Nucleic Acids, Hormones & Vitamins Why this matters for NEET DNA and RNA store and express life’s information. Hormones coordinate body functions at a distance. Vitamins are tiny dietary molecules that keep enzymes working. NEET loves straight comparisons (DNA vs RNA), classic rules (Chargaff, base pairs), and deficiency diseases (scurvy, rickets, pellagra). Master the logic first, then the lists. DNA double helix vs RNA single strand, and a nucleotide made of three parts: pentose sugar, phosphate, and nitrogenous base. Nucleic acids: components and vocabulary Nucleic acids are polymers of nucleotides. Each nucleotide has: a pentose sugar, a phosphate group, and a nitrogenous base. In DNA, the sugar is β-D-2-deoxyribose (no OH at 2'). In RNA, it is β-D-ribose (OH at 2'). Bases are of two types: purines (adenine A, guanine G — bicyclic) and pyrimidines (cytosine C, thymine T, uracil U — monocyclic). DNA uses A, G, C, T; RNA uses A, G, C, U. Sugar + base. Linked by a β-N-glycosidic bond between C1' of sugar and N9 (purine) or N1 (pyrimidine). No phosphate. Nucleoside Nucleotide Nucleoside + phosphate. Phosphate esterified typically at the 5' position of the sugar. Polymer linkage joining 3'-OH of one nucleotide to 5'-phosphate of the next, giving a sugar-phosphate backbone with 5' → 3' direction. Phosphodiester bond Schematic chemical idea (biochemically formed via enzyme-catalysed phosphorylation). Conceptual build-up Feature DNA RNA Aspect DNA vs RNA — components and structure Pentose sugar β-D-2-deoxyribose (no 2'-OH) β-D-ribose (has 2'-OH) Bases A, G, C, T (thymine) A, G, C, U (uracil) Typical structure Double-stranded, antiparallel helix Mostly single-stranded; folds into secondary structures Primary function Long-term genetic information storage Information transfer and functional roles (mRNA, tRNA, rRNA) remember Purine always pairs with pyrimidine. This keeps the helix width uniform. DNA structure: primary and Watson–Crick secondary Primary structure is the linear order of nucleotides joined by 3'→5' phosphodiester bonds. One end has a free 5'-phosphate (5' end), the other a free 3'-OH (3' end). Secondary structure (Watson–Crick, 1953): two antiparallel strands (one 5'→3', the other 3'→5') coil into a right-handed double helix stabilized by hydrogen bonding between complementary bases and by base stacking. Key geometry to remember: diameter ≈ 20 Å; ~10 base pairs per turn; pitch (rise per full turn) ≈ 34 Å (so ~3.4 Å rise per base pair). Chargaff's rules (double-stranded DNA) Explains base-pair complementarity; overall %purines = %pyrimidines. Base pairing in DNA: A=T has two H-bonds; G≡C has three H-bonds. Right-handed double helix with 10 bp per turn and 20 Å diameter. gpt-image-2 2026-05-26T17:05:51.556Z Clean vector diagram showing A=T (2 H-bonds) and G≡C (3 H-bonds) with dotted lines; right-handed double helix with labels: 10 bp/turn, 34 Å pitch, 20 Å diameter; antiparallel strands 5'→3' and 3'→5'. Neutral textbook palette; red curved arrows for strand direction; no internal text beyond labels. A = T Less H-bonding; relatively less thermal stability G ≡ C More H-bonding; GC-rich DNA melts at higher temperature Pair Base pair H-bonds Implication Base pairs and hydrogen bonds remember GC-rich DNA is more thermally stable because G≡C has three H-bonds (and stronger stacking). RNA types and the central dogma RNA acts as the working copy and as a functional molecule in protein synthesis. Three key RNAs: mRNA carries the code from DNA to ribosome; tRNA brings specific amino acids, using its anticodon to read mRNA codons; rRNA forms the structural and catalytic core of ribosomes (ribozyme activity). The flow of genetic information is called the central dogma. DNA also replicates (copies itself) before cell division. Central dogma Central dogma: DNA → RNA → Protein, with a note that B vitamins act as coenzymes in energy-yielding pathways. Quick features mRNA: linear, transient copy of a gene; template for protein synthesis. tRNA: cloverleaf secondary structure; anticodon loop reads mRNA, 3' end carries amino acid. rRNA: major structural and catalytic RNA in ribosomes. Besides mRNA, RNA includes tRNA (adapter) and rRNA (structural/catalytic). Many RNAs fold into complex shapes; some show catalytic activity (ribozymes). RNA only acts as a messenger and has no structural or catalytic roles. RNA is always single-stranded in all organisms. Most cellular RNAs are single-stranded but fold into double-helical regions; some viruses have double-stranded RNA genomes. Hormones: chemical messengers Hormones are signals secreted by endocrine glands, released into blood, and acting at distant target cells via specific receptors. They regulate growth, metabolism, reproduction, stress, and more. They are not used for energy; tiny amounts cause big effects. Classifying hormones (structure → examples → typical mechanism) Type Class Examples Solubility Usual receptor & effect Steroid (from cholesterol) Cortisol; Sex hormones: testosterone, estrogen, progesterone Lipid-soluble Intracellular receptors; regulate gene expression (transcription) Peptide/protein Insulin, Growth hormone, Vasopressin Water-soluble Membrane receptors; second messengers (e.g., cAMP, Ca2+) Amine (modified amino acids) Epinephrine (adrenaline), Thyroxine (T4) Epinephrine: water-soluble; Thyroxine: lipid-soluble Epinephrine: membrane receptors; Thyroxine: nuclear receptors gpt-image-2 Two-panel vector: left shows peptide hormone binding GPCR → cAMP second messenger; right shows steroid crossing membrane → hormone–receptor complex binding DNA. Label classes and receptors; arrows in red; clean white background; no extra text. 2026-05-26T17:05:51.901Z Schematic of hormone signaling: peptide hormone acts via membrane receptor and cAMP; steroid hormone diffuses into cell, binds nuclear receptor, alters transcription. Hormones are regulatory signals, not catalysts. They bind receptors to trigger responses and are metabolized/cleared after action. Enzymes are the true catalysts. Hormones act like catalysts and are not consumed in reactions. Instant classification trick: If derived from cholesterol → steroid; peptide names often end with -in (insulin, vasopressin); rapid membrane effects suggest peptide/amine, gene transcription changes suggest steroid/thyroid. neet-alert Vitamins: tiny molecules, big consequences Vitamins are small organic compounds needed in minute amounts for normal metabolism. Most cannot be synthesized by the body and must come from diet. They often act as coenzymes or antioxidant protectors. Two groups: fat-soluble (A, D, E, K) and water-soluble (B-complex, C). Water-soluble vitamins are generally not stored and need regular intake; fat-soluble can accumulate. Vitamin molecules and food sources: oranges (Vitamin C), carrots (Vitamin A), and sunlight for Vitamin D — with fat- vs water-soluble cues. Vitamin Chemical name Solubility Key deficiency feature(s) Common sources Vitamin Fat-soluble vs Water-soluble vitamins — quick map Retinol (and provitamin A: β-carotene) Fat-soluble Night blindness; xerophthalmia Carrots, leafy greens, dairy, fish liver oil Calciferol (D3: cholecalciferol) Fat-soluble Rickets (children); osteomalacia (adults) Sunlight (skin synthesis), fortified milk, fish liver oil Tocopherol Fat-soluble Infertility/sterility (classically in rats); neurological issues if severe Vegetable oils, nuts, seeds Phylloquinone (K1) Fat-soluble Defective blood clotting (bleeding tendency) Green leafy vegetables; gut flora contribution Ascorbic acid Water-soluble Scurvy: bleeding gums, poor wound healing Citrus fruits, amla, tomatoes B1 Thiamine Beri-beri (neuropathy, cardiac failure) B2 Riboflavin Cheilosis/angular stomatitis (cracked lips), glossitis B3 Niacin (nicotinic acid) Pellagra — the 3 D's: dermatitis, diarrhea, dementia B5 Pantothenic acid Burning feet sensation (rare) B6 Pyridoxine Microcytic anemia, seizures/convulsions B7 Biotin Hair loss, dermatitis B9 Folic acid (folate) Megaloblastic anemia; neural tube defects in fetus B12 Cobalamin Pernicious/megaloblastic anemia; neurologic signs B-complex vitamins — names and classic deficiencies B-vitamin Chemical name Key deficiency sign(s) Fat-soluble? Think DEKA (D, E, K, A) — these sit in fat stores. Pellagra’s 3 D’s: Dermatitis, Diarrhea, Dementia. Antioxidant vitamins: C (water-soluble) and E (fat-soluble). remember More vitamins are always better; megadoses are harmless. Excess fat-soluble vitamins can accumulate (hypervitaminosis). Balance matters; water-soluble vitamins are excreted but still can cause issues in very high doses. clinical PCR diagnostics target nucleic acids (e.g., viral RNA in COVID-19). Vitamin knowledge guides diet and treating scurvy (Vit C) or rickets (Vit D). High-yield contrasts and traps DNA vs RNA — at a glance Sugar: DNA has 2-deoxyribose; RNA has ribose (extra 2'-OH). Base: DNA uses T; RNA uses U. Structure: DNA usually double-stranded; RNA usually single-stranded but folds. Role: DNA stores info; RNA expresses it (mRNA/tRNA/rRNA). neet-alert Chargaff applies strictly to double-stranded DNA: %A=%T and %G=%C. Single-stranded genomes need not obey it. Industrial and medical connections Insulin therapy produced by recombinant DNA technology. Vaccines: subunit and mRNA platforms; COVID-19 mRNA vaccines released in 2020. CRISPR-based gene editing therapies are in development/clinical use. Oral contraceptives use progesterone derivatives (steroid hormones). Food fortification: iodized salt, B-vitamin-fortified flour; vitamin supplement industry. Glossary — speak NEET with precision DNA poly(deoxyribonucleotide) Deoxyribonucleic acid; genetic storage polymer with β-D-2-deoxyribose, bases A, G, C, T; usually double helix. poly(ribonucleotide) Ribonucleic acid; β-D-ribose sugar; bases A, G, C, U; usually single-stranded but folded. RNA Nucleoside + phosphate (usually at 5'); monomer unit of nucleic acids. Nucleotide Sugar + nitrogenous base; no phosphate. Nucleoside Bicyclic base family: adenine, guanine. Purine Monocyclic base family: cytosine, thymine, uracil. Pyrimidine 3'→5' linkage in nucleic acid backbone. Phosphodiester bond Right-handed DNA helix with A=T and G≡C pairing; ~10 bp/turn, 20 Å diameter. Watson-Crick double helix In double-stranded DNA: %A=%T and %G=%C. Chargaff's rules Messenger RNA; carries coding information from DNA to ribosome. mRNA Transfer RNA; adapter with anticodon that delivers amino acids during translation. tRNA Ribosomal RNA; structural and catalytic core of ribosomes. rRNA Information flow: DNA → RNA → Protein. Central dogma Change in DNA sequence; may alter phenotype or cause disease. Mutation Endocrine chemical messenger acting at distant targets via receptors. Hormone Cholesterol-derived, lipid-soluble hormone acting via intracellular receptors. Steroid hormone Water-soluble polypeptide hormone acting via membrane receptors/second messengers. Peptide hormone Small organic nutrient required in trace amounts; often coenzymes/antioxidants. Vitamin Vitamins A, D, E, K; stored in body fat; risk of hypervitaminosis. Fat-soluble vitamin B-complex and C; not stored significantly; require regular intake. Water-soluble vitamin Molecule that limits oxidative damage (e.g., Vitamins C and E). Antioxidant