lysosomes Digests Ingested materials Defective cell components Degrades macromolecules of all types: Proteins Nucleic acids Carbohydrates Lipids Single membrane bound vesicle, contains up to 50 digestive enzymes. Hydrolytic Enzymes are active at low ph 5. The enzymes are imported from the ER lumen via recognition of mannose - 6- P signal. This vesicle fuses with the various endosome vesicles, bringing substrates for hydrolysis. Lysosome Membrane: allows passage of uncharged molecules upon entry molecules are charged and cannot leave Budded off Golgi apparatus 1
Lysosomal enzymes 50 different hydrolytic enzymes Acid hydrolases Active at ph 5 (inside lysosome) Inactive if released into cytosol (ph 7.2) Acidic ph of lysosomes maintained by a proton pump in the lysosomal membrane Requires ATP, thus presence of mitochondria Lysosome Types 1. Primary Lysosome newly formed Contain only digestive enzymes without substrate. formed from budding Golgi apparatus. 2. Secondary Lysosome - the active form. - enzyme + substrate (Fused with food vacuole or organelle) 3. Residual bodies - storage of undigested materials 2
Primary Lysosome Buds from trans face of Golgi exogenous materials, deteriorating organelles Secondary Lysosome primary fuses with an endosome or phagosome Usually look more electron dense Primary, secondary lysosomes and Residual body Primary Secondary Residual body 3
Functions of lysosomal enzymes Digest food Destroy bacteria Recycle damaged organelles (autophagy) Waste storage (residual body) Function in embryonic development in animals (tissue remodeling) Metamorphosis ( loss of tail in tadpole) Wound healing Products delivered to lysosomes by four routes: Pinocytosis Cell drinking Receptor Mediated Endocytosis Specific materials imported into the cell. Phagocytosis Cell eating of material Autophagy self eat of old worn out organelles, Important in cell degradation during Apoptosis 4
Rough ER Transport vesicle (containing inactive hydrolytic enzymes) Plasma membrane Golgi apparatus Food Engulfment of particle LYSOSOMES Lysosome engulfing damaged organelle Food vacuole Digestion Autophagy 5
Macrophages consuming debris and invaders in connective tissue. Osteoclasts Break down bone Neutrophil Phagocytic cells First defenders in case of an infection 6
Lysosomes & cell death in normal development Programmed cell Death- Apoptosis take place during embryonic development and day to day basis. - example is digit formation. cells between digits die because of lysosomes Syndactyly Peroxisomes Similar structure to lysosomes Single membrane Degrades hydrogen peroxide (H 2 O 2 ) can be toxic to cells Using catalase to degrade hydrogen peroxide to water catalase converts H 2 O 2 -> H 2 O + O 2. In liver and kidney cells to deal with toxic molecules. Glyoxisomes are specialized peroxisome in fat storing seeds - these provide substrates for fat conversion into sugars and polysaccharides. 7
Liver cell and plant leaf cell peroxisomes. peroxisomes accumulate proteins from the cytoplasm and divide by fission. 8
Exogenous Heavy metals Lead and silver Endogenous Lipid droplets Glycogen Zymogen Mucigen Melanin Cellular inclusions Lipid droplets Found in adipose, hepatic cells, and steroid secreting cells. Important nutritional reserves Glycogen Storage form of carbohydrates in Liver, muscle, adrenal cortex Zymogen precursors of many enzymatic proteins Pancreas trypsinogen Chief cells of stomach pepsinogen 9
Mucigen Secreted by goblet cells Found in respiratory and gastrointestinal tract epithelial linings When mucigen released by exocytosis, mixes with water to form mucus Used for protection Melanin Gives color to skin and hair 10