18. Amino Acids and Proteins

What is the sequence of atoms along the "backbone" of a protein?

How many ways can four different amino acids be arranged in a peptide so that each peptide is unique?

What atoms are present in a planar unit in a protein chain?

How many amino acid units do these atoms come from? Why are these units planar?

Bradykinin, a peptide that helps to regulate blood pressure, has the primary structure Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg.

a. Draw the complete structural formula of bradykinin.

What is meant by the following terms as they apply to protein structure, and what bonds or molecular interactions stabilize that level of structure?

a. Primary structure

Do the following peptides have an identical primary structure?

Explain why each of the following pairs are complementary proteins:

a. beans and oats

Draw the condensed structural formula for Ser–Lys–Asp.

Seeds and vegetables are often deficient in one or more essential amino acids. Using the following table, state whether each combination provides all of the essential amino acids:

b. lima beans and cornmeal

Seeds and vegetables are often deficient in one or more essential amino acids. Using the table in problem 16.63, state whether each combination provides all of the essential amino acids.

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a. rice and lima beans

Seeds and vegetables are often deficient in one or more essential amino acids. Using the table in problem 16.63, state whether each combination provides all of the essential amino acids.

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c. oatmeal and lima beans

How many different tripeptides that contain one leucine, one glutamate, and one tryptophan are possible?

The endorphins are a group of naturally occurring neurotransmitters that act in a manner similar to morphine to control pain. Research has shown that the biologically active parts of the endorphin molecules are simple pentapeptides called enkephalins. Draw the structure of the methionine enkephalin with the sequence Tyr-Gly-Gly-Phe-Met. Identify the N-terminal and C-terminal amino acids.

Draw the structure of the following amino acids, dipeptides, and tripeptides at low pH (pH 1) and high pH (pH 14). At each pH, assume that all functional groups that might do so are ionized.

a. Val