8 public questions tagged with this topic.
The ntrosome, containing ntrioles, is responsible for organizing microtubules and forming spindle fibers during mitosis. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Cell Structure and Function, Cell Cycle and Biomolecules, Topic: Cell organelles and biomolecular structure.
The ntrosome, containing ntrioles, is involved in organizing spindle fibers during ll division in animal lls. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
Photorespiration involves three organelles: chloroplast, peroxisome, and mitochondrion. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
Secretory proteins undergo co-translational modification ensuring solubility, folding, and functional diversity needed for extracellular environment. N-glycosylation begins in rough ER lumen where oligosaccharyltransferase complex scans nascent polypeptide emerging from Sec61 translocon, transferring preassembled 14-sugar oligosaccharide Glc3Man9GlcNAc2 from dolichol phosphate lipid anchor to asparagine in consensus sequon Asn-X-Ser/Thr, followed by trimming by glucosidase I and II and binding to lectin chaperones calnexin-calreticulin that monitor folding, with UGGT reglucosylating misfolded species for another folding attempt. Correctly folded glycoproteins packaged into COPII vesicles transport to Golgi apparatus where sequential cisternae house mannosidases and glycosyltransferases mediating O-glycosylation initiation by GalNAc-T family adding N-acetylgalactosamine to serine/threonine, elongation, branching, sulfation, and terminal sialylation by ST6GAL1 generating complex glycans dictating serum half-life and receptor binding. Mitochondria produce ATP via electron transport chain, lysosomes degrade via cathepsins at low pH, peroxisomes handle oxidative reactions, but bulk glycosylation resides in ER-Golgi secretory pathway essential for antibody effector function and Notch signaling.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 12: Protein Glycosylation in ER and Golgi.
Ribosome biogenesis requires coordinated synthesis of forty seven S pre-ribosomal RNA containing eighteen S, five point eight S and twenty eight S sequences separated by internal transcribed spacers. This transcription occurs in nucleolus, a nonmembranous nuclear condensate nucleated by tandem repeats of ribosomal DNA located on nucleolar organizer regions of acrocentric chromosomes. RNA polymerase I machinery with upstream binding factor and selectivity factor SL1 concentrates in fibrillar centers, nascent transcripts enter dense fibrillar component where snoRNP-guided cleavages, two prime O methylation and pseudouridylation occur guided by fibrillarin and dyskerin. Granular component then assembles pre-forty S and pre-sixty S particles with imported ribosomal proteins. Pre subunits export via CRM1 for final maturation. Endoplasmic reticulum and Golgi modify secretory proteins, peroxisomes detoxify lipids, none produce rRNA. Actinomycin D at low doses selectively inhibits Pol I disrupting nucleoli, proving synthetic role. Consequently nucleolar hypertrophy correlates with growth rate and is upregulated in transformed cells requiring high protein synthesis.
Ref: Hernandez-Verdun Trends Cell Biol; nucleolus Pol I 47S pre-rRNA ribosome factory, phase separated.
Cristae identify X as a mitochondrion, while thylakoids and stroma identify Y as a chloroplast. Mitochondria perform aerobic respiration and generate ATP; chloroplasts trap light energy. Their circular DNA and 70S ribosomes support some protein synthesis within both organelles.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles
Lysosomes contain hydrolytic enzymes, while vacuoles contain water, sap, excretory products and other materials. Mitochondria possess inner-membrane cristae, whereas chloroplasts contain thylakoids arranged into grana.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles
Both mitochondria and chloroplasts contain circular DNA and 70S ribosomes, so those features alone do not distinguish them. Pigment-bearing thylakoids and enzymes for carbohydrate synthesis in the stroma identify the organelle as a chloroplast.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles
