Lysosomes Flashcards
What is the key function of lysosomes?
To carry out digestive, hydrolytic reactions
Give some examples of enzymes found in lysosomes and what molecule they break down
Proteases (proteins) Lipase (lipids) Glycosidases (carbohydrates) Nucleases (nucleic acids) Phosphatases (phosphates) Sulfatases ( sulfates)
What are the conditions like inside the lysosome?
Acidic (pH4-5)
What does heterogenous contents mean?
Lots of different molecules inside
Give examples of membrane proteins found in lysosome membranes
V-ATPase Ion channels Cholesterol transporters Sugar transporters Nucleoside transporters Amino acid transporters
Give examples of molecules found on the lysosome membrane
Small GTPases
Tethering factors
SNAREs
What is a SNARE responsible for?
The final fusion process in the residue targeting process
What does V-ATPase do?
Pumps proteins into the lysosome (to make it acidic)
How do lysosomes move around the cell and what must the have to facilitate this?
Microtubules so must contain motor signals to attach to the micro tubules
Also signalling complexes ( involved in immune response and metabolic signalling)
Where are transcription factors regulated?
On the surface of lysosomes
What cell contains melanosomes and what is the clinical feature when defective?
Melanocyte- ocular and Cutaneous hyperpigmentation
Give the features of melanosomes
- Very high conc of melanin
- Formed in a four-step process
Once formed where are melanosomes transported to?
Keratinocytes
How are extracellular substrates delivered to the lysosome?
Endocytosis
Fluid phase endocytosis of molecules and lipoproteins (inducts receptor- mediated endocytosis)
- phagocytosis of small particles (> 50 micrometers)
How are intracellular substrates moved around the lysosome?
Microautophagy
invagination
Macroautophagy
Selective protein transport
What does microautophagy mean?
Self eating
What does invagination mean?
Where budding takes place into the lysosomes
How does macroautophagy work?
Cytosol or organelles wrapped in the ER membrane which then fuses with the lysosomal membrane
What group of molecules takes part in receptor-mediated endocytosis?
Low-density lipoproteins
Give the steps of phagocytosis
1- particle binds to the cell surface
2- particle is engulfed (plasma membrane wraps itself around the particle - forms a phagosome)
3-lysosome fuses with the phagosome (phagolysosome)
4-digestion
What gets broken down in phagocytosis?
- Bacteria
- dead cells
- ageing blood cells (B-cells, RBCs)
Are macrophages able to pick up particles bigger than themselves?
Yes
Give the specialist names for the autophagy of mitochondria
Mitophagy
Give the specialist names for the autophagy of peroxisomes
Pexophagy
Give the specialist names for the autophagy of ribosomes
Ribophagy
Give the specialist names for the autophagy of lipid droplets
Lipophagy
Give the specialist names for the autophagy of chloroplasts
Chlorophagy
Give the specialist names for the autophagy of infectious particles
Xenophagy
How does HIV deliver its virus?
Binds directly with the cell membrane
How does influenza deliver its virus
Taken up by endocytosis and the drop in pH means that the endosomal and viral membranes break, releasing the viral contents
How does polio and adenovirus deliver its virus?
Endocytosis
What are the steps in the secretory pathway?
- the mannose sugar is added in the Golgi body
- the sugar is recognised by the MGP receptor
- the receptor/sugar complex forms a clathrin-coated pit (and consequently a Clathrin coated vesicle)
- this vesicle then carries the complex into the lysosome
What causes most lysosomal storage disorders?
The lack of an enzyme in the lysosome which leads to the accumulation of a substrate
What can mutations in lysosomal hydrolayses cause?
Substrate accumulation
What does I cell disease mean?
No lysosomes are made so nothing can be digested
What are the symptoms of I cell disease?
Skeletal abnormalities
Developmental delay
Enlarged liver and spleen
What causes death (usually) from I cell disease?
Pneumonia or congestive heart failure
What is I cell disease caused by?
A deficiency of UDP-N (acetylglucosamine)
What does mutations in the M6P tag in the golgi cause?
Persistant stuttering
