amino acid properties

Question 1

Which two functional groups are found in all amino acids?

Answer 1

An amino acid must contain an amine and a carboxylic acid

Question 2

What functional group is present in all peptide bonds?

Answer 2

Peptide bonds contain amides. In fact, they are sometimes alternatively known as amide linkages

Question 3

In a peptide bond synthesis reaction, what molecule is lost?

Answer 3

Water (H2O)

Since water is lost in this reaction, it (in addition to being a nucleophilic substitution reaction) can also be termed a dehydration synthesis reaction

Question 4

When amino acids are incorporated into a peptide (that is, when multiple amino acids have joined together via peptide bonds), those amino acids are termed:

Answer 4

residues.

As such, a tripeptide can be said to contain three residues. Larger peptides may contain hundreds of residues or more

Question 5

The individual properties of amino acids (acidic, basic, polar, etc.) are entirely dependent on which part of the amino acid?

Answer 5

The side chain

Since all amino acids share a common backbone (consisting of an amino terminal, an alpha carbon, and a carboxylic acid terminal), their varying properties are entirely dependent on their individual side chains.

Question 6

Define the isoelectric point of an amino acid

Answer 6

The isoelectric point, or pI, is the pH at which an amino acid is neutral overall.

When the surrounding pH is lower than the isoelectric point, the amino acid in question will have a net positive charge. When the surrounding pH is higher, its net charge will be negative

Question 7

Explain how to calculate the pI of an amino acid with an uncharged side chain

Answer 7

To calculate the pI, simply average the pKas of the carboxylic acid and amino groups.

For example, the two pKas of glycine are 2.34 (carboxylic acid) and 9.60 (amine). The pI of glycine is thus (2.34 + 9.60) / 2, or 5.97

Question 8

Explain how to calculate the pI of an amino acid with a charged side chain.

Answer 8

For acidic amino acids, average the two most acidic pKas. For basic amino acids, average the two most basic pKas. Remember, do not average all three values!

For example, the three pKas of lysine are 2.18 (carboxylic acid), 8.95 (amine), and 10.53 (side chain). Since its R group is basic, its pI is thus (8.95 + 10.53) / 2, or 9.74

Question 9

With the exception of glycine, every amino acid can exist in two potential configurations. What names are given to these forms?

Answer 9

Amino acid configurations can either be D (dextrorotatory) or L (levorotatory). These forms are enantiomers.

These configurations are similar to those used in sugars. When drawn as Fischer projections, a D amino acid has the amino group pointing to the right, while the amino group of an L isomer points to the left

Question 10

What word describes the interactions between polar amino acids and water?

Answer 10

Amino acids with nonpolar side chains tend to be hydrophobic. This means that they interact poorly with water and generally cluster with other nonpolar groups