Skip to content
Login Register

#exam preparation

1067 public questions tagged with this topic.

Transgenic Plant -1

Gene subtraction strategy mainly results in:

Functional removal of undesirable endogenous activity defines subtraction approach. Native genes responsible for fruit softening, browning, lignin deposition, or allergenicity can be downregulated via antisense transcription, RNA interference using hairpin constructs processed into siRNAs, or targeted knockout via CRISPR. Resulting lines lack specific enzyme activity, leading to accumulation of precursors or alternative metabolites. For example antisense polygalacturonase tomatoes retain firmness, and RNAi suppression of polyphenol oxidase reduces bruising in potato. Subtraction does not introduce new enzymatic function but eliminates existing one, complementing addition strategy. Inheritance usually dominant due to transgene encoded silencing signal spreading systemically. Careful design ensures specificity to avoid off-target silencing of related family members. Hence main outcome of subtraction is inactivation of existing plant genes to improve quality, shelf life, or processing attributes without adding foreign protein products. Technology examples include antisense polygalacturonase tomato delaying softening and RNAi mediated non-browning Arctic apple silencing polyphenol oxidase. Small interfering RNAs of 21 nucleotides incorporate into RISC complex guiding cleavage of target transcript. Stable inheritance follows Mendelian ratio, though epigenetic silencing may occur. Gene subtraction therefore complements addition by removing detrimental activities without introducing new metabolic enzymes, improving postharvest quality attributes.

Ref: Watson Ch 8 silencing; NCBI NBK21471 antisense RNAi subtraction; Lodish Ch 8 inactivation; PubMed 11340117.

View Details
Protein Sorting and Trafficking

Which of the following is TRUE about AP (adapter protein) complexes?

Heterotetrameric adapter protein complexes link cargo sorting signals to clathrin and other coats decoding destinations. AP2 composed of alpha, beta2, mu2, sigma2 about 300 kDa localizes exclusively to plasma membrane where alpha appendage ear binds PIP2 and accessory proteins Eps15 and epsin. Mu2 middle domain recognizes YXXPhi tyrosine signals where tyrosine sits in deep hydrophobic pocket and phi bulky hydrophobic; affinity enhanced by phosphorylation at Thr156 by AAK1 kinase upon membrane recruitment. Dileucine [DE]XXXL[LI] also recognized. Transferrin receptor YTRF, LDL receptor FXNPXY via co-adaptor ARH linking to AP2, and many signaling receptors use this for rapid internalization forming pits 0.5 percent surface. AP1 at TGN and endosomes contains gamma adaptin and mediates TGN to endosome traffic, not Golgi to ER which uses COPI dilysine. AP3 delivers to lysosomes and lysosome-related organelles melanosomes via tyrosine and dileucine; COPII formation depends on Sec24 not AP3. AP complexes use clathrin or related coats; interaction with cargo tails not SNAREs defines sorting specificity bridging membrane, signal, and coat.

Ref: Robinson, Trends Cell Biol 2015: AP2 adaptor complex in clathrin-mediated endocytosis at plasma membrane.

View Details
Applications of d and f Block Elements

Which of the following is NOT a use of transition metals or their compounds?

Transition metals and their compounds are used as catalysts, pigments, and in alloy formation. While platinum is used as an inert electrode in many electrochemical setups, the option 'inert electrodes' may be considered not primary/general for most transition metals.

Ref: NCERT Class 12 Chemistry > Chapter 4: d and f Block Elements > Topic: Applications of d and f Block Elements

View Details