Lysosomes

Question 1

What is the structure of lysosomes?

Answer 1

• single membrane bound organelles
• contain ~ 60 different enzymes
• acidic pH of 5
• size ranges from 0.1 micrometers to 1.2 micrometers

Question 2

How many lysosomes are found in a human cell ?

Answer 2

~300

Question 3

What is the function of lysosomes ?

Answer 3

Lysosomes act as the digestive system of a cell and digest intracellular proteins and carbohydrates but also molecules and pathogens from outside the cell

Question 4

Where do lysosomes originate from ?

Answer 4

They bud off of the trans face of the Golgi apparatus

Question 5

Why are lysosomal membrane proteins glycosilated ?

Answer 5

Because the glycosilation protects the proteins from the proteases present in the lumen

Question 6

What are the main lysosomal pathways ?

Answer 6

• Endocytosis
• Phagocytosis
• Pinocytosis
• Autophagy

Question 7

What is heterophagy ?

Answer 7

The digestion of material of extracellular origin

Question 8

What is autophogy ?

Answer 8

The digestion of material of intracellular origin

Question 9

How is the internal acidic environment of a lysosome maintained ?

Answer 9

V-ATPase pumps protons from the cytoplasm to the lysosomal lumen which maintains the acidic environment within the lysosome

Question 10

What is the role of mannose-6-phosphate ?

Answer 10

It targets proteins to lysosomes
It allows lysosomal hydrolases and membrane proteins to be delivered to lysosomes

Question 11

What are lysosomal storage diseases ?

Answer 11

They are inherited metabolic diseases characterised by abnormal build up of materials in cells as a result of enzyme deficiencies

Question 12

Give some examples of lysosomal storage diseases

Answer 12

• Hunter & Hurler syndrome
• Tay-Sachs disease
• Gaucher disease
• Inclusion cell disease

Question 13

Summarise Hunter & Hurler syndrome

Answer 13

It develops as a result of large sugar molecules building up in body tissues

Symptoms include an enlarged head, thickening of the lips and a distended abdomen due to enlarged internal organs

Question 14

Summarise Tay-Sachs disease

Answer 14

Develops as a result of deficiency of the hexosaminidase enzyme which means lipids accumulate in the brain and other organs

Symptoms include mental challenges, blindness and death within 3 years

Question 15

Summarise Gaucher disease

Answer 15

Develops due to the accumulation of glycolipids

Symptoms include enlargement of the liver and spleen, anaemia and lung disease

Question 16

Summarise Inclusion cell disease

Answer 16

Caused by deficiency of N-glucosamine phosphotransferase which is what transfers M6P

Symptoms include psychomotor challenges and death

Question 17

What is the endosomal-lysosomal system ?

Answer 17

The endosomal-lysosomal system is made up of a set of intracellular membranous compartments which interconvert
It is comprised of early endosomes, recycling endosomes, late endosomes and lysosomes

Question 18

What are the membrane compartments used for in the endosomal-lysosomal system ?

Answer 18

• for traffic and digestion of endocytosed molecules
• for sorting and recycling cellular components
• for autophagy

Question 19

What are endosomes ?

Answer 19

Membrane bound vesicles formed by endocytosis and found in every animal cell

Question 20

Describe the process of endocytosis

Answer 20

1) Endocytosed molecules are delivered in vesicles to small, irregularly shaped intracellular organelles called early endosomes
2) Some of these molecules are recycled to the plasma membrane whilst some pass into late endosomes
3) They are then passed to lysosomes where they are degraded

Question 21

Describe the process of phagocytosis

Answer 21

1) Phagocytes engulf objects to form a phagosome
2) The phagosome fuses with a lysosome to form a phagolysosome
3) The hydrolysed products enter the cytosol

Question 22

Describe the process of pinocytosis

Answer 22

Pinocytosis is the intake of liquid particles to form vesicles known as pinosomes
It balances exocytosis because the cell surface area and volume remain constant by recycling cell membrane parts to maintain the size of the cell

Question 23

Describe the process of autophagy

Answer 23

1. the target organelle or protein is wrapped in a double membrane from the ER which produces an auto-phagosome
2. the autophagosome fuses with a lysosome to produce a autophagolysosome
3. indigestible remnants are retained as granules that accumulate with age in residual bodies
4. debris is released from the cell surface via exocytosis