Lecture - 6 Cytoskeleton Flashcards
What are the three types of cytoskeleton componets?
Microfilaments
intermediate filaments
Microtubles
What are the characteristics of actin monormers and filaments
- highly conserved
- WxL = 7nm x 7 um
- monomers “depolarized” = G- actin
- longchain “polarized”= F acrin
- r varieties = alpha, beta, gamma
- actin filaments are Polarized b/c actin monomers added in the same direction
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What is actin polymerization?
G actin monomers have to oriented in same direction to form trimer (polarity)
Nucleation when 3 ATP-G Actins form a trimer
Trimer polmerization : adds more G actins via Additsions of ATP to the growin plus or barbed end
Causes ATP to be Hydrolized into ADP
THis action is REVERSIBLE ; Leads into treadmilling
PS: F actin is a double helical chain of G actin
What is treadmilling?
A dynamic equalibrium b/w the pointed (minus) and the (plus) barbed end.
How does actin monomer concentration affect G actin?
- The addition of G actin filaments occur more rapidly and at a lower concentration at the plus or barb end. (5 -10 X)
- The minus of slow growing end is the slow growing one.
- Higher concentrations of G actin facor net addition at both ends
- AT VERY LOW, concentrations G actin f avor disassembly of actin
What drugs affect polymerization and Control Tread milling?
- Cytochalasins
- Bind to barbed ends, block elongations, can inhibit movements
- Phalloidin
- Binds to actin filamaents and prevents dissocation
What is list the Actin binding proteins.
Hint there are 13 of them
- Spectrin:
- Dystrophin:
- Villin and Fimbrin:
- Calmodulin and Myosin 1:
- Alpha- Actin
- Filamin:
ACtin binding molecules that control treadmiling
- Thymosin
- Profilin
- Gelsolin
- Cofilin
- Arp 2/3
- Phalloidin
- Latrunculins
What is Thymosin: ?
• Captures actin monomers; prevents monomers from being polymerized.
actin binding molecule that controls treadmilling
What is Profilin?
- BInds to actin monomers and prevents monomers from being polymerized
- MAIN FUCNTION
- FACILITATE THE EXCHANGE OF BOUND ADP FOR ATP WHICH FAVORS POLYMERIZATION
- (only atp monomers can assemble into f actin)
- Actin binding molecule that controls treadmilling
What is gelsolin?
Destablizes F actin and caps actin filaments
Prevents loss and addition of G actin
In presence of Calcium ion, fragments actins filaments remain vound to plus end
Actin binding molecule that controls tread milling
What is Spectrin?
- Found in red blood cells
- maximizes SA for O2 exchange
- binds cortical skeleton to PM
- Actin Binding Protein
What is Dystrophin
Binds to the cortical skeleton to PM
Actin binding protein
WHat are villin and Fibrin?
Actin bind protein
Cross links in microvilli
WHat is calmodulin and myosin I?
Cross links actin to PM in microvilli
Actin Binding Protein
What is alpha Actin?
Cross links stress fibers and connects actin to protein plasma membrane complexes.
Actin bind protein
What is Filamin?
Actin binding protein
Cross links actin at wide angles to form screen like gels
What is cofilin?
Triggers the depolymerization of ADP bound actin at the minus end
It is an actin bind ing molecule that controls treadmilling
WHat is Arp 2/3
Initiaties the growth of F actin from sides of existing filament-causing branching
Actin binding molecule that control treadmilling
what is Phalloidin
Prevents the depolymerization by binding to actin fialments
What are Latrunculins?
Binds to G actin and induces F actin depolermization
Actin molecules that control treadmilling
What is the basic structure and assembly of intermediate fialments ?
- 8-10 nm thick
- Head and tail domains that determine function
- central rod of two poly peptides forma dimer
- rods aligned tail to tail and head to haed
- Associate in a staggered antiparallel fash to form tetramers
- b/c antiparallel association they lose their polarity
- more stable than actin doesnt require treadmilling
- 8 tetra wound together form Unit length filament
- ULF connected together form an intermediate
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What is the structure of microtubles
- 25 micrometers in diameter
- composed of tublin dimers
- alpha and beta
- protofilaments formed are from long chains of dimers
- fast growing plus end and slow growing minus end
- microtubles consist of 13 protofilaments arranged parallel to form a cylinder with a hollow core.
How does treadmilling and dynamic instability relate to microtubles assembyl and dissembly?
- Tublin dimers with bound GTP (energy ) assocate bind to Growing END
- Plus end also grow more raplidly than minus end (in presence of low calcoium ion concentrion)
- After polymerization, GTP (their energy) is hydrolyzed to GDP and the tubulin is less stable.
- Dimers at the minus end dissociate
- At high concentratiosn of tublin GTP the dimers are added more rapidly than GTP is hydrolzed and microtuble grows
- If concentration of GTP tublin is drops, GTP at the plus end is hydrolyzed and dimers are lost.
WHat are the different types if intermediate filaments?
- Type I
- acidic keratins
- Type II
- neutral to basic keratins
- Type III
- vimentin, Desmin, Glial fibrillary Protein, and preipherin
- Type IV
- Neurofilaments
- Type V
- nuclear lamins
- Type VI
- NEstin
