Download Answers to Test Your Ability to Analyze and Apply Your Knowledge

Answers to Test Your Ability to Analyze and Apply Your Knowledge
1. The primary structure of a protein is its amino acid sequence that is coded for by genes in
the DNA. Secondary structure is the shape of the protein due to weak hydrogen bonds
that may form between the hydrogen atom of one amino group and an oxygen atom from
a different amino acid nearby (alpha helix, or alternatively, the beta pleated sheet).
Tertiary structures refers to the complex three-dimensional shape of the polypeptide as it
bends and folds in response to chemical interactions between particular amino acids
located in different regions of the chain. Substituting amino acids in the original primary
sequence would greatly affect the complex interactions between amino acids along the
chain and therefore affect the secondary and tertiary structures of the protein as well.
Since the tertiary structure determines the physiological activity of the protein (such as
the active site of enzymes and the oxygen-carrying ability of hemoglobin), any alteration
in the tertiary structure can seriously disrupt the three-dimensional shape and hence, its
physiological activity.
2. If the aqueous (polar) organ solvent extract does not work but the benzene (nonpolar)
solvent extract does have an effect, one might conclude that the active substance(s) is
(are) lipid soluble. This is not surprising since many lipid hormones already exist within
the steroid family and are derivatives of cholesterol.
3. The lipid family includes a large and variable group of molecules including mono-, di-,
and triglycerides, phospholipids, steroids, and other molecules such as prostaglandins.
The slogan “cholesterol free” may be used on the label of a package containing high-fat
foods because as a member of the steroid subgroup of lipids, indeed cholesterol may not
be present. Since the public associates cholesterol in foods with health risk and heart
disease the slogan may seem to be attractive or at least somewhat healthier than a similar
food choice. This product may not have cholesterol but may be loaded with other high
calorie lipids, such as saturated and unsaturated fats (triglycerides). With recent evidence
about trans fatty acids, the product may present an equal or greater health risk. The
general public is misled because “cholesterol free” and “fat free” are not synonymous.
4. Butter is derived from churned milk fat, mainly (66%) triglycerides (triacylglycerols). As
a subcategory of lipids, triacylglycerols are composed of a glycerol molecule to which are
attached three molecules of fatty acids. Animal fatty acids, like those in milk are
saturated since carbon atoms along the fatty acid molecular chain are joined to each other
by single covalent bonds and also bond with two adjacent hydrogen atoms. Saturated
animal fats, such as butter, tend to be solid at refrigeration temperatures and white in
color. By contrast, another subcategory of lipids are the oils that are unsaturated and
tend to be liquid at refrigeration temperatures and amber in color. Oils are unsaturated
because somewhere along the fatty acid chain a carbon atom is missing one hydrogen
atom (of two), is therefore unsaturated (not saturated with two hydrogen atoms) and is
linked to the next carbon atom by one double bond. This type of fatty acid double bond
is a site of unsaturation and is usually in the more natural cis- configuration with H atoms
extended on the same side. Since animal fats have been long associated with the
increased risk of coronary heart disease and with elevated LDL cholesterol levels,
industry has attempted to reduce the amount of animal fat in butter and food preparation
and so has started with vegetable oils (polyunsaturated), artificially added hydrogen
atoms to the fatty acid chains in a process called hydrogenation. The problem is artificial
hydrogenation places hydrogen opposite each other in the unnatural trans- configuration
4
around the carbon atom. Furthermore, trans fats have also been associated with increased
risk of heart disease and they are currently strongly implicated in association with cancer.
5. Proteins consist of long, blended chains of twenty different amino acids. Neighboring
amino acids are joined to form a primary structure of a polypeptide by the removal of
water, forming a strong covalent bond. Since polypeptide (protein) chains in muscle
tissue of a pot roast are typically very long, weak hydrogen bonds between the H atom of
an amino group and an O atom from nearby amino acids twist the protein into its
secondary structure—an alpha helix or, alternatively, the shape of a pleated sheet. Large
proteins also tend to bend and fold upon themselves in a characteristic tertiary structure
caused by interactions between amino acids distant from one another. One final weak,
temporary force found between electrically neutral molecules that come close to one
another are van der Waals forces. High temperatures, such as roasting, easily disrupts
van der Waals forces, as well as tertiary and secondary structural shapes, but will not
affect the strong covalent bonds of the primary structure and so will not result in an
amino acid “soup”.
5