Multiple choice questions on Cell Junction

1- A skin disease pemphigus, in this disease affected individuals make antibodies against one of their own non classical cadherine of desmosomes. These antibodies bind to desmosomes and disrupt it, that hold their epidermal cells (keratinocytes) together – 

a- Cause severe blistering of body fluids into the loosened epithelium  

b- Block the exchange of materials in these cells

c- Disruption of gap junction 

d- All of the above 

2- Protein claudins are essential for tight junction, mice that lack claudin-1 gene fail to make tight junction between cells epidermal layer of skin; as a result 

a- Skin become loose due to accumulation of fluid, and baby mice die

b- Skin remain normal

c- baby mice die within a day after birth, due to lose of water rapidly by evaporation through the skin

d- baby mice servive with less fluid

3- In kidney epithelial cells, a specific claudin is found which is needed to reabsorb mg++ from urine to blood, mutation in claudin gene cause 

a- Mg++ reabsorb through other protein which allow reabsorption 

b- Excessive lose of mg++ ion in the urine

c- No effect because there is no reabsorption through claudin, it’s a protein of tight junction

d- Both a & c

4- Gap junction have channel forming protein namely connexins & innexins. ----- have connexins, ----- have innexins

a- Humans, other mammals

b- Mammals, birds

c- Vertebrates, invertebrates

d- Chordates, hemichordates

5- A rare human genetic disease, deficiency of dermatan sulfate disaccharide ( a type of GAGs) the affected individuals have-

a- Short stature, a prematurely aged appearance, and generalized defects in their skin, joints, muscles, and bones.

b- Normal face & stature with a weak bone

c- Only defect in skin

d- No effect 

6- Defect / dificiency of type I collagen lead to mutant phenotype – 

a- Severe bone defects, fractures ( osteogenesis imperfecta )

b- Fragile skin

c- Cartilage deficiency, dwarfism ( chondrodysplasia )

d- Osteoarthritis  

7- Defect / deficiency of types II collagen lead to mutant phenotype –

a- Severe bone defects, fractures ( osteogenesis imperfecta )

b- Fragile skin

c- Cartilage deficiency, dwarfism ( chondrodysplasia )

d- Osteoarthritis  

8- Defect / deficiency of types III collagen lead to mutant phenotype –

a- Severe bone defects, fractures ( osteogenesis imperfecta )

b- Fragile skin, loose joint, blood vessels prone to rupture ( Ehlers-Danlos syndrome ) 

c- Cartilage deficiency, dwarfism ( chondrodysplasia )

d- Osteoarthritis  

9- Type XI collagen which fibril associates with type I, a defect or deficiency of this collagen types lead to mutant phenotype –

a- Fragile skin

b- Cartilage deficiency, dwarfism ( chondrodysplasia )

c- Osteoarthritis

d- Myopia, blindness

10- Type IX collagen which form lateral association with type II, present in -----, defect or deficiency of this collagen cause -----

a- Cartilage, osteoarthritis 

b- Bone, osteoarthritis

c- Epithelium, fragile skin

d- All of the above

Answers: 1-a, 2-c, 3-b, 4-c, 5-a, 6-a, 7-c, 8-b, 9-d, 10-a

Contributed by: Ms. Nargis K.