Download Biomacromolecules

Biomacromolecules
Part 1: Lipids
Biomacromolecules
• Biomacromolecules are BIG molecules.
• They play an essential role in both the
structure and functions of cells.
• Understanding the chemical basis of life is
about understanding macromolecules –
how they are made and how they
function.
Cells make biomacromolecules
• Cells import water, mineral ions and a host of
small organic molecules, such as simple sugars,
fatty acids and amino acids.
• Other small organic molecules are made and
altered in different chemical reactions within the
cell.
In contrast
• Cells can only acquire macromolecules by
making them.
• They are simply too big to be imported into a
cell.
CLASS OF
MACROMOLECULE
BUILDING BLOCKS
CELLULAR
FUNCTIONS OF
MACROMOLECULES
Lipids
Fatty acids and
glycerol
Energy store,
component of cell
membranes, signalling
molecules
Polysaccharides
(complex
carbohydrates)
Simple sugars
Energy store,
structural components
Nucleic acids
Nucleotides
Informational
molecules that make
up genetic material
Proteins
Amino acids
The workhorse of the
cell: controls and
regulates reactions,
transport, movement,
receptors, defence and
structure.
Are macromolecules polymers?
• Polysaccharides, nucleic acids and proteins are polymers.
• Lipids are not polymers.
• A polymer is made of small molecules (called sub-units
or monomers) which are repetitively linked together to
form long strands called polymers.
• The huge variety of polymers arises from the infinite
number of possibilities in the sequencing and
arrangement of monomers.
• Although lipids are large molecules, they are not made
up of repeating monomers – they are made up of two
distinct chemical groups of atoms (fatty acids and
glycerol).
Lipids
• Lipids are largely composed of carbon, hydrogen
and oxygen atoms (less oxygen atoms compared
to hydrogen and carbon).
• They are generally known as fats and oils.
• The name applies to a diverse group of
molecules that, due to their large molecular
mass, are commonly grouped as
macromolecules.
Lipids are DEFINITELY NOT polymers.
Lipids
• Are largely insoluble in water.
– This is their defining characteristic rather than any
particular chemical property.
• Contain large non-polar hydrocarbon regions.
– This explains their hydrophobic character.
• Like any non-polar substance, lipids readily
dissolve in non-polar substances such as
chloroform.
Functions of Lipids
Lipids have three main functions in cells:
– Energy storage: lipids have twice as much
useable energy, gram for gram, as sugars or
starch
– Various lipids are essential components of cell
membranes
– Lipids can have specific biological roles as
signalling molecules (hormones), receptor
sites, vitamins and coenzymes.
How are lipids formed
• Lipid molecules are formed when fatty acids combine
with an alcohol called glycerol.
• A water molecule is eliminated when the acid groups
reacts with the alcohol group and an ester bond is
formed that links the two molecules together.
A little about fatty acids
• Fatty acids are hydrocarbon chains, of various length,
that end in an acid functional group.
• Fatty acids in biological systems usually contain an even
number of carbon atoms, typically 14 to 24.
• The length of the chain and the amount of saturation
largely determine the properties of fatty acids and other
lipids derived from them.
• Unsaturated fatty acids have a lower melting point
compared to saturated fatty acids, given the
hydrocarbon chains are of the same length.
• Animal fats contain saturated fatty acids and are
usually solids at room temperature.
• Oils contain unsaturated fatty acids and are liquids at
room temperature
Saturated vs Unsaturated
• Saturated hydrocarbons
– All carbon-carbon bonds are single bonds.
– Results in long straight chains that can be packed tightly together
• Unsaturated hydrocarbons
– One or more carbon bonds are double bonds
– Double bonds produce kinks or bends which stop the hydrocarbon
chains from being packed closely together
Classes of Lipids
CLASS
EXAMPLE
FUNCTION
Fatty acids
Stearic acid
Oleic acid
Energy source
Subunit of other lipids
Triglycerides
Fats and oils
Energy storage
Phospholipids
Phospholipids
Structural component
of plasma membranes
Glycolipids
Glycolipids
Recognition sites on
plasma membranes
*Steroids
Cholesterol
Sex hormones
Component of plasma
membrane
Signalling molecules
Vitamin A
Antioxidant
*(only found in eukaryotic
cells)
Terpenes
Triglycerides
• Formed by combining three fatty
acids with glycerol.
• The three fatty acid hydrocarbon
chains can come from different
fatty acids and so can vary in
length and their degree of
saturation.
• Main function is as a fuel storage
molecule for the cells – stores fatty
acids when they are not needed as
energy.
• Lipase (produced in the pancreas)
acts on the ester bond linking fatty
acids to glycerol in order to break
down triglycerides.
Phospholipids
• Consist of two fatty acid chains
linked to a glycerol molecule.
• Importantly, the glycerol
molecule is also linked to a
negatively charged phosphate
functional group with a small
alcohol group attached.
• This attached group makes the
glycerol end of the molecule a
polar region and hence
hydrophilic.
• The fatty acid hydrocarbon
chains are non-polar and
hydrophobic.
• Any molecule that contains
both hydrophilic and
hydrophobic regions is called
an amphipathic molecule.
Phospholipids
• Phospholipids are an essential structural component of cell
membranes.
• Membrane formation is a consequence of their amphipathic
character.
• The hydrocarbon tails of each layer interact with one another
forming a hydrophobic interior that acts as a permeability barrier.
• It is hydrophobic interactions that drive the formation of the lipid
bilayer.
Steroids
• Cholesterol is a steroid molecule built up from four hydrocarbon
rings linked together with a hydrocarbon tail at one end and an OH
group at the other.
• Cholesterol is found in varying amounts in virtually all eukaryotic
animal cell membranes.
• It is arranged between the fatty acid chains of phospholipids, with
the OH group being attracted to the polar end.
• Cholesterol is the precursor for the production of other important
steroid derived molecules including: bile salts, cortisol and sex
hormones.