Question

1. In order to construct an Intermediate Filament in an epithelial cell:
   1. Two keratin dimers are lined up in an opposite orientation
   2. Individual keratin proteins are lined up in an opposite orientation
   3. Heterodimers of keratin and vimentin are added at one end
   4. Tetramers of keratin and lamin protein are lined up end to end
   5. None of the answers are correct
2. When a neuron stimulates a muscle cell to contract:
   1. Levels of Na+ inside the muscle cell cytoplasm increase
   2. An increase in Ca2+ inside the muscle cell causes a change in membrane potential
   3. A voltage-gated Ca2+ channel opens
   4. T tubules fuse with the SR membrane
3. Place the following steps of muscle cell differentiation in order:
   1. muscle cells turn on the actin and myosin genes
   2. muscle cells proliferate (divide many times)
   3. muscle cells become multinucleate
   4. muscle cells contract
   5. muscle cells fuse
4. True or False?
   1. ____ The plus end of a microfilament contains actin-ATP.
   2. ____ Cilia contain bundles of microtubules.
   3. ____ All intermediate filament genes are expressed in a tissue-specific manner.

Answer 1

1. (e)

Actin filaments, Intermediate filaments and microtubules comprise the cytoskeletal elelments which form the structural framework of the cell.

The intermediate filaments are of several types -

Nuclear lamins

Vimentin

Desmin

Glial fibrillary acidic protein

Peripherin

Type I Keration (Acidic)

Type I Keration (Basic/ Neutral)

Neurofilaments

Each monor hass an helical region which assemble to form dimers.

Dimers associate in an anti-parallel manner to form a tetramer. This arrangement causes them to lack a polarity.

Tetramrs pack laterally, held by strong hydrophobic interactions. This gives the intermediate filaments its ropelike character. they are easy to bend but not to break.

Keratins are made of both the type I and type II Keratins held by disulfide bonds. they are particularly hard and are found in nail, claws, hair, etc.

Present in desmosomes (cell-cell contacts) and hemidesmosomes (sell-matrix contacts).

2. (a)

3. b-->e-->c-->a-->d

4. False (Actin/ GTP is present)

5. True

6. False (Nuclear lamins are present in nucleus of every cell, although expression of vimentins and neurofilaments is pretty much tissue specific still the question asks all so NO for all)