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#false statement

8 public questions tagged with this topic.

Paracrine Factor

Which of the following statements about FGF signaling is FALSE?

FGF signaling is canonical RTK pathway central to embryogenesis requiring heparan sulfate proteoglycan cofactor for high affinity. FGFR dimerization activates FRS2 adaptor and downstream Ras-ERK, PI3K-AKT, PLCγ-STAT cascades controlling proliferation. In limb, FGF10 from mesenchyme induces FGF8 in apical ectodermal ridge which maintains Sonic Hedgehog in zone of polarizing activity via Formin-Gremlin loop, but Sonic Hedgehog protein does not biochemically activate FGF receptors; interaction occurs via transcriptional regulation maintaining FGF expression, not direct receptor phosphorylation. Thus claiming direct activation misrepresents hierarchy. FGFs indeed function through receptor tyrosine kinases and participate in limb outgrowth and segmentation clock.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 18: Limb feedback loop FGF in AER and Shh in ZPA interaction.

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Membrane Transportation

Which of the following statements about osmosis is false?

Osmosis defined as net movement of water across selectively permeable membrane driven by difference in water chemical potential. Water moves from region of higher free water concentration, meaning low solute, to lower free water where solute high, until equilibrium of potentials or balance by hydrostatic pressure. Membrane restricts solute passage due to size or polarity exclusion. Process requires no metabolic energy, purely passive diffusion using thermal kinetic energy. Aquaporins may accelerate but do not require ATP. Common misconception conflates solute diffusion with osmosis. Solutes also diffuse down own concentration gradients from high to low via simple lipid diffusion if hydrophobic or via carriers channels, but that transport is termed diffusion or facilitated diffusion, not osmosis. Water pathway involves hydrogen bonding network transient breaking. Saying solutes move from high to low as part of osmosis mislabels transport; during osmosis solutes largely remain on original side, otherwise gradient would dissipate without water shift. Correct distinction clarifies tonicity effects: water moves, solutes generally retained, establishing osmotic pressure.

Ref: Nelson & Cox, Lehninger Principles, Chapter 11: Osmosis vs Solute Diffusion - Definition Clarification.

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Cytoskeleton

Which statement about dynein function is FALSE?

Dynein heavy chains are among the largest AAA+ machines, containing six concatenated AAA modules forming an asymmetric ring. AAA1 is primary catalytic site where ATP binding closes interface with AAA2, straightening linker and detaching stalk from microtubule. Hydrolysis and phosphate release trigger linker swing from pre to post power stroke, pulling tail forward while microtubule-binding domain reattaches downstream. This cycle strictly depends on ATP concentration and hydrolysis; nonhydrolyzable analogs such as AMP-PNP arrest motility in strong binding state, vanadate traps ADP-Pi intermediate. Dynein moves toward minus ends, positioning Golgi ribbon adjacent to centrosome and driving retrograde transport of autophagosomes, endosomes and interphase nuclei. Disruption fragments Golgi into scattered ministacks. Claiming independence from ATP contradicts enzymology and single molecule assays showing velocity dependence on Mg-ATP with Michaelis-Menten kinetics, while other statements regarding Golgi positioning, organelle transport and directionality align with extensive siRNA, dominant negative p150 and knockout studies in mammalian culture and in vivo models.

Ref: Alberts Ch 16 Motor proteins; dynein AAA+ requires ATP hydrolysis, minus-end directed transport.

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RDT Basics

Which is NOT true about molecular cloning?

Molecular cloning involves several enzymatic manipulations. Klenow fragment, lacking 5' exonuclease activity, can fill 5' overhangs to blunt ends using dNTPs. Isocaudomers XhoI and SalI generate compatible TCGA overhangs permitting cross-ligation. Alkaline phosphatase removes 5'-phosphate groups rather than 3'-phosphates, blocking self-ligation. Blue-white screening depends on alpha-complementation of lacZ; insertion inactivates beta-galactosidase producing white colonies on X-gal. However, white phenotype does not guarantee recombinant insert because vector mutations, primer dimers, or small non-disruptive inserts can also abolish activity, necessitating PCR or restriction verification rather than relying solely on color.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Enzyme Kinetics

Which of the following statements about the lock and key model is false?

The enzyme undergoes a conformational change upon binding is the correct choice because it does not accurately describe or belong to the category addressed in this question. In the context of Enzymes Basics, the other options (The substrate fits perfectly into the enzyme’s active site, This model explains high specificity of enzymes, and It was proposed by Emil Fischer) are all valid and well-established concepts. The enzyme undergoes a conformational change upon binding is either unrelated to the topic, describes a different biological process, or represents a common misconception. Questions framed as 'which is NOT' require students to identify the exception among otherwise correct statements, demanding comprehensive knowledge of the topic rather than recognition of a single fact.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 6

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