LECTURE 4 NEW

Question 1

What are the two types of microtubule motor proteins and their direction

Answer 1

Kinesins: Microtubule-based motor proteins moving cargo towards the (+) end (anterograde).

Dyneins: Transport cargo towards the (-) end (retrograde).

Question 2

Structure of kinesis (composition and domains)

Answer 2

Composition: Dimer of two heavy chains and two light chains, with a total molecular weight of ~380,000 Da.

Domains:
Head Domain: Binds microtubules and ATP, responsible for motor activity.
Linker Domain: Critical for forward movement.
Stalk Domain: Involved in dimerization via coiled-coil interactions.
Tail Domain: Binds to receptors on membrane vesicles carrying cargo.

Question 3

Kinesins: Mechanism of Movement

Answer 3

Leading head binds strongly while trailing head is weakly bound.

ATP binding to leading head induces a conformational change, moving the trailing head forward.

Cycle repeats with new leading head binding 16 nm ahead

The leading head releases ADP and becomes strongly bound again.

Question 4

Kinesins: regulation

Answer 4

Kinesin-1 is regulated by a head-to-tail interaction that inhibits ATPase activity when in an inhibited state.

Upon encountering a receptor on a vesicle, the kinesin unfolds and can transport cargo towards the (+) end of microtubules.

Question 5

Structure of dynein

Answer 5

Head Domain: Contains the AAA ATPase domain (six repeats) - responsible for ATP hydrolysis and movement
Linker domain: Facilitates conformational changes as ATP is hydrolyzed.
Stalk domain: Protrudes from the head domain and contains the microtubule-binding region
Stem domain: It associates with cargo through the dynactin complex

Question 6

Dynein: Mechanism of movement

Answer 6

Bind: Dynein binds to microtubules in the absence of nucleotides.
Pre-Stroke: ATP binding leads to a bent linker and dissociation from the microtubule.
Power Stroke: ATP hydrolysis and Pi release straighten the linker, moving the cargo.
Release: ADP is released, allowing a new ATP molecule to bind and repeat the cycle.

Question 7

Types of MTs in mitotic spindles

Answer 7

Kinetochore Microtubules: Connect chromosomes to spindle poles.
Polar Microtubules: Maintain pole-to-pole distance.
Astral Microtubules: Position the spindle during cytokinesis.

Question 8

Cilia and Flagella Structure and movement

Answer 8

Contain an organized core of microtubules (axoneme) with a 9 + 2 arrangement.
Movement results from axonemal dyneins generating bending.

Question 9

Basic structural properties of IFs

Answer 9

Composition: Made of various evolutionarily related proteins, forming strong rope-like polymers.
Polarity: Unlike microfilaments and microtubules, IFs have no intrinsic polarity; their subunits do not bind nucleotides.
Stability: More stable and less dynamic than microfilaments and microtubules.

Question 10

Domains of IFs

Answer 10

Central Rod Domain: A conserved α-helical coiled-coil domain crucial for dimerization.

N-terminal and C-terminal Domains: Globular domains that vary among IF types; important for filament assembly, organization, and interactions with other cellular components

Question 11

How are IFs assembled

Answer 11

Parallel Dimers: Two IF protein monomers form a parallel coiled-coil dimer through their central rod domains.
Tetramers: Two dimers associate antiparallel and staggered to form a tetramer.
Protofibrils and Filaments: Tetramers align end-to-end and laterally to form protofibrils, which bundle into mature intermediate filaments composed of four protofibrils.

Question 12

Describe the 5 different IF classes

Answer 12

Desmin: Provides structural integrity in muscle cells.
Neurofilaments: Regulate axon diameter and nerve impulse propagation.
Keratins: Diverse, found in hair, nails, and epithelial cells; provide strength and protection.
Vimentin: Found in mesenchymal cells, involved in cell structure and function.
Lamin: Forms the nuclear lamina, maintaining nucleus integrity

Question 13

Describe intraflagellar transport

Answer 13

Intraflagellar transport (IFT) involves the movement of particles between the plasma membrane and outer doublet microtubules.
Kinesin-2 mediates transport toward the tip of the flagellum.
Cytoplasmic dynein directs transport back toward the base.
IFT is crucial for the assembly and maintenance of cilia and flagella.

Question 14

Pathological Conditions Related to Intermediate Filaments

Answer 14

Epidermolysis bullosa simplex is an inherited disorder where skin becomes fragile due to faulty keratin assembly, leading to blistering.

Laminopathies are diseases caused by mutations in lamin A, affecting nuclear integrity and resulting in conditions like muscular dystrophies and progeria.