Peroxisomes

Question 1

Describe the structure of a peroxisome

Answer 1

Surrounded by a single membrane
No DNA or ribosomes
All proteins encoded by the nucleus
Contains oxidative enzymes

Question 2

What is the equation for the peroxisomes enzyme and oxygen?

Answer 2

RH2+O2 -> H2O2

Question 3

What is the hydrogen peroxide produced by the peroxisomes used for?

Answer 3

Catalases use H2O2 to oxidise
eg, in liver oxidises ethanol
breakdown fatty acid molecules

Question 4

State the peroxidation reaction

Answer 4

H2O2 + R’H2 -> R’ + 2H2O

Question 5

How to Peroxisome replicate?

Answer 5

can undergo fission to replicate

Question 6

Describe the peroxisome biogenesis and maturation

Answer 6

Peroxisomal precursor vesicles from the ER and proteins are imported and recruit these peroxisomes
C-terminal Ser-Lys-Leu Signal sequence ‘addresses’ the peroxisome

Question 7

Lysosomes contain how many soluble hydrolytic enzymes?

Answer 7

40 enzymes pH4-5

Question 8

Name 5 of the enzymes in lysosomes

Answer 8

proteases
nucleases
Phospholipases
Phosphatases
Sulfatases

Question 9

How is the the acid environment maintained in the lysosome?

Answer 9

A vascular H+ ATPase in the membrane that uses ATP hydrolysis for energy to pump the H+ into the lysosome

Question 10

What are the 4 pathways to degradation

Answer 10

Endocytosis
Phagocytosis
Micropinocytosis
Autophagy

Question 11

What is endocytosis?

Answer 11

Macromolecules taken up from extracellular fluid

Question 12

What is Phagocytosis?

Answer 12

Engulfment of large particles to form phagosomes

Question 13

What is Micropinocytosis?

Answer 13

Nonspecific uptake of fluids, membranes and particles attached to the membrane

Question 14

What it is autophagy?

Answer 14

digestion of self contents

Question 15

Describe the 5 stages of Autophagy

Answer 15

1) Protein Kinases activate and signal to autophagic machinery
2) Nucleation and extension of delimiting membrane into crescent shaped cup. Membrane vesicles with ATG9 are recruited to assembly site to nucleate autophagosome formation ATG9 is not in this autophagosome and removed
3) Close membrane to form sealed double membrane enclosed
4) Fusion of autophagosome with lysosome catalysed by SNARES
5) Digestion of the inner membrane and lumenal contents

Question 16

Why does the lysosome not digest itself?

Answer 16

Its membrane is modified with highly glycosylated proteins. Digestion products are removed or recycled
Vascular H+ ATPase hydrolyses ATP and pumps protons into the lysosome

Question 17

What are the endosomes role?

Answer 17

Endosomes sort and deliver the material to the lysosome and vacuoles.

Question 18

How to endosomes mature?

Answer 18

Early endosomes mature to late endosomes via endosome maturation

Question 19

What do we know about VAULT complexes?

Answer 19

Large ribonucleoprotein structure found in most eukaryotes
3x larger than a ribosome
Function suggested to be associated with NPC

Question 20

What are the suggested function of the VALUT complexes

Answer 20

mRNA localisation
Drug resistance
Cell Signalling
Nuclear-cytoplasmic transport

Question 21

What is a proteasome?

Answer 21

Central hollow cylinder comprising 4 stacked heptameric rings

Question 22

Why are proteasomes important for?

Answer 22

Make correctly folded functional proteins

Role in rapid cell turnover of short lived proteins and proteins that need to be removed dependent on conditions

Question 23

How much of the cell volume in plants and fungal cells is the vacuole?

Answer 23

30%

Question 24

How are vacuoles related to lysosome?

Answer 24

They both contain hydrolytic enzymes

Question 25

What is the function of the vacuole

Answer 25

Nutrient and waste storage
degradative compartment 
economical way of increasing cell size 
Provide turgid pressure regulation
Regulating pH in the cell

Question 26

How does the vacuole regulate turgid pressure?

Answer 26

Changes osmotic pressure of cytosol and vacuole

Question 27

How does the vacuole regulate the pH in the cell?

Answer 27

Proton pump in and out