Question 1

Which of the following statements about amino acid configuration in proteins is correct?

Accepted Answer

Life almost exclusively uses L-amino acids to build proteins.

Question 2

Which amino acid is achiral and thus does not have L or D configuration?

Accepted Answer

Glycine

Question 3

In the standard Fischer projection for amino acids, which group is placed at the top?

Accepted Answer

The carboxyl group ($$\mathrm{COOH})$$

Question 4

Which of the following is true regarding the configuration of L-amino acids (excluding cysteine)?

Accepted Answer

They all have an S configuration.

Question 5

A biochemist is analyzing a protein sample and finds that all amino acids except one are in the L-configuration. Which amino acid is most likely to be the exception due to its achirality?

Accepted Answer

Glycine

Question 6

Which method is commonly used to determine the L/D configuration of amino acids?

Accepted Answer

Fischer projection

Question 7

In a Fischer projection of an L-amino acid, which group is typically drawn on the left side?

Accepted Answer

The amino group ($$\mathrm{NH_2$})$$

Question 8

Which amino acid is an exception to the rule that all L-amino acids have an S configuration?

Accepted Answer

Cysteine

Question 9

A researcher is trying to synthesize a peptide using D-amino acids. What is a likely consequence for the resulting protein?

Accepted Answer

It will be resistant to proteolytic enzymes found in most organisms.

Question 10

Which of the following representations is NOT a standard way to depict an L-amino acid?

Accepted Answer

Haworth projection

Question 11

Given the following Fischer projection, identify the configuration:

$$
\begin{array}{c}
\mathrm{COOH} \
| \
\mathrm{H_2N} - \mathrm{C} - \mathrm{H} \
| \
\mathrm{R}
\end{array}
$$

The amino group is on the left. What is the configuration?

Accepted Answer

L-configuration

Question 12

Why is glycine not chiral?

Accepted Answer

It has two identical hydrogen atoms attached to its alpha carbon.

Question 13

Which of the following is a correct statement about the stereochemistry of amino acids in proteins?

Accepted Answer

Proteins are composed almost exclusively of L-amino acids.

Question 14

A student is asked to draw the Fischer projection of an L-amino acid. Which of the following must be true for their drawing?

Accepted Answer

The amino group is on the left.

Question 15

Which of the following is a consequence of the predominance of L-amino acids in biological proteins?

Accepted Answer

Proteins have a consistent handedness in their secondary structures.

Question 16

Which of the following amino acids has a side chain that can form a disulfide bond?

Accepted Answer

Cysteine

Question 17

If a protein is synthesized using only D-amino acids, which property will most likely differ from a natural protein?

Accepted Answer

Its susceptibility to enzymatic degradation.

Question 18

Which of the following is NOT a correct statement about the representation of amino acids?

Accepted Answer

Amino acids can be represented using Haworth projections.

Question 19

Which of the following is the correct order of priority for assigning configuration to the chiral center of an amino acid according to the Cahn-Ingold-Prelog rules?

Accepted Answer

Carboxyl group \u003e Amino group \u003e R group \u003e Hydrogen

Question 20

A patient is found to have a rare genetic disorder that incorporates D-amino acids into their proteins. Which of the following is a likely effect?

Accepted Answer

Their proteins will be more resistant to proteolytic enzymes.

L- and D- Amino Acids: Configuration, Representation, and Biological Relevance

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