जीव विज्ञान – Biology MCQ
जीव विज्ञान – कृषि/वन प्रवेश
Biology · Agriculture, Veterinary & Forestry Entrance · ८४० प्रश्न
८४० प्रश्न उपलब्ध। मोड छान्नुहोस्:
जीव विज्ञान: प्रश्न र उत्तर
सही लागेको विकल्पमा थिच्नुहोस्। सही भए हरियो, गलत भए रातो देखिन्छ; ३ सेकेन्डपछि सही उत्तर र व्याख्या देखिन्छ।
सही: ० / ०
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The tryptophan (trp) operon of E. coli is an example of a/an:
सही उत्तर: ख) Repressible operon
In the trp operon, the end product tryptophan acts as a co-repressor that switches the operon off; the lac operon, in contrast, is inducible.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The attachment of a specific amino acid to its tRNA ('charging' of tRNA) is catalysed by:
सही उत्तर: ख) Aminoacyl-tRNA synthetase
Each aminoacyl-tRNA synthetase links its particular amino acid to the matching tRNA using energy from ATP.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The Shine-Dalgarno sequence of prokaryotic mRNA is:
सही उत्तर: क) A ribosome-binding site located just upstream of the start codon
The purine-rich Shine-Dalgarno sequence pairs with the 16S rRNA, positioning the ribosome at the AUG start codon.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In bacteria, the peptidyl transferase activity that forms peptide bonds during translation resides in the:
सही उत्तर: ग) 23S rRNA of the large subunit
Peptidyl transferase is a ribozyme: the 23S rRNA of the 50S subunit catalyses peptide bond formation.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In eukaryotes, the 28S, 18S and 5.8S ribosomal RNAs are transcribed by:
सही उत्तर: घ) RNA polymerase I
RNA polymerase I transcribes the large rRNA precursor in the nucleolus; RNA polymerase III makes tRNA and 5S rRNA.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The sigma (σ) factor of bacterial RNA polymerase is required for:
सही उत्तर: ख) Recognising the promoter and initiating transcription
The sigma factor helps the core RNA polymerase recognise and bind the promoter; rho factor is involved in termination.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In E. coli, the main enzyme that elongates new DNA strands during replication is:
सही उत्तर: ख) DNA polymerase III
DNA polymerase III is the chief replicative enzyme in prokaryotes; DNA polymerase I removes RNA primers and fills the gaps.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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The classic example of competitive inhibition is the inhibition of succinic dehydrogenase by:
सही उत्तर: क) Malonate
Malonate closely resembles the substrate succinate and competes with it for the active site of succinic dehydrogenase.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Enzymes that catalyse the joining of two molecules using energy from ATP hydrolysis (for example DNA ligase) belong to the class:
सही उत्तर: ग) Ligases
Ligases (synthetases) link two molecules coupled with ATP breakdown; lyases remove groups to form double bonds without hydrolysis.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Cholesterol is chemically classified as a:
सही उत्तर: ख) Steroid
Cholesterol is a sterol (steroid) with four fused carbon rings; it is the precursor of steroid hormones and vitamin D.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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