Cytoskeleton Flashcards
What are the three types of cytoskeleton?
Microtubules, actin filaments, intermediate filaments
What is listeria?
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
Where is listeria found?
Ubiquitous in the soil, animal products (dairy/meat), and unwashed lettuce.
What are symptoms of listeria?
-Headache
-Stiff neck
-confusion
-Loss of balance
-Convulsions
-Fever and muscle aches
FOOD POISONING
What is the treatment for listeria?
HOSPITALIZATION
IV antibiotics
Incidence down since hotdogs of 1988
What are other risks associated with listeria infection?
1 in 5 people die.
Pregnancy: miscarriage, stillbirth, new born death
20% chance of fetal loss and new born death in 3%
How does Listeria infect cells?
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.
What type of movement do Listeria present?
Actin-based motility, smashing through organelles causing serious damage.
Like speed boats
Actin track=comet tail
0.2 um per second (50 ft/sec)
What is the bacterial makeup of the human biome?
There are 10x more bacterial cells than human cells
“You are an ecosystem”
Actin Filaments
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
ARP Complex
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
Formin
Actin subunit-
Uncleared assembly of long, unbranded chains + remains associated with growing plus end
Thymosin
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
Profilin
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
Filament Nucleation
A process of formation of initial aggregate or nucleus
Arp2/Arp3
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
Cofilin
Makes the branched actin disassemble
Actin filaments can form…
Cell surface projections that help move cells over solid substrate
2 types (lamellipodia and filopodia)
Catalyze by ARP complex and formins (regulation factors)
The actin filaments of the cell cortex…
Determine the shape and movement of the cell surface.
Lamellipodia
Flat protrusive veils
Filopodia (or microvilli)
Spiky bundles
Formins nucleate the growth of…
Formins come from…
Each formin subunit has…
Dimers nucleate…
The dimeric complex…
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
Thymosin vs Profilin
Thy- No binding, no growth
Pro- Rapid growth, competes with thy for binding sites
