Senior Biology: Biological Molecules

Why do we eat food?

We eat food to get the building blocks for making molecules our body needs, to get minerals to enable reactions to occur and to get energy via respiration.

Metabolism: all chemical reactions, catabolic and anabolic, that occur within an organism.

Respiration: a process in living organisms involving the release of energy from food.

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Molecular Bonding

REVISION:

You need to know TWO types of chemical bonding from your GCSE Chemistry days.

IONIC BONDING

Ionic bonding occurs between positive and negative ions, which attract each other and bind together to form ionic compounds.
For example, lithium chloride consists of Li⁺ ions and Cl^- ions bound together.

Each ion is surrounded by oppositely charged ions held in place by electrostatic attraction and forming an ionic crystal lattice. The ions in a crystal lattice are very strongly bonded - a high temperature is required to melt the crystal.

Where do the ions come from?

Metal ions

In some circumstances metal atoms may lose electrons. The atom then has more protons than electrons and so it will be positively charged, a positive ion.

Diagrams of a sodium atom (2,8,1) and a sodium ion (2,8)+

Diagrams of a sodium atom (2,8,1) and a sodium ion (2,8)+

Diagrams of a magnesium atom (2,8,8,2) and a magnesium ion (2,8)2+

Non-metal ions

Diagrams of a chlorine atom (2,8,7) and a chloride ion (2,8,8)-

Diagrams of an oxygen atom (2,6) and an oxide ion (2,8) 2-

Non-metal atoms may gain electrons and become negatively charged.

Example: An oxygen atom may gain two electrons and become an O^2- ion.

COVALENT BONDING

A covalent bond is formed between non metal atoms, which combine together by sharing electrons. Covalent compounds have no free electrons and no ions so they don't conduct electricity.