Lecture 12 Flashcards
What are the 3 filamentous structures that compose the Cytoskeleton?
Microtubules, actin filaments, intermediate filaments
List the 5 functions of the cytoskeleton
Structure support
Positioning of cell organelles
directing of material movement
generating movement
cell division
what are properties of microtubules, what protein are they made from, what are they called when organized into longitudinal rows?
they’re hollow, rigid and tubular
Made of the protein tubulin
called protofilaments when arranged
what are the building blocks of protofilaments? what are their properties?
Made of Alpha & Beta-Tubulin subunits
the subunits fit tightly together, organized in a linear array, asymmetric and polar
What is the function of microtubules?
Provides mechanical support (resist compression), determines cell shape, directs movement within the cell
how do microtubules move objects in cells?
serves as a track for motor proteins that generate force
motor proteins are kinesin and dynein
what are some properties of Kinesin motor proteins? what do they bind to in order to move and what do they use?
Smallest motor protein, made of 2 identical heavy & light chains
binds to microtubules and uses ATP for force generation
True for false?
the movement of Kinesin motor proteins is proportional to ATP concentration
True
towards what to kinesin tend to move vesicles and organelles to?
an outwards direction towards the cell’s plasma membrane
What is some properties of the Cytoplasmic Dynein motor protein?
Huge protein, made of 2 identical heavy chains, variety of medium and light chains, moves towards the negative end of microtubules (opposite of Kinesin)
What are some functions of Cytoplasmic Dynein motor protein?
Positions spindle and moves chromosomes during mitosis
positions centrosome and Golgi complex
moves organelles, vesicles and particles through cytoplasm
what does microtubule-organizing centers control?
Number & polarity of microtubules, number of protofilaments and time/location of assembly
what do Centrosomes contain? What is it a major site of?
Contains 2 centrioles surrounded by electron dense pericentriolar material
is a major site of microtubules initiation and is the center of the microtubule network
what is a Basal body another type of? where does it form? How does it compare to centrioles?
another type of microtubule-organizing center that forms at cilium or flagellum (movement locations)
identical in structure to centrioles
centrioles and basal bodies can each turn into one another
what do Microtubule-organizing centers have in common and what does it do?
contain Gamma-Tubulin, critical for microtubule nucleation
What are some of the dynamic properties of microtubules?
can shorten, lengthen, disassemble and reassembleq
what are some things that can initiate microtubules to disassemble?
Modifications, temperature, pressure, High Ca2+ conc., chemicals
what are the interactions between GTP and Beta-Tubulin?
GTP binds to Beta-tubulin during assembly. GTP becomes GDP and stays bound
When being disassembled, GDP is replaced by a new GTP
What do microtubules depend on for growth or shrinking?
They depend on the tubulin dimers at the positive end
What is Dynamic instability and what does it explain?
phenomenon that explains microtubule behavior
Explains:
Growth and shrinkage can coexist in the same region of a cell
A microtubule can switch back and forth unpredictably between growing and shortening
What end is Dynamic instability important for?
Important for the positive end of the microtubule where subunits are added for growth and lost for shrinkage
What are the 2 types of Cilia
motile cilia - occurs in large numbers on a cell’s surface. moves fluid and particulate material
nonmotile cilia - acts as a sensory organelle to monitor mechanical and chemical properties of the ECF
What is the Axoneme?
core of the cilium containing an array of microtubules running longitudinally
made of a 9 + 2 array (9 peripheral and a central pair)
What do the Central tubules in anoxeme connect to and with what??
the A tubules with radial spokes
What process transports materials to the cilium / flagella?
the intraflagellar transport
What is the process of intraflagellar transport?
proteins assemble into a complex called IFT particle
particles line up to form a linear array (IFT trains)
IFT particles carry cargo proteins
How does motion for the cilia and flagella occur?
Dynein undergoes a conformation change after binding from the B tubule to the A tubule
A stroke occurs, the dynein then detach from B and cycle continues
True or false?
At any given time, the dynein arms on both sides of the axoneme can be active or inactive
False, only 1 side is active while the other is inactive
Describe the components and major functions of the cytoskeleton.
▪ Describe the structure and the functions of microtubules.
▪ Explain how kinesins and dyneins function as motor proteins within
a cell.
▪ Explain the activities that occur at microtubule-organizing centers
(MTOCs) and the underlying basis of microtubule dynamics.
▪ Explain how the movement of cilia and flagella relates to their
structure.
