Peroxisomes

Question 1

what type of transport do peroxisomes use?

Answer 1

transmembrane transport

Question 2

what are peroxisomes? what do they do and who discovered them?

Answer 2

peroxisomes are small ubiquitous organelles that are responsible for hydrogen peroxide (along with other toxic substances) break down and creation. First discovered by Christian de Duve (first seen by Johannes Rhodin)

Question 3

what are cyanobacteria?

Answer 3

cyanobacteria are algae that began to perform reactions that increased O2 in the atmosphere (photosynthesis). Basically we think the ozone layer was created by cyanobacteria and the ozone is what allowed organisms to live on land

Question 4

what is a possible explanation of peroxisome evolution?

Answer 4

peroxisomes may have originally evolved to reduce intracellular O2 levels by exploiting oxygen’s chemical reactivity to oxidize other molecules

Question 5

major functions of peroxisomes

Answer 5

1. Rid the cell of toxic substances like ethanol and hydrogen peroxide via soluble oxidative enzymes.
2. perform beta oxidation of fatty acids, involved in cellular metabolism.
3. perform first reactions that yield plasmalogens

Question 6

what are some examples of soluble oxidative enzymes in the peroxisome?

Answer 6

1. D-amino acid oxidase
2. Uric acid oxidase (not in humans/primates)
3. Catalase: important especially because it uses H2O2 generated by other enzymes to oxidize toxins, therefore reducing H2O2 concentrations.

Question 7

How are peroxisomes involved in cellular metabolism?

Answer 7

Peroxisomes perform beta oxidation of fatty acids. a product of this is Acetyl-CoA which conveys carbon atoms to the Citric Acid cycle for energy production. beta oxidation also occurs in animal cell mitochondria.

Question 8

what are glyoxysomes?

Answer 8

peroxisomes in plant seeds

Question 9

what are plasmalogens?

Answer 9

the most abundant class of phospholipids in the PM of glial cells that form myelin. important for myelin sheaths of neurons. structure similar to phosphatidylethanolamine

Question 10

How are peroxisomes made?

Answer 10

1. peroxisomes can self replicate by enlarging and then dividing
2. pre-peroxisomes are formed by fusion of vesicles that bud from mitochondria and ER. these must contain peroxins before they can import key membrane import proteins and enzymes (like catalase)

Question 11

what is a key difference between transmembrane transport of peroxisomes vs other organelles?

Answer 11

proteins fold before they are imported into peroxisomes.

Question 12

describe the process of protein import into peroxisomes

Answer 12

PTS1 and PTS2 (peroxisomal targeting sequences) have many different PEX proteins that carry them to the membrane. PTS1 requires ATP hydrolysis and PEX5 is exported to the cytosol for reuse with help of other PEX proteins

Question 13

what is Zellweger syndrome?

Answer 13

it’s caused by mutations in proteins that mediate protein import into peroxisomes.
Fatal: Pex2 mutation, no protein import occurs, peroxisomes are empty
Non-fatal: mutation in receptor that recognizes PTS1, so PTS2 still works and proteins can be imported, peroxisomes are partially functional.