Biology GOLGI APPARATUS, LYSOSOMES AND VACUOLES

KEY TOPICS

`star` Golgi Apparatus
`star` Lysosomes
`star` Vacuoles

GOLGI APPARATUS

● `color{brown}("Camillo Golgi (1898)")` first observed densely stained reticular structures near the `color{violet}("nucleus.")`

● These were later named `color{brown}("Golgi bodies")` after him.

● They consist of many `color{violet}("flat, disc-shaped sacs or cisternae")` of 0.5 µm to 1.0 µm diameter.

● These are `color{violet}("stacked parallel")` to each other.

● Varied number of `color{brown}("cisternae")` are present in a `color{violet}("Golgi complex.")`

● The `color{violet}("Golgi cisternae")` are concentrically arranged near the `color{violet}("nucleus")` with distinct `color{brown}("convex 𝘤𝘪𝘴")` or the `color{brown}("forming face")` and `color{brown}("concave 𝘵𝘳𝘢𝘯𝘴")` or the `color{brown}("maturing face.")`

● The `color{violet}("cis")` and the `color{violet}("𝘵𝘳𝘢𝘯𝘴 faces")` of the organelle are entirely different, but interconnected.

● The `color{violet}("golgi")` apparatus principally performs the function of `color{brown}("packaging materials")`, to be delivered either to the intra-cellular targets or secreted outside the cell.

● Materials to be packaged in the form of vesicles from the ER fuse with the `color{violet}("cis")` face of the `color{violet}("golgi")` apparatus and move towards the `color{violet}("maturing face.")`

● This explains, why the `color{violet}("golgi")` apparatus remains in close association with the `color{violet}("endoplasmic reticulum.")`

● A number of proteins synthesised by `color{violet}("ribosomes")` on the `color{violet}("endoplasmic reticulum")` are modified in the `color{violet}("cisternae")` of the `color{violet}("golgi")` apparatus before they are released from its `color{violet}("𝘵𝘳𝘢𝘯𝘴 face.")`

● `color{violet}("Golgi")` apparatus is the important site of formation of `color{brown}("glycoproteins and glycolipids.")`

LYSOSOMES

● These are `color{violet}("membrane bound vesicular structures")` formed by the process of packaging in the `color{violet}("golgi")` apparatus.

● The `color{violet}("isolated lysosomal vesicles")` have been found to be very rich in almost all types of `color{brown}("hydrolytic enzymes")` (hydrolases – lipases, proteases, carbohydrases) optimally active at the `color{brown}("acidic pH.")`

● These `color{violet}("enzymes")` are capable of digesting carbohydrates, proteins, lipids and nucleic acids.

VACUOLES

● The vacuole is the `color{violet}("membrane-bound space")` found in the `color{violet}("cytoplasm.")`

● It contains water, sap, excretory product and other materials not useful for the cell.

● The vacuole is bound by a `color{violet}("single membrane")` called `color{brown}("tonoplast.")`

● In `color{violet}("plant cells")` the vacuoles can occupy up to `color{brown}("90 %)` of the volume of the cell.

● In `color{violet}("plants,")` the tonoplast facilitates the transport of a number of ions and other materials `color{brown}("against concentration gradients")` into the vacuole, hence their concentration is significantly higher in the vacuole than in the `color{violet}("cytoplasm.")`

● In `color{violet}("𝘈𝘮𝘰𝘦𝘣𝘢")` the `color{brown}("contractile vacuole")` is important for excretion.

● In many cells, as in protists, `color{brown}("food vacuoles")` are formed by `color{violet}("engulfing the food particles.")`

 
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