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Explain why covalent bonds restrict flexibility while noncovalent bonds do not.

Covalent bonds are relatively stable because a large amount of energy is required to break them. Thus, subunits bound by these bonds are less able to move relative to one another. Noncovalent bonds require less energy to break. Because of their lower stability, they can more easily break and reform than covalent bonds, allowing for flexibility of movement between interacting subunits.


Why is RNA more unstable than DNA?

The 2' hydroxyl group in RNA can perform a nucleophilic attack to sever the phosphodiester backbone of RNA. DNA does not have this hydroxyl group.


Suppose a substitution of a serine for a leucine residue is made in a protein. How do you think this will affect the overall structure of the protein? What if, instead of aspartic acid, an isoleucine was substituted for leucine?

Hydrophobic residues like leucine often associate into hydrophobic pockets in a protein's interior. Because serine is hydrophilic, it would probably not be tolerated in a hydrophobic pocket in a protein and could lead to unfolding or misfolding. Isoleucine, like leucine, is hydrophobic and would probably be a good substitute for leucine.


How does the amino acid sequence of a protein affect its secondary structure?

The amino acid sequence determines how the protein will fold based on the potential interactions of different types of amino acids with hydrophobic and electrostatic properties.


Which macromolecule stores the most energy?