Topic 5: Cytoskeleton

Question 1

What is the cytoskeleton?

Answer 1

A network of protein fibres involved in structure, support, and movement in cells

Question 2

What are protein filaments? What are the three types?

Answer 2

Protein filaments are hundreds of proteins put together.

The three types are:

1. Microtubules (MT)
2. Intermediate filaments (IF’s)
3. Microfilaments (MF’s)

Question 3

What is the function of the cytoskeleton?

Answer 3

•Structural support;

•stabilization (through opposing forces
between protein filaments – interior layer);

•involved in cell motility and movement:

• cell crawling,
• muscle contractions,
• vesicle&organelle movement

Question 4

What is the structure of a microfilament?

Answer 4

• Made of actin (protein)
• 2 chains of actin twist to form a filament
• 7 nm diameter

Question 5

What is the function of microfilament?

Answer 5

• Maintain cell shape – concentrated near cell membrane;
• involved in muscle contraction.
• Reshape cell for crawling and phagocytosis.
• During cell division, pinches cell into two

Question 6

What is the structure of intermediate filament

Answer 6

• made of various proteins (eg keratin, Desmin, lamen)
• forms rod-like, STABLE filaments
• proteins resemble rods/ropes
• 8-12 nm

Question 7

Function of intermediate filaments?

Answer 7

Anchorage of organelles and the nucleus within the cytoplasm

-Connects cells together in desmosome structures

Question 8

Structure of Microtubule?

Answer 8

• Tubulin proteins attached to one another
• Two isoforms of the protein combine into dimers
• Dimers align to create a hollow cylinder
• 25 nm diameter

Question 9

Function of microtubules?

Answer 9

• concentrated within the cytoplasm
• Resists cellular compression
• Separate chromosomes during mitosis (creates spindle)
• Provides pathway for vesicle movement (creates roads)
• Structural basis of flagella and cilia (in eukaryotes)

Question 10

What motor proteins interact with cytoskeletal protein filaments?

Answer 10

Microfilaments: Myosin
Microtubules: Dynein
Intermediate Filaments: None

Question 11

What is the result of coordinated shape changes in the motor protein?

Answer 11

• Allows motor protein to bind/attach and then release from the cytoskeletal filament
• How: addition of phosphate (from hydrolyzed ATP) binds and changes shape
• Directional Movement* can only go one way

Question 12

Location of Microtubule?

Answer 12

-microtubules grow (are created) from microtubule organizing centers (MTOC’s) found in the cytoplasm
(ie centrosome is a mtoc in animal cells)

Question 13

What is the centriole?

Answer 13

• Animal cell structure located in centrosomes

- Consists of 9 sets of triplet MT’s arranged in a ring

Question 14

Difference in Motility of cilia and flagella?

Where are they both anchored?

Answer 14

Cilia: Many - move like oars or windshield wipers
Flagella: One or few; undulated like a snake
Anchored in Basal Bodies

Question 15

Eukaryotic Cilia and flagella structure?

Answer 15

Made of MT core surrounded in plasma membrane.
-MT doublets connected to each other through a series of MOTOR PROTEINS called DYNEIN

-anchored in Basal Body

Question 16

Flagella: prokaryote vs Eukaryote

Answer 16

50% of prokaryotes are motile and usually have flagella

Flagella: scattered all over cell surface or concentrated on one end
Eukaryotes: usually have only one or a few made of TUBULIN
Prokaryotes: Have many - smaller (1/10 width); not covered in plasma membrane; made of FLAGELLIN

Question 17

Flagella (Prokaryotic): mechanism of movement? Powered by?

Answer 17

Moves by: rotating (rather than bending)
Powered by? Diffusion of Protons into cell.
-Proton gradient (established via Membrane Proton Pump) provides ATP.