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Summary Biological molecules
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AS Bio notes Raida 12DBiological molecules
2.1 Biochemistry
The sum total of all the biochemical reactions in the body is known as metabolism, a
limited variety of molecules makes it easier to control metabolism
2.2 The Building blocks of life
The four most common elements in living organisms are hydrogen, carbon, oxygen and
nitrogen
Carbon atoms can join together to form long chains or ring structures
The simple biological molecules are relatively limited in variety and act as the building
blocks for larger, complex biological molecules
2.3 Monomers, polymers, and macromolecules
> Polymer: giant molecule made from many similar repeating subunits joined together in a
chain; the subunits are much smaller and simpler molecules known as monomers
> Monomer: simple molecule which is used as a basic building block for the synthesis of a
polymer; many monomers are joined together by covalent bonds to make the polymer, usually
by condensation reactions
> Condensation reaction: a chemical reaction involving the joining together of two molecules by
removal of a water molecule
> Hydrolysis: a chemical reaction where chemical bond is broken by the addition of a water
molecule; used to break down complex molecules into simpler molecules
A macromolecule is a large molecule, there are 3 types of macromolecule in living organisms:
Polysaccharides (sugars)
Polypeptides (proteins)
Polynucleotides (nucleic acids)
Macromolecules are described as Polymers because they are made up of many
repeating subunits that are similar/identical to each other called Monomers
, Monomers are joined together by covalent bonds which are bonds where the atoms are
joined by sharing electrons
Covalent bonds are relatively strong bonds
Making biological polymers from monomers is simple because the same reaction is
repeated many times
Reaction involves joining together two monomers by the removal of a water molecule
which is Condensation reaction (removal of water)
The opposite reaction involves adding water and can be used to break down the polymer
again which is Hydrolysis
The monomers from which polysaccharides, proteins, and nucleic acids are made are,
monosaccharides, amino acids and nucleotides
Cellulose and rubber are examples of naturally occurring polymers
Polyester, Polyethene, nylon and PVC are examples of industrially produced polymers
2.4 Carbohydrates
All carbohydrates contain the elements carbon, hydrogen and oxygen
The hydrogen and oxygen atoms are present in the ratio of 2:1 as in water
The general formula for a carbohydrate is : Cx(H2O)y
> Carbohydrates are divided into three main groups:
Monosaccharides
Disaccharides
Polysaccharides
(‘ saccharide’ means a sugar)
Monosaccharides:
Monosaccharides are sugars (sugars dissolve easily in water)
Monosaccharides consist of a single sugar molecule (‘mono’ means one)
They have the general formula: (CH2O)n
The names of all sugars end with -one
Main types of monosaccharides are:
trioses (3C)
Pentoses (5C)
Hexoses (6C)
Common hexoses are glucose, fructose, and galactose
Two common pentoses are deoxyribose and ribose
Molecular and structural formulae:
The molecular formula for a hexose can be written as C6H12O6
, Ring structures:
One important aspect of the structure of pentoses and hexoses is that the chain of
carbon atoms is long enough to close up on itself to form a more stable ring structure
When glucose forms such a ring, carbon atom 1 joins to the oxygen on carbon atom 5
The hydroxyl group, -OH, on carbon atom 1 may be ABOVE or BELOW the plane of the
ring
-OH below the ring is known as alpha-glucose
-OH above the ring is known as beta-glucose
Two forms of the same chemical are known as isomers
[the extra variety provided by the existence of alpha and beta isomers had important biological
consequences seen in the structure of starch, glycogen and cellulose]
Functions of monosaccharides in living organisms
Monosaccharides have two major functions:
1. Commonly used as a source of energy in respiration
This is due to the large number of carbon-hydrogen bonds
These bonds can be broken to release a lot of energy which is transferred to help make
ATP (adenosine triphosphate) from ADP (adenosine diphosphate) plus phosphate
during the process of respiration
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