Nucleic Acids ā DNA vs RNA, base pairing
Biomolecules
8
JEE Qs
8%
Hard
75
min
Pay close attention to the structural differences between DNA and RNA, specific base pairing rules, and the number of hydrogen bonds involved, as these are frequent points of questioning.
š§® Key Formulas
ā Key Points for JEE
- 1Distinguish DNA from RNA based on sugar (deoxyribose vs. ribose), bases (T vs. U), and general structure (double-stranded helix vs. typically single-stranded but variable).
- 2Master the specific base pairing rules: Adenine (A) always pairs with Thymine (T) in DNA (or Uracil (U) in RNA) via two hydrogen bonds, and Guanine (G) always pairs with Cytosine (C) via three hydrogen bonds.
- 3Understand the components of a nucleotide (nitrogenous base, pentose sugar, phosphate group) and how they polymerize via 3'-5' phosphodiester linkages to form polynucleotide chains with distinct 5' and 3' ends.
- 4Recognize the antiparallel nature of the two strands in a DNA double helix, where one strand runs 5'ā3' and the other 3'ā5'.
ā ļø Common Mistakes
- āConfusing the specific nitrogenous bases for DNA and RNA (e.g., placing Thymine in RNA or Uracil in DNA).
- āIncorrectly recalling the number of hydrogen bonds between A-T/A-U (two) and G-C (three).
- āMixing up purines (Adenine, Guanine) and pyrimidines (Cytosine, Thymine, Uracil) or their respective structures.
- āNot understanding the structural difference between deoxyribose and ribose sugar (presence/absence of -OH group at the 2' carbon).
š Practice Questions
See allQ51.Given below are two statements: Statement I: Fructose does not contain an aldehydic group but still reduces Tollen's reagent Statement II: In the presence of base, fructose undergoes rearrangement to give glucose. In the light of the above statements, choose the correct answer from the options given below (1) Both Statement I and Statement II are true (2) Both Statement I and Statement II are false (3) Statement I is true but Statement II is false (4) Statement I is true but Statement II is false
Q51.The carbohydrate "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in ā-anomeric form Choose the correct answer from the 2025 (24 Jan Shift 1) JEE Main Previous Year Paper options given below: (1) A, D and E Only (2) A, C and D Only (3) A, B and E Only (4) B, D and E Only
Q60.Which of the following acids is a vitamin? (1) Adipic acid (2) Ascorbic acid (3) Saccharic acid (4) Aspartic acid
Q61.Identify the number of structure/s from the following which can be correlated to D-glyceraldehyde. (1) four (2) one (3) two (4) three
Q59.The Ī±-Helix and Ī² - Pleated sheet structures of protein are associated with its : (1) tertiary structure (2) quaternary structure (3) secondary structure (4) primary structure ā£ā£ā£ ā£ā£ā£ ā£ā£ā£ ā£ā£ 2025 (23 Jan Shift 2) JEE Main Previous Year Paper
Q51.Given below are two statements: Statement I : D-glucose pentaacetate reacts with 2, 4-dinitrophenylhydrazine Statement II : Starch, on heating with concentrated sulfuric acid at 100āC and 2-3 atmosphere pressure produces glucose. In the light of the above statements, choose the correct answer from the options given below 2025 (28 Jan Shift 1) JEE Main Previous Year Paper (1) Statement I is false but Statement II is true (2) Both Statement I and Statement II are false (3) Both Statement I and Statement II are true (4) Statement I is true but Statement II is false
NCERT Chapters
- Class 12 Chemistry Ch 14: Biomolecules