Peroxisomes Flashcards
Describe the structure of a peroxisome
Surrounded by a single membrane
No DNA or ribosomes
All proteins encoded by the nucleus
Contains oxidative enzymes
What is the equation for the peroxisomes enzyme and oxygen?
RH2+O2 -> H2O2
What is the hydrogen peroxide produced by the peroxisomes used for?
Catalases use H2O2 to oxidise
eg, in liver oxidises ethanol
breakdown fatty acid molecules
State the peroxidation reaction
H2O2 + R’H2 -> R’ + 2H2O
How to Peroxisome replicate?
can undergo fission to replicate
Describe the peroxisome biogenesis and maturation
Peroxisomal precursor vesicles from the ER and proteins are imported and recruit these peroxisomes
C-terminal Ser-Lys-Leu Signal sequence ‘addresses’ the peroxisome
Lysosomes contain how many soluble hydrolytic enzymes?
40 enzymes pH4-5
Name 5 of the enzymes in lysosomes
proteases nucleases Phospholipases Phosphatases Sulfatases
How is the the acid environment maintained in the lysosome?
A vascular H+ ATPase in the membrane that uses ATP hydrolysis for energy to pump the H+ into the lysosome
What are the 4 pathways to degradation
Endocytosis
Phagocytosis
Micropinocytosis
Autophagy
What is endocytosis?
Macromolecules taken up from extracellular fluid
What is Phagocytosis?
Engulfment of large particles to form phagosomes
What is Micropinocytosis?
Nonspecific uptake of fluids, membranes and particles attached to the membrane
What it is autophagy?
digestion of self contents
Describe the 5 stages of Autophagy
1) Protein Kinases activate and signal to autophagic machinery
2) Nucleation and extension of delimiting membrane into crescent shaped cup. Membrane vesicles with ATG9 are recruited to assembly site to nucleate autophagosome formation ATG9 is not in this autophagosome and removed
3) Close membrane to form sealed double membrane enclosed
4) Fusion of autophagosome with lysosome catalysed by SNARES
5) Digestion of the inner membrane and lumenal contents
Why does the lysosome not digest itself?
Its membrane is modified with highly glycosylated proteins. Digestion products are removed or recycled
Vascular H+ ATPase hydrolyses ATP and pumps protons into the lysosome
What are the endosomes role?
Endosomes sort and deliver the material to the lysosome and vacuoles.
How to endosomes mature?
Early endosomes mature to late endosomes via endosome maturation
What do we know about VAULT complexes?
Large ribonucleoprotein structure found in most eukaryotes
3x larger than a ribosome
Function suggested to be associated with NPC
What are the suggested function of the VALUT complexes
mRNA localisation
Drug resistance
Cell Signalling
Nuclear-cytoplasmic transport
What is a proteasome?
Central hollow cylinder comprising 4 stacked heptameric rings
Why are proteasomes important for?
Make correctly folded functional proteins
Role in rapid cell turnover of short lived proteins and proteins that need to be removed dependent on conditions
How much of the cell volume in plants and fungal cells is the vacuole?
30%
How are vacuoles related to lysosome?
They both contain hydrolytic enzymes
