Peroxisomes in the flesh... (9-21-16)

Question 1

Peroxisomes are found in what types of eukaryotic cells?

Answer 1

ALL OF THEM!!! It’s ubiquitous.

Question 2

In an electron micrograph, there will often be dark inclusion within a peroxisome. What are these?

Answer 2

These are aggregations of oxidative enzymes. In other words protein crystal structures within the peroxisomes.

Question 3

How many membranes do peroxisomes have?

Answer 3

One.

Question 4

How do peroxisomes receive their proteins?

Answer 4

From protein-gated channels. The proteins do not need to be unfolded to enter the membrane.

Question 5

What percentage of cell volume is taken up by peroxisomes?

Answer 5

Less then 1%

Question 6

What is the origin of peroxisomes?

Answer 6

It could be endosymbiotic but that is somewhat controversial.

Question 7

When did the great oxidation event occur? What caused it?

Answer 7

~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.

Question 8

What were the implications of the increase of oxygen in the atmosphere?

Answer 8

Made oxygen metabolism possible.

Allowed formation of the ozone layer (after ocean was oxygenated, and the rock).

Question 9

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?

Answer 9

600 mya

Question 10

What are the three major functions of the Peroxisome?

Answer 10

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.

Question 11

Where is D-amino acid oxidase found?

Answer 11

Within the peroxisome?

Question 12

What is the function of uric acid oxidase? What is the consequence of its absence in human cells?

Answer 12

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.

Question 13

Which two reaction does Catalase catalyze?

Answer 13

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

Question 14

Can catalase make H2O2.

By what process is it made?

Answer 14

No it is made by other enzymes.

Let R be a specific organic substrate.
RH2+O2 –> R + H202

Question 15

What are three major oxidoreductase enzymes of the peroxisome?

Answer 15

D-amino acid oxidase
Catalase
uric acid oxidase

Question 16

What is the end result of beta oxidation?

Answer 16

The formation of Acetyl-CoA from Fatty Acids.

Question 17

In what cells does beta oxidation occur exclusively in the peroxisomes?

Answer 17

Yeasts and plant cells.

Question 18

Why can disorders in the peroxisome lead to neurological disease?

Answer 18

The peroxisome produces plasmalogens. Which are ~90% of the phospholipids in the myelin nerve coat.

Question 19

Which phospholipid is Plasmalogen chemically similar too?

Answer 19

Phophatidylethanolamine.

Question 20

Why are peroxisomes located near mitochondria and chloroplasts.

Answer 20

In plants they consume O2 –> CO2

They also help convert fatty acids to sugars in seeds.

Question 21

What are peroxisomes called in seeds? What do they do?

Answer 21

Glyoxysomes. They convert fatty acids to sugars (gluconeogenesis) in seeds

Question 22

Where do peroxisomes come from?

Answer 22

Most are self replicating.

They can also bud off from the ER. These newly formed peroxisomes must import some molecules from the cytosol.

Question 23

Do peroxisomal proteins appear to use signal patches?

Answer 23

No.

Question 24

What is a translocation channel?

Answer 24

It is a channel which allows entry of proteins into the peroxisome. It allows folded proteins, which use peroxins to find target proteins.

Question 25

What is a peroxin?

Answer 25

One of the proteins which help carry proteins into peroxisomes. They are specific, and use a signal sequence.

Question 26

How many peroxins are there at least?

Answer 26

at least 32 exist.

Question 27

What are the two forms of Zellweger Syndrome?

Answer 27

Fatal Zellwinger syndrome:

Non-fatal Zellweger syndrome:

Question 28

What causes Fatal Zellwinger syndrome? What are its effects?

Answer 28

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)

Question 29

What causes Non-fatal Zellweger syndrome? What are its effects?

Answer 29

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.