Biochemistry : Identifying Amino Acids

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #11 : Identifying Biochemical Molecules

Why is it unlikely that proline will be found in an alpha helix protein structure?

Possible Answers:

Proline is too large to fit inside of an alpha helix protein structure

Proline has its side chain covalently bound to its amino group

Proline is so hydrophilic that it will pull water molecules into the alpha helix, disrupting its structure

Proline will be found within alpha helices, but will not be found in kinks

Proline is too small to remain stable within an alpha helix protein structure

Correct answer:

Proline has its side chain covalently bound to its amino group

Explanation:

Because proline has part of its R-group side chain attached to its amino group, it has a unique structure that differs from all other amino acids. The ring structure that it forms with its amino groups causes it to be unable to be found in alpha helix protein structures - if it were to be in one the structure would be disrupted. However, proline is important in kinks and turns because of its small, unique structure.

Example Question #11 : Identifying Amino Acids

Which amino acid has the one-letter symbol Q?

Possible Answers:

Glutamic acid

Glutamine

Aspartic acid

Lysine

Correct answer:

Glutamine

Explanation:

Amino acids can be identified by their full names, three-letter codes, and one-letter symbols. Glutamine has the three-letter code "gln" and the one-letter symbol "Q." Glutamic acid has the three-letter code "glu" and the one-letter symbol "E." Lysine has the three-letter code "lys" and the one-letter symbol "K." Aspartic acid has the three-letter code "asp" and the one-letter symbol "D."

Example Question #12 : Identifying Amino Acids

Shown below is the molecular structure of an amino acid. What is its identity?

Histidine structure

Possible Answers:

Tyrosine

Proline

Isoleucine

Histidine

Phenylalanine

Correct answer:

Histidine

Explanation:

The structure of this amino acid classifies it as histidine.

Example Question #14 : Identifying Biochemical Molecules

You want to purify a particular protein using a cation exchange column. The protein runs very slowly through the column. What does this tell you about the amino acid content of your protein?

Possible Answers:

It is rich in Val, Ile, and Ala

It is rich in Trp, Phe, and Tyr

It is rich in Glu and Asp

It is rich in Ser and Thr

It is rich in Lys and Arg

Correct answer:

It is rich in Lys and Arg

Explanation:

Considering that the protein was run through a cation exchange column, one would expect that the more positively charged proteins would flow very slowly through the column. A cation exchange column is coated with negatively charged beads that would become attracted to the positively charged elements of the protein, causing them to elute out of the column slowly. Lysine and Arginine are positively charged amino acids that would cause this to happen, and a protein rich in these amino acids would elute slowly when run through a cation exchange column.

Example Question #13 : Identifying Amino Acids

Which amino acid has the one-letter symbol W?

Possible Answers:

Tryptophan

Lysine

Glutamine

Aspartic acid

Correct answer:

Tryptophan

Explanation:

Amino acids can be identified by their three-letter codes and one-letter symbols. Tryptophan has the one-letter symbol "W" and the three-letter code "Trp." Glutamine has the one-letter symbol "Q" and the three-letter code "Gln." Aspartic acid has the one-letter symbol "D" and the three-letter code "Asp." Lastly, lysine has the one-letter symbol "K" and the three-letter code "Lys."

Example Question #11 : Identifying Biochemical Molecules

Which amino acid(s) contain(s) sulfur?

Possible Answers:

Neither cysteine nor methionine

Only methionine

Only cysteine

Methionine and cysteine

Correct answer:

Methionine and cysteine

Explanation:

Cysteine and methionine are the only two amino acids that are incorporated into proteins which contain sulfur. However, only cysteine can form disulfide bonds due to its free SH group. Methionine does not have a free SH group and thus cannot form these bonds.

Example Question #11 : Identifying Biochemical Molecules

A protein molecule is converted from a Beta-pleated sheet conformation to an alpha helix conformation. Bonds between which of the following amino acids are broken during this process?

Possible Answers:

Both of these are involved

None of these are involved

Cysteine

Proline

Correct answer:

Both of these are involved

Explanation:

Beta-pleated sheets and alpha helical conformation are types of protein secondary structures. Recall that secondary structures of proteins are formed through the formation of hydrogen bonds and disulfide bonds between adjacent amino acids in the polypeptide chain. Converting one type of secondary structure to another involves breaking these hydrogen and disulfide bonds. Disulfide bonds between amino acids occur between cysteine amino acids. Hydrogen bonds occur between a hydrogen atom on one amino acid and either a fluorine, oxygen or nitrogen atom on another amino acid. Hydrogen bonds can be formed between any amino acids because all amino acids have the essential atoms required for hydrogen bonds; therefore, both amino acids listed are involved in bonds that are broken during the conversion of one secondary structure to another.

Example Question #18 : Identifying Biochemical Molecules

Maple syrup urine disease (MSUD) is a rare congenital disorder that involves poor metabolism of branched amino acids. Which of the following amino acids could accumulate in an infant diagnosed with MSUD?

Possible Answers:

Tryptophan

Lysine

More than one of these is correct

Isoleucine

Correct answer:

Isoleucine

Explanation:

There are three main branched amino acids that accumulate in a patient with MSUD. These are isoleucine, leucine and valine. Accumulation of these branched amino acids occurs because of depletion of enzymes essential for their breakdown. The breakdown products of branched amino acids are used for several processes, including energy production via glycolysis and oxidative phosphorylation. Accumulation of these amino acids is toxic and is often fatal to a child with MSUD.

Example Question #19 : Identifying Biochemical Molecules

A researcher is analyzing a transmembrane protein found on cell membranes. He observes lots of valine residues on the membrane spanning portion of the protein. What can you conclude about these results?

Possible Answers:

The results seem valid because valine is hydrophilic

The results seem invalid

The results seem valid because valine is hydrophobic

The intracellular portion will also have lots of valine residues

Correct answer:

The results seem valid because valine is hydrophobic

Explanation:

A transmembrane protein consists of two hydrophilic regions (that are found on the ends facing the cytoplasmic and extracellular sides) and one hydrophobic region (inserted into the hydrophobic interior of the phospholipid bilayer). The question states that the region is saturated with valine amino acid residues. Recall that valine is a hydrophobic amino acid; therefore, the region containing lots of valine residues must be the hydrophobic region of the transmembrane protein.

Example Question #231 : Biochemistry

How many water molecules are produced upon synthesis of myoglobin, a 154-amino acid protein?

Possible Answers:

0

154

153

1

Correct answer:

153

Explanation:

Amino acid polymerization (translation) involves condensation, or the production of free water. For each peptide bond that is formed, one molecule of water is also formed. Myoglobin contains 154 amino acids, thus contains 153 peptide bonds and 153 molecules of water produced per protein synthesized.

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