Microtubules Flashcards
isoforms of tubulin
α tubulin, ß tubulin, gamma tubulin
α tubulin
always bound to & never hydrolyzes GTP; GTP binding site is blocked by beta tubulin
ß tubulin
can hydrolyze GTP
gamma tubulin
part of nucleation
building block of microtubules
αß tubulin dimer
describe how a microtubule is formed
an individual protofilament (linear) is formed & laterally associates protofilaments to create cylindrical structure
How do the plus and minus ends of microtubules differ?
”+” end has significantly lower critical concentration than “-“ end (preferential building at “+” end)
creates “treadmilling” effect
describe “treadmilling” effect
preferential addition of tubulin at “+” end, & disassembly at “-“ end
singlet
made of 13 porotofilaments; found in the cell body
doublet
made of 23 protofilaments (13+10); found in cilia/flagella
triplet
made of 33 protofilaments (13+10+10); found in basal body/centriole
MTOC
microtubule organizing center
MTOC types
centrosome & basal body
centrosome
MTOC in center of every cell, attaches to - end of microtubule singlets and triplets
basal body
MTOC found just inside cell body in cells with cilia/flagella, attaches to - end of microtubule doublets
gamma-TURC complex
made of gamma tubulin & other proteins; functions as a nucleation site for microtubule formation
dynamic instability
microtubules undergo regular cycles of growth and shrinkage; microtubules experience a growth phase until a “catastrophe” initiates the disassembly phase - continues until “rescue”; necessary for mitosis
What proteins contribute to dynamic instability?
kinesin-13, stathmin, katanin
kinesin-13
binds to dimers at the + end (uses energy), curves end of tubulin protofilament, removes GDP bound dimers
stathmin
binds 2 dimers of curved protofilament & removes them
katanin
severs microtubules
What are kinesins and dyneins?
motor proteins
kinesin
”+” end directed motor protein, head region binds/hydrolyzes ATP & walks “hand-over-hand” along microtubule (similar to myosin structure)
dynein
”-“ end directed motor protein, large complex that includes dyanctin (which interacts with the microtubule), light & heavy chains, etc.
microtubule structures in flagella
axomeme = central bundle nexin = connects outer doublets dynein = moves flagella by allowing central singlets to slide past one another, creating a whipping motion
roles of microtubules in cell division or mitosis
capture, alignment, and movement of chromosomes
kinetochore
structure where kinetochore microtubules attach to chromosome
centromere
structure where sister chromatids attach to each other
classes of microtubules in the mitotic spindle
kinetochore microtubule, polar microtubule, & astral microtubule
microtubule containing structures
cell body - contains singlets
cilia/flagella - contain doublets for motion
basal body/centriole - contain triplets
MAPs
microtubule associated protein - stabilize microtubules
What are the roles of motor proteins, microtubules, and microfilaments in the movement of cell contents?
Organelles will have motor proteins (kinesin/dynein/myosin) on them based on where they want to move materials & what structure the material will move along (microtubules/microfilaments). They will likely have more than one type.
phases of mitosis
interphase, prophase, prometaphase, metaphase, anaphase, & telophase/cytokinesis
interphase
microtubules radiate away from MTOC (microtubule organizing center)
prophase
centrism has replicated and moved
prometaphase
microtubules capture chromosomes - motor proteins move chromatids to end of the microtubules until attached on both sides and stabilized by the tension (bioriented)
metaphase
microtubules line up the chromosomes through a combination of treadmilling and motor proteins
anaphase
microtubules pull chromosomes to opposite poles through microtubules shrinkage & sliding
telophase/cytokinesis
each cell has 1 centrisome and 1 set of chromosomes
kinesin 3
located at kinetochore; enhances microtubule disassembly during mitosis
