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Macromolecules
Atoms Molecules
Macromolecules
A few common
macromolecules in biology
are POLYMERS of a
particular class of molecule.
Monomers
Polymers
POLYMERS
Biological polymers are
formed by a common
reaction known as
CONDENSATION or
DEHYDRATION
(dehydration synthesis).
CONDENSATION or
DEHYDRATION (dehydration
synthesis).
Water is removed
(dehydration) to form a bond
between the growing polymer
and the next monomer
subunit.
Large biological polymers are
broken down through the
reverse reaction--HYDROLYSIS
Water (H-OH) is added to break
a covalent bond between
subunits in a polymer.
Three Major Polymers in Biology:
Polysaccharides: Polymers of
sugars (carbohydrates)
Proteins: Polymers of amino
acids
Nucleic Acids: Polymers of
nucleotides
A Fourth Important Class of
Macromolecules:
Lipids: Macromolecules
constructed from fatty acids
& glycerol (not simple
polymers of many
monomers linked end-toend)
POLYSACCHARIDES:
Carbohydrates have the general
chemical formula:
(CH2O)n
where "n" is greater than 3
Monosaccharides
Polysaccharides
two primary classes of
monosaccharides:
5 carbon sugars: ribose &
deoxyribose
6 carbon sugars: glucose (see
Figure 3.4C):
Two common forms of glucose: a
&b
Two common forms of glucose: a &
b
Differ only in the configuration of
the -OH group on the no. 1
carbon (a: -OH is down, b: -OH is
up)
This slight difference in structure
makes a huge difference in terms
of biological function
Polymers of monosaccharides
are formed by dehydration synthesis
reactions.
Note: the bond formed is between two aglucose molecules.
a-1,4 linkage (between the no. 1 carbon
on one a-glucose molecule and the no. 4
carbon on the other)
Polymers of monosaccharides
Compare the structure of an a1,4 linkage to a b-1,4 linkage
Note the difference in
structure, which results in
differences in function
Polymers of a-1,4 linkages:
Starch (plants)
Glycogen
(animals)
Polymers of b-1,4 linkages:
Cellulose (plant cell walls,
wood)
Chitin (exoskeleton of
lobsters, insects)
Biological Importance:
Most organisms CAN digest a-1,4
linkages to extract carbon and
energy from polysaccharides
Most organisms CANNOT digest
b-1,4 linkages