Cytoskeleton

Question 1

What is the cytoskeleton sold in mitosis?

Answer 1

During anaphase to pull the chromosomes apart and to split the dividing cell into two.

Question 2

What are the three types of filaments in the cytoskeleton?

Answer 2

Actin, microtubules and intermediate filaments.

Question 3

What is actin for?

Answer 3

To determine the shape of the cells surface as it lies under the plasma membrane and it’s necessary for whole-cell locomotion.

Question 4

Describe actin?

Answer 4

5-9 nm diameter, 375 amino acids and 42 kD double-stranded helical polymers of the protein actin in bundles

Question 5

How many types of actin are there?

Answer 5

Three, alpha (muscle), beta and gamma (both non-muscle).

Question 6

What are the plus and minus ends of actin?

Answer 6

Plus end is the fast growing end and the minus end, aka the barbed end, is the slow growing end.

Question 7

What disease are associated with actin?

Answer 7

Congenital myopathies, duchene muscular dystrophy, blood disorders

Question 8

What’s the most common congenital myopathy?

Answer 8

Nemaline

Question 9

What symptoms do congenital myopathies have?

Answer 9

Weak muscles due to lack of sarcomeres, floppy and may require support breathing (ventilation), feeding, standing, sitting etc. Facial weakness and scoliosis are also common.

Question 10

Do congenital myopathies get worse with age?

Answer 10

No.

Question 11

What are the different types of congenital myopathies?

Answer 11

Nemaline, actin, intranuclear rod and nemaline with core like areas.

Question 12

What is duchene muscular dystrophy caused by?

Answer 12

Mutations in dystrophin.

Question 13

Why does duchene muscular dystrophy mostly effect boys?

Answer 13

As the gene is on an X chromosome, 100 Boyes per year.

Question 14

What is dystrophin?

Answer 14

A protein found close to the plasma membrane in skeletal and cardiac muscle which links internal cytoskeleton to extracellularly matrix.

Question 15

What are the symptoms of duchene muscular dystrophy?

Answer 15

Muscle weakness and necrosis.

Question 16

Does duchene muscular dystrophy get worse with age?

Answer 16

Yes

Question 17

Name a blood disorder from mutations in non-muscular myosin?

Answer 17

Griscelli syndrome and usher syndrome

Question 18

What are some symptoms of blood disorders due to actin?

Answer 18

Deafness and blindness in usher syndrome.

Question 19

What does the cytoskeleton allow?

Answer 19

Organisation in space, correct shape, robust and proper structure and the ability to rearrange the internal components and mechanical interaction with the environment.

Question 20

What do microtubules do?

Answer 20

Determine the positions of membrane-enclosed organelles and direct intracellular transport.

Question 21

Describe microtubules?

Answer 21

25 nm long, rigid, straight, hollow cylinders made of the protein alpha-beta dimer tubulin

Question 22

What is one end of the microtubule usually attached to?

Answer 22

Centrosome: MTOC- microtubule organising centre

Question 23

Why could microtubules be a good target for cancer?

Answer 23

As they are required for the rapid division of cells. Taxol has been used as a cancer treatment.

Question 24

What can microtubules form?

Answer 24

The core of the flagella and cilia.

Question 25

Why could microtubules be described as tentacles?

Answer 25

As they are dynamic and grown and shrink to explore the cytoplasm.

Question 26

What two MAPs are microtubules tracks for?

Answer 26

Kinesin and dynein.

Question 27

How are kinesin and dynein different?

Answer 27

Kinesin takes 8nm steps, powered by ATP towards the plus end whereas dynein goes towards the minus end.

Question 28

What can bind to stabilise/destabilise microtubules?

Answer 28

Other MAPs, eg. Tau binds to the end and MAP2 binds to the cell body.

Question 29

What disease are found in microtubules/kinesin/MAPs?

Answer 29

Tauopathies, lissencephaly, hereditary specific paraplegia.

Question 30

Name some tauopathies?

Answer 30

Alzheimer's, progressive supra nuclear palsy, corticol-basal degeneration, dementia, Parkinson's etc.

Question 31

What does tau do in tauopathies?

Answer 31

Binds and stabilises microtubules normally but when hyper phosphorylated due to the down regulation of protein phosphatase 2A it is released. This causes the microtubules to dissemble, and the tau can for, paired helical filaments and neurofibrial tangles which compromise axonal transport.

Question 32

What is lissencephaly?

Answer 32

Absence of normal folds in the brain caused by a tubulin mutation.

Question 33

What are the symptoms of lissencephaly?

Answer 33

Abnormally small head, unusual facial appearance, difficulty swallowing, failure to thrive, muscle spasms, seizures and severe psychomotor retardation, usually death before 2 years of age.

Question 34

Describe the mutation that causes lissencephaly?

Answer 34

Tubulin mutation results in missfolding of the tubulin effecting dimerisation and binding to other microtubule proteins. First mutation to be found was a missense Arg264 to Cys264 and since many others have been found.

Question 35

What mutation causes hereditary specific paraplegia?

Answer 35

Missense mutation in motor domain of kinesin-1, effecting movement and binding of cargo.

Question 36

What are the symptoms of hereditary specific paraplegia?

Answer 36

Progressive weakness, stiffness in legs all due to synapses not being used and therefore wasting away. Can be late onset (24 years etc) and is very rare.

Question 37

What do intermediate filaments do?

Answer 37

Provide mechanical strength. One type forms a mesh-like nuclear lamina lining the inner face of the nuclear envelope, which is a protective cage for the cell's DNA. Important for cell-to-cell and cell-to-ECM adhesion.

Question 38

Describe intermediate filaments?

Answer 38

10 nm diameter, rope-like fibres which twist into sting cables.

Question 39

What disease can occur due to intermediate filaments?

Answer 39

Keratin mutations: epidermolysis bullosa Desmin mutations: desminopathies Nuclear lamina mutations

Question 40

What are the symptoms of epidermolysis bullosa?

Answer 40

Blistering of the skin due to lack of cell-to-cell adhesion.

Question 41

What do desminopathies effect?

Answer 41

Skeletal, cardiac and smooth muscles.

Question 42

What can lamin A mutations cause?

Answer 42

Progeria, emery dreiffus muscular dystrophy, limb girdle muscular dystrophy, dilate cardiomyopathy and charcot-marie-tooth disease.

Question 43

What are accessory pigments?

Answer 43

Proteins that are vital for lining the filaments to other cell components as well as to each other and the controlled assembly of the cytoskeletal filaments to articulate locations.