Answers to Review Questions - Chapter 3
1. Sketch the following functional groups: methyl, amino, carbonyl, hydroxyl,
carboxyl, and phosphate - use non-ionized forms where appropriate.
See Figure 3-1 for drawings of these functional groups.
2. How is the fact that a group is nonpolar, polar, acidic, or basic related to its
hydrophilic or hydrophobic properties?
Polar functional groups have an electronegative oxygen atom and are therefore
hydrophilic. Nonpolar functional groups are hydrophobic. Acidic and basic
functional groups are both hydrophilic, as they ionize slightly (i.e. are ions at
body pH).
3. Why is the equivalent of a water molecule important to both condensation
reactions and hydrolysis reactions?
Most monomers are small molecules with a free hydroxyl (OH) or H atom, and
polymers are formed by cleaving these off by enzymatic action, forming water in
the process (condensation reactions). Degradation of large molecules requires the
input of the hydroxyl and the hydrogen from splitting water (hydrolysis).
4. Define monosaccharide, disaccharide, and polysaccharide. Give an example of
each.
Monosaccharides are simple sugars containing 3-7 carbons - it cannot be
degraded by hydrolysis to any other simple sugar. Examples (any ONE of these) glucose, fructose, ribose, galactose, deoxyribose, glyceraldehydes,
dihydroxyacetone
Disaccharides are the preferred form of transport for simple sugars, and consist of
two monosaccharides. Examples - lactose, maltose, sucrose
Polysaccharides are macromolecules consisting of repeating units of simple
sugars (3 or more), usually glucose. Examples (any ONE of these) - starch,
cellulose, glycogen.
5. How does the primary structure of a polypeptide influence its secondary and
tertiary structures?
The primary structure is the amino acid sequence. The sequence of the amino
acids determines whether the protein will take on an alpha-helix or beta-pleated
sheet (or both) in its secondary structure. Likewise, the R groups of adjacent
amino acids result in a variety of interactions that forms the tertiary structure of a
protein.
6. How can the conformation of a protein be disrupted?
Denaturation is a disruption of the secondary, tertiary, and/or quaternary structure
of a protein by an external factor such as temperature or pH. As the correct
molecular conformation unravels, the functioning of the protein is also
dramatically affected.
7. Describe saturated, unsaturated, and trans fatty acids.
Saturated fats have the maximum possible number of hydrogen atoms, resulting in
a carbon chain with all single bonds and a linear form. Unsaturated fats have one
or more adjacent double bonds between carbon atoms, resulting in a chain that is
non-linear (i.e. "kinked". When unsaturated fats are artificially hydrogenated, the
double bonds result in a trans configuration, and therefore mimic the properties of
saturated fatty acids.
8. Why do phospholipids form lipid bilayers in aqueous conditions?
Phospholipids are amphipathic molecules, with a hydrophilic glycerol end and a
hydrophobic fatty acid end, and so naturally form a bilayer with the hydrophobic
tails all in the middle, with the hydrophilic glycerol portions oriented out in either
direction, interfacing with the aqueous medium.