Lesson test: Shape and movement

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Shape and movement

1.[3p]
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?

Instability, since GDP-bound subunits are strained and the filament falls apart when its cap is lost

Correct

The energy required for subunits to join the polymer

The answer is: Instability, since GDP-bound subunits are strained and the filament falls apart when its cap is lost

Protection against motor proteins

The answer is: Instability, since GDP-bound subunits are strained and the filament falls apart when its cap is lost

A permanent, unchanging structure

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.

True

Correct

False

The answer is: True

4.[3p]
Why do taxol, which stabilises microtubules, and the vinca alkaloids, which destabilise them, both kill dividing cells?

What mitosis needs is dynamics, so removing either growth or shrinkage disables the spindle

Correct

Both drugs happen to bind the same site

The answer is: What mitosis needs is dynamics, so removing either growth or shrinkage disables the spindle

Both drugs also damage DNA

The answer is: What mitosis needs is dynamics, so removing either growth or shrinkage disables the spindle

Both prevent the cell from making tubulin

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 $8.3 \times 10^{- 20}$ J per step. What is its efficiency as a percentage?

CorrectNot quite: 48

6.[2p]
Fast axonal transport runs at about 1 µm/s. How many days does a cargo take to travel one metre?

CorrectNot quite: 11.6

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?

Polymerisation on its own can generate force

Correct

Bacteria carry their own myosin

The answer is: Polymerisation on its own can generate force

Actin filaments are not polar

The answer is: Polymerisation on its own can generate force

The host cell is actively expelling the bacterium

The answer is: Polymerisation on its own can generate force

8.[3p]
For a swimming bacterium the Reynolds number is about $6 \times 10^{- 5}$ . What follows?

Inertia is irrelevant, so a reciprocal back and forth motion produces no net movement and swimming needs a rotating helix or a travelling wave

Correct

The bacterium coasts a long way after it stops

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

Water behaves as an ideal frictionless fluid

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 bacterium must swim faster to overcome inertia

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?

Select all that apply

Chronic airway disease from unswept mucus

Correct

Infertility

Correct

Reversal of internal organ position in about half of cases

Correct

Loss of skeletal muscle contraction

The answer is: Chronic airway disease from unswept mucus, Infertility, Reversal of internal organ position in about half of cases

1.[3p] Match each filament system to its distinguishing feature.

2.[3p] What does nucleotide hydrolysis buy a microtubule, given that tubulin polymerises without it?

3.[1p] A microtubule shrinks roughly ten times faster than it grows.

4.[3p] Why do taxol, which stabilises microtubules, and the vinca alkaloids, which destabilise them, both kill dividing cells?

5.[3p] Kinesin takes 8 nm steps against a load of about 5 pN, using one ATP worth 8.3×10-20 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?

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?

8.[3p] For a swimming bacterium the Reynolds number is about 6×10-5. What follows?

9.[2p] Which are consequences of defective ciliary dynein in humans?

1.[3p]
Match each filament system to its distinguishing feature.

2.[3p]
What does nucleotide hydrolysis buy a microtubule, given that tubulin polymerises without it?

3.[1p]
A microtubule shrinks roughly ten times faster than it grows.

4.[3p]
Why do taxol, which stabilises microtubules, and the vinca alkaloids, which destabilise them, both kill dividing cells?

5.[3p]
Kinesin takes 8 nm steps against a load of about 5 pN, using one ATP worth $8.3 \times 10^{- 20}$ 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?

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?

8.[3p]
For a swimming bacterium the Reynolds number is about $6 \times 10^{- 5}$ . What follows?

9.[2p]
Which are consequences of defective ciliary dynein in humans?