intermediate filaments

Question 1

what types of intermediate filaments are there?

Answer 1

lamins - located in the nuclei
keratins - found in epithelial cells 
vimentin - found in fibroblasts
neurofilaments - found in neurones 
design - found in muscle cells

Question 2

what is the conserved structure of intermediate filaments?

Answer 2

• single monomer is comprised of a head domain and a tail domain that is separated by a region of coils
• the coiled region promotes dimerisation
• the different N and C termini give them different properties

Question 3

what are the characteristics of intermediate filaments?

Answer 3

• filaments are non-polar
• they are more stable and less dynamic than actin or microtubules
• bendy, elastic
• high tensile strength

Question 4

what is the function of intermediate filaments in the cell?

Answer 4

provide the cell with tensile strength and resistance to mechanical stress

Question 5

what are nuclear lamins?

Answer 5

a type of intermediate filament that forms a proteinaceous meshwork underneath the nuclear envelope. provides structural support to the nuclear envelope

Question 6

what can LNMA knockout cells tell us about nuclear lamins?

Answer 6

• these cells are made not to express the laminA gene
• the cells have abnormal nuclear shape and disorganised heterochromatin
• shows us lamins are required to maintain shape for the nucleus

Question 7

why is the lamin A gene linked to so many different diseases?

Answer 7

lamin A/C interacts with many nuclear proteins and contributes to most nuclear processes
different mutations may disrupt specific interactions or processes

Question 8

explain the molecular basis for Emery-Dreifuss muscular dystrophy

Answer 8

the nuclei are abnormally shaped and subject to rupture. the disease is caused by weakening of the nuclear lamina. muscle cells are more likely to be affected due to mechanical strain

Question 9

what is Hutchinson-Gilford progeria caused by?

Answer 9

a mutation resulting in the incomplete post-translational processing of lamin A, there is retention of a farnesyl lipid group which is toxic for the cell

Question 10

what are the effects of farnesylation on lamin A?

Answer 10

• increased membrane association
• lamina is thickened and loses elastic properties
• DNA damage cannot be repaired
• cells senesce prematurely

Question 11

what is the structure of keratins?

Answer 11

• formed from heterodimers of acidic and basic chains
• disulphide bonds cross-link the filaments, forming very strong networks
• cysteine comprises 14% of residues in hair keratins

Question 12

what are desmosomes?

Answer 12

complexes that sit in the plasma membrane, connecting adjacent cells together. they maintain epithelial integrity and facilitate both connections between neighbouring cells and with the basal lamina

Question 13

what are neurofilaments?

Answer 13

IFs found in neurones. they can be light, medium or heavy depending on the amount of C-terminal tail they have. they provide tensile strength to axons