STRUCTURE
AND FUNCTION OF MACROMOLECULES
Chapter
1.2
Functional
Groups Table 1
(background in chemistry available in section 1.2 and on
“great science pages”)
Groups of atoms can be added to the carbon skeleton,
adding even more
diversity in
structure and function. These functional groups often
represent the
reactive part of the molecule. There are several functional
groups with which
you should familiarize yourself.
1. Hydroxyl (-OH) is polar and increases
solubility of molecules to which it
is attached. Often
hydroxyl groups will form H-bonds with hydroxyl
groups of
neighbouring molecules.
2. Carbonyl (- CO )
if carbon-oxygen double bond occurs at the end of a
chain, the molecule
is called an aldehyde. When the same group is
attached
to the internal
part of a molecule, the result is a ketone. Sugars
can be
classified in
groups of ketoses or aldoses. This group can also
participate
in H-bonding.
3. Carboxyl (-COOH) the carbon is double
bonded to an oxygen and single
bonded to a
hydroxyl group. It is polar and increases solubility.
It often
ionizes in cells to
act as an acid (donates an H‑).
4. Amino ( - NH2)
is also polar and increases solubility. This group can
accept H+ from a
solution, acting as a weak base.
5. Sulphydral
group (-SH) helps to stabilize proteins (more on this later)
6. Phosphate (-PO4) is polar and
can act as an acid. Phosphates make up all
living membranes and
all genetic material (DNA and RNA)
Macromolecules are large organic molecules
made from simple building
blocks. There are
four classes of macromolecules
1. Carbohydrates
2. Fats
3. Proteins
4. Nucleic acids
A polymer is a macromolecule made of
identical or similar subunits
A monomer is a subunit or building block of
polymers (Fig 4, Table 3)
To build a macromolecule, a condensation or
dehydration reaction occurs.
A molecule of water is removed by taking
away a hydrogen from one
monomer, and a
hydroxyl group from the other. A covalent bond forms
between the two
subunits. To remove a subunit, or to break apart the
polymer (as happens
in digestion), a molecule of water is added.
This
process is called
hydrolysis ("water-breaking") Fig 5
Carbohydrates
- include sugars
and their polymers Fig 6
- simple sugars called monosaccharides
have a ratio of 1C:2H:1O in their
formulas
- monosaccharides form rings in
solution Fig 7
- in glucose, the -OH group
on carbon #1 can end up
below the plane of
the ring (α configuration)
or above the plane
(β configuration)
Starch - α
glucose in 1-4 glycosidic linkages
Glycogen - α glucose in 1-4 and 1-6 glycosidic linkages
Cellulose - β glucose in 1-4 glycosidic linkages
- smallest sugar contains 3 carbons, the largest is 7
- Glucose is a common 6C aldose
(C6H12O6) used as a fuel in respiration
and found as a
product of photosynthesis
- fructose and galactose are
structural isomers of glucose
- two monosaccharides may join
covalently to form a disaccharide
- common disaccharides include
sucrose (glucose + fructose)
maltose (2 glucose)
lactose (glucose + galactose) Fig
8
- polysaccharides contain hundreds or thousands of monosaccharides
- may differ
structurally only in the linkages Fig 9, 10, 11
- may differ in
type of monosaccharide (review Fig 7)
- function as energy storage molecules (plant
starch/animal glycogen)
OR a
structural role Fig 12,13
(cellulose in plant cell walls/ chitin in insect exoskeletons
and cell walls of fungi)
Animals do not
have the enzyme that can break down cellulose
Chitin is an amino
sugar (modified glucose) found in invertebrate exoskeletons
and the cell walls of certain fungi
Additional info