is known as an amine or amino group.
The second group is COOH which is the carboxyl group this group is acidic due to the high
electronegativity of the two oxygen atoms.
They pull electrons away from the hydrogen and hence the molecule is able to lose the
H quite easily.
Third bond is with a hydrogen atom.
These are the bonds which are present in every amino acid.
The fourth group is what makes each amino acid unique R-group or side chains
Side chains can be one single H atom or a large group of atoms
Different amino acids in the body can have:
Polar Side Chains
Non-Polar Side Chains
Electrically Charged Side Chains
o R-groups also influence the reactivity of the amino acids.
There can either be R-groups that are made up entirely of C and H. Or they can be made up of hydroxyl, carboxyl, sulfhydryl groups.
o Isomers – molecules of the same molecular formula may not have the same molecular structure.
Structural Isomers – same atoms but differ in order that the covalently bonded atoms are
Geometric Isomers – same atoms but differ in the arrangement of atoms or groups on either
side of a double bond or ring structure.
Optical Isomers – same atoms but differ in the arrangement of atoms or groups around a carbon
atom that has four different groups attached to it. Eg – refer to DOPA in lecture notes
Amino acids mostly have Optical Isomers these isomers cannot be super imposed on one
another they are mirror images and are not in a plane cannot be bisected to produce
All amino acids have optical isomers except for Glycine.
Cells have “left-handed” version of amino acid and if the other is introduced into the cell it will
not function properly.
Once again the structure of the amino acid determines the function.
o How are amino acids linked to form proteins?
Amino acid = molecular subunit that joins to form a larger molecule = MONOMER
Protein = large molecules made up of numerous subunits of the same kind = POLYMER
Process of forming Polymers = POLYMERIZATION
A MACROMOLECULE = large molecules made up of smaller molecules joined together
Chemical evolution states that the monomers in the prebiotic soup polymerized to form
proteins and other types of macromolecules found in organisms.