Molecular Biology & Biotechnology

विस्तृत व्याख्या:

Bacterial Cell Envelope and Membrane Architecture (जीवाणु कोशिका झिल्ली संरचना):

• Statement (I) is CORRECT: The inner cytoplasmic membrane of all eubacteria is a symmetrical phospholipid bilayer (predominantly phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin) intercalated with proteins.
• Statement (II) is CORRECT: Gram-negative bacteria possess an asymmetric outer membrane: the inner leaflet is composed of standard phospholipids, whereas the outer leaflet is composed of complex lipopolysaccharides (LPS / endotoxin) consisting of Lipid A, core polysaccharide, and O-antigen side chains.

विस्तृत व्याख्या:

Microbiology of Yogurt Production (योगर्ट स्टार्टर कल्चर):

• Traditional commercial yogurt is produced by the synergistic proto-cooperative symbiotic activity of two specific thermophilic lactic acid bacteria:

• Streptococcus thermophilus (C)
• Lactobacillus delbrueckii subsp. bulgaricus (syn. Lactobacillus bulgaricus) (D)
  • S. thermophilus rapidly produces acid and lowers pH, stimulating L. bulgaricus, which produces acetaldehyde (providing characteristic yogurt aroma) and releases amino acids/peptides.

• Bacillus cereus is an opportunistic food poisoning pathogen and B. amyloliquefaciens produces industrial amylases; neither is a yogurt starter culture.

विस्तृत व्याख्या:

Tumor-Inducing (Ti) Plasmid (टीआई प्लास्मिड):

• The Ti (Tumor-inducing) plasmid is a large circular extrachromosomal plasmid found in the soil bacterium Agrobacterium tumefaciens.
• It is the etiological determinant of Crown gall disease (क्राउन गॉल रोग), an oncogenic plant disease affecting hundreds of dicotyledonous species.
• During infection, the T-DNA (transferred DNA) region of the Ti plasmid is stably transferred and integrated into the host plant nuclear genome, directing host cells to overproduce phytohormones (auxin and cytokinin) resulting in autonomous crown gall tumor proliferation.

Correct Answer: Option 1 (Crown gall).

विस्तृत व्याख्या:

Restriction Endonucleases and Recognition Sequences (प्रतिबंधन स्थल):

• Restriction endonucleases (molecular scissors) cleave double-stranded DNA at or near specific nucleotide sequences.
• The specific 4 to 8 base-pair DNA sequence recognized and bound by a restriction endonuclease is officially known as the Recognition sequence or Restriction site (पहचान अनुक्रम या प्रतिबंधन स्थल).
• In Type II restriction enzymes (such as EcoRI, recognizing $5'\text{-GAATTC-}3'$), these sites are typically palindromic sequences with two-fold rotational symmetry.

Correct Answer: Option 3 (Recognition sequence or restriction site).