Cytoskeleton

Question 1

What is the cytoskeleton?

Answer 1

A complex network of protein filaments and tubules that extend throughout the cytoplasm to provide:
Structural integrity,
Organisation
And stability.

Question 2

Describe the structure of actin.

Answer 2

2 forms:
G-actin (monomers)
F-actin (filament)
>A twisted chain of G-actin monomers 7nm in width
>Isoelectric
3 isoforms
Alpha-muscle
Beta-non muscle
Gamma-non muscle

Question 3

What are the functions of actin binding proteins?

Answer 3

1) Profilin-Increases the rate of polymerisation
2) Thymosin beta 4-Decreases the rate of addition causing the filament to decrease in size
3) Actin bundling proteins-Keep F actin in a parallel arrangement
4) Cross linking proteins-Keep F actin in a gel like mesh work
5) F actin severing proteins-Breakdown of F actin
6) Motor proteins(Myosin)-transport of vesicles/organelles through actin filaments

Question 4

What are the functions of F actin?

Answer 4

Skeletal muscle-Interaction with myosin motors allow for contraction
Cytokinesis-Acin myosin ring
Cell migration:
1)Elongation- protrusions (lamellipodia & filopodia)
2)Adhesion-Integrins link the filaments to the extracellular matrix
3)Contraction- actin and myosin interaction

Question 5

Describe the structure of intermediate filaments.

Answer 5

N terminal (amine)
C terminal (carboxyl)
Elongated rod like domain
48nm long, 8-12nm wide
2 filaments= dimer
2 dimers= tetramer
8 tetramers= rope like structure
Toughest filament

Question 6

What are the types of Intermediate filaments?

Answer 6

Cytoplasmic:

1) Keratins in epithelia
2) Vimentin/vimentin related in connective tissues, muscle cells and neuroglial cells
3) Neurofilaments in nerve cells

Nuclear:
1)Nuclear lamins in all nucleated cells

Question 7

What are the functions of Intemediate filament binding proteins?

Answer 7

1) Fillagrin-binds keratin into bundles
2) Synamin and Plectin-bind desmin and vimentin, link IF to the filaments and microtubules
3) Plakins- keep contact between desmosomes

Question 8

What are the functions of intermedia filaments?

Remember SOS!

Answer 8

Cytoplasm:
>Tensile strength- withstand mechanical stress
>Deformable 3D framework
>Fixed organelle position
Nucleus:
>Form a Mesh like structure
>Line inner nucleus envelope- strength and attachment sites for chromatin
>Able to disassemble during cell division

Question 9

Describe the structure of microtubules?

Answer 9

> Hollow tubes made of tubulin
Polarized
Width 25nm
relatively stiff

Question 10

Describe the polymerisation of microtubules?

Answer 10

> Microtubules organising centre (MTOC)- special centres where assembly of Tublin starts
Centrosome (MTOC in most cells)-contains a gamma tubulin ring that initiates growth
Heterodimers of alpha and beta tubulin constitute growth-they are alternating

Question 11

What are the functions of microtubules?

Remember SOS!

Answer 11

1)Intracellular transport 
Like motorways for molecular motors
Motors can only travel in 1 direction
2)Organises position of organelles
causes polarisation of cells
3)Rhythmic beating of cilia 
9 microtubule pairs around axenome(2 microtubules)
Dynein is the motor protein that allows for bending

Question 12

There are 2 main molecular motors. In which direction does Kinesin run? In which direction does Dynein run?

Answer 12

Motor proteins; Dynein and Kinesin.
• Dynein – moves cargo towards the –ve end of microtubules.
• Kinesin – moves cargo towards the +ve ends of microtubules.

Question 13

Give 2 examples of where flagella and where cilia can be found.

Answer 13

1. Cilia in the respiratory tract, sweeping mucus and debris from lungs.
2. Flagella on spermatozoa