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#biochemical reactions

3 public questions tagged with this topic.

Eukaryotes gene regulation

PylC enzyme catalyzes

PylC functions as ATP-dependent ligase catalyzing second step of pyrrolysine pathway, condensation of (3R)-3-methyl-D-ornithine with second L-lysine molecule via amide bond formation between ornithine carboxylate and lysine epsilon-amino group, producing N6-((2R,3R)-3-methylornithyl)-lysine. Mechanism employs ATP to activate carboxylate as acyl-adenylate intermediate then nucleophilic attack by lysine amine, similar to glutathione synthesis. PylC structure resembles D-alanine-D-alanine ligase fold. Deletion of pylC accumulates methylornithine and ablates pyrrolysine formation preventing amber suppression and methylamine methyltransferase synthesis in Methanosarcina. This condensation generates pseudopeptide intermediate essential for subsequent oxidation cyclization into pyrrolysine heterocycle.

Ref: NCBI Bookshelf, Ligases: PylC Condensation Reaction in Pyrrolysine Pathway

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RDT Basics

Which enzyme is inhibited by small amounts of ammonium ions?

T4 polynucleotide kinase possesses 5'-kinase activity transferring the gamma-phosphate of ATP to 5'-hydroxyl ends of DNA or RNA, plus 3'-phosphatase activity. Biochemical studies demonstrate that ammonium ions act as potent inhibitors, even at concentrations as low as a few millimolar, by interfering with active site conformation. Because many DNA purification protocols use ammonium acetate for precipitation, residual ammonium can block phosphorylation and subsequent ligation. Therefore, sodium acetate precipitation followed by ethanol washing is preferred before kinase treatment to ensure efficient 5'-end labeling and vector phosphorylation.

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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Endocrinology

C-peptide is released during conversion of:

Answer: B) Proinsulin to insulin. For Endocrinology, once you lock onto the key mechanism or definition, Proinsulin to insulin is the clear fit. If you restate the concept in your own words, Proinsulin to insulin is the option that correctly names the structure, process, or principle asked for in Endocrinology. So Proinsulin to insulin is the clean, accurate selection. If a similar stem appears later, start from the same core fact and you will land on the same kind of answer. In class notes, highlight this same phrase next to the related diagram so the wording and the picture reinforce each other.

Ref: Animal physiology is Unit 7 of the CSIR NET Life Science Syllabus, covering core body systems. It accounts for roughly 10% of the total marks in Sections B and C.

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