Recombinant DNA Technology, Transgenic Crops, Gene Editing and PPV&FRA/IPR

विस्तृत व्याख्या:

Size of Human Proteome vs. Genome (मानव प्रोटिओम की विविधता):

• The human genome contains approximately 20,000 to 25,000 protein-coding genes, which is surprisingly comparable to much simpler organisms like C. elegans or Arabidopsis.
• However, the human proteome consists of several hundred thousand distinct proteins.
• The principal biological mechanisms responsible for this vast proteomic diversity are:

• Alternative Splicing (वैकल्पिक स्प्लिसिंग): A single pre-mRNA transcript can be spliced in multiple different ways by combining different exons, producing diverse mRNA transcripts and distinct polypeptide isoforms from a single gene.
• Post-Translational Modifications (PTMs): Phosphorylation, glycosylation, ubiquitination, and proteolytic cleavage further diversify functional proteins.
  • Therefore, an individual gene can encode many distinct polypeptides.

विस्तृत व्याख्या:

Polypeptide Combinations (पॉलीपेप्टाइड संयोजन गणित):

• There are 20 standard proteinogenic amino acids specified by the genetic code.
• At each position in a polypeptide chain of length $n$, any of the 20 amino acids can be incorporated.
• Therefore, for a peptide composed of $n$ amino acid residues, the total number of unique sequence combinations is:

• For a heptapeptide containing $n = 7$ amino acids:

Correct Answer: Option 3 ($20^7$).

विस्तृत व्याख्या:

Catabolite Repression of the Lac Operon (अपचयी दमन):

• In E. coli, when glucose is readily available in the medium, the cell prefers glucose as its carbon/energy source over lactose.
• High glucose levels inhibit adenylate cyclase, resulting in very low levels of cyclic AMP (cAMP).
• Without sufficient cAMP, the CAP (Catabolite Activator Protein) or CRP cannot bind cAMP to form the active cAMP-CAP transcriptional activator complex.
• As a consequence, RNA polymerase binds very weakly to the promoter, preventing high-level transcription of the lac genes even if lactose is present.
• This phenomenon is universally known as Catabolite Repression (the 'glucose effect').

Correct Answer: Option 2 (Catabolite repression).

विस्तृत व्याख्या:

Enzyme Induction (एंजाइम प्रेरण):

• Induction (प्रेरण) is the process by which gene expression is turned on or activated in response to an environmental signal or specific substrate (termed an inducer). For example, the addition of lactose or IPTG induces transcription of the lac operon enzymes.
• Repression (दमन) is the process where gene expression is turned off or silenced in response to a signal or co-repressor (e.g., tryptophan turning off the trp operon).
• Constitutive expression: Genes that are continuously transcribed at a constant rate regardless of environmental conditions (housekeeping genes).

Correct Answer: Option 2 (Induction).