cytoskeleton Flashcards
list two types of tubule family
- alpha and beta tubulin- a/b heterodimers form microtubules. Major constituents of microtubules. Found in all eukaryotes
- gamma microtubules -Major component of g-tubulin ring complex (y-TURC) recruited to microtubule organizing centres (MTOCs) - usually the centrosome. Found in all eukaryotes
Three types of MT
Astral , Kinetochore, Interpolar
Microfilament
Microtubule
Intermediate filament
7-9nm
25nm
10nm
Map2 and tau accessory proteins and their locations
- bind via a positively charged tail which binds the negatively charged surface of the lattice
- MAP2 is only found in dendrites where it forms fibrous cross-links btw MT and intermediate filaments
- Tau is found in dendrites and axons and act as a bridge btw parallel MTs
List the structure and location of complex microtubule structures
-single (13 protofilaments) /doublet ( cilia and flagella)/triplet ( basal bodies and centrioles)
-singlet( A tubule)- 13 protofilaments
-doublet - (A+B)
triplet - (A+B+C)
List the structure of Actin
- globular protein subunit of helical twist microfilament (two strands)
- ATP binding cleft
- 1 repeated unit-72nm
- The ATP binding cleft always binds to the opposite side of the adjoining actin molecule. This gives the filament polarity with the actin binding cleft exposed at the minus end.
proteins which bind to actin - Filament capping proteins/ Monomer binding proteins
- cap Z and tropomodulin/ profilin & thymosin beta 4
motor proteins - myosin
cofilin
- actin destabilising factor
- binds to side of actin-ADP
- fragmentation of actin fialments
State the proteins require for dissociation of ADP-actin filaments.
cofilin -CHOP OFF INTO 18-19 monomers
AIP1 - actin interactin protein-1- chop into single monomer
Function and the protein which activate Arp2/Arp3 complex
- branching of nuclear filaments
- WASp
State one actin binding toxin
-cytochalasin B,D
Binds monomers and barbed ends, inhibits polymerization
How actin filaments can be bundle into and proteins required ? location
-contractile bundle( alpha-actinin) and parallel bundle (fimbrin)
contractile bundle- enable myosin-2 to enter
parallel bundle - does not enable myosin-2 to enter
CB - muscle , PB - microvilli
What is troponin complex composed of?
TN-T, TN-C(bind to calcium), TNI
State the method by which step size of a myosin motor is measured
- laser beam optical tweezers\
- beads connect to myosin 2, ATP added
- stimulation of ATPase causing movement of MT will be recorded by computer using laser beam
State step size of myosin 1, 2 and 5 and their function
myosin 1 : 10-14nm , membrane association, endocytosis
myosin 2 - 5-10nm, contraction
myosin 5 : 36nm , organelle transport
Drugs which cause MT instability and how they destroy MT
Colchicine and colcemid - bind to tubulin dimer and prevent its polymerisation
-block mitosis by dissolving the spindle
Nocodazole : bind to tubulin dimer and prevent polymerization
Actin binding toxins
Cytochalasin- binds monomers and barbed ends / inhibitis polymerization
Botulinum toxin : ADP ribosylates the monomer and stabilise G actin
Contrast kinesin and myosin movement on MT
myosin : releases from the actin filament when ATP binds, cocking is induced by ATP hydrolysis and the power stroke is provided by dissociation of Pi.
kinesin :kinesin is bound to MTs (in rigor) with ATP bound and is released when ATP is hydrolysed to ADP and ATP binding produces the power stroke that throws the partner head forward.
Describe locomotion of keratocytes
- extension of one or more lamellipodia from the leading edge of the cell -actin polymerization
- new focal adhesions are made - involves capping
- the bulk of the cytoplasm is pushed forward(acto-myosin bundles at the rear of cell) -translocation
- trailing edge detaches from the subtratum and retracts into the cell body(recycle adhesion molecuels to the frint of cell)
How is chemotaxis/locomotion in keratocyte controlled with gradient?
Front edge : cdc42 activation : Rac activation ; activate wasp& Arp2/Arp3 ; branching/assembilign of actin filaments
Lagging edge : Rho GTPase activation- stress fibres and myosin 2 activation - forward movement of bulk of cell contents
- rapid movement
Assay for wound healing
- fibroblast move to replace the gap after scratching
- experiment with dominant negative Rho-GTpase and Rac and Cdc42 shows that they are all required for chemotaxi
key constistuents of cilia and flagella
- microtubules and dyneim
location of flagella
sperm and protozoa
function of cilia
- propel cells
- immobilised - propel liquid and particles over their apical surfaces
DIfference btw intermediate filament, microtubules and microfilament
IF - no nucleotide bind
MT - GTP
Actin filament ; ATP
IF - unpolarized, less dynamic, no motors
State type I and type II intermediate filaments/their function
- cytokeratins
- provide mechanical strength to epithelial cells and their derivatives when crosslinked
How is intermediate filaments formed?
antiparallel, 310-355 reisdue coiled-coil domain in each IF molecule
- form protofilament by making end-on-end contacts with other dimers (N and C of adjacent dimers interact)
- tetramers of protofilament twist around each other to from mature IF
Type 3 IF
smooth muscle - desmin (crosslinked)
Skeletal muscle - skelemin ( M line) and Synemin (Z disk)
Type 4 intermediate filaments and their function
- neurofilaments
- determine the correct orientation of axon and the rate by which nerve impulses are propagated along the axon
Type 5 IF
- Nuclear lamins
- The nuclear lamina is located on the inside of the nuclear envelope and provides structural support for it.
- Nuclear lamins (A, B, C) associate to form a meshwork.
- . The C-terminus of B lamin is covalently attached to the membrane via polyisoprenyloid lipids.
cyclin and cdk (G1, G2, S and M)
mid G1 : Cyclin D CDK4, CyclinD CDK6
late : Cyclin E CDK2
M : cyclin A CDK 2
S : cyclin A CDK 1/cyclin B CDK1
pathway of how entry into cell cycle is regulated.
Mitogen binds to mitogen receptor - Ras - Raf - MAPkinase - enter nucleus -Fos/Jun Transcription - immediate early gene expression- myc - delayed response-gene expression- cyclin D - activation of G1/CDK - entry intocell cycle
State the inhibitor of cyclin D CDK 1
P16INK4A
How mutation of TS genes and oncogenes affect cell cycle?
- Overexpression of oncogenes force cells to enter S phase
TS -normally suppress tumour by inhibition of passing restriction point into S phase - but when P16INK4A mutated, can pass restriction point
- When the cells are not ready yet!!! -cause replication stress ( eg not enough nucleotides for DNA replication/ chromosome rearrangement when some parts of the genome are damaged)
Function of gene product of Rb and INK4A
Rb : inhibitor of G1/S gene expression
INK4A : Cdk inhibitor of P16INK4A
State the enzyme required for dding N-linked oligochride in the ER
oligosaccharyltrnfere
