week 5 Flashcards
how are cells held together?
- you need intracellular and extracellular adhesion
- proteins inside and outside will hold things in place
- ## cell-cell adhesion proteins
what moves in the cell?
- organelles, cells and tissues
how do tings move in cells and how do cells move
cytoskeletal proteins
cytoskeleton
- intricate network of protein filaments that extend throughout the cytoplasm
what makes up the cytoskeleton?
- microfilaments
- microtubles
- intermediate filaments
microfilaments
- 7-9 nm width
- actin subunits
- this is the thinnest component
mictotubules
- alphabeta- tubulin dimer subunits
- this is the thickest component
- 25 nm width
intermediate filaments
- various subunits
- 10 nm width
how can the cytoskeleton be visualized
- through immunofluorescence
DNA length. of one turn?
- 10 nm = 100 A
is there any empty space in a cell
NO- solvents like cytoplasm or RBC floating blood stream
microtubules
- polymer of alpha and beta tubulin
- 25 nm in diameter
- can be up to 100s of micrometers long
- organize the
alpha and beta tubulin
- monomer of microtubules
- 55 kDa each
- alpha-beta dimer
- have polarity
why does the alpha beta dimer have polarity
- polyervizes faster on the positive side
- the positive is the beta tubulin end
- the negative is the alpha tbulin end
how long is one dimer of alpha beta tublin
8 nm
how is a seam created in microtubule protofilaments
- not folding properly, all the subunits ar not lined up
protofilaments
- dimers of the Dublin subunits strung together
- long strands
how many protofilaments ar included in the hollow tubes of mictobtules
13
what are the largest cytoskeletal filaments that we discuess
microtubules
in what form do the subunits have to be in, in order to polyermize
in GTP form
- the order of polymerization is alpha beta alpha beta
dimeric tubulin subunit
- very stable (dimer is not easily separated)
- alpha tunulin binds gTP only
- beta tubulin can hydrolyze GTP (can be bound to either)
- beta gTP is hydrolyzed as the protofilament polymer grows
how can MT protofilaments be arranged
- singlet
- doublet
- triplet
singlet
- found in cytoplasm
- 13 protofilmanets form a single tube of 25 nm.
- 13 protofilaments
doublet
- made up of two microtubules
- 13 A protofilaments and 10 B protofilaments subunits
- in cilia nd flagella
mictorbuulse in cytoplasm
- the cytoplasm of all cell have these
- e.g. nerve axon
- singlet mmicrotbules
axonemela microtubules
- specific organization and type of microtbubule found in cilia and flagella
- doublet microtubules
what do singlet mictobrubles in cytoplasm and nerve axons fo
transport things along axons to nerve cell boies
MTOC
- main one = centrosome
- where microsomes polyermize from
centrosome
- contains centrioles
- centrioles are not found in plantscen
centriole
- triplet microtubules
- two triplets that are ninety degrees to erah other
- striplets = pretty stable, and dont really polyermzie or depolyermize, which makes centrioles stable.
- has pericentriolar matrix
mother and daughter centrioles
- centrioles must replicate during mitosis
pericentriolar matrix
has proteins like gamma tubulin, augmen, - surrounds the centrioles
augment and gamma tubulin
- found in the pericentrioar matrix
- form complexes that allow the singlet microtubules to polyermize
in what direction are singlet microtubules polyermized
- with plus end going away from the centrosome
- the e end is in the pericentrular matrix
How many triplets in a centriole ring?
9
gamma tubulin ring complex
- provides nucleating sites for mcirotiubules.
- facilitates microtbubuel branching with agumin
- gamma tubulin ring complex = nucleating site
where does polymerization start
- gamma tubulin and gamma tubulin ring complex, located at negative end
where do microtubule assembly and disassembly occur
at plus end
what does a nucleation site do
accelerates initial polyermization
nucleaiton
- ## micotunule can grow on already existing microtubules (these are used a a nucleus)
why is the - end never capped
- because ti is capped
- but plus end will grow and shrink
why is elongating/poymerizing from single subunits so time consuimg/
- must form nuclei
- adding nuclei already means no need for formation, means faster poylermization, if enough subunits to be above the critical concentration
actin example of closed system polyermization
- add actin monomers above citric concentration
- slow growth initially, because monomers must come together to form nuclei
- after that, can get rapid elongation.
- if u add nuclei from the start, no lag phase (.e.g having gamma tubullin ring complex which acts a. nucleus in the centrosome)
dynamic instability
oscillations in length
- cells need this in order to get to different locations
what does dynamic instability depend on
- the presence or absence of a GTP beta tubulin cap
microtubule disruption drugs
colchicine
taxol
anticancer drugs
colchicine
depolyermization of all teh singlet microtubules
taxol
stabilizes
