Actin+Microtubules Flashcards
What are the 3 main parts of the cytoskeleton?
Actin, Microtubules and Intermediate tubules
What is the function of the cytoskeleton?
Gives the cell its shape Capacity to move or alter its shape Organisation of organelles Transport of organelles Cell Division Chromosomes organisation and movement
What is the actins function?
In the plasma membrane of animal cells to give strength and shape to the thin lipid bilayer
What is the function of the intermediate tubules?
Lines the inner face of the nuclear envelope protecting DNA like a cage
What is the function of the microtubules ?
Determines position of membrane bound organelles Rearrange themselves to form bipolar mitotic spindle during cell division to from cilia
What is the abundance of the parts of the cytoskeleton?
In order of decreasing abundance, Microfilaments, Intermediate filaments then microtubules
What is the 4th part of the Cytoskeleton, and its function?
Accessory Protein interacts w/ CS to regulate + link filaments together. Essential for controlled assembly of CS filaments at certain locations
What are the 3 parts of the cytoskeleton made from?
Microfilaments and microtubules are made from subunits that can rapidly assemble and dissemble
Intermediate filaments are made of more stable fibrous protein subunits
What is the structure of the Actin?
What domains, polymers did it have?
4 domains with a central cleft where divalent cation Mg2+ and nucleotide bind Helical Polymers
Flexible structure with 8nm diameter
Mammals have how many types of actin?
6 types
Alpha only in muscle
Beta found with gamma
Lower Eukaryotes like Yeast have how many actin genes?
One
What is the relationship between G- actin and F-actin?
G-actin have 1 Ca2+ and non-covalently bound ATP
G-actin is polymerised to F-actin
What is the shape of the actin monomer?
What is the shape/structure of the microfilament?
Actin monomer is pear shaped
Microfilament is polar with a plus/barbed and minus/pointed end
What is the difference between barbed/pointed ends?
Barbed end grows faster and its easier for subunits to add. Pointed end requires conformational change in change in subunits
What is the structure of the actin filament?
2 strands of F-actin which are twisted with 13.5 molecules per repeat 36nm
Right handed heliex
What is the rate determining step in actin formation?
Nucleation
Describe nucleation of actin polymerisation
Arp2 and Arp3 cannot polymerise but an ARP2/3 complex acts as a primer for the polymerisation and bind MF together
How is actin polymerisation regulated?
Profilin and thymosin modulate micro filament synthesis
How is the length of the actin micro filaments regulated?
Ca2+ binding to gelsolin causes cleaving of the mf
This gelosin/microfilament complex can act as a primer for cell elongation
Gelsolin is freed by PIP2 producing free + ends for rapid cell elongation
How are the subunits in microtubules bound?
By covalent bonds to form a 100kDa hetrodimer/ polymerising subunit.
What is the structure of the microtubules?
Tubular structure either Alpha or Beta Tublin
Alpha- GTP bound that doesnt hydrolyse
Beta- GTP may be bound so is exchangeable
What is the Major Microtuble Organising Centre (MTOC) of animal cells?
In the centrosome
In the cytoplasm near the nucleus
Describe microtuble complex of proteins
Mix of proteins including the gamma-tubule ring complex that nucleates the microtuble growwth.
Matrix is organised by pair of centriloes with acessory proteins .
What drives polymerisation of the microtubules?
GTP hydrolysis
