Cytoskeleton

Question 1

What are the three types of cytoskeleton?

Answer 1

Microtubules, actin filaments, intermediate filaments

Question 2

What is listeria?

Answer 2

Pathogenic bacteria that invade intestinal cells.
Causes a serious infection.
Esp serious in immunologically deficient or compromised patients.
Pregnant women 10x greater risk.
1600 people/year in US

Question 3

Where is listeria found?

Answer 3

Ubiquitous in the soil, animal products (dairy/meat), and unwashed lettuce.

Question 4

What are symptoms of listeria?

Answer 4

-Headache
-Stiff neck
-confusion
-Loss of balance
-Convulsions
-Fever and muscle aches
FOOD POISONING

Question 5

What is the treatment for listeria?

Answer 5

HOSPITALIZATION
IV antibiotics
Incidence down since hotdogs of 1988

Question 6

What are other risks associated with listeria infection?

Answer 6

1 in 5 people die.
Pregnancy: miscarriage, stillbirth, new born death
20% chance of fetal loss and new born death in 3%

Question 7

How does Listeria infect cells?

Answer 7

Attaches to receptors on enterocytes, enters cells and replicates in intestinal cells.
Performs unusual behavior due to actin cytoskeleton and accessory proteins.

Looks like sperm or comets moving around within cell membrane. Tails or comet tails are made of actin. Cells stop to divide then redevelop tails and regain movement.

Question 8

What type of movement do Listeria present?

Answer 8

Actin-based motility, smashing through organelles causing serious damage.
Like speed boats
Actin track=comet tail
0.2 um per second (50 ft/sec)

Question 9

What is the bacterial makeup of the human biome?

Answer 9

There are 10x more bacterial cells than human cells

“You are an ecosystem”

Question 10

Actin Filaments

Answer 10

Accessory Proteins control assembly and position of cytoskeleton filaments

3 Types:

1) affect actin subunits
2) affects actin filaments
3) affects filaments bundling, cross linking and attachment to membranes

Question 11

ARP Complex

Answer 11

Actin related protein
Uncleared assembly to form weblike, highly branched chains remains associated with minus end
Nucleation of actin filaments occurs at or near nuclear membrane, thus actin filaments accumulate peripherally

Question 12

Formin

Answer 12

Actin subunit-

Uncleared assembly of long, unbranded chains + remains associated with growing plus end

Question 13

Thymosin

Answer 13

Binds actin subunits, prevents assembly

Allows for a large pool of actin polymers to be available for nucleation of filaments in cell (regualtes)

Keeps monomers soluble so they are readily available

When bound to thymosin are considered locked state and cannot associate with a filaments causing high concentration of soluble actin monomers in cells

Question 14

Profilin

Answer 14

Binds actin subunits, speeds elongation

Recruits actin monomers to filament for polymerization

Binds to actin monomer, exposes site of actin that binds to plus end, addition of monomers induces conformational change (reducing affinity for profilin), pro falls off leaving filament one subunit longer

Question 15

Filament Nucleation

Answer 15

A process of formation of initial aggregate or nucleus

Question 16

Arp2/Arp3

Answer 16

45% identical to actin, proteins

The ARP comple nucleates actin filament growth from the minus end, allowing elongation at the plus end

Requires activation factor

In absence of act factor Arp2/3 are masked by other proteins to prevent them from nucleating a new actin filament

Binding to act factor induces conformational change

Mimics the plus end of actin filament
Allows actin monomers to bind
Bypasses rate-limiting step of filament numeration

ARP allows the actin track and listeria movement

Causes local nucleation and presents a surface protein ActA (blue) which cross links of actin

Filament growth is the driving force of cell movement

Most efficient when bound to side of preexisting actin filament, grows at 70 degree angle, repeated branching nucleation

Question 17

Cofilin

Answer 17

Makes the branched actin disassemble

Question 18

Actin filaments can form…

Answer 18

Cell surface projections that help move cells over solid substrate

2 types (lamellipodia and filopodia)

Catalyze by ARP complex and formins (regulation factors)

Question 19

The actin filaments of the cell cortex…

Answer 19

Determine the shape and movement of the cell surface.

Question 20

Lamellipodia

Answer 20

Flat protrusive veils

Question 21

Filopodia (or microvilli)

Answer 21

Spiky bundles

Question 22

Formins nucleate the growth of…

Formins come from…

Each formin subunit has…

Dimers nucleate…

The dimeric complex…

Answer 22

Straight and un-branched actin filaments

A large family of dimeric subunits

A binding site for actin monomers

Actin fil polymerization by capturing two monomer at the plus or growing end of the filament

Stays associated with the rapidly growing plus end as it elongates

Question 23

Thymosin vs Profilin

Answer 23

Thy- No binding, no growth

Pro- Rapid growth, competes with thy for binding sites