Chemistry MCQs for NEET — Practice Questions with Answers

In cellulose, two β-D-glucose molecules are joined by β(1→4) glycosidic bonds. This means that the linkage between the glucose units is a C1-O-C4 bond. This specific linkage allows the formation of straight chains that can hydrogen bond with each other, providing strength and stability to the cellulose fibers.

All \alpha-amino acids possess a primary amino group (\text{NH}_2) except for proline, which has a secondary amino group. Therefore, the correct answer is primary.

Proline is unique among the standard amino acids because it contains a secondary amino group. In proline, the amino group is part of a five-membered ring, making it secondary. Therefore, the correct answer is secondary.

Valine, histidine, and methionine are all essential amino acids, meaning they must be obtained through diet as the body cannot synthesize them. Therefore, the correct answer is all.

Non-essential amino acids are termed 'non-essential' because they can be synthesized by the human body. Unlike essential amino acids, which must be obtained through diet, non-essential amino acids do not need to be consumed through food as the body can produce them from other compounds. This is why option o2 is correct.

Amino acids contain both an amino group (-NH2) and a carboxyl group (-COOH). These functional groups are critical for the structure and function of amino acids in proteins. Hence, option o4, which includes both groups, is the correct answer.

In the dry solid form, amino acids exist as zwitterions, where the carboxyl group is present as a carboxylate ion (-COO-) and the amino group is present as an ammonium ion (-NH3+). The term 'zwitterion' (from German 'Zwitter', meaning hybrid) refers to this dipolar ion form. Therefore, option o2 is correct.

The pH value at which an amino acid does not migrate towards any electrode is called the isoelectric point. At this pH, the amino acid exists as a zwitterion with no net charge, hence it does not move in an electric field.

A mixture of amino acids can be separated by both electrophoresis and chromatography. Electrophoresis separates molecules based on their charge and size, while chromatography separates them based on their affinity to the stationary and mobile phases.