Carbon Chains and Rings
Atoms are at their most stable when their outer shell is full - 8 electrons.
Carbon covalently bonds.
A molecule is very stable because each atom in the molecule is sharing electrons to give a stable, full outer shell.
Carbon can form a vast variety of molecules by bonding with other atoms and by forming chains or rings of carbon atoms with other atoms bonded to the chain.
In some cases, carbon forms two bonds with another atom, e.g. alkenes and C=O bonds found in many molecules, such as organic acids.
Monomers and Polymers
Biological molecules are grouped according to their chemical properties. The most important groups of biological molecules are:
- nucleic acids
Monomer refers to a single, small molecule, many of which can be joined together to form a polymer.
Lipids are NOT polymers because the smaller molecules are very different from each other.
Condensation = a type of chemical reaction in which two moleculea are joined together by means of a covalent bond to form a larger molecule, and at the same time a water molecule is released
In condensation reactions:
- a water molecule is released
- a new covalent bond is formed
- a larger molecule is formed by the bonding together of smaller molecules
Hydrolysis = a reaction in which a molecule is broken down into two smaller molecules by the addition of a water molecule and the breaking of a covalent bond
Hydrolysis is the reverse of condensation:
- a water molecule is used
- a covalent bond is broken
- smaller molecules are formed by the splitting of a larger molecule
Hydrogen bonds form when a slightly negatively charged part of a molecule comes close to a slightly positively charged hydrogen atom in the same or a different molecule. This is most easily seen in water.
Hydrogen bonds are not strong bonds. They are often described as "interactions". They can be broken easily by heat energy.