Module 4 - Protein Targeting

Question 1

characteristics of peroxisomes

Answer 1

• bound by a single membrane
• oxidative and synthetic reactions
• do not have a genome
• reproduction by fission

Question 2

function of peroxisomes in animal cells

Answer 2

responsible for cholesterol synthesis

Question 3

function of peroxisomes in nerve cells

Answer 3

they synthesize plasmalogen for cell membranes. plasmalogen increases insulating capacity of cell membrane

Question 4

function of peroxisomes in liver cells

Answer 4

site of oxidation of toxins

Question 5

function of peroxisomes in plant cells

Answer 5

required for conversion of fatty acids into carbohydrates

Question 6

major function of peroxisomes

Answer 6

• breakdown of long-chain fatty acids by beta oxidation
• in animal cells, long-chain fatty acids are oxidized to medium-chain fatty acids, and then shuttled to mitochondria for further processing
• this is necessary for releasing metabolic energy
• toxic-by-product of hydrogen peroxide but catalase converts it to water and oxygen

Question 7

peroxisome biogenesis

Answer 7

• formation of new peroxisomes by division and incorporation of new proteins
• peroxisomal proteins are synthesized in the cytosol and then transported to peroxisome
• peroxisomal membrane proteins are used to transport peroxisomal matrix proteins into the interior of the organelle
• more peroxisomes can form by fission

Question 8

luciferase

Answer 8

enzyme that allows for bioluminescence that we see in fireflies; present in peroxisomes

Question 9

5 rules for protein transport

Answer 9

1) signal sequence on transported protein
2) receptors for signal sequences
3) translocation channels
4) coupling to ATP hydrolysis (energy requirement)
5) a way of targeting proteins to the different locations within the organelle

Question 10

peroxisome - rule 1

Answer 10

• PTS1 = peroxisomal-targeting sequence
• PTS1 is found at C-terminus upon completion of translation
• is PST1 necessary for transport? yes: when c-terminus amino acids were missing in luciferase, biofluorescence of luciferase was seen in big spreads throughout the cytosol, meaning it was not transported to peroxisomes.
• is PTS1 sufficient for transport? yes: to test this, c-terminal luciferase was added to DHFR to see if it would be enough. it was enough to redirect DHFR to peroxisome