Hierarchical Structures
and Biology
Main Types of
Biological Molecules
1.
Lipids
(fats)
Fatty
acids have a backbone of up to 36
carbon atoms and end with a –COOH group.
The carbon chains can have unsaturated bonds as well as saturated.
Triglycerides such as butter and lard, are the most abundant fats
in the body and are its richest energy source.
They consist of 3 fatty acid tails attached to a glycerol molecule. Again chains can be saturated or
unsaturated.
Phospholipids also have a glycerol ‘backbone’, but the third
attachment to the glycerol is a hydrophilic head consisting of a phosphate plus
another hydrophilic group.
e.g.
Phosphatidylcholine – one of the commonest
Recall
phospholipids are the main constituent of animal cell membranes in a double
layer.
Bonding
is always A-T and C-G (base pairing), and the pairs are linked through a sugar
phosphate backbone..
RNA
has uracil in place of thymine.
3 Polysaccharides
Polysaccharides are long chains of simple sugar molecules.
Sugars are 5 or 6 membered saturated carbon rings.
Polysaccharides are particularly important in plants. Examples include starch and cellulose.
Peptide bond forms with release of water.
Proteins
vary hugely in size i.e. how many amino acids are strung together.
Proteins
are not random coils.
They
have very precise secondary structure, and this is vital for their function.
Two
commonly repeating motifs:
a helix
This is the most abundant type of secondary structure in proteins.
The helix has an average of 3.6 amino acids per turn with a hydrogen bond formed between C=O and N-H groups about every fourth residue.
Average length is 10 amino acids
b sheet
Again
stabilised by hydrogen bonding, with neighbouring chains running parallel or
antiparallel
.
Hydrogen bonding forms between an average of 5-10 consecutive amino acids in one portion of the chain with another 5-10 further down the chain.
The interacting regions may be adjacent, with a short loop in between or far apart with other structures in between.
The tertiary shape of a
protein is determined by the location of these standard motifs and how the
chains pack in between.
Shape determines function