Transcript Chemistry_for_Biolog..

Chemistry for Biologists
Chemistry for Biologists
Define the following:
• Element
• Atom
• Proton
• Neutron
• Electron
• Isotope
Chemistry for Biologists
• An element is a substance made up of
atoms with the same number of protons.
Elements are the simplest substances
known. They can be metals (e.g. iron,
copper, sodium magnesium) or non-metals
(e.g. carbon, hydrogen, oxygen, nitrogen).
There are just over 100 of them.
Chemistry for Biologists
• Atoms are the building blocks of all
matter. They consist of three sub-atomic
particles: protons, neutrons and
electrons.
Chemistry for Biologists
• Proton
• particle in the nucleus with a positive charge of +1 and an
atomic mass number of 1 Dalton.
• Neutron
• a non-charged nuclear particle with the same mass as the
proton.
• Electron
• negatively charged particle (-1) with a mass 1/1837 of that
of a proton.
Particle
Proton
Neutron
Whereabouts in atom
Nucleus
Nucleus
Electron
Outside the nucleus
Relative mass
1
1
1/
1840
Charge
+1
0
-1
• Many elements have different isotopes.
Although the numbers of protons and
electrons are the same in all atoms of a
given element, the number of neutrons
may differ.
Chemistry for Biologists
• Electrons are outside the nucleus, and
determine properties of the atom.
Chemical reactions involve sharing or
exchanging electrons. Electrons move
about the nucleus in atomic orbitals
Chemistry for Biologists
• A molecule is two or more atoms linked
by a chemical bond.
• Molecules can contain different types
of bonds. What are these?
Formation of sodium chloride
Na, 2,8,1
One electron is
transferred from a sodium
atom to a chlorine atom
Na+, 2,8
forming a sodium ion
and a chloride ion
Cl, 2,8,7
Cl-, 2,8,8
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Covalent bonding in methane, CH4
Carbon atom has 4 electrons available for bonding
Each hydrogen atom has one electron available for
bonding
A carbon atom shares one of its
electrons with a hydrogen atom to
make a covalent bond
H
● ●
H
●
●
●
C
●
●
●
H
H
In the same way, three other
carbon-hydrogen covalent bonds
are formed
For simplicity we usually replace the
two dots representing the electrons
by a single straight line
Represents two electrons being shared between a carbon atom
and a hydrogen atom to form a single covalent bond
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Covalent bonding in ethane, C2H6
There are other ways that carbon and hydrogen atoms can
combine – and still obey the combination rules
Remember: electrons available for bonding: Carbon: 4
Hydrogen: 1
Suppose a carbon atom forms a single bond with another carbon atom
●
●
● C ●
● C●
●
●
This leaves enough electrons to bond
6 hydrogen atoms
C2H6
H
H
●● ●●
● C ● H
H ●
C
●
●
●
●● ●●
H
H
Two carbon
atoms in the
molecule
Six hydrogen
atoms in the
molecule
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Chemistry for Biologists
Non-covalent bonds and other weak
forces are important in biological
structures.
Electrostatic bonds (ionic)
Result from the electrostatic attraction between two
ionized groups of opposite charge, such as carboxyl
(-COO-) and amino (-NH3+). In water, these bonds are
very weak.
Ionic attractions are important in stabilising the three
dimensional shapes of proteins
Hydrogen bonds
Result from electrostatic attraction
between an electronegative atom (O or
N) and a hydrogen atom that is bonded
covalently to a second electronegative
atom.
N-H ----- O=C- -O-H----- O=C-
Van Der Waals
These bonds-are short range attractive forces
between chemical groups in contact. Caused by
slight charge displacements.
• Hydrophobic attractions
• These cause non-polar groups such as
hydrocarbon chains to associate with each
other in an aqueous environment.
• Multiple weak bonds or forces can cause
strong interactions
Chemistry for Biologists
Organic molecules contain carbon
Alcohol
hydrocarbon with a hydrogen replaced by "OH".
A hydroxyl group
Acid
hydrocarbon with a hydrogen replaced by "COOH".
A carboxyl group
This disassociates in solution to form COOH -> COO- +
H+
Chemistry for Biologists
Amine
A hydrocarbon with a hydrogen replaced by an
amine "NH2". Basic- accepts protons. NH2 + H+
-> NH3+
Phosphate
The addition of -PO4
• Amino Acid
A hydrocarbon with amino and carboxyl groups
Chemistry for Biologists
Chemical groups found in organic
molecules
Group name
• Aldehyde group
CHO
• Keto group
C=O
• Hydroxyl group
COH
• Carboxyl group
COOH
• Primary alcohol group