Cell 5 Flashcards
How are Multicellular Organisms are held together?
Cytoskeleton found inside the cells help hold cells together.
Plasma membranes are not strong enough to hold cells together.
Proteins within the plasma membrane and extracellular proteins forming the extracellular matrix hold cells together and thoseare crucial to the function of the type of tissue.
How is “movement” achieved?
Things are moving with purpose.
Organelles are moving through the cytoskeleton and so are the cells themselves.
White blood cells and macrophages.
Cytoskeleton is used in muscle contractions.
The cytoskeleton
Intricate network of protein filaments that extend throughout the cytoplasm.
Microtubules
Microfilaments
Intermediate filaments
There is no _____ ______ in a cell.
empty space
Microtubules: Structure
Polymer of alpha and beta tubulin
Monomers 55 kDa each
AB dimer is basic “subunit”, dimer builds up a microtubule (never seperated)
Has polarity
Hollow tubes (25 nm diameter)
Microtubule has ________.
Polarity
Alpha (-) and Beta (+) ends.
Arranged alpha-beta polymer
Microtubule ________ come together with other ________ (_ _) to form the tube that becomes the microfilament.
protofilament
protofilaments
13
Motor Proteins moves along _ _ nm per step.
16 nm
8 nm is the length of the dimer.
Dimer tubulin subunit
VERY STABLE
alpha dimer binds permenantly to GTP
beta dimer can hydrolyze GTP so it can be bound to GTP or GDP
As the polymer grows beta GTP is hydrolyzed
Arrangement of MT Protofilaments
Singlets (13 protofilament forming a single tube 25 nm in diameter; found in the cytoplasm) Dynamic
Doublets (23 protofilaments a ring of 13 bound to a ring of 10 protofilaments; found in the flagella, cilia) Stable
Triplets (33 protofilaments, a ring of 13 bound to two rings of 10; basal bodies, centrioles) Stable
Microtubules ______ the interior of all cells.
The _______ of all cells have microtubules.
organize
cytoplasm
Singlet microtubule functions
Microtubules found in the spindle apparatus formed during mitosis.
Form axons
Microtubule Organization
Dynamic process
Assembly centered around the Microtubule Organizing Center
Types of Microtubule Organizing Center
The centrosome is the main MTOC of the cell, the microtubules polymerize from this organizing center.
Singlet microtubules come form the centrosome.
Spindle Poles are the MTOC in the cell during mitosis
Cilia/Flagella come from the Basal Bodies.
Microtubule (_) end always grow away from the _____.
+
MTOC
Minus end is always found in the MTOC.
If you want to go away from the middle cell to the cell surface you move towards the plus end (anterograde)
Gives the cell a sense of directionality
Centrosome
Major MTOC in animal cells
Contain centrioles (plants don’t have centrioles)
Centrioles
Barrel shaped structures that are 90 degress to one another.
Two centrioles inside in the centrosome.
Centrioles triplet microtubules are not being extended to make the singlet microtubules.
Singlet microubules come from the _____ ____ the centrioles the ________ _______.
space around
pericentriolar matrix
the proteins around are responsible for the synthesis of microtubules
Centriole Details (Structure)
9 triplets in a ring.
Centrioles can divide (into unidentical mother/daughter centrioles)
Centrioles surrounded by pericentriolar matrix.
Pericentriolar Matrix (2 main roles)
Contains dozens of proteins around the centrioles.
the proteins polymerize the singlet microtubules.
proteins are responsible for centriole replication.
Gamma-tubulin Nucleates polymerization
Gamma tubulin ring complex (γTuRC): Augmin + other proteins.
Nucleating sites for microtubules: add alpha and beta subunits to the complex growing the MT.
possibly facilitates microtubule branching (augmin).
Gamma tubulin is always at the minus end, it caps it so it can’t grow.
Plus end grows and shrinks.
Microtubules do not _______ but they can ______.
branch
overlap
branching only occurs during the formation of the mitotic apparatus (caused by augmin).
Polarity of Tubulin Polymerization: Assembly and dissasembly occurs at the (_) end.
Nucleation site _____ initial polymerization.
+
accelerates
Nucleus
monomers building blocks act as a nucleus.
Flagella have a triplet microtubule nucleus and we add alpha and beta subunits.
If you are above the _______ _______ you get growth.
Critical Concentration
Effect of nucleation
There is a lag in polymerization when no nucleus is present.
Lag is when nucelus is being polymerized.
Elongations speed depends on if a nucleus is formed.
You have to be above or at the critical contration to make polymers
At what temperature does dissasembly begin
4 Celsius
After the crititical concentration
Concentration of dimers is constant
Dynamic instability
microtubules are constantly growing and shrinking
Why do microtubules shrink in certain regions of the cell?
Concentration of tubulin dimers fall above and below the critical concentration in certain areas of the cell.
As the microtubule polymerizes it may move away from its store of dimers.
When its depolymerizing it can be rescued by moving into an area with concentration of dimers above the critical concentrations.
Dynamic instability depends on the _______ (or _______) of a _ _ --______ _____.
presence or absence
GTP-beta-tubulin cap.
It provides for lateral cohesion = smooth (+) end.
In order to polymerize the beta subunit needs to be bound to GTP, the allows for smooth cohesion between the protofilaments.
When _ _ _ to _ _ _ hydrolysis reaches the (_) ends it weakens cohesion between protofilaments.
GTP to GDP
+
the tubulin is being hyseolized after synthesis, we start losing cohesion between the filaments.
ends begin to fray (when we reach a region of low critical concentration)
Microtubule disrupting drugs
Colchicine: depolymerizes; disrupts anterograde transport.
Taxol: stabilizes; mitosis is interfered with because the cell can’t divide, the microtubules can’t disassemble.
Microtubule Associated Proteins (MAPs)
MAPs can alter microtubule stability
They bundle microtubules; coat them stabilizing and preventing depolymerization.
Can be regulated-phosphorylated can promote disassembly (CDKs in cell cycle); phosphorylated MAPs fall off
Some MAPs contain MT binding domain and a “projection” domain
_ _ _ _ and ___ stabilize microtubules by coating them so that even if they are in area below their _____ _______ they will not depolymerize.
MAP2 (axon) and Tau
critical concentration
Speciasl MAPS are associated with the (+) end of MTs called _ _ _s
+TIPs
EB1 is a +TIP that binds unique structures found on growing + end.
EB1 is dynamic it is removed during disassembly but present during growth
It stabilizes the + ends and reduce catastrophe but these TIPs could be transporting something.
EB1 is moving to the (+).
MT End Binding and Severing Proteins
XMAP215 and CLASP TOG domains stabilize growing protofilaments: TOG help the (+) end protofilaments adhere to each other, they prevent fraying by slowing down hydrolysis.
Kinesin 13: Uses ATP to rip dimers from the (+) end, regardless of concentration dimers depending on the amount of K13 you will rip dimers off.
Stathmin: binds to the microfiaments and promotes GTP hydrolysis by promoting fraying.
