28 public questions tagged with this topic.
The Golgi apparatus is involved in modifying, sorting, and packaging proteins, but it does not synthesize DNA. 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.
The sperm acrosome is a cap-like lysosome-related organelle containing hydrolytic enzymes like acrosin, hyaluronidase, and proteases for egg coat penetration. During spermiogenesis in round spermatids, Golgi stacks produce proacrosomal vesicles carrying mannose-6-phosphate-tagged enzymes that fuse and spread over the condensing nucleus, forming single acrosomal sac. Subsequent acrosomal maturation involves Golgi-dependent glycosylation and sorting of adhesion molecules such as bindin. Origin explains acidic interior, lysosomal enzyme content, and receptor-mediated sorting, distinguishing it fr
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Spermiogenesis - Golgi origin of acrosome and acrosomal enzymes.
Sperm acrosome is specialized cap-like secretory vesicle positioned anterior to nucleus, containing hydrolytic enzymes to penetrate egg coats during fertilization. Ultrastructural studies and pulse-chase labeling demonstrate it derives from Golgi apparatus during spermiogenesis stage of spermatid differentiation. Golgi complex packages enzymes like acrosin, hyaluronidase, and recognition protein bindin into proacrosomal granule which progressively coalesces and flattens over condensing nucleus. Lysosomal markers appear secondarily but origin is Golgi-mediated regulated secretory pathway, not e
Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 20: Spermiogenesis - Golgi origin of acrosome.
Sea urchin sperm head contains acrosomal vesicle originating from Golgi complex during spermiogenesis. This membrane-bound vesicle caps nucleus and stores enzymes like bindin localized on acrosomal process and acrosin protease. During acrosome reaction triggered by egg jelly fucose sulfate polymer and calcium influx, vesicle fuses with sperm plasma membrane, exposing bindin for egg binding and releasing lytic enzymes that digest jelly coat. Cortical granules are egg structures, micromeres and macromeres are embryonic blastomeres, not sperm organelles. Acrosomal vesicle thus mediates gamete int
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Sea urchin sperm acrosomal vesicle Golgi-derived enzymes.
Acrosome is large secretory vesicle capping anterior half of sperm nucleus, formed during spermiogenesis from Golgi apparatus of developing spermatid. Golgi cisternae generate proacrosomic vesicles containing hydrolytic enzymes that coalesce into single acroblast near nucleus then flatten over it, under manoeuvre of acroplaxome. Contents include acid hydrolases typical of lysosome-like organelle but origin is Golgi, not mitochondria, lysosomes or endoplasmic reticulum. Enzyme sorting involves mannose-6-phosphate-like pathways; disruption of Golgi trafficking proteins such as Pick1 results in g
Ref: Toshimori K, Reproductive Medicine and Biology: Golgi origin of acrosome and acrosome biogenesis in mammalian spermiogenesis.
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
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 12: Protein Glycosylation in ER and Golgi.
Teaching analogy depicts Golgi as postman because secretory pathway requires centralized sorting distribution center that receives products from ER, completes addressing via covalent modifications, then dispatches parcels to correct cellular addresses. Proteins exiting rough ER in COPII vesicles contain transient signals; upon arrival cis Golgi they undergo processing removing signal peptides, trimming N-glycans, adding terminal sugars that create affinity for lectins. Trans Golgi network acts as sorting station with lipid microdomains and adaptors selecting mannose-six-phosphate tagged lysoso
Ref: Farquhar Annu Rev Cell Biol; Golgi postman receives ER modifies sorts to PM lysosome secretion.
In animal cells Golgi modifies proteins, but plant cells possess additional requirement to produce noncellulosic cell wall polysaccharides that constitute matrix embedding cellulose microfibrils. Golgi stacks, often four hundred per cell moving along actin tracks, synthesize pectins homogalacturonan methylesterified in cis medial then de-esterified and calcium crosslinked in trans and at wall, rhamnogalacturonan I II highly branched, and hemicelluloses xyloglucan backbone synthesized by CSLC glucan synthases, xylan, arabinan, galactan sidechains added by glycosyltransferases GT47, GT8 families
Ref: Richmond Annu Rev Plant Biol; plant Golgi pectin hemicellulose synthases cell plate wall.
Protein glycosylation diversity arises from distinct enzyme locations. N-linked glycosylation defined by oligosaccharide attachment to asparagine within Asn-X-Ser/Thr consensus begins cotranslationally in ER where oligosaccharyltransferase transfers preassembled Glc3Man9GlcNAc2 from dolichol, then trimmed by glucosidases. Extension into complex types continues in Golgi but core attachment ER-specific. O-linked glycosylation where N-acetylgalactosamine alpha linked to serine threonine initiated by family of twenty polypeptide GalNAc transferases transferring GalNAc from UDP-GalNAc directly to p
Ref: Spiro Glycobiology; O-GalNAc transferase initiates O-glycosylation in Golgi, N-linked starts ER.
Golgi polarity defined by cis entry face adjacent to ER exit sites and trans exit face oriented toward plasma membrane. Newly synthesized cargo packaged into COPII coated vesicles decorated with Sec23/24 cargo selection and Sar1 GTPase buds from ER after BiP quality control, fuses via TRAPP tethering to ER-Golgi intermediate compartment then to cis Golgi network marked by Rab1 and cis golgin GM130 and GRASP65. Here resident enzymes mannosidase I and N-acetylglucosamine transferase I begin processing, and retrieval of ER proteins via KDEL receptor and COPI retrograde occurs. Medial cisternae co
Ref: Lippincott-S Cell Bio; COPII ER exit to cis Golgi CGN receives cargo, Rab1, VSV-G trafficking.
Lysosomal enzymes traverse secretory pathway originating from rough ER translocation, folding and initial N-glycosylation, then Golgi where specific modification marks them for diversion from default secretion. Cis-Golgi N-acetylglucosamine phosphotransferase recognizes lysine-containing conformational patch present only on soluble hydrolases, transferring GlcNAc-one-phosphate onto terminal mannose residues of high mannose oligosaccharides, forming phosphodiester. Uncovering enzyme in trans-Golgi removes GlcNAc leaving mannose-six-phosphate monoester. Trans-Golgi network clathrin adaptors AP1
Ref: Kornfeld Annu Rev Biochem; Golgi M6P pathway GlcNAc phosphotransferase tags lysosomal hydrolases.
Golgi apparatus comprises four to eight flattened cisternae forming cis entry, medial processing and trans exit network with distinct enzyme gradients maintaining glycosylation sequence. Cargo arriving via COPII vesicles from ER undergoes mannose trimming by mannosidase I in cis, addition of N-acetylglucosamine by GlcNAc transferase I and II in medial, galactose and sialic acid in trans, creating complex glycans affecting half-life and receptor binding. Phosphorylation of mannose residues marks lysosomal enzymes, sulfation of proteoglycans occurs. Trans-Golgi network functions as major sorting
Ref: Rothman Cell 1994; Golgi cisternae glycosylation phosphorylation sorting TGN clathrin AP1 GGA.
