Peroxisomes in the flesh... (9-21-16) Flashcards
Peroxisomes are found in what types of eukaryotic cells?
ALL OF THEM!!! It’s ubiquitous.
In an electron micrograph, there will often be dark inclusion within a peroxisome. What are these?
These are aggregations of oxidative enzymes. In other words protein crystal structures within the peroxisomes.
How many membranes do peroxisomes have?
One.
How do peroxisomes receive their proteins?
From protein-gated channels. The proteins do not need to be unfolded to enter the membrane.
What percentage of cell volume is taken up by peroxisomes?
Less then 1%
What is the origin of peroxisomes?
It could be endosymbiotic but that is somewhat controversial.
When did the great oxidation event occur? What caused it?
~2.3 bya (billion years ago). It was caused by cyanobacteria production of O2. Which up to this point was absent. It is the arrival of oxygen in the atmosphere which mandated the use of peroxisomes in cells.
What were the implications of the increase of oxygen in the atmosphere?
Made oxygen metabolism possible.
Allowed formation of the ozone layer (after ocean was oxygenated, and the rock).
What time period did the oxygen build up in the atmosphere sufficiently to allow life on land life? When did the ozone layer become sufficient to shelter land life?
600 mya
What are the three major functions of the Peroxisome?
1, Rid the cell of toxic substances, like H202 or ethanol
2, perform beta oxidation of fatty acids
3, peroxisomes make plasmalogens, which are ~90% of the phospholipids in myelin.
Where is D-amino acid oxidase found?
Within the peroxisome?
What is the function of uric acid oxidase? What is the consequence of its absence in human cells?
Normally found in the peroxisome, it breaks down uric acid, gout is a result of humans and primates lack of the uric acid oxidase enzyme.
Which two reaction does Catalase catalyze?
Use of H2O2, to break down other toxic substances like ethanol and phenols.
H2O2 + R’H2 –> R’ + 2H2O
It can also break down H2O2 by itself using the following reaction.
2H202 –> 2H2O + O2
Can catalase make H2O2.
By what process is it made?
No it is made by other enzymes.
Let R be a specific organic substrate.
RH2+O2 –> R + H202
What are three major oxidoreductase enzymes of the peroxisome?
D-amino acid oxidase
Catalase
uric acid oxidase
What is the end result of beta oxidation?
The formation of Acetyl-CoA from Fatty Acids.
In what cells does beta oxidation occur exclusively in the peroxisomes?
Yeasts and plant cells.
Why can disorders in the peroxisome lead to neurological disease?
The peroxisome produces plasmalogens. Which are ~90% of the phospholipids in the myelin nerve coat.
Which phospholipid is Plasmalogen chemically similar too?
Phophatidylethanolamine.
Why are peroxisomes located near mitochondria and chloroplasts.
In plants they consume O2 –> CO2
They also help convert fatty acids to sugars in seeds.
What are peroxisomes called in seeds? What do they do?
Glyoxysomes. They convert fatty acids to sugars (gluconeogenesis) in seeds
Where do peroxisomes come from?
Most are self replicating.
They can also bud off from the ER. These newly formed peroxisomes must import some molecules from the cytosol.
Do peroxisomal proteins appear to use signal patches?
No.
What is a translocation channel?
It is a channel which allows entry of proteins into the peroxisome. It allows folded proteins, which use peroxins to find target proteins.
What is a peroxin?
One of the proteins which help carry proteins into peroxisomes. They are specific, and use a signal sequence.
How many peroxins are there at least?
at least 32 exist.
What are the two forms of Zellweger Syndrome?
Fatal Zellwinger syndrome:
Non-fatal Zellweger syndrome:
What causes Fatal Zellwinger syndrome? What are its effects?
A mutation in an integral membrane peroxin. Virtually no proteins can enter the peroxisome. Victims die soon after birth. (severe abnormality in brain, liver, and kidney)
What causes Non-fatal Zellweger syndrome? What are its effects?
A mutation in the receptor which recognizes C terminus signal sequence. The peroxisome can still take in proteins with an amino terminus recognition site so it is not lethal.
