Lysosoms, Mitochondria, Peroxisomes Flashcards
What is an endomembrane system?
Lysosomes, Endosomes, Golgi Network and ER
What is the function of an endosome?
Sorts ingested molecules and recycles them into plasma membranes
What do peroxisomes do?
Involved in oxidative reactions by breaking down lipids and destroying toxic molecules
What is structure of the lysosome?
Single membrane Acid interior pH 4-5 Heterogenous contents = contents varies depending on the lysosome Membrane contains a thick layer of polysaccharides and transmembrane proteins to prevent from being broken down by hydrolytic 40 enzymes - proteases -lipases -nucleases -phosphatases -glycosidases
What is the pH inside a lysosome?
pH of 4-5
What are the different ways in which a substrate is delivered to a lysosome?
(Extracellular)
Extracellular substrates will be delivered by receptor mediated endocytosis.
They will form an early and then late endosome. The pH will drop and they will form a lysosome
How is a intracellular substrate delivered to the lysosome?
Autophagy = the cell will ingest its own contents
Microautophagy - the substrate will be taken up by the invagination of the lysosomal membrane
Macroautophagy - the organelle or cytosol will be wrapped by the ER membrane which will
fuse with the lysosome and the contents will become degraded.
What is the general mechanism of receptor mediated endocytosis?
Molecule will bind to complementary cell surface receptors on the membrane. The cell membrane will invaginate and enter the cell as a receptor macromolecule complex in a clarthin coated vesicle.
What is a specific example of receptor mediated endocytosis?
Animal cells will take up cholesterol to make new membranes.
Cholesteryl containing LDL will bind to the LDL receptors on the surface. This causes it to become ingested and forms an endosome. The receptor will aggregate in coated pits and will dissociate and become recycled once the pH drops.
The drop in pH will result in the endosome forming a lysosome
What are the steps in phagocytosis?
Engulfment
Lysosome fusion
Digestion
How are lysosomal membranes targeted to lysosomes.
Lysosomal hydrolases are synthesised on a ribosome on the ER.
In the ER a complex sugar structure is added onto the NH2 side chain of asparagine amino acid using the enzyme oligosaccharide transferase.
In the Golgi they will receive an mannose-6-phosphate marker using the enzyme GlcNAc-phosphotransferase. This is added onto the N-linked oligosaccharide marker.
The M6P marker is recognised by receptor proteins in the trans Golgi network.
Vesicle will bud from the trans Golgi and form an endosome as the pH drops
The pH will further drop and the lysosomal hydrolase will be transferred to the lysosome
What are examples of mutations in GlcNAc-phosphotransferase
Enzyme is encoded by GNPTG, NAPGA and GNPTG if there are mutations it can result in certain disease
GNPTAB = I cell disease, Mucolipidosis Type II
GNPTG= Pseudo-Hurler Dystrophy, Mucolipidosis Type III
GNPTAB, GNPTG, NAPGA = cause persistent stuttering
What is I cell disease
Mutation in UDP-N-acetylglucosamine (GlcNac-phospotransferase) will result in the M6P marker to not be transferred to the N-linked oligosaccharide marker therefore the lysosomal hydrolase will not be transported to the lysosome which can result in substrate accumulation.
What type of disorder is I cell disease?
Autosomal recessive
How can you see that someone has I cell diseqase
Substrate accumulation in the lysosome = results in a dense granular image of lysosomes
