Zoology 2022 Paper II 50 marks Draw

Q6

(a) Draw the molecular structure of ATP synthase and diagrammatically explain the chemiosmotic concept of ATP synthesis. 20 (b) Illustrate the following : (i) A = T and G ≡ C base pairing as a part of DNA double strand (ii) Michaelis-Menten kinetic pattern of an enzymatic reaction 15 (c) Explain the cellular mechanism of action of steroid hormones. 15

हिंदी में प्रश्न पढ़ें

(a) ए० टी० पी० सिन्थेज की आण्विक संरचना का चित्र बनाइए तथा ए० टी० पी० संश्लेषण की रसोप्रसरणी (केमिऑस्मोटिक) संकल्पना को आरेखीय रूप से समझाइए। 20 (b) निम्नलिखित को सचित्र समझाइए : (i) डी० एन० ए० द्वैलड़ी के एक भाग के रूप में A = T तथा G ≡ C का बेस युग्मन (ii) एक प्रकिण्व की अभिक्रिया की माइकेलिस-मेंटेन गतिक प्राक्रता 15 (c) स्टेरॉयड हार्मोनों की क्रिया की कोशिकीय कार्यप्रणाली की व्याख्या कीजिए। 15

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Directive word: Draw

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How this answer will be evaluated

Approach

The directive 'draw' for part (a) demands precise structural diagrams alongside explanatory text. Allocate approximately 40% effort to part (a) given its 20 marks, with 30% each to parts (b) and (c). Structure as: brief introduction → detailed diagrammatic explanation for (a) with chemiosmotic coupling → illustrations for (b)(i) base pairing and (b)(ii) enzyme kinetics with graphs → mechanism explanation for (c) → concluding synthesis on bioenergetics and regulation.

Key points expected

ATP synthase F0-F1 structure: rotary mechanism with α3β3 hexamer, γ subunit, ε subunit, a-b2 subunits, and c-ring; proton flow through F0 drives rotation
Chemiosmotic theory: Mitchell's proton-motive force (Δp = Δψ - 59ΔpH), proton gradient across inner mitochondrial membrane, coupling of oxidation to phosphorylation
Watson-Crick base pairing: A=T with two hydrogen bonds (adenine N1-NH2 to thymine N3-O4), G≡C with three hydrogen bonds (guanine O6-N1-N2 to cytosine N4-N3-O2), antiparallel strands, major/minor grooves
Michaelis-Menten kinetics: hyperbolic curve, Vmax, Km definition, Lineweaver-Burk double reciprocal plot, significance of Km as substrate affinity measure
Steroid hormone mechanism: intracellular receptors (cytoplasmic/nuclear), ligand binding, receptor dimerization, HRE binding, coactivator/corepressor recruitment, transcriptional activation with examples (cortisol, estrogen, testosterone)

Evaluation rubric

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	25%	12.5	Accurately describes rotary catalysis mechanism of ATP synthase with binding change mechanism; correctly states chemiosmotic coupling with proton-motive force equation; precise hydrogen bond geometry for base pairs; correct Michaelis-Menten equation and kinetic parameters; accurate steroid receptor domains and signaling cascade	Basic description of ATP synthase structure without rotary mechanism detail; general chemiosmotic concept without quantitative aspect; correct base pairing but missing hydrogen bond specifics; recognizes hyperbolic curve but confuses Km/Vmax definitions; general steroid mechanism but misses receptor dimerization or HRE details	Confuses ATP synthase with ATPase; describes substrate-level phosphorylation instead of chemiosmosis; incorrect base pairing (A-C, G-T); linear or sigmoidal enzyme kinetics; describes peptide hormone mechanism for steroids
Diagram / labelling	25%	12.5	Clear hand-drawn ATP synthase with F0 base, F1 head, stalk, and rotor stator labelled; chemiosmotic gradient shown with proton flow arrows; DNA double helix with base pairs in correct orientation; Michaelis-Menten hyperbolic plot with asymptote and ½Vmax line; steroid receptor structure with Zn-finger domains	Basic ATP synthase sketch missing subunit detail; simple membrane gradient without directional flow; ladder-like DNA without helical twist; curve drawn but axes unlabelled or inverted; generic cell diagram for steroid action without receptor detail	No diagrams despite explicit 'draw' and 'illustrate' directives; mislabelled structures; confused ATP synthase with electron transport chain; random curves without biological meaning; entirely text-based response
Examples & nomenclature	15%	7.5	Names specific ATP synthase subunits (α, β, γ, δ, ε, a, b, c8-15); cites Peter Mitchell and Nobel 1978; uses systematic base nomenclature (purine/pyrimidine, glycosidic bond, phosphodiester backbone); identifies specific enzymes (hexokinase, chymotrypsin) for kinetics; names specific steroid receptors (GR, ERα, AR) and HRE sequences	Generic 'head' and 'base' terminology; mentions chemiosmosis without Mitchell; basic A, T, G, C naming; enzyme E and substrate S notation; general 'steroid receptors' without specificity	Incorrect terminology throughout; confuses ATP synthase with synthase/synthetase distinction; wrong base names; no enzyme examples; confuses steroids with sterols or peptide hormones
Process explanation	20%	10	Stepwise rotary catalysis: loose-tight-open conformational changes; detailed proton translocation through a-c interface; DNA replication implications of complementary base pairing; steady-state versus rapid equilibrium assumptions in enzyme kinetics; complete steroid signaling from entry to transcription with chromatin remodeling	General rotation concept without conformational states; proton flow mentioned without mechanism; base pairing described without replication context; curve explained without underlying mechanism; hormone entry and nuclear action mentioned but steps unclear	No mechanistic explanation; static description only; confused oxidative phosphorylation with photophosphorylation without distinction; enzyme kinetics as mere graph description; steroid action as direct enzyme activation
Evolutionary / applied context	15%	7.5	Evolutionary conservation of ATP synthase from bacteria to mitochondria (endosymbiotic theory); clinical relevance: mitochondrial disorders, uncouplers like DNP/thermogenin; base pairing in PCR, DNA fingerprinting, CRISPR; enzyme kinetics in drug design (statins, HIV protease inhibitors); steroid therapeutics in Indian context (corticosteroids in TB meningitis, oral contraceptives)	Mentions bacteria and mitochondria without evolutionary link; notes uncoupling without clinical example; DNA applications listed superficially; drug inhibition mentioned without example; general medical use of steroids	No evolutionary or applied context; purely academic description; misses all real-world connections; irrelevant examples from unrelated fields

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