Lecture 4

Question 1

What are the 3 types of protein filaments

Answer 1

Actin filaments, microtubules , intermediate filaments

Question 2

Describe the microtubule structure

Answer 2

Made up of repeating units of Tubulidentata dimers. These dimers are composed of alpha and beta Tubulin. this forms protofilament. With alpha tubulin on minus end and beta tubulin on plus end. 13 parallel protofilaments then move together to form long cylindrical microfilament.

Question 3

What causes microtubule nucleations

Answer 3

Gamma tubulin ring complexes at microtubule organising centres

Question 4

Describe the structure of tubulin dimers

Answer 4

Made up of alpha tubulin and beta tubulin

Question 5

Describe how tubulin dimers eventually become microtubule

Answer 5

Dimers build up to form heterodimer protofilaments with polarity as alpha is on minus end and beta on plus end. 13 of these protofilaments then form a cylindrical microtubule.

Question 6

Discuss the nucleation of microtubules

Answer 6

Gammas trcs attach to plus end of protofilament and plus end is growing upwards

Question 7

Describe dynamic instabilities

Answer 7

Microtubule is growing rapidly. GTP hydrolysed to GDP and shrinkage begins. Catastrophe. GTP returns and rapid growth returns. This continues.

Question 8

Name two motor proteins associated with microtubules

Answer 8

Kinesins and dyneins

Question 9

Describe kynesins

Answer 9

They move towards the plus end of microtubules. Serve role in cell division. Similar structure to myosin .

Question 10

Describe dyneins

Answer 10

Move towards minus end of microtubules.

Question 11

Give two examples of dyneins and their function

Answer 11

Cytoplasmic dyneins: vesicle trafficking and Golgi localisation
Axonemal dynein : sliding movement of microtubules that drive ciliary and flagella beating.

Question 12

Describe the structure of intermediate filament monomers

Answer 12

The have rod like middle with n-terminus head and c-terminus tail.

Question 13

Describe the process of the incorporation of monomers into filaments

Answer 13

Pair of monomers associate to form dimer. 2 dimers associate in parallel manner to form tetramer. Tetramers further assemble to form protofilament . 8 protofilaments make up final rope-like filament.

Question 14

Discuss type 1 and 2 IF proteins

Answer 14

Consist of acidic and basic epithelial keratins. They dimerise to form keratin filament structures. Found loosely in cytoplasm of epithelial cells.

Question 15

Discuss type 3 IF proteins

Answer 15

Vimentin and vimentin related IFs. In connective tissues, muscle cells and glial cells.

Question 16

Discuss type 4 IF proteins

Answer 16

Neurofilament proteins in nerve cells. Examples, internexin and nexin gives structural support to axons.

Question 17

Discuss type 5 IF proteins

Answer 17

Form network of lamins under the nuclear envelope.

Question 18

Discuss type 6 IF proteins

Answer 18

Filensin and Phakanin assemble to form unique beaded filament structures which are highly specific to the eye lense.