The Cytoskeleton and Molecular Motors (11/6-11/8)

Describe Microtubules (Hint: 3)

Tubulin dimers form into little tubes

Thickest diameter

Forms a network of tubules thorugh the cytoplasm

Tubulin Dimers

Protein building blocks

Protofilament

Made of tubulin dimers that wrap around to form a small tube

Plus (+) end (Microtubules)

Rapid assembly and disassembly

Minus (-) end (Microtubules)

Relatively stable and usually capped

Dynamic Instability

Microtubules alternate between growing and shrinking phases

Centrosome

What microtubules usually grow from

Kinesin

Plus end directed motor

Dynein

Minus end directed motor

Cilla

Small, slender, hair-like structures present on the surface of all mammalian cells

Basal Body

Cilia microtubule organizing center

Dynein Arms

Hydrolyze ATP and causes a whip like movement

What protein makes microtubules?

Tubulin dimers

Name the two types of tubulin dimers

α-tubulin

β-tubulin

How do tubulin dimers assemble into a microtubule?

They assemble end to end forming 13 protofilaments that wrap around to form small tube

Which end is mostly static and which end repeated grows and shrinks?

Minus end is mostly static

Plus end grows and shrinks

What role does the centrosome play in growing microtubules? (Hint: 2)

Microtubules usually grow from a centrosome

They are the microtubule’s organizing center

What is the structure of centrioles?

9 triplet microtubules formed into a ring

What is the polarity of the microtubules inside the cell?

Plus end is near the plasma membrane

Minus end is near the nucleus

List the structure of the cilium (Hint: 4)

2 central singlet microtubules

9 outer doublet microtubules

Connected by linking proteins

Dynein arms

Cytoskeleton

A network of protein fibers in the cytoplasm that supports the cell’s shape

Motility (General Definition)

Interacts with motor proteins to provide movement

List the 3 components of the cytoskeleton

Microtubules

Microfilaments (Actin)

Intermediate Filaments

List the 2 molecular motors in microtubules

Dynein

Kinesin

Molecular Motors (General Definition)

“Walk” on microtubules and move organellles and vesicles around the cytoplasm

Are microtubules polar or non polar

Polar

The centrosome contains how many centrioles?

2

What provides energy to the molecular motors?

ATP hydrolysis

Cytoplasmic Stretching

Vesicles and organelles are moved around the cytoplasm by microtubule molecular motors

Which way do vesicles move on microtubule tracks in teh axon or neurons?

Both directions

What is another name for Cilia?

Eukaryotic flagella

What is basal body similar in structure to?

Centrioles

Are basal bodies necessary for function?

No

G-actin

The protein building block for actin microfilaments

F-actin

Long thin filaments made when G-actin monomers assemble

Plus (+) End (Microfilaments)

Actin filaments grow form the plus end

Minus (-) End (Microfilaments)

Actin filaments shorten from the minus end

Describe Pseudopodia (Hint: 3)

False feet

A temporary extension of the cytoplasm

Used for motility and phagocytosis

ARP Complex

Nucleate new actin filaments

Listeria

Intracellular bacterial parasite

Comet Tails

Formed when Protein A on Listeria binds and nucleates actin filaments

Myosin

A family of molecular motors that “walk” on actin filaments

Intermediate Filaments

A large family of filaments that play many different structural roles in eukaryotic cells

Keratin

Intermediate filaments in skin cells that help cells resist mechanical stress

Epidermolysis bulosa simplex

When skin blisters from an inability to resist pressure due to defective keratin

Nuclear Lamina

Formed from Intermediate filaments

Nuclear Lamins (Hint: 3)

Intermediate filaments of the nuclear lamina

Lines the inner nuclear membrane but does not cover the nucelar pores

Supports the nuclear envelope

Progeria

Severe premature aging

ATP bound G-actin subunits are added to what end?

The plus (+) end

ADP bound G-actin subunits are removed from what end?

The minus (-) end

How does actin polymerization underly cell motility? (Hint: 2)

Actin polymerization pushes the leading edge of the cell forward

Myosin motors attached to the plasma membrane walk on bundles of actin filaments to pull the rest of the cell behind the leading edge

How does Listeria hijack actin polymerization?

It has a protein related to the ARP complex on its cell surface called Protein A that binds and nucleates actin filaments

Which direction do myosins walk on actin filaments?

Directed to the plus (+) end

What does myosin use as an energy source?

ATP

List three functions that actin and myosn perform

Cytoplasmic streaming

Muscle contraction

Cell motility

Describe different structural roles that intermediate filaments play (Hint: 2)

Intermediate in diameter between microtubules and actin

Provie a network of elastic structural fibers

Describe Microfilaments (Hint: 3)

G-actin forms fine fine filaments

Thinnest diameter

Forms a network of fibers in the cytoplasm

Actin filaments provide what?

Structure

What drives the formation of pseudopodia?

Actin polymerization

Hemidesomes

Link the cell to the extracellular matrix

Mutations of intermediate filaments cause what?

Laminopathies