Chemical Bonds And Groups In Biological Molecules Reference Sheet

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106
PANEL 2–1: Chemical Bonds and Groups Commonly Encountered in Biological Molecules
CARBON SKELETONS
Carbon has a unique role in the cell because of its
ability to form strong covalent bonds with other
carbon atoms. Thus carbon atoms can join to form
or branched trees
or rings
chains.
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
also written as
also written as
also written as
HYDROCARBONS
COVALENT BONDS
A covalent bond forms when two atoms come very close
together and share one or more of their electrons. In a single
Carbon and hydrogen combine
bond one electron from each of the two atoms is shared; in
together to make stable
a double bond a total of four electrons are shared.
compounds (or chemical groups)
Each atom forms a fixed number of covalent bonds in a
called hydrocarbons. These are
defined spatial arrangement. For example, carbon forms four
nonpolar, do not form
single bonds arranged tetrahedrally, whereas nitrogen forms
hydrogen bonds, and are
three single bonds and oxygen forms two single bonds arranged
generally insoluble in water.
as shown below.
Atoms joined by two
or more covalent bonds
C
N
O
cannot rotate freely
H
H
around the bond axis.
H
C
H
H
C
This restriction is a
Double bonds exist and have a different spatial arrangement.
major influence on the
H
H
three-dimensional shape
of many macromolecules.
methane
methyl
group
C
N
O
H
C
2
CH
2
ALTERNATING DOUBLE BONDS
H
C
2
The carbon chain can include double
Alternating double bonds in a ring
CH
2
bonds. If these are on alternate carbon
can generate a very stable structure.
H
C
atoms, the bonding electrons move
2
within the molecule, stabilizing the
CH
2
structure by a phenomenon called
H
C
resonance.
H
H
2
CH
2
H
H
H
H
H
C
C
C
C
C
C
2
´
CH
C
C
C
C
C
2
H
H
H
H
H
C
2
the truth is somewhere between
CH
2
H
H
these two structures
benzene
H
C
3
C
C
C
C
C
often written as
part of the hydrocarbon “tail”
C
C
C
C
C
of a fatty acid molecule

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