Zoology 2021 Paper II 50 marks Discuss

Q6

(a) What are peptide hormones ? With the help of schematic diagram, discuss the epinephrine cascade for the glucose release from hepatocytes. 20 (b) Cyclic AMP is a second messenger, justify. Discuss the importance of cyclic AMP in intracellular signal transduction with suitable example. 15 (c) What is bioenergetics ? Discuss the role of second law of thermodynamics in energy transduction. 15

हिंदी में प्रश्न पढ़ें

(a) पेप्टाइड हार्मोन क्या हैं ? व्यवस्था आरेख (स्कीमेटिक डायग्राम) की सहायता से यकृताणुओं (हैपेटोसाइट्स) से ग्लूकोज विमोचन के लिए एपिनेफ्रिन कैस्केड की विवेचना कीजिए । 20 (b) चक्रीय (साइक्लिक) ए.एम.पी. एक द्वितीयक दूत (सेकेंड मैसेंजर) है, सिद्ध कीजिए । अन्तःकोशिक संकेत पारक्रमण (इंट्रासेल्युलर सिग्नल ट्रांसडक्शन) में चक्रीय ए.एम.पी. के महत्व की उपयुक्त उदाहरण सहित विवेचना कीजिए । 15 (c) जैव ऊर्जिकी (बायोएनर्जेटिक्स) क्या है ? ऊर्जा पारक्रमण में उष्मागतिकी के द्वितीय नियम की भूमिका की विवेचना कीजिए । 15

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Directive word: Discuss

This question asks you to discuss. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

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How this answer will be evaluated

Approach

The directive 'discuss' demands a comprehensive, analytical treatment with logical progression. Allocate approximately 40% of word budget to part (a) [20 marks], 30% to part (b) [15 marks], and 30% to part (c) [15 marks]. Structure: brief definition of peptide hormones → detailed epinephrine cascade with diagram → cAMP as second messenger justification → signal transduction examples → bioenergetics definition → thermodynamic principles in biological systems. Conclude with integrative synthesis showing how signal transduction exemplifies thermodynamic efficiency.

Key points expected

  • Part (a): Definition of peptide hormones (amino acid-derived, water-soluble, membrane receptor binding); complete epinephrine cascade from β-adrenergic receptor → Gs protein → adenylyl cyclase → cAMP → PKA → phosphorylase kinase → glycogen phosphorylase → glucose-1-phosphate → glucose release
  • Part (a): Schematic diagram showing membrane receptor, G-protein activation, cAMP generation, PKA activation cascade, and glycogenolysis endpoint with correct enzyme nomenclature
  • Part (b): Justification of cAMP as second messenger (intracellular diffusion, signal amplification, rapid degradation by phosphodiesterase, multiple downstream targets); detailed signal transduction example (glucagon action on hepatocytes or ACTH on adrenal cortex)
  • Part (c): Definition of bioenergetics as study of energy flow and transformation in biological systems; explanation of second law (entropy increase) and its role in driving spontaneous reactions, coupled reactions, and maintenance of cellular nonequilibrium states
  • Part (c): Application of thermodynamic principles to ATP synthesis, proton gradients, and efficiency limitations in energy transduction (ΔG, ΔH, TΔS relationships)
  • Integration: Connection between epinephrine cascade energetics and thermodynamic efficiency; evolutionary significance of G-protein signaling conservation across phyla

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Precise definitions: peptide hormones as <50 amino acids (e.g., insulin, glucagon, ACTH); accurate G-protein nomenclature (Gs, Gi, Gq); correct thermodynamic equations (ΔG = ΔH - TΔS; negative ΔG for spontaneity); distinguishes first vs second messenger correctly; no confusion between phosphorylase kinase and glycogen phosphorylaseGenerally correct definitions with minor errors (e.g., conflating cAMP with cGMP, vague G-protein classification, incomplete thermodynamic equation); some biochemical pathway gapsFundamental misconceptions (steroid hormones as peptide hormones, cAMP as first messenger, violation of thermodynamic laws stated, incorrect enzyme sequence in cascade)
Diagram / labelling20%10Clear, self-drawn schematic for part (a) showing: extracellular epinephrine → 7-TM receptor → Gsα-GTP → adenylyl cyclase → cAMP → PKA tetramer dissociation → phosphorylase kinase activation → glycogen phosphorylase b → a; includes inhibitory Gi protein for completeness; arrows indicate activation/inhibition; correct subcellular localizationDiagram present but incomplete (missing PKA step, no G-protein subunit distinction, unclear membrane topology) or poorly labelled; may use block arrows without specificityNo diagram, or diagram with major errors (receptor orientation reversed, cAMP shown entering from outside, missing critical enzymatic steps, confusing glycogenolysis with gluconeogenesis)
Examples & nomenclature15%7.5Specific examples: for (a) epinephrine/β-adrenergic receptor system; for (b) glucagon in hepatocytes or ACTH in adrenal fasciculata with receptor specificity; for (c) mitochondrial proton gradient or Na+/K+-ATPase as energy transduction example; correct abbreviations (cAMP, PKA, ATP, ΔG°')Generic examples without specificity (e.g., 'hormones' instead of named hormones); some nomenclature errors (c-AMP instead of cAMP, protein kinase A without specifying A); missing Indian research context where applicableIncorrect examples (steroid hormones for peptide hormone section, cGMP for cAMP functions); invented terminology; no examples for signal transduction or bioenergetics applications
Process explanation25%12.5Stepwise mechanistic clarity: for (a) conformational change in receptor → GDP-GTP exchange → Gsα dissociation → AC activation → 100-1000x cAMP amplification → PKA R2C2 dissociation → serine/threonine phosphorylation cascade; for (b) signal amplification and termination via phosphodiesterase; for (c) entropy-enthalpy compensation in coupled reactions, nonequilibrium thermodynamics of open systemsSequential description without mechanistic depth (lists steps without explaining molecular interactions); partial explanation of amplification or feedback; superficial thermodynamic treatmentDisordered sequence of events; no explanation of amplification; confuses cause-effect relationships; states second law without applying to biological energy transduction; no mention of coupled reactions
Evolutionary / applied context15%7.5Evolutionary conservation: G-protein signaling from yeast to mammals; β-adrenergic receptor polymorphisms in human populations; clinical relevance: β-blockers in cardiovascular disease, phosphodiesterase inhibitors (sildenafil), metabolic syndrome implications; thermodynamic efficiency of ATP synthesis (~40% vs theoretical maximum); Indian context: endocrine disorders prevalence, ICMR studies on metabolic diseasesBrief mention of conservation or clinical relevance without elaboration; generic statement about evolution; no specific disease applications or Indian research referencesNo evolutionary or applied context; isolated facts without integration; irrelevant examples (e.g., discussing evolution of hormones without G-protein conservation)

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