2. • Golgi complex functions as factory to receive proteins from ER and further
processed and sorted to different locations within cell.
• Most of the glycolipids and sphingomyelin are synthesised.
• Involved in processing the broad range of cellular constituents that travel
along secretory pathway.
3. • Golgi is composed of flattened
membrane-enclosed sacs called
as cisternae and linked vesicles.
• Proteins from ER enter through the
cis face oriented towards nucleus
and exist from trans face after
several modifications and sorting.
• Golgi have four functionally distinct
regions: cis, medial, trans
compartments and trans-golgi
4. Protein processing within Golgi is an extensive modification involving
around 250 enzymes catalysing different sugars to glycoproteins.
Glycoproteins are modified in different ways depending on structure
of protein and type of enzyme processing it during the passage in
the golgi complex.
Proteins destined for lysosomes are modified by addition of
phosphate groups to number 6 position of mannose residue.
Proteins are also modified in golgi by addition of carbohydrates to
the side chain of serine and threonone residues.
5. • Sphingomyelin(non-glycerol phospholipid in cell membrane) is synthesised on
lumenal surface of Golgi by transfer of phosphorylcholine group from
phophatidylchoine to ceramide.
• Alternatively addition of carbohydrates to ceramide yield variety of glycolipids.
• Oligosaccharide portions of glycoproteins are important surface markers in
6. Proteins, lipids and polysaccharides are
transported through secretory pathway
by different kind of transport vesicles;
which bud off from trans-Golgi network
and deliver them to appropriate cellular
Proteins carried from Golgi to plasma
membrane; either directly or via
Protein within Golgi mostly reside as
transmembrane protein and function in
7. • Plasma membrane of epithelial is polarized. Plasma
membrane of such cells is divided into two separate
regions which contain specific proteins related to their
i) apical domain- lumen of intestine specialized for efficient
ii) basolateral domain- lies just above the basal lamina
Protein transport to such cells take place by packaging of
proteins into transport vesicle targeted for different domains
leaving through trans-Golgi network or in. recycling
- If receptor is mannose-6-phosphate which is derived from
N-linked oligosaccharide will move protein to late
endosome which mature into lysosomes.
- NPXY-signal carry protein to plasma membrane
- Protein with C-terminal KDEL signal carry protein to ER
8. • Membrane proteins and lumenal secretory
proteins with their receptors are collected
into selected regions of donor membrane
where the formation of a cytosolic coat
result in budding of transport vesicle.
• Vesicle is transported by motor proteins
along cytoskeletal filaments to its target .
• Transport vesicle then settle at its target
membrane, the coat is removed and
vesicle fuses with target.
• Three families of protein coat: Clathrin,
COPI and COPII-coated vesicles.
9. • Transport vesicle must recognize the correct target membrane.
• Example- vesicle having lysosomal enzyme must be delivered to
• vesicle and target membrane must fuse.
• Vesicle fusion is two step process:-
i) interaction between vesicle and target membrane is mediated by
tethering factors and small-GTP binding proteins (Rab proteins).
• 60 different types of proteins have been identified.
ii)Tethering is followed by formation of complexes called SNAREs
which provide energy to drive fusion of phospholipid bilayers bringing
two membrane in direct contact of lipid bilayers.
Notas del editor
Golgi also synthesize hemicellulose and pectin by plasma membrane bound enzyme.
-Synthesis of sphingomyelin and glycolipids Ceramide, which is synthesized in the ER, is converted either to sphingomyelin (a phospholipid) or to glycolipids in the Golgi apparatus. In the first reaction, a phosphorylcholine group is transferred from phosphatidylcholine to ceramide. Alternatively, a variety of different glycolipids can be synthesized by the addition of one or more sugar residues (e.g., glucose).
-In plant cells, the Golgi apparatus has the additional task of serving as the site where complex polysaccharides of the cell wall are synthesized
-Some cells also possess a distinct regulated secretory pathway in which specific proteins are secreted in response to environmental signals. Examples of regulated secretion include the release of hormones from endocrine cells and the release of digestive enzymes from the pancreas.
-Proteins are sorted in the trans-Golgi network and transported in vesicles to their final destinations. Proteins can be transported to the plasma membrane either directly or via recycling endosomes. In addition, proteins can be sorted into distinct secretory granules for regulated secretion. Alternatively, proteins can be targeted to late endosomes, which develop into lysosomes.
-Some cells also possess a distinct regulated secretory pathway in which specific proteins are secreted in response to environmental signals. Examples of regulated secretion include the release of hormones from endocrine cells and the release of digestive enzymes from the pancreas
-The plasma membranes of polarized epithelial cells are divided into apical and basolateral domains. In this example (intestinal epithelium), the apical surface of the cell faces the lumen of the intestine, the lateral surfaces are in contact with neighbouring cells, and the basal surface rests on a sheet of extracellular matrix (the basal lamina). The apical membrane is characterized by the presence of microvilli, which facilitate the absorption of nutrients by increasing surface area. Specific proteins are targeted to the apical or basolateral membranes either in the trans-Golgi network or in a recycling endosome. Tight junctions between neighbouring cells maintain the identity of the apical and basolateral membranes by preventing the diffusion of proteins between these domains.
Trans Golgi network involved in protein sorting in presence of receptors .
If receptor is mannose-6-phosphate which is derived from N-linked oligosaccharide will move protein to late endosome which mature into lysosomes.
NPXY-signal to plasma membrane
Protein with C-terminal KDEL signal protein to ER
-the coat proteins drives the budding of vesicles containing selected cargo proteins from the donor membrane
-COPII-coated vesicles –carry protein –ER-ERGIC(ER Golgi Intermediate Compartment) and on to the Golgi surface.
COPI-coated vesicle- retrieve ER-resident proteins from the ERGIC and cis Golgi and carry Golgi-resident enzymes back from the trans Golgi to earlier Golgi cisternae.
Clathrin-coated vesicles carry cargo outward from the trans-Golgi network and also carry cargo back from the plasma membrane to endosomes and other organelles such as the trans-Golgi network and lysosomes
Vesicle docking and fusion A Rab protein on the vesicle mem- brane binds to a tethering factor associated with the target membrane. This is followed by the formation of complexes between SNAREs on the vesicle and target membranes. The coiled-coil domains of the SNAREs zip together, bringing the vesicle and target membranes into close proximity, and the membranes fuse.