BIOCHEMISTRY OF LIFE
ORGANIC COMPOUNDS
Water
Water is a very unusual substance and has some very
important properties; it has a very high melting and
boiling point (0oC and 100oC), it has a high viscosity,
it’s solid form is less dense than the liquid form and
has high surface tension.
• Water is the main solvent in our bodies and many of the chemical
reactions of the body take place in water.
• The total of the reactions that take place in our bodies is called
metabolism
• Water (H2O) consists of 2 hydrogen atoms and 1 oxygen atom linked by
a covalent bond
• Water is a polar molecule meaning that due to uneven distribution of
electrons, one end of the molecule has a positive electrical charge and
the other end has a negative electrical charge – it has electrical poles
• In water, the oxygen end has a slightly negative charge and the
hydrogen ends have a slightly positive charge.
Water
• An electrostatic attraction between the positive charge at the hydrogen
end and the negative charge at the oxygen end result in the formation
of a hydrogen bond.
• Many of the unique properties of water are caused by the hydrogen
bonding of the molecules.
• The ability of ions and other molecules to dissolve in water is due to it’s
polarity.
• Substances that readily dissolve in water are called hydrophillic or
polar
• Substances that do not tend to dissolve in water are called
hydrophobic or non-polar
• For Example Sodium chloride (NaCl) will dissociate into its two parts
Na+ and Cl- when it comes into contact with water. The positive
sodium (Na) ions are attracted to the negative oxygen and the negative
chloride (Cl-) is attracted to the positive hydrogen of water. A ring of
water molecules surround each sodium and chloride atom and they
remain in solution.
Water
• Water exists in three states; solid, liquid & gas
• The hydrogen bonds that hold water molecules
together are relatively weak and continually break and
reform when in liquid state.
• When water is heated to temperatures of 100oC or
greater the movement of the molecules is so great that
the hydrogen bonds can no longer hold them together
and the water is converted into a gas (steam)
• At temperatures below 4oC the movement of molecules
is such that the hydrogen bonds do not break and
reform They form a lattice structure which holds each
water molecule further away from each other than
would normally occur in the liquid form and causes
water to become solid (ice).
• Ice is less dense than liquid water, and therefore floats
on the liquid water – an very important property.
In ice every water molecule is bonded to
4 others.
Organic Molecules
• Organic molecules are the chemicals of life. They
are compounds composed of more than one type
of element, that are found in and produced by
living organisms.
• Organic molecules contain carbonhydrogen bonds, whereas inorganic
molecules do not.
• The four major groups of organic molecules are
carbohydrates, proteins, lipids and nucleic acids
ORGANIC COMPOUNDS
• Organic compounds are immensely important in
living things, they:
▫ Make up the structures of the body
▫ Regulate chemical processes going on in the body
Organic Molecules
• Organic molecules are often very large and made
up of smaller sub-units bonded together in
various ways.
• Compounds formed in this way are called
polymers
• The sub-units that make up the polymers are
called monomers
What is an organic compound?
• Organic compounds are all complex compounds of
carbon (excluding oxides, carbonates & bicarbonates)
• This means that they are chemicals that contain the
element carbon
▫ Organic compounds were originally thought to only be found in
living things. It is now known that it is not the case.
▫ However, organic compounds make up about 30% of what makes
up a cell (a substantial amount)
What are some organic compounds?
• The main organic compounds found in living
organisms are:
▫
▫
▫
▫
Carbohydrates
Lipids
Proteins
Nucleic acids
Carbohydrates
• Carbohydrates include sugars and starches
• When combusted carbohydrates release energy
• The main function of carbohydrates in
organisms is to produce and store energy
Carbohydrates
• Carbohydrates are organic compounds composed of
carbon (C), hydrogen (H) and oxygen (O).
• The basic unit of a carbohydrate is a sugar molecule
(monosaccharide)
• When two sugar molecules are joined a water
molecule is released
• Carbohydrates that contain one or two sugar units
are called simple carbohydrates
• Those that contain many sugar molecules are called
complex carbohydrates
Types of carbohydrates
• Monosaccharides
▫ (means single sugars)
▫ All monosaccharides are sweet, soluble in water
and will crystallize (form crystals)
▫ Glucose and fructose are monosaccharides
▫ Glucose and fructose are found in…
C6H12O6
Types of Carbohydrates
• Disaccharides
▫ (means double sugar)
▫ Dissarcharides are made up of two
monosaccharides
▫ Maltose, sucrose & lactose are types of
disaccharides
C12H22O11
Types of Carbohydrates
• Polysaccharides (means multi-sugar)
▫ Polysaccharides are not soluble in water, do not
taste sweet and do not form crystals
▫ They form long chains of many units of sugars
▫ This makes them ideal storage units
Starch (plants) & glycogen (animals) are how energy
is stored in organisms
Cellulose is another form of polysaccharide. It is
used in plants cell walls.
Proteins
• Proteins are vital in the formation of structures in organisms.
• Proteins are made from amino acids (there are 20 occurring
naturally)
• Humans need all 20 but cannot make all 20 so must rely on
their food in order to get them.
• Proteins form enzymes which are extremely important in
speeding up chemical reactions in organisms.
• Proteins such as keratin is found in hair, nails, hooves, horns
& feathers.
• Elastin and collagen are important connective tissue proteins.
• Protein is also important in muscles.
• Haemaglobin is a protein present in blood (it is the pigment
that carries oxygen in our blood)
Proteins
• Each amino acid has one part
of its molecule different from
other amino acids. The R
group in the general formula is
the part that varies.
• Two amino acids join together
as a dipeptides when a peptide
bond forms between the amino
group of one amino acid and
the carboxyl group of another.
• When a number of amino
acids join this way a
polypeptide is formed.
• Each type of protein has its
own particular sequence of
amino acids.
• Polypeptide chains become
folded in different ways
depending on their function.
Structure and Shape of Proteins
• Primary Structure
▫ The specific linear sequence of amino acids in the protein.
• Secondary Structure
▫ The folding of amino acid chains. Hydrogen bonds form between
segments of folded chain that have come close together & help
stabilise the 3D shape.
 Alpha helix– spiral molecule
 Beta-pleated sheet
 Random coiling – doesn’t fit into either the alpha or beta coiling
• Tertiary Structure
▫ Total irregular folding held together by ionic or hydrogen bonds
forming a complex shape
• Quaternary Structure
▫ Two or more polypeptide chains interact to form a protein (eg.
Haemaglobin, collagen)
Proteins
Type of Protein
Function
Example
Structural
Fibrous support tissue in skin, bone,
Collagen, keratin
tendons, cartilage, blood vessels, heart
valves and cornea of the eye
Enzyme
Catalyse reactions
ATP Synthase
Contractile
Muscle movement
Myosin, actin
Immunoglobulin
Defence against disease
Antibodies
Hormone
Regulate body acitivty
Insulin
Receptor
Respond to stimuli
Insulin receptors
transport
Carry other molecules
haemoglobin
Proteins
• In every living organism proteins are involved in one way or another
in almost every chemical reaction.
• They may be the enzymes involved, the reactants or the products, or
all three
• The complete array of proteins produced by a single organism in a
particular environment is called the proteome of the cell or
organism
• The study of the proteome is called proteomics
Lipids
• Lipids include natural fats, oils and waxes
• At room temperature fats are solid and at room
temperature oils are liquid
• Lipids supply energy, in fact more energy than
carbohydrates as they contain very little water.
• Lipids are essential in the plasma membrane (cell
membranes) and in sub-cutaneous fat (essential for
preventing heat loss in animals)
• Fats have little or no attractions for water and are
insoluble in it (hydrophobic)
Lipids
• A fat molecule is made of two kinds of
molecules; fatty acids and glycerol
• Triglycerides are a common form of fats they
have a single glycerol and three fatty acid
molecules attached
• Phospholipids are another kind of fat and
have TWO fatty acids attached to a glycerol, and,
a phosphate group attached to the glycerol.
• Phospholipids are a major component of cell
membranes
Nucleic Acids
• Nucleic acids are found in cells
• There are two types of nucleic acid
▫ DNA – deoxyribonucleic cid
▫ RNA – ribonucleic acid
• Nucleic acids are the genetic material of all organisms
• They are responsible for the features of an organism
• Both DNA & RNA are made up of long chains of subunits
called nucleotides
• (DNA/RNA = polymer, nucleotides = monomer)
Nucleic Acids
• Each nucleotide has a sugar (deoxyribose), phosphate
and a nitrogen containing base.
• The sugar and phosphate are the same in each unit, but
there are four different nitrogen containing bases:
adenine (A), thymine (T), cytosine (C) & guanine (G)
• Nucleotide sub-units are assembled to make a chain in
which the sugar of one nucleotide is bonded with the
phosphate of the next nucleotide in the chain.
• Each DNA molecule contains two chains that bond with
each other because the bases in one chain pair with the
bases in another (A & T, and C & G)
• The two chains form the double helix of DNA
Nucleic Acids
• DNA controls all of the functions of a cell
through the production of proteins.
• The DNA sequence codes for amino acids to be
produced, which produce chains of polypeptides
(proteins) which control all metabolic processes
in the cell.
• (How does DNA code for proteins?)
Nucleic Acid
Ribonucleic Acid (RNA)
• Is also a polymer of nucleotides
• It is an unpaired chain of nucleotides (single strand)
and exists in three forms
▫ messengerRNA (mRNA)
 Carries the message to the ribosomes where the message
is translated into a particular protein
▫ ribosomalRNA (rRNA)
 Together with proteins makes the ribosomes found in the
cytosol
▫ transferRNA (tRNA)
 Carry amino acids to ribosomes where they are used to
construct proteins