Lec-5-Cytoskeleton. MEDIUM.OSR

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Questions and Answers

What type of intermediate filament is found in epithelial cells?

Nuclear lamins

Keratin filaments (correct)

Neurofilaments

Vimentin filaments

Where are neurofilaments primarily located?

In the nuclear envelope

In epithelial cells

In muscle cells

In nerve cells (correct)

What process controls the disassembly and reassembly of the nuclear lamina during cell division?

Mitosis and cytokinesis

Transcription and translation

Phosphorylation and dephosphorylation (correct)

Cell differentiation

What happens to lamins during mitosis when they are phosphorylated?

They dissociate into individual proteins Signup and view all the answers

Which of the following correctly describes microtubules?

Hollow tubes made from tubulin dimers Signup and view all the answers

What are the two proteins that compose the dimer of tubulin?

Alpha and beta tubulin Signup and view all the answers

During cell division, what occurs to cytoplasmic intermediate filaments?

They undergo disassembly Signup and view all the answers

What occurs after dephosphorylation of lamins at the end of mitosis?

Lamins reassemble to reform the nuclear lamina Signup and view all the answers

What characterizes the movement cycle of a cilium?

It includes a power stroke and a recovery stroke. Signup and view all the answers

How do flagella differ from cilia in terms of their primary function?

They are designed for cell propulsion rather than fluid movement. Signup and view all the answers

What is the arrangement of microtubules in cilia?

A ring of nine doublet microtubules with two single microtubules in the center. Signup and view all the answers

What is the typical duration of a complete cycle of ciliary movement?

0.1–0.2 seconds Signup and view all the answers

What propels the movement of cilia and flagella?

The action of dynein moving along the stable microtubules. Signup and view all the answers

What structural feature characterizes microtubules?

They are hollow tubes formed by tubulin dimers. Signup and view all the answers

What distinguishes the plus end of a microtubule?

It experiences growth through addition of dimers. Signup and view all the answers

What is the function of γ-tubulin in the centrosome?

It forms ring complexes that nucleate microtubule growth. Signup and view all the answers

What describes the dynamic instability of microtubules?

Microtubules grow and shrink in length unpredictably. Signup and view all the answers

Which component of microtubules is involved in structural polarity?

α-tubulin and β-tubulin arrangement. Signup and view all the answers

In animal cells, where is the centrosome typically located?

Near the cell nucleus. Signup and view all the answers

How many protofilaments constitute a microtubule?

13 Signup and view all the answers

Where does microtubule growth primarily occur?

At the plus end extending into the cytoplasm. Signup and view all the answers

What type of bonding connects tubulin dimers in microtubules?

Noncovalent bonding. Signup and view all the answers

What role do centrioles play in the centrosome?

They organize the microtubule array radiating from the centrosome. Signup and view all the answers

What is the term for the behavior of microtubules switching back and forth between polymerization and depolymerization?

Dynamic instability Signup and view all the answers

What happens to microtubules when their plus end is stabilized?

They are prevented from depolymerizing. Signup and view all the answers

What drives the dynamic instability of microtubules?

GTP hydrolysis Signup and view all the answers

What is the consequence of losing the GTP cap on a microtubule?

It causes the microtubule to shrink. Signup and view all the answers

How do tubulin dimers carrying GTP behave compared to those carrying GDP?

They bind more tightly to one another. Signup and view all the answers

What occurs if the growth of a microtubule is slow?

GTP dimers may hydrolyze to GDP before more GTP dimers attach. Signup and view all the answers

What is a possible outcome when a microtubule completely disappears?

It can be replaced by a new microtubule from the γ-tubulin ring complex. Signup and view all the answers

What effect does GTP hydrolysis have on the microtubule structure?

It can lead to the peeling away of protofilaments. Signup and view all the answers

What role does the γ-tubulin ring complex play in microtubule dynamics?

It serves as a template for the formation of new microtubules. Signup and view all the answers

Which statement best describes the polarization of differentiated animal cells?

One end of the cell exhibits distinct structural or functional properties. Signup and view all the answers

What is the primary role of kinesins in a nerve cell?

To move towards the plus end of microtubules. Signup and view all the answers

How do motor proteins interact with microtubules?

By attaching in a specific directional manner based on stereospecificity. Signup and view all the answers

What role does the tail of a motor protein play in intracellular transport?

It binds to a cell component, determining the type of cargo transported. Signup and view all the answers

Which motor protein family generally moves toward the minus end of a microtubule?

Dyneins Signup and view all the answers

What is a primary function of cilia in cells?

To move fluid over the cell's surface or propel cells in fluid. Signup and view all the answers

Which component of a motor protein dictates its cargo transport nature?

The tail Signup and view all the answers

What structure do axons in nerve cells rely on for the transport of cellular components?

Stable microtubules Signup and view all the answers

In a nerve cell, what direction do microtubules typically point?

Towards the axon terminals Signup and view all the answers

What is the main effect of motor proteins on intracellular transport?

They enable movement of various cellular components along microtubules. Signup and view all the answers

Study Notes

Intermediate Filaments and Nuclear Lamina

Intermediate filaments are classified into four groups: keratin (epithelial cells), vimentin (connective tissue, muscle, glial cells), neurofilaments (nerve cells), and nuclear lamins (nuclear envelope).
Cytoplasmic intermediate filaments disassemble during mitosis, while nuclear lamina reform after cell division, regulated by phosphorylation and dephosphorylation of lamins.
Phosphorylation by protein kinases weakens the lamin tetramers, leading to filament disassembly. Dephosphorylation allows for reassembly at the end of mitosis.

Microtubule Structure

Microtubules consist of tubulin dimers (α-tubulin and β-tubulin), which align to form 13 parallel protofilaments, creating a hollow cylindrical structure.
Microtubules display structural polarity with a plus end (β-tubulin) and a minus end (α-tubulin).

Centrosome and Microtubule Organization

The centrosome is the primary microtubule-organizing center in animal cells, typically located near the nucleus.
It contains centrioles and a matrix of proteins, including gamma-tubulin, which serve as nucleation sites for microtubule growth.

Dynamic Instability of Microtubules

Microtubules experience dynamic instability, alternating between phases of growth (polymerization) and rapid shrinkage (depolymerization).
Stabilization of microtubules occurs when their plus end is attached to other structures, preventing disassembly.

GTP Hydrolysis and Microtubule Dynamics

GTP hydrolysis by tubulin dimers contributes to microtubule dynamic instability. GTP-bound dimers promote growth, while GDP-bound dimers lead to disassembly.
Loss of the GTP cap results in the peeling away of protofilaments and shrinkage of the microtubule.

Polarity and Transport in Nerve Cells

Differentiated animal cells exhibit polarity, crucial for the orientation of organelles and transport processes.
In nerve cells, microtubules in axons point toward axon terminals, facilitating bidirectional transport.

Motor Proteins in Intracellular Transport

Kinesins and dyneins are the two families of motor proteins that transport cargo along microtubules, with kinesins moving toward the plus end and dyneins toward the minus end.
Motor proteins possess globular ATP-binding heads for interaction with microtubules and a tail for binding to cargo.

Functionality of Cilia and Flagella

Cilia beat in a whiplike manner to either move fluid across the cell surface or propel entire single cells, characterized by alternating power and recovery strokes.
Flagella, longer than cilia, generate regular wave-like movements to propel cells, such as sperm, through fluid environments.

Microtubule Arrangement in Cilia and Flagella

The internal structure of cilia and flagella features a distinctive arrangement of microtubules, consisting of nine doublets forming a ring with two central microtubules, differing from cytoplasmic microtubules.

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Description

This quiz explores the role of intermediate filaments in strengthening cells against mechanical stress. It covers the four classes of intermediate filaments, including their types and functions in various cell types. Test your knowledge on this essential aspect of cell biology.