Cell Biology: Actin, Myosin, and Microtubules

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Questions and Answers

What function does myosin V perform in cells?

Cell division

Carrying cargo (correct)

Muscle contraction

Detoxification

Microtubules grow faster at the minus end than at the plus end.

False

What is the role of the GTP cap in microtubule dynamics?

It favors growth.

Myosin V has a long lever arm which allows it to take a bigger step along an actin filament than _____ II.

myosin Signup and view all the answers

Match the following components with their descriptions:

Myosin V = Carries cargo in cells GTP-tubulin = Promotes microtubule growth GDP-tubulin = Leads to microtubule depolymerization Axoneme = Stable bundle of microtubules in cilia Signup and view all the answers

What happens to microtubules when the GTP cap is lost?

They undergo depolymerization. Signup and view all the answers

The -tubulin monomer in microtubules is less tightly bound compared to the other subunit.

True Signup and view all the answers

How many protofilaments make up a microtubule?

13 Signup and view all the answers

What phenomenon describes the ability of microtubules to alternate between growth and rapid disassembly?

Dynamic instability Signup and view all the answers

A catastrophe refers to the event when a microtubule begins to grow after losing its GTP cap.

False Signup and view all the answers

Microtubules can undergo a phase of __________ when free tubulin subunits are added, which rescues the microtubule from shrinking.

rescue Signup and view all the answers

Match the following terms related to microtubules with their descriptions:

GTP cap = Stabilizes the microtubule growth Catastrophe = Transition from growth to shrinkage Rescue = Restoration of microtubule growth Centrosome = Structure that organizes microtubules Signup and view all the answers

Which structure is responsible for nucleating microtubules at their minus end?

g-tubulin ring complex Signup and view all the answers

Individual free tubulin subunits exist in different conformations that affect microtubule stability.

True Signup and view all the answers

What is the significance of the arrangement of microtubules in centrioles?

Centrioles have a barrel shape with ninefold symmetry, which is important for organizing microtubules. Signup and view all the answers

Study Notes

Actin and Myosin in Non-Muscle Cells

Most non-muscle cells have contractile actin-myosin II assemblies that change cell shape
These assemblies are regulated by myosin phosphorylation, not troponin
Contractile actin and myosin in the cell cortex creates tension, leading to changes in cell shape
Bundles form stress fibers that connect cells to the extracellular matrix or link cells together
Myosin can be one-headed (myosin I) or two-headed (myosin II).
Many different types of myosin exist with varying tail structures and functions.
Myosin V is a type with a long lever arm that allows for large steps on an actin filament.

Microtubules

Microtubules are more complex than actin filaments but also highly dynamic
They are made of tubulin heterodimers (α-tubulin and β-tubulin)
The GTP bound to α-tubulin is fixed, but β-tubulin can be GTP or GDP
Microtubules have a plus and a minus end. The plus end grows and shrinks faster
Microtubules show dynamic instability, alternating between growth and shrinkage periods
Microtubule growth is favored by GTP-tubulin at the plus end, forming a GTP cap.
Loss of the cap leads to depolymerization
Dynamic instability involves catastrophe (shrinking) and rescue (growing)
Nucleation: Microtubules are formed through a complex involving γ-tubulin, which is key component in the complex
Centrosome: Many animal cells have this microtubule organizing center (MTOC).
Centrioles: Cylindrical structures embedded in the centrosome.

Centrosome

Centrosomes function as a microtubule organizing center
They duplicate before mitosis.
Centrosomes move apart to form the mitotic spindle poles.
Centrioles reside within the centrosome, and they are crucial for proper microtubule nucleation.

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Description

This quiz delves into the roles of actin and myosin in non-muscle cells, emphasizing their functions in cell shape and tension. Additionally, it covers the structure and dynamics of microtubules, including their complex assembly and the significance of tubulin heterodimers. Test your understanding of these essential cytoskeletal components.