Comprehension - L14-L15 Flashcards
What is it called when there is an absence of stabilization in microtubules?
Protofilaments curl outward and undergo catastrophic shrinkage
What do +TIPS do?
- Bind to +ve end of microtubule and regulate the rate of growth or shrinkage
- Mediate attachement to subcellular structure
- Microtubule polymerization/disassembly can push and pull material within the cell
What is the purpose of microtubules?
- Provide mechanical support: are stiff enough to resist compression or bending forces
-Determine the shape of a cell - Maintains intracellular location of organelles
What do motor proteins do?
Utilize ATP hydrolysis to generate mechanical forces that move the motor protein and attached cargo along the cytoskeleton
What are examples of cargo that are transported on microtubules?
- Membraneous vesicles
- Non membrane bound ribos, RNA
- Organelles (lysosomes, mitos)
- Chromosomes
- Other cytoskeletal filaments
What are the three types of motor proteins?
- Microtubule motor proteins (kinesins and dyneins)
- Actin motor proteins (myosins)
In kinesin, what are part of the globular head?
- Binds microtubules
- ATP hydrolysis
- Conserved sequences
In kinesin, what is part of the tail?
- Binds to cargo
- Diverse sequences
Which direction does kinesin move?
Towards the positive end
How does kinesin move?
Leading head binds 1 ATP: hydrolysis and release of ADP + Pi = power stroke that swings the trailing head forward
How does dynein bind to cargo?
Via an adaptor protein, called dynactin
Which direction does dynein move?
Towards the negative end
What does dynein do?
- Positioning the spindle and moving chromosomes during mitosis
- Positioning organelles and moving vesicles
What is the axonome?
Core contains microtubules oriented longitudinally
How are all microtubules oriented?
+ at the distal end
- at the basal body
In the axoneme, how many doublets are there and how are they connected to each other?
There are 9 peripheral doublets and they are connected to each other via nexin
Describe the 4 steps of the movement of flagella
- dynein tails attached to the A tubule and dynein stalks bind to B tubules
- Power stroke
- Dynein stalks detach
- Dynein stalks reattach
What does actin do?
Involved in cellular motile processes
- movement of vesicles
- Phagocytosis
- Cytokinesis
Provides structure support
Actin filaments have polarity. The positive and negative ends are…
+: barbed
-: pointed
Is ATP actin added to just the positive end of the filament?
No. IT is added to both ends, but there is faster addition at the barbed end
What is the critical concentration?
- Minimal concentration of available ATP-actin required to elongate
- critical concentration of the barbed end is lower
What are the steps of actin filament and disassembly?
- Preformed actin seed in presence of ATP-actin
- at high [ ] its added to both ends
- [ ] reaches critical [ ] of the pointed end; addition stops at pointed end
- loss of subunits at the pointed end but addition continues at barbed end (steady state)
5.relative position of subunits is continually moving (treadmilling)
Which way does myosin move?
all myosin move towards the + barbed end
What are the 3 components of Conventional Myosin Type 2?
Motor: binds actin filament, binds and hydrolyzes ATP, conserved sequences
Neck: lever arm, moves during power stroke
Tail: Intertwining of 2 heavy chains, allows the formation of filaments of myosin
What does Unconventional Myosin Type V do?
Moves processively along actin filament
Moves hand over hand
Long necks act as swinging arms
Can take very large steps\
What is the adaptor called that binds Myosin type V to a vesicle?
Rab 27a
Movement over long distances occurs mostly on:
Movement locally in the outskirts of the cell occurs on:
Microtubules
Actin filaments
