| What are Lysosomes? | Small organelles bounded by a single bilayer of lipids and rich in enzymes. Actively involved in metabolic activity such as intracellular digestion and storing of substances. They occur in animal cells, whereas plants have vacuoles that have a similar function and properties in addition to osmotic pressure regulating role. But not found in bacteria except cyano. Bacteria have instead of lysosomes a variety of Hydrolases in space between cell wall and membrane called pericytoplasmic spaceor peiplasmic. |
| What do lysosomes contain? And what is their role? | About 50 different types of enzymes in their lumen and membrane. And they are able to virtually hydrolyze every type of macromolecules and have a role in defense and cell nutrition and renewal of membranes and organelles. |
| What is another name of lysosomes? | Acid Hydrolases since their hydrolyzing activity is acid dependent (acidic pH) containing an ATP controlled proton pump so that intralysosomal pH is 4.6-5. Which serves in protection so that lysosomal enzymes only active in lysosome and not cytoplasm and membrane is protected from getting digested by enclosed enzymes in high glycosylation state. |
| Talk about the digestive role of lysosomes. | They find their substrates in endosome and phagosomes (autophagic and heterophagic) and digest them into low weight molecules that may be transported for cell metabolism. Permeases accept certain substrates into lumen for digestion. For some digestion may be incomplete which leads to producing wastes that will be exocytosis. |
| Talk about the general structure of lysosomes. | Heterogenous group that have variable sizes and shapes comparable size to mitochondria (50nm- 1 microm diameter) and bounded by single membrane similar to other cell membranes and divided into three main structures:
Primary
Secondary
Residual bodies. |
| Talk about primary lysosomes. | AKA protolysosomes. Newly derived organelles from TGN, small vesicles delimited by membrane and contains digestive enzymes which have not hydrolyzed anything yet.
These enzymes were synthesized by attached ribosomes and matured in RER and Golgi where they are sorted and packed into a coat with a specific address code or signal, destined to form primary lysosome after removal of coat. |
| Talk about secondary lysosomes. | Result from fusion of one or more primary lysosomes with vesicles containing material to be hydrolyzed. These substances may derive from the cell or from the outside. Particles captured by phagocytosis are enclosed in heterophagic vacuoles or heterophagosomes, which fuse with primary lysosomes and form heterolysosmes or heterophagolysosomes. where digestion takes place.
Autophagic vacuoles result from enveloping of an organelle to be destroyed by an ER fragment that fuses with primary lysosomes forming autophagolysosomes. |
| Talk about the importance of Autodigestion. | Plays a key role in organelles turnover (destruction and replacement), it is a common event in cell repair, tissue repair growth differentiation and metamorphosis of larva of insects and reduction of uterus size after delivery. It is also found when nutrients are scarce. |
| Are lysosome types distinguished after a while of digestion? | No, so they are called digestive vacuoles or secondary lysosomes and substances may be recycled totally or partially and transported out of the lysosomal lumen to cytosol. |
| Talk about residual bodies. | AKA lipofuscin pigment granules, larger than primary lysosomes and irregular in shape, derive from secondary lysosomes after the end of digestion, because digestion is incomplete, they produce wastes enclosed by a membrane making the residual body, which are expelled outside through exocytosis. But some residues are expelled into cytosol in long living cells, those kept are called lipofuscin granules composed of lipid (yellow brownish) which disturbs the cell metabolic activity and causes aging. |
| Talk about the origin of lysosomes. | Enzymes are distinguished in trans cisternae by phosphorelated mannose and eventually separated from TGN. |
| Talk about plant vacuoles. | Lysosomes are absent in plants since no endocytosis or phagocytosis are possible in cell wall, but vacuoles are present.
Formed from many small vacuoles (meristems) that fuse together, bounded by a membrane called tonoplast with many transport enzymes, which makes ion concentration in vacuole higher than that of cytosol, and it is hypertonic (accepts water by osmosis and turgor pressure providing support to unwoody plant tissues, and helps in stretching and growth pH is acidic. |
| Talk about vacuole functions. | variety of functions: storage of molecules in lumen, storage for toxic compounds necessary for defense against pest, site for undesired molecules and pollutants since they lack a excretion system, for then leaves fall getting rid of undesired molecules, Intracellular digestion may occur. |
