Shape and movement
1.[3p] Match each filament system to its distinguishing feature.
Match each filament system to its distinguishing feature.
Actin filaments
Microtubules
Intermediate filaments
25 nm hollow tubes of tubulin dimers, tracks for kinesin and dynein
about 10 nm, not polar, bind no nucleotide, resist tension
7 nm across, polar, tracks for myosin
Show the answer
Actin filaments: 7 nm across, polar, tracks for myosin Microtubules: 25 nm hollow tubes of tubulin dimers, tracks for kinesin and dynein Intermediate filaments: about 10 nm, not polar, bind no nucleotide, resist tension
2.[3p] What does nucleotide hydrolysis buy a microtubule, given that tubulin polymerises without it?
What does nucleotide hydrolysis buy a microtubule, given that tubulin polymerises without it?
The answer is: Instability, since GDP-bound subunits are strained and the filament falls apart when its cap is lost
The answer is: Instability, since GDP-bound subunits are strained and the filament falls apart when its cap is lost
The answer is: Instability, since GDP-bound subunits are strained and the filament falls apart when its cap is lost
3.[1p] A microtubule shrinks roughly ten times faster than it grows.
A microtubule shrinks roughly ten times faster than it grows.
The answer is: True
4.[3p] Why do taxol, which stabilises microtubules, and the vinca alkaloids, which destabilise them, both kill dividing cells?
Why do taxol, which stabilises microtubules, and the vinca alkaloids, which destabilise them, both kill dividing cells?
The answer is: What mitosis needs is dynamics, so removing either growth or shrinkage disables the spindle
The answer is: What mitosis needs is dynamics, so removing either growth or shrinkage disables the spindle
The answer is: What mitosis needs is dynamics, so removing either growth or shrinkage disables the spindle
5.[3p] Kinesin takes 8 nm steps against a load of about 5 pN, using one ATP worth J per step. What is its efficiency as a percentage?
Kinesin takes 8 nm steps against a load of about 5 pN, using one ATP worth J per step. What is its efficiency as a percentage?
6.[2p] Fast axonal transport runs at about 1 µm/s. How many days does a cargo take to travel one metre?
Fast axonal transport runs at about 1 µm/s. How many days does a cargo take to travel one metre?
7.[2p] Listeria propels itself through a host cell's cytoplasm on a tail of polymerised actin, with no motor protein involved. What does that demonstrate?
Listeria propels itself through a host cell's cytoplasm on a tail of polymerised actin, with no motor protein involved. What does that demonstrate?
The answer is: Polymerisation on its own can generate force
The answer is: Polymerisation on its own can generate force
The answer is: Polymerisation on its own can generate force
8.[3p] For a swimming bacterium the Reynolds number is about . What follows?
For a swimming bacterium the Reynolds number is about . What follows?
The answer is: Inertia is irrelevant, so a reciprocal back and forth motion produces no net movement and swimming needs a rotating helix or a travelling wave
The answer is: Inertia is irrelevant, so a reciprocal back and forth motion produces no net movement and swimming needs a rotating helix or a travelling wave
The answer is: Inertia is irrelevant, so a reciprocal back and forth motion produces no net movement and swimming needs a rotating helix or a travelling wave
9.[2p] Which are consequences of defective ciliary dynein in humans?
Which are consequences of defective ciliary dynein in humans?
Select all that apply
The answer is: Chronic airway disease from unswept mucus, Infertility, Reversal of internal organ position in about half of cases