Biomolecules and the Chemistry of Life Questions
Bring on the tough stuff
- Compare and contrast ionic, covalent, and hydrogen bonds. How do these bonds work? Do they form between atoms, molecules, or ions? What is the role of electrical charge? How strong are the bonds, and how do they relate to the dissolving properties of water?
- What kind of food would you want to eat for breakfast before running a mile in gym class? Why? If you were a rodent preparing for hibernation, or a bird preparing for an autumn migration, what type of biomolecule would you want to use for energy storage? Why?
- During the winter, many species of amphibians and reptiles go into a hibernation-like state called overwintering. They eat little or no food, slow their metabolism and breathing rate dramatically, and most of their bodily functions shut down. Interestingly, many of these species choose to spend the winter underwater. Why might it be advantageous to overwinter at the bottom of a pond rather than on land?
- Why are fats and waxes solid at room temperature, whereas oils are liquids? With your answer to that question in mind, how do you think the phospholipids of coldwater fish compare to warmwater fish? Would you expect to see differences in the amounts of saturated and unsaturated fatty acids?
- In humans, blood pH is maintained fairly precisely around 7.4, and this is largely accomplished with the help of bicarbonate ion (HCO3-) and carbonic acid (H2CO3), both of which are floating around in the blood. If blood suddenly becomes acidic for some reason, bicarbonate turns into H2CO3. If blood suddenly becomes too basic, some H2CO3 turns into HCO3-. What’s going on here? Using your knowledge of acids, bases, and buffers, explain how pH is maintained at a constant level in this system.
- Compare and contrast proteins and nucleic acids. What do these biomolecules have in common? In what ways are they different? Be sure to consider both their structures and their functions.
Biomolecules and the Chemistry of Life Answers
- Answer: The three kinds of bonds (ionic, covalent, and hydrogen) can be ranked
in terms of strength: covalent bonds are the strongest, followed by ionic
bonds, and finally, hydrogen bonds as the weakest. Ionic bonds occur
between two differently charged ions, or atoms that have gained or lost
electrons. What holds them together is the fact that opposites attract:
electrons are stolen rather than shared in the ionic bond. In
contrast, in covalent bonding, the electrons are shared between the two
atoms. In hydrogen bonds, the weakest kind of bond, the partial charge
of the hydrogen atom is what attracts it to the slightly negative charge
of another atom. The hydrogen bond is important in biologically
significant macromolecules such as DNA, RNA, and proteins. In this
case, no electrons are exchanged or shared. The best explanation of
hydrogen bonding is in the case of the water molecule. Because hydrogen
is such a poor electrophile, when it is covalently bound to oxygen,
instead of evenly sharing this single electron, the electron spends more
time around the oxygen atom. Therefore, the hydrogen becomes slightly
positively charged while the oxygen becomes slightly negatively
charged. These opposite charges on separate but adjacent molecules can
then work to create hydrogen bonds between the molecules. Because of
this special property of water, ionically bound molecules can easily
dissolve in aqueous solution, as their negative and positively charged
atoms can associate with the slightly negative and slightly positive
charges on the water molecule.
- Answer: Before running a mile in gym class, you would want to eat a simple carbohydrate. This would be a good idea because a mile is not a very long distance, and what you would need
is quick energy. If you were preparing for hibernation, however, or a
long distance migration, you would want to use fat for storage because fat
stores, per gram, twice as much energy as carbs or protein, and can
therefore last the distance.
- Answer: It might be advantageous to overwinter in water because of water's heat
of fusion. This fact means that you would be less likely to freeze to death
during your overwintering.
- Answer: Fats and waxes are solid at room temperature because they are made of
saturated fatty acids. In contrast, oils are mostly
unsaturated fatty acids. Saturated fatty acids are called as such because
they do not have many double or triple bonds in their structure; each
carbon is bound to four other atoms, and this fact makes it quite easy to stack
the fatty acid molecules together closely. Therefore, saturated fats are solid at room
temperature. In contrast, unsaturated fatty acids have several kinks in
their structure and therefore, are liquid at room temperature. We would
expect the phospholipids of cold water fish to be more heavily
unsaturated compared to the phospholipids of warm water fish, due to
their adaptation to temperature.
- Answer: pH refers to the concentration of hydrogen in a solution. A buffer is a
molecule that can help to control the pH of a solution by taking up a
hydrogen or releasing one into solution, depending on the surrounding
pH. If blood becomes too acidic, that fact means that there is an excess of
hydrogen ions in the blood. The bicarbonate ion can then take up the
excess hydrogen ion and become H2CO3.
If, in contrast, the blood becomes too basic, that fact means that there is a
lack of hydrogen ions, and bicarbonate can then release its extra
hydrogen into solution, becoming HCO3-.
- Answer: Proteins and nucleic acids are both important biological macromolecules. They both have carbon, nitrogen, and hydrogen, but are made of different molecular components. Proteins are made of amino acids, and nucleic acids are made of nucleotides. They are similar in that, during the synthesis of the macromolecules, these molecular components are covalently bound to each other, making a string of nucleotides or a string of amino acids. Proteins and nucleic acids are also similar in that both have tertiary structure to them. In proteins, the kinds of folds are alpha helices and pleated sheets, and in nucleotides, helices are formed by the DNA molecule, and a similar kind of structure is formed by the single-stranded RNA molecule. They are different in their functions. Proteins are synthesized from DNA, with an RNA intermediate.
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