Essential Cell Biology
Chapter 2 Chemical components of cells
Chemistry of life is based on carbon compounds à organic chemistry
Atom: is the smallest particle that still retains its distinctive chemical propeties. The centre is
a massive posetively charged nucleus, surrounded by a negatively charged cloud of electrons.
They stay in orbit by electrostatic attraction. The nucleus containes positively charged protons
and non-charged neutrons. The cloud of electrons has the exact opposite charge of the
protons. Neutrons contribute to the structural stability of the nucleus.
Isotopes have a different neutron-count, but an equal proton-count. They are chemically
The number of protons and neutrons determines the atom weight. The electrons are too light.
One Dalton = equal to the mass of a hydrogen atom.
Avogadro’s number = 6,2 x 10 gram
(mol x Na = gram)
Atoms are able to react because of their incomplete outer electron shells.
Ionic bond = when electrons are donated by one atom to another
Covalent bond = when two atoms share a pair of electrons
Valence = number of atoms that an atom must acquire or loose in order to attain a filled outer
When an electron jumps from Na to Cl, both atoms become electricically charged ions.
Positive ions = cations
Negative ions = anions
Na and Cl are bonded by an ionic bond. The structure is called a salt. It is a noncovalent
A molecule is a cluster of atoms held by covalent bonds. Electrons are shared.
Bond strength is measured by the amount of energy that must be supplied to break the bond.
The making and breaking of covalent bonds are violent events. In living cells catalysts called
enzymes control them.
Non-covalent bonds are weaker.
Covalent bond between multiple atoms is characterized by specific bond lengths, angles and
A double bond is shorter and stronger than a single bond.