67. Which one of the following properties of naturally occurring D-amino acids is INCORRECT:
A. Peptides arising from them are more susceptible to attack by peptidases.
B. They are components of bacterial cell wall.
C. Peptides arising from them are not synthesized by ribosomal machinery.
D. They are components of many bacterially produced peptide antibiotics.
Which one of the following is NOT a food rich in Vitamin A?
A. Potato
B. Squash
C. Sweet potato
D. Spinach

Introduction:

In biochemistry and nutrition, understanding the roles of different compounds is crucial. D-amino acids, though not commonly found in proteins, play an essential role in various biological processes. Similarly, Vitamin A is vital for numerous body functions, and some foods are particularly rich in it. Let’s delve into the key properties of naturally occurring D-amino acids and the foods rich in Vitamin A, identifying one incorrect statement about each topic.

Naturally Occurring D-Amino Acids: Incorrect Property

D-amino acids, unlike their L-isoforms, are not typically components of proteins in most organisms. However, they are crucial in certain biological processes, especially in bacteria and fungi. Let’s examine the properties of naturally occurring D-amino acids:

1. A. Peptides arising from them are more susceptible to attack by peptidases: This statement is correct. D-amino acids are less stable in the context of enzymatic degradation, and thus peptides containing D-amino acids can be more easily broken down by peptidases.

2. B. They are components of bacterial cell walls: This statement is correct. D-amino acids are commonly found in bacterial cell walls, particularly in peptidoglycan structures, which are essential for maintaining the integrity of bacterial cells.

3. C. Peptides arising from them are not synthesized by ribosomal machinery: This statement is correct. D-amino acids are not incorporated into peptides by the ribosomal machinery, as the ribosome primarily recognizes L-amino acids. Instead, D-amino acids are often incorporated into peptides by non-ribosomal mechanisms.

4. D. They are components of many bacterially produced peptide antibiotics: This statement is correct. D-amino acids are important components of certain peptide antibiotics, such as bacitracin, which are produced by bacteria for defense against other microorganisms.

Incorrect Property of D-Amino Acids:

All the statements above about D-amino acids are correct. Therefore, none of these are incorrect based on the context provided. However, if you’re looking for a general incorrect property of D-amino acids, it would typically be related to their role in protein synthesis or their natural occurrence in human proteins.

Vitamin A-Rich Foods: Identifying the Non-Rich Source

Vitamin A is crucial for vision, immune function, and skin health. It is found in various plant and animal sources, primarily in the form of beta-carotene (a provitamin A) in plants, and retinol in animal products. Now, let’s explore which of the following foods is NOT rich in Vitamin A:

1. A. Potato: This is NOT a good source of Vitamin A. While potatoes are nutritious and provide several vitamins and minerals, they do not contain significant amounts of Vitamin A.

2. B. Squash: Squash, particularly varieties like butternut squash, is rich in Vitamin A due to its high content of beta-carotene, which the body converts into Vitamin A.

3. C. Sweet Potato: Sweet potatoes are an excellent source of Vitamin A, especially in the form of beta-carotene. They are one of the top plant-based sources of this essential nutrient.

4. D. Spinach: Spinach is also a rich source of Vitamin A, providing a substantial amount of beta-carotene, which is converted into Vitamin A in the body.

Correct Answer:

A. Potato is the food that is NOT rich in Vitamin A. Unlike squash, sweet potatoes, and spinach, potatoes do not provide significant amounts of this essential nutrient.

Conclusion:

To summarize:

• D-amino acids play essential roles in bacteria and some antibiotic-producing organisms, but they are not typically incorporated into peptides by ribosomal machinery and are more susceptible to enzymatic attack.

• Potatoes are not a rich source of Vitamin A, while squash, sweet potatoes, and spinach provide excellent sources of this vital nutrient.