Lysosomes

Question 0

What is the pH of the lysosome and why?

Answer 0

Acidic: 4.5-5, to allow for the acid hydrolases to work.

Question 1

Describe a lysosome as an organelle?

Answer 1

A membrane-bound organelle which contains many acid hydrolase enzymes to act as the ‘digestive system’ of the cell.

Question 2

Describe endocytosis?

Answer 2

The movement of extracellular molecules in the fluid phase and plasma membrane into the cell for degradation by the lysosome.

Question 3

Describe autophagy?

Answer 3

The disposal of whole cell, organelles or molecules from the cytosol.

Question 4

How is autophagy enhanced?

Answer 4

By the starving conditions and the drug rapamycin which inhibits mTOR.

Question 5

How do lysosomes help the plasma membrane?

Answer 5

They act as a reserve of plasma membrane proteins to repair the ‘holes’, an influx of calcium ions after damage prompts lysosomes to exocytose.

Question 6

What are the three causes of lysosomal storage diseases?

Answer 6

Inability to deliver newly synthesised hydrolases to them, deficiencies in specific lysosomal hydrolases and the inability to transport lysosomal breakdown products into the cytosol.

Question 7

What is the mutation in I-cell disease?

Answer 7

A mutation in the gene that encodes N-acetylglucosiminidase-1-phosphotransferase.

Question 8

What is N-acetylglucosiminidase-1-phosphotransferase?

Answer 8

An enzyme that is localised in the cis-golgi and modifies mannosylated glycans that are attached to newly synthesised acid hydrolases, in order for the acid hydrolases to be recognised by the receptors for transport to lysosome.

Question 9

What are the symptoms of I-cell disease?

Answer 9

Facial and skeletal abnormalities, severe pyschomotor retardation, heart failure usually occurs within 10 years.

Question 10

Is there treatment for I-cell disease?

Answer 10

Yes but it is limited to reducing symptoms.

Question 11

What is the mutation in pompe disease?

Answer 11

A mutation in the gene that encodes lysosomal hydrolase alpha-D-glucosidase.

Question 12

What are the symptoms of Pompe disease?

Answer 12

Progressive cardiac and skeletal myopathy, death due to cardio respiratory failure.

Question 13

What does the mutation in alpha-D-glucosidase cause and why?

Answer 13

The accumulation of glycogen in cells as it is usually used to cleave glycogen to glucose for transportation to the cytosol- loss of specific hydrolase activity.

Question 14

How can pompe and fabry disease be treated?

Answer 14

With enzyme replacement therapy.

Question 15

What is the mutation the causes fabry disease?

Answer 15

A mutations in alpha-galactosidase.

Question 16

What are the symptoms of fabry disease?

Answer 16

Facial abnormalities, renal and cardiac problems, progressive organ and tissue damage, reduction in life expectancy (40 years).

Question 17

What are the symptoms of fabry disease all due to?

Answer 17

Deposition of glycolipid globotraosylceramide in the walls of capillaries, kidney tubule and glomerular cells, nerves and dorsal root ganglia.

Question 18

Where is the mutation in infantile sialic acid storage disease?

Answer 18

In the sialin gene.

Question 19

What are the symptoms of infantile sialic acid storage disease?

Answer 19

Facial abnormalities, mental retardation, enlarged heart, liver and spleen, death within 1-2 years.

Question 20

What does the mutation in infantile sialic acid storage disease result in?

Answer 20

Accumulation of sialic acids in the lysosomes as the gene mutation is for the lysosomal membrane transporter which transports the breakdown products out to the cytosol.

Question 21

What is Salla disease?

Answer 21

Similar to infantile sialic acid storage disease, found in the Finnish populations and less severe.