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INI-CET 2013 — Biochemistry

Q: Which of the following induces apoptosis in a cell?

Glucocorticoids. ***Glucocorticoids*** - **Glucocorticoids** are known to induce apoptosis in various cell types, particularly lymphocytes, making them useful in **lymphoid malignancies**. - They activate a complex signaling pathway that leads to the activation of pro-apoptotic proteins and the suppression of anti-apoptotic proteins, ultimately resulting in **programmed cell death**. *Isoprenoids* - **Isoprenoids** are a large class of organic compounds derived from isoprene, involved in various metabolic processes like cholesterol synthesis and protein prenylation, but do not directly induce apoptosis. - While some isoprenoid precursors or inhibitors of isoprenoid synthesis can affect cell proliferation or survival, isoprenoids themselves are not primary apoptosis inducers. *Myristic acid* - **Myristic acid** is a saturated fatty acid primarily involved in protein myristoylation, a post-translational modification essential for various cellular functions. - It is not known to be a direct inducer of apoptosis but can influence signaling pathways that may indirectly impact cell survival or death. *Oleic acid* - **Oleic acid** is a monounsaturated fatty acid that is a major component of cell membranes and is involved in energy storage and signaling. - It is generally considered cytoprotective and can even inhibit apoptosis in some contexts, rather than inducing it. [Practice more Biochemistry PYQs on OnCourse]

Q: What is true about ribozymes?

Peptidyl transferase activity. **Explanation:** **Ribozymes** are non-protein enzyme molecules composed of RNA that possess catalytic activity. This discovery challenged the traditional dogma that all enzymes are proteins. 1. **Why Option A is Correct:** The most clinically significant ribozyme in human biology is the **23S rRNA** (in prokaryotes) or **28S rRNA** (in eukaryotes) of the large ribosomal subunit. This RNA molecule acts as a **Peptidyl transferase**, catalyzing the formation of peptide bonds during protein synthesis (translation). This confirms that the ribosome is essentially a ribozyme. 2. **Analysis of Incorrect Options:** * **Option B (Cut DNA):** Enzymes that cut DNA at specific sites are **Restriction Endonucleases**, which are protein-based enzymes, not ribozymes. * **Option C (DNA Synthesis):** DNA synthesis is mediated by **DNA Polymerases**, which are complex protein enzymes. While RNA primers are needed, the catalytic synthesis is not ribozyme-mediated. * **Option D (GTPase activity):** GTPase activity in translation is associated with protein factors like **EF-Tu or EF-G**, not the catalytic RNA itself. **High-Yield Facts for NEET-PG:** * **Examples of Ribozymes:** Peptidyl transferase, RNase P (cleaves tRNA precursors), and SnRNAs (involved in splicing/spliceosomes). * **Mechanism:** Like protein enzymes, ribozymes lower activation energy through specific tertiary folding and metal ion stabilization. * **Nobel Prize:** Thomas Cech and Sidney Altman won the Nobel Prize in 1989 for the discovery of catalytic properties of RNA. * **Clinical Relevance:** Ribozymes are being researched as "molecular scissors" for gene therapy to target and destroy viral RNA (e.g., HIV) or oncogenic mRNA. [Practice more Biochemistry PYQs on OnCourse]

2 Previous Year Questions with Answers & Explanations

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All Subjects Biochemistry (2)Forensic Medicine (1)Obstetrics and Gynecology (2)Ophthalmology (1)Orthopaedics (1)Pediatrics (2)Pharmacology (2)Surgery (1)

Which of the following induces apoptosis in a cell?

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What is true about ribozymes?