Golgi Complex and Apparatus

Golgi Complex

• Secretory cells have Golgi complexes dispersed and well-developed throughout.
• Intestine cells have mucus-secreting cells, which create mucopolysaccharides.
• Pancreas cells have digestive enzymes secreting cells.
• The quantity of Golgi complexes varies based on function.
• Animal cells usually have 10 to 20 Golgi complexes per cell.

Golgi Apparatus Information

• Endoplasmic reticulum transfers lipids and proteins to the Golgi apparatus for modification.
• The Golgi apparatus is composed of flattened membranous sacs referred to as cisternae.
• Cisternae look like pita bread.
• The Golgi apparatus contains two distinct faces, or poles.
• The cis-face is the entry face.
• The trans-face is the exit face.
• The cis-face exists close to the ER, allowing proteins to enter the Golgi complex for processing.
• Proteins exit via the concave trans-face of the Golgi.
• The Golgi apparatus has a structural and functional directionality.
• The cis face receives vesicles containing ER products, meanwhile, the trans face dispatches vesicles.
• Golgi cisternae mature and move from the cis face to the trans face.

Golgi Apparatus Function

• The Golgi apparatus receives, sorts, ships, and processes molecules after transport vesicles deliver them from the ER.
• It acts as a warehouse for molecules.
• The Golgi apparatus sorts and packages molecules into transport vesicles.
• Some destination Examples are the plasma membrane, endosomes, lysosomes, and secretory granules.
• There are five functional regions found on the Golgi Complex, connected by the cis and trans faces.
• Those functional regions are the cis-Golgi network, cis-Golgi, medial-Golgi, trans-Golgi, and trans-Golgi network.
• Regions contain different enzymes that can modify proteins in their area.
• Enzymes that catalyze early processing steps are found in cisternae near the cis face.
• Enzymes that catalyze later processing steps are located toward the trans face.

Golgi Complex Functions

• Glycosylation of proteins aids protein folding and transports misfolded proteins to the cytosol for their degradation.
• It controls protein quality exiting the ER, protecting against protease digestion.
• Proteins gain functions in the Golgi via modification of oligosaccharides.
• It functions in the modification of carbohydrates and sorting of proteins.
• Proteolytic processing of protein precursors, glycolipid, and Sphingomyelin biosynthesis also take place.
• The Golgi apparatus has functions in lipid metabolism, specifically the synthesis of glycolipids and Sphingomyelin, which occurs in Golgi.
• Ceramide is synthesized in the ER, then Sphingomyelin, and glycolipids are formed from ceramide in Golgi.
• Sulfation catalyzes the transfer of a sulfo group with a sulfotransferase enzyme and occurs on proteoglycans.
• Sulfation strengthens protein-protein interactions, and types of human proteins undergo tyrosine sulfation.
• Adhesion molecules, G-protein-coupled receptors, coagulation factors, and extracellular matrix proteins/hormones are impacted.
• Sulfation supports animal growth through impacts on body weight and postnatal viability.
• The Golgi apparatus modifies, sorts, and packages macromolecules for secretion or use within the cell.
• As well as modifies proteins from the rough endoplasmic reticulum.
• It is involved in phospholipid and lipid transport.
• The synthesis of proteoglycans, the creation of lysosomes, and carbohydrate synthesis also happen.
• Protein maturation can also occur in the Golgi.

Lysosomes

• Lysosomes are principal sites of intracellular digestion and are membrane-enclosed organelles.
• They are filled with hydrolytic enzymes that control the digestion of macromolecules.
• Lysosomes contain about 50 different hydrolytic enzymes, called Lysosomal Acid Hydrolases.
• Lysosomal Acid Hydrolases consist of proteases, nucleases, glycosidases, Lipases, Phosphatases and Sulphatases
• Enzymes are effective at an acidic pH between 4.5 and 5, and are inactive in neutral pH of 7.2.
• Lysosomal enzymes include RNases, DNases, a/ß Galactosidases, Lysosyme, a glucuronidase, Hyaluronidases, Catepsin, Collagenases, Acid Phosphatases, Acid phosphodiesterases, and Aryl Sulphatases.
• Hydrolytic enzymes and lysosomal membranes are made by the rough ER and go to the Golgi apparatus for further processing.
• Lysosomes arise by budding from the trans face of the Golgi apparatus.
• They require H+ ions to maintain their acidic pH and use ATP hydrolysis energy to pump H+ ions.
• Acidic pH requirement protects against uncontrolled digestion of the cell.
• The lysosome membrane keeps digestive enzymes out of the cytosol, but enzymes would be inactive if they leaked into the 7.2 pH of the cytosol.
• Lysosomes are dense, rounded bodies from 0.5 - 1 µm in diameter.
• They vary in size and shape based on the material being digested.
• Lysosomes exist in all animal cells besides erythrocytes.
• Plant cells do not have lysosomes, but have vacuoles related to lysosomes that contain hydrolytic enzymes.
• Roughly 300 lysosomes are found in each cell.
• They are abundant in phagocytosis cells, such as macrophages and leucocytes.
• Vesicles containing lysosomal enzymes are primary lysosomes, which fuse with vesicles containing material to be digested and forming late endosomes.
• Primary lysosomes fuse with vesicles to form secondary lysosomes.
• There are three pathways that deliver materials to lysosomes: digestion of macromolecules taken up via endocytosis, digestion of material taken up by phagocytosis, and autophagy that digests the cell's components.
• Endocytosis degrades material from outside of the cell, which can be done through Pinocytosis and Phagocytosis.
• The nutrient of sugar/amino acids aids cell growth, while pathogens are engulfed by immune cells to be destroyed.
• Pinocytosis is cell-drinking.
• Phagocytosis is cell-eating.
• Old or damaged cells are removed to prevent harming the surrounding cells with endocytosis.
• During Phagocytosis, foreign material is engulfed to form a phagosome.
• The phagosome fuses with a primary lysosome and converts to a phagolysosome.
• The plasma membrane folds in, forming a pinocytic vesicle, that contains the molecules and extracellular fluid.
• The vesicle fuses with early endosomes, then the remaining digestion is released to the environment via exocytosis.
• Autophagy occurs when the cell degrades its components, and the steps are: formation of a crescent-shaped membrane, forming a double-membrane bounded compartment, fusion of the new compartment with lysosomes, and digestion of inner autophagosome membrane.

Peroxisome

• A peroxisome is a small vesicle-like organelle.
• It is surrounded by a single membrane and similar to lysosomes.
• Peroxisomal proteins are synthesized on free ribosomes and transported to peroxisomes.
• All eukaryotic cells include peroxisomes, with the exception of erythrocytes.
• There are roughly 500 peroxisomes per cell.
• They contain oxidative enzymes, such as Catalase, which converts H2O2 to H2O and oxydases.
• Peroxisomes detoxify toxic molecules like alcohol.

Mitochondria

• Mitochondria are among the largest organelles in eukaryotic cells and take up 25% of cytoplasm volume.
• An individual mitochondrion is the size of E. coli bacterium.
• Bacteria are believed to be the evolutionary precursors.
• All eukaryotic cells contain mitochondria that convert energy.
• ATP synthesis is the primary activity that happens there.
• Mitochondria convert food molecules' energy into ATP through cellular respiration.
• They can be examined in living cells using a phase-contrast microscope or under a light microscope with Janus green.
• Flourescein dyes by IHC can also be used to visualize.
• Mitochondria are usually oval, granular, spherical, or rod-shaped.
• The number and distribution varies across cell types.
• For example, a single liver cell can have 1500 to 2500 mitochondria, S cerevisia has 1000, and Chlorella fusca has 1.
• Mitochondria's localization varies, with cytoplasm being a place with high metabolic activity.
• Mitochondria are believed to have evolved from bacteria where they have a symbotic relationship with larger cells.

Nucleus

• Nearly all eukaryotic cells contain a nucleus, except mammalian erythrocytes/blood platelets .
• It contains the DNA.
• DNA replication, transcription, and RNA processing happen within, while translation happens in the cytoplasm.
• A nucleus consists of a nuclear envelope, chromatin, nucleolus, and nucleoplasm .
• The nucleus is surrounded by two parallel membranes, forming an inner and outer membrane separated by perinuclear space.
• Ribosomes attach to the outer membrane, surrounding the nuclear envelope and form the nuclear pores.
• Those pores provide communication between the nucleus and the cytoplasm.
• Nuclear lamina, a protein meshwork, gives support and regulates some cellular events like cell division and DNA replication.
• The nuclear envelope acts as a selective permeability barrier preventing passages between the nucleus and cytoplasm, but supports communication between the two.
• It maintains the nucleus as a separate biochemical compartment.
• The nuclear envelope regulates the transport of molecules into and out of the nucleus.
• A nucleolus is responsible for producing ribosomes, forming around the NOR region.
• Nucleolus consists of the DNA, RNA and proteins.
• It is responsible for rRNA transcription and processing like ribosome assembly and biogenesis.
• Nucleolus is well-developed in young cells, cells active in protein synthesis, and malignant tumors.
• Nuclear matrix is insoluble material left in the nucleus after series extraction procedures, such as treatment with DNase, RNase, and high salt buffers.
• The matrix contains proteins with some that bind specific DNA sequences, leaving a highly branched fiber network.