Biochemistry

This question asks which amino acids from the list contain an –OH group (hydroxyl group) in their side chains. Here’s the analysis of each amino acid: 1. Lysine (A):
Lysine contains an amino group ( ) at the end of its side chain, but does not have a hydroxyl group ( ) in its side chain. Therefore, lysine does not contain an –OH group.
2. Serine (B):
Serine contains a hydroxymethyl group ( ) in its side chain. This hydroxymethyl group contains a hydroxyl ( ) group, making serine one of the amino acids with an –OH group. 3. Tyrosine (C):
- Tyrosine contains a phenolic group (-OH attached to a benzene ring) in its side chain. This is another amino acid that contains a hydroxyl group, specifically attached to a benzene ring, which is characteristic of tyrosine. 4. Valine (D):
- Valine is a branched-chain amino acid with a nonpolar, hydrophobic side chain. It does not contain a hydroxyl group. From this, we can conclude that Serine (B) and Tyrosine (C) are the amino acids that contain an –OH group in their side chains. Thus, the correct answer is B) Serine and C) Tyrosine (Option 3).

Step 1: Understand the definition of a nucleoside.
A nucleoside is a biochemical compound that consists of a nitrogenous base (either purine or pyrimidine) linked to a sugar molecule (ribose or deoxyribose). Crucially, nucleosides do not contain any phosphate groups. When a phosphate group is added to a nucleoside, it becomes a nucleotide.
Step 2: Identify the components in the given options.
Option (1) contains a phosphate group, so it represents a nucleotide, not a nucleoside.
Option (2) also contains a phosphate group, making it a nucleotide.
Option (3) does not contain a phosphate group, consisting only of the sugar and the nitrogenous base. Therefore, it correctly represents a nucleoside.
Option (4) contains only the sugar molecule and is missing both the nitrogenous base and phosphate group. Therefore, it is not a nucleoside.
Step 3: Conclude the correct answer.
Based on the analysis in Step 2, Option (3) is the correct answer because it is the only structure that fits the definition of a nucleoside, consisting only of a sugar and a nitrogenous base. Thus, the correct answer is (3).

Step 1: Understanding Tooth Enamel Hardening
- Hydroxyapatite:
- Fluoride treatment replaces OH⁻ with F⁻, forming fluorapatite, which is stronger.

- contributes OH⁻.
- provides F⁻.