Topic 5: Macromolecules. Proteins, Carbohydrates, and Nucleic Acids
1.) Review the various proportions of each type of molecule in cells. (Fig 3.3)
Living tissues are 70% water. About 5% are ions and small molecules, and 25% are macromolecules. Of
the macromolecules, about 60% are proteins, about 25% are nucleic acids, and about 10% are
carbohydrates, and about 5% are lipids.
2.) What is meant by the “biochemical unity of life”?
The biochemical unity of all life on Earth, the fact that macromolecules are in the same proportions in
ALL cells is strong evidence in support of the theory of evolution by natural selection, and the descent of
all life from a common ancestor. All cells have specific types of molecules in the same proportions.
3.) What are monomers (building blocks) for each of the 3 classes of macromolecule polymers?
The three classes of polymers; Proteins, Carbohydrates, and Nucleic Acids all consist of covalently
bonded monomers. Proteins (polypeptides) are made of amino acid monomers with 20 different
monomers. Carbohydrates (polysaccharides) are made of monosaccharides (simple sugars) with a dozen
different monomers. Nucleic acids are made of nucleotides with 5 different monomers. (A,T,G,C,U).
4.) How do monomers come together to form polymers? How are they split apart?
Condensation reactions: An enzyme (a protein catalyst) brings the two monomers together, and connects
them to one another by removing an –OH from one, and –H
from the other, thereby removing a water
molecule, and building a covalent bond between the monomers. This usually requires an input of energy
(building bonds require energy). This process is repeated over and over during polymer synthesis.
Polymers are broken through hydrolosis, which results when a different enzyme binds to the polymer and
inserts an H
O: an OH to one monomer and the H onto the other, thus splitting the two monomers apart.
Energy is usually released in this process. (Breaking molecules releases the energy in their bonds).
5.) What are the functions in cells of each of the classes of polymers?
Proteins: Fibrous structures in cells. (Cytoskeleton, Connective Tissue), enzymes (catalyze reactions),
cell messengers such as hormones, movement (cytoskeleton tubules, flagella), immune system proteins
Carbohydrates: Energy storage (starch, glycogen), structural support (cellulose).
Nucleic acids: Storage, transmission, and regulation of genetic information. RNA can act as an enzyme.