TBL 3 Intracellular Transport

Question 1

Robinow Syndrome is caused by a mutation in the ____ receptor, which is a receptor tyrosine kinase responsible for bone and cartilage growth.
The mutation of this receptor causes it to undergo ER retention and degradation.

Answer 1

ROR2

Question 2

Cystic fibrosis, caused by a ______ mutation resulting in the loss of ______ (AA), results in a mutation in the gene coding for the ______, which is responsible for the transport of salt and water across epithelial cells.

Answer 2

Cystic fibrosis:

• Deletion mutation of 3 nucleotides at the 508th position of the protein
• Loss of phenylalanine
• CFTR

Question 3

Exocytosis is mediated by the fusion of donor and acceptor membranes by ___________.

Answer 3

SNARE proteins

v-SNARE on vesicles and t-SNARE on target membranes

Question 4

Balance of exocytosis and endocytosis (known as the ___________) is critical in maintaining a cell surface area and volume.

Exocytosis - (adds/removes) membrane

Endocytosis - (adds/removes) membrane

Answer 4

Endocytic-exocytic cycle

Exocytosis - adds membrane

Endocytosis - removes membrane

Question 5

There are 3 modes of endocytosis.

Answer 5

1. Pinocytosis
2. Phagocytosis (Macropinocytosis)
3. Receptor-mediated endocytosis

Question 6

Phagocytosis is clathrin-(independent/mediated) endocytosis.

Answer 6

Phagocytosis: Clathrin-independent endocytosis

Question 7

LDL binding to LDL receptor on the plasma membrane is taken up by ____________.

Answer 7

clathrin-mediated endocytosis

(Clathrin coat is shed and endocytosed vesicle fuses with endosome, which fuses with lysosomes to release the free cholesterol)

Question 8

Familial hypercholesterolemia results from the mutation in ________ gene, resulting in defects of clathrin-mediated LDL uptake.

Answer 8

LDLR

high cholesterol levels in the blood as it is unable to be taken up

Question 9

________ are added as a tag of the N-linked ogliosaccharides of the lysosomal hydrolase precursor (to be sent to the lysosome) as they pass through the lumen of the GA.

Answer 9

Mannose-6-phosphate (M6P)

Question 10

The most severe form of lysosomal storage disease is the ______________, in which almost all of the hydrolytic enzymes are missing from the lysosomes, resulting in large inclusions in the cells.

_____________ is defective or missing in such patients, resulting in the failure of M6P tagging to the lysosomal hydrolase precursor.

Answer 10

Inclusion-cell disease (I-cell disease)

• Defective GIcNAc phosphotransferase, resulting in the failure of M6P tagging or mannose phosphorylation (for the proteins to be sorted to the lysosomes)

Question 11

Organelles and membranes contact with each other, forming unique sites for __________.

Answer 11

organelle crosstalk

non-vesicular transport

Question 12

Lack/mutation of clathrin affects the synapses of neurons, causing neurodegenerative disorders such as __________.

Answer 12

Parkinsons’ disease

Question 13

There are 3 main types of intracellular protein transport.

Answer 13

1. Gated transport
   - from cytosol to nucleus
2. Protein translocation through transmembrane protein receptors
   - from cytosol to ER/mitochondria/peroxisomes
3. Vesicular transport through the budding and fusion of vesicles
   - from ER to organelles such as lysosome and GA

Question 14

Proteins synthesised in the ER are usually

Answer 14

1. Integral membrane proteins

2. Proteins destined for secretory pathway

Question 15

Proteins synthesised in the ER are usually glycosylated by the addition of ______________.

Answer 15

N-linked ogliosaccharide

- important in protein folding for the exit of ER

Question 16

Unfolded proteins in the ER have 2 fates:

Answer 16

1. UPR

2. ERAD (degradation)