Download BCH 201 lect2

Each
of these types of
biomolecules are polymers
that are assembled from
single units called
monomers.
Biomolecule
Carbohydrates
Lipids
Proteins
Monomer ( building
blocks)
Monosaccharide
Not always polymers;
Hydrocarbon chains
Amino acids
Nucleic acids
Nucleotides
• In condensation reactions (also called
dehydration reaction), a molecule
water is removed from two monomers and
they are connected together .
Strengths of Bonds Common in
Biomolecules
Versatility of carbon bonding. Carbon can form covalent
single, double, and triple bonds (in red), particularly with other carbon
atoms.
Triple bonds are rare in biomolecules.
- The four single bonds that can be formed by a carbon
atom are arranged tetrahedrally, with an angle of
about 109.5 between any two bonds (Fig.) and an
average length of 0.154 nm.
- There is free rotation around each single bond, unless
very large or highly charged groups are attached to both
carbon atoms, in which case rotation may be restricted.
- A double bond is shorter (about 0.134 nm) and rigid and
allows little rotation about its axis .
- Thus organic molecules with many single bonds can
assume a number of different shapes , called
conformation , depending on the degree to which each
single bond is rotated .
Geometry of carbon bonding.
(a) Carbon atoms have a characteristic tetrahedral arrangement of their four
single bonds.
(b) Carbon–carbon single bonds have freedom of rotation, as shown for the
compound ethane (CH3OCH3).
(c) Double bonds are shorter and do not allow free rotation. The two doubly
bonded carbons and the atoms designated A, B, X, and Y all lie in the same rigid
plane.
To these carbon skeletons are added groups of
other atoms, called functional groups, which
confer
specific chemical properties on the molecule.
In the following figure :
R is used to represent “any substituent.” It may
be as
simple as a hydrogen atom, but typically
it is a carbon-containing moiety.
When two or more substituents are shown in a
molecule, we designate them R1, R2, and
so forth.