AP Biology Unit 1 Review

Multiple Choice

Which of the following types of molecules has the most energy available per unit of carbon?

• carbohydrates

• lipids

• proteins

• nucleic acids

​explanation: Fats have high potential to produce a lot of energy when broken down. This is because they are saturated, which means they have a lot of bonded hydrogens. They also have a lot of carbon-carbon bonds which have a lot of potential energy. There are not as many of these bonds in carbs, or proteins. Proteins require a lot of energy to break down.

Multiple Choice

Pharmaceutical researchers are often interested in blocking particular receptor proteins on cell surfaces. What chemical property of a molecule would be most important for it to bind a receptor active site?

• The molecule's structural shape

• the type of bonding

• the number of double bonds in the molecule

• the number of valence electrons

​To block a receptor protein a molecules must structurally resemble a natural ligand. The active sites of proteins are highly specific, and will only bind certain molecules. The chemical formula, valence electrons and bonding can all influence small regions of the molecules structure, but the overall shape must ultimately match the active site of a target protein.

Multiple Choice

A reaction between an alpha carboxylic acid and an alpha amino group creates a peptide bond. Which of the following describes this process?

• Hydrogenation

• Dehydration Synthesis

• Hydrolysis

• Esterification

​Hydrolysis reactions involve breakdown of molecules (lysis) in the presence of H2O. Water is a reactant in hydrolysis reactions. Dehydration synthesis reactions involve formation of bonds between molecules (synthesis) and removal of water at the end of the reaction (dehydration). During the formation of peptide bonds a hydroxyl group from carboxylic acid and a hydrogen atom from amino group are released and form water. Formation of peptide bonds is a dehydration synthesis reaction because bonds are synthesized and water is released.

Multiple Choice

Which of the following structures remains constant when a protein is in its denatured form?

• Primary

• Secondary

• Tertiary

• Quarternary

​Denaturation of a protein involves the breakdown of non-covalent bonds between amino acids residues. The formation of noncovalent bonds (hydrogen and van der Waals forces) lead to a higher order structures such as secondary, tertiary and quarternary structure. Upon denaturation these noncovalent bonds in the protein chain are broken and the protein reverts back to its primary structure. The primary structure of a protein consists of the amino acid sequence joined together by peptide bonds (covalent). Covalent bonds are much stronger and more permanent than hydrogen and other intermolecular forces and can endure denaturation. Environmental conditions such as temperature and pH contribute to denaturation of a protein.

​When a solution of a protein is boiled, the protein frequently becomes insoluble—i.e., it is denatured—and remains insoluble even when the solution is cooled. The denaturation of the proteins of egg white by heat—as when boiling an egg—is an example of irreversible denaturation. The denatured protein has the same primary structure as the original, or native, protein. The weak forces between charged groups and the weaker forces of mutual attraction of nonpolar groups are disrupted at elevated temperatures, however; as a result, the tertiary structure of the protein is lost. In some instances the original structure of the protein can be regenerated; the process is called renaturation.

Denaturation can be brought about in various ways. Proteins are denatured by treatment with alkaline or acid, oxidizing or reducing agents, and certain organic solvents. Interesting among denaturing agents are those that affect the secondary and tertiary structure without affecting the primary structure.

Multiple Choice

How is protein primary structure formed?

• Hydrogen bonds between the amine group of one amino acid and the side chain of another

• Hydrogen bonding between the hydrogen of one amino acid and carboxylic acid of another

• Peptide bonds between the amine group of one amino acid and the carboxylic acid group of another

• Peptide bonds between side chains (R-Groups)

​peptide bonds form between the amine group of one amino acid and the carboxylic acid of another via a covalent linkage. The formation of a polypeptide chain from amino acid residues constitutes the protein primary structure.

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secondary structure is formed by hydrogen bonding between the amino and carboxyl backbone units of the polypeptide.

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tertiary structure is formed by disulfide covalent bonds, hydrophobic interactions and R-group hydrogen bonding.

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quaternary structure is the joining of multiple polypeptide subunits. https://www.youtube.com/watch?v=PPJ7C3hcnPw