13.3 Peroxisomes

Question 1

() are single-membrane organelles containing enzymes involved in many metabolic reactions

Answer 1

peroxisomes

Question 2

what are the functions of peroxisomes

Answer 2

1. oxidation of fatty acids
2. lipid synthesis (in animal cells)
3. carbohydrate synthesis

Question 3

oxidative reactions in peroxisomes lead to the production of ()

Answer 3

hydrogen peroxide

Question 4

oxidative reactions in peroxisome are efficient and effective due to the presence of (), which is an enzyme that converts hydrogen peroxide to water or uses it to oxidize another organic compound

Answer 4

catalase

Question 5

in animal cells, fatty acids are oxidized both in peroxisomes and mitochondria; but in yeast and plant cells, this only occurs in ()

Answer 5

peroxisomes

Question 6

what are the lipids synthesized in peroxisomes

Answer 6

1. cholesterol
2. dolichol

Question 7

() are a family of phospholipids synthesized in peroxisomes that are important membrane components in tissues like the heart and brain; one of the hydrocarbon chains is joined to glycerol by an ether bond

Answer 7

plasmalogens

Question 8

peroxisomes in seeds are responsible for the conversion of (), this aids in growth of plant tissue from seeds

Answer 8

stored fatty acids to carbohydrates

Question 9

peroxisomes in leaves function in coordination with chloroplasts to metabolize a side product of the Calvin cycle that allowed for the () during photosynthesis

Answer 9

conversion of CO2 to carbohydrates

Question 10

peroxisome assembly is mediated by the intersection of ()

Answer 10

proteins synthesized by free ribosomes and proteins transported to peroxisomes from the ER

Question 11

() are transmembrane proteins invovled in peroxisome assembly

Answer 11

peroxins/Pex proteins

Question 12

some peroxins form () through which internal (matrix) peroxisome proteins are imported

Answer 12

membrane channels

Question 13

() are conditions that result from the mutations in the genes that code for peroxins → lead to defective peroxisome assembly

Answer 13

peroxisome biogenesis disorders

Question 14

peroxins are exported from a specialized region in the ER called the ()

Answer 14

peroxisomal ER

Question 15

what makes the vesicles budding off from the peroxisomal ER unique?

Answer 15

1. they do not have a COPII coat; formation may be driven by peroxins
2. instead of going to the Golgi, they may fuse to form peroxisomes into which matrix proteins can be imported

Question 16

passage of large proteins and complexes into peroxisome lumen are mediated by ()

Answer 16

protein translocation

Question 17

targeting of peroxisome matrix proteins can be done through 2 pathways (conserved from yeasts to humans), presence of either:

Answer 17

1. PTS1 (peroxisome targeting signal 1)
2. PTS2 (peroxisome targeting signal 2)

Question 18

describe PTS1 and its cytosolic receptor

Answer 18

• simple amino acid sequence Ser-Lys-Leu at the C-terminus of a polypeptide
• recognized by Pex5

Question 19

describe PTS2 and its cytosolic receptor

Answer 19

• a sequence of 9 amino acids at the N-terminus of a polypeptide
• recognized by Pex7

Question 20

describe the mechanism for importing proteins with PTS1

Answer 20

1. the Pex5/cargo complex binds to a docking complex (consisting of Pex13, Pex14, and Pex17) on the peroxisome membrane
2. Pex5 and Pex14 then form a pore in the membrane through which the cargo is translocated into the peroxisome
3. Pex5 is then recycled into the cytosol

Question 21

formation of peroxisomes is done in response to the cell’s metabolic needs and can be done by either:

Answer 21

1. formation by vesicle budding from ER, followed by import of peroxisomal matrix proteins
   
   • de novo formation yields peroxisomes with entirely new contents
2. growth and division of existing peroxisomes
   
   • new peroxisomes are formed more rapidly by this division of old ones