Cytoskeleton

Question 1

What is pinocytosis?

Answer 1

Ingestion of liquids by budding of small vesicles

Question 2

What is phagocytosis?

Answer 2

Ingestion of whole cells and large insoluble particles

Question 3

Outline endocytosis

Answer 3

1. Coates vesicles formed from coated pits
2. Vesicles are uncoated
3. Vesicles fuse to endosomes

Question 4

How are secondary lysosomes formed?

Answer 4

Joining of endosomes and primary lysosomes from phagocytosis of bacteria

Question 5

Where would you find a targeting sequence?

Answer 5

In a protein destined for a certain organelle

Question 6

What are the functions of the cytoskeleton?

Answer 6

• Integration of compartments (membrane traffic) and response to cell signals
• Organelle distribution
• Cell motility and division

Question 7

What are the main features of polymers in the cytoplasm?

Answer 7

• Dynamic
• Rapid assembly and dissassembly
• May be polar

Question 8

What is the protein concentration in cytoplasm?

Answer 8

~20%

Question 9

What are the main properties of cytoplasm?

Answer 9

• non-Newtonian- can behave like a solid
• non-uniform- microdomains exist
• resists sudden impacts, melts under slow persistent shear

Question 10

What diameters are microtubules, microfilaments and intermediate filaments?

Answer 10

Microtubules- 25nm
Microfilaments- 7nm
Intermediate filaments- 10nm

Question 11

How easily deformed and ruptured are individual actin filaments, microtubules and vimentin networks (intermediate filaments)

Answer 11

Actin filaments- easily d and r
Microtubules- rigid- easily r not d
Vimentin- easily d not r

Question 12

What reagents can be used to study the cytoskeleton?

Answer 12

• Antibodies- markers for proteins

* Antibiotics- target elements of cytoskeleton

Question 13

Which antibiotics target microtubules?

Answer 13

Colchicine and taxol

Question 14

Which antibiotics target F-actin?

Answer 14

Phalloidin and cytochalasins

Question 15

What instrumentation can be used to study the cytoskeleton?

Answer 15

Low-light digital videomicroscopy

Question 16

What genetic manipulations can be used to study the cytoskeleton?

Answer 16

• Gene tagging (GFP)

* Modification of gene expression

Question 17

What are the functions of microtubules?

Answer 17

• Cell shape and polarity
• Cell organisation and positioning of organelles
• Cell division
• Cell motility:
-Intracellular transport
-Cilia and flagella
-Sensory systems

Question 18

Outline the composition of microtubules

Answer 18

• Tubulin- alpha beta heterodimer
• Assemble head to tail- protofilaments
• 13 protofilaments make up the wall of a microtubule
• Exist in dynamic equilibrium- added to one end, removed from other

Question 19

Where do microtubules arise and how do they assemble?

Answer 19

• Arise from centrosome- microtubule organising centre (MTOC)
• Assemble with +be end (beta) distal to centrosome

Question 20

What is a centrosome?

Answer 20

Pair of centrioles enclosed in shell of pericentriolar material (contains lambda tubulin)

Question 21

What do low temperatures do to microtubules?

Answer 21

Reversibly disassembles then

Question 22

What effect does cochicine have on a cell?

Answer 22

Depolymerises cytoplasmic microtubules, therefore causes organelle dispersal
(As microtubules determine the 3D organisation of organelles)

Question 23

What are microfilaments made up of?

Answer 23

Dynamic polymer of G-actin monomers

Question 24

What effect does cytochalasin have on actin filaments?

Answer 24

Depolymerises them

Question 25

What effect does phalloidin have on actin filaments?

Answer 25

Stabilises them

Question 26

How abundant is actin in a cell?

Answer 26

Most abundant protein | 10-15%

Question 27

Outline microfilament assembly?

Answer 27

* Assembly at +ve end, disassembly at -ve | * ATP dependant- one ATP for each monomer lost from -ve

Question 28

What are actin binding proteins?

Answer 28

Regulate actin filament function | Eg. In the brush border actin filaments are cross linked by villin

Question 29

Why are intermediate filaments stable during interphase?

Answer 29

No cytoplasmic pool of subunits and filaments

Question 30

What protein composition do intermediate filaments have?

Answer 30

Alpha helix rich Alpha type fibrous proteins (Not globular like mf and mt)

Question 31

Describe intermediate filament function

Answer 31

* Very heterogenous and tissue specific | * Mechanical integrators of cells into tissues

Question 32

Describe the composition of intermediate filaments

Answer 32

Monomers are an alpha helix rod and two globular heads | 4 monomers form a tetramer filament

Question 33

What are four intermediate filament proteins and where are they used?

Answer 33

1. Lamin- nuclear lamina 2. Vimentin- cells of mesenchymal origin 3. Keratin- epithelial cells and derivatives 4. Neurofilaments- neurons

Question 34

Where are intermediate filaments found in epithelial cells?

Answer 34

* Keratin filaments- structure * Nuclear lamina * Dermosomes (join cells together) * Hermidermosones (to basement membrane) * Basement membrane

Question 35

What makes up a cytoskeletal motor?

Answer 35

An ATPase and a linear polymer with intrinsic polarity

Question 36

Which ATPases pair with which linear polymers to form cytoskeletal motors?

Answer 36

Myosin with F-actin | Dynein and kinesin with microtubules

Question 37

What are cross-bridge cycles?

Answer 37

Vectorial movement- direction determined by polarity | Step distance ~8nm