Lec-5-Cytoskeleton. EASY.OSR

Questions and Answers

What are the three types of protein filaments that make up the cytoskeleton?

Intermediate filaments, tubulin, and actin filaments

Intermediate filaments, microtubules, and actin filaments (correct)

Microtubules, actin filaments, and collagen

Actin filaments, myosin, and intermediate filaments

What type of protein subunit do intermediate filaments consist of?

Transmembrane proteins

Fibrous proteins (correct)

Enzymatic proteins

Globular proteins

What is the primary structural feature of the rod domain in intermediate filament proteins?

Irregular looped regions

Coiled-coil structure with loops

Extended α-helical region (correct)

Short hydrophobic segments

How do two coiled-coil dimers associate to form a staggered structure?

By running in opposite directions Signup and view all the answers

What characteristic allows intermediate filaments to provide tensile strength?

Their ropelike structure Signup and view all the answers

What happens to tetramers of intermediate filaments after formation?

They associate side-by-side Signup and view all the answers

What is a key property of intermediate filaments compared to microtubules and actin filaments?

They are strong and ropelike Signup and view all the answers

Which of the following correctly describes the formation of the final ropelike structure of intermediate filaments?

It is assembled by staggered tetramers associating Signup and view all the answers

What is the primary function of microtubules in differentiated animal cells?

They facilitate intracellular transport. Signup and view all the answers

In a nerve cell, which direction do microtubules in the axon point?

They point towards the axon terminals. Signup and view all the answers

Which family of motor proteins generally moves toward the plus end of a microtubule?

Kinesins Signup and view all the answers

What determines the type of cargo a motor protein can transport?

The motor protein's tail Signup and view all the answers

What is a distinguishing feature of motor proteins like kinesins and dyneins?

They have two globular ATP-binding heads. Signup and view all the answers

What motion do cilia perform?

A whiplike motion. Signup and view all the answers

Dyneins primarily move toward which end of a microtubule?

The minus end Signup and view all the answers

What is a characteristic feature of the interaction between motor proteins and microtubules?

They interact in a stereospecific manner. Signup and view all the answers

What role do kinesins and dyneins play in cellular function?

They mediate intracellular transport. Signup and view all the answers

Which term best describes differentiated animal cells?

Polarized Signup and view all the answers

What is the role of the myosin heads during muscle contraction?

They walk along the actin filaments in repeated cycles. Signup and view all the answers

What triggers muscle contraction at the cellular level?

An action potential from a motor nerve. Signup and view all the answers

What structural components are responsible for the sliding filament mechanism in muscle cells?

Actin and myosin filaments. Signup and view all the answers

What is the function of the sarcoplasmic reticulum in muscle cells?

Releasing calcium ions during contraction. Signup and view all the answers

Where are the Z discs located in a sarcomere?

At either end of the sarcomere. Signup and view all the answers

What is the role of actin-binding proteins in relation to actin filaments?

They enable actin filaments to perform various functions in cells. Signup and view all the answers

Which of the following structures can actin filaments form?

Dynamic protrusions like those at the leading edge of a crawling cell. Signup and view all the answers

What is the significance of myosin in relation to actin?

Myosin is a motor protein that facilitates actin-dependent movements. Signup and view all the answers

What phenomenon describes the addition of actin monomers at the plus end while losing them at the minus end?

Treadmilling. Signup and view all the answers

What occurs at the plus end of an actin filament during intermediate concentrations of free actin?

Monomers add faster than ATP is hydrolyzed. Signup and view all the answers

Which of the following describes the behavior of naked actin filaments?

They can disassemble from both ends. Signup and view all the answers

What is the effect of ATP hydrolysis on actin filaments?

It leads to the destabilization of ADP-actin at the minus end. Signup and view all the answers

In what type of cellular structures do actin filaments often contribute to contraction?

Contractile rings. Signup and view all the answers

What happens at very high concentrations of free actin monomers?

Actin filaments grow rapidly by adding monomers at both ends. Signup and view all the answers

What type of movement do actin filaments primarily facilitate in cells?

Fluid and dynamic structures. Signup and view all the answers

What is the primary function of the network of fibrous proteins in human red blood cells?

To maintain the cell's discoid shape Signup and view all the answers

Which process is NOT essential for cell crawling?

Nuclear division during movement Signup and view all the answers

What role does actin polymerization play in cell crawling?

It pushes the plasma membrane forward Signup and view all the answers

What is the function of myosin motor proteins during cell movement?

To draw the cell body forward Signup and view all the answers

Where are new anchorage points established during cell crawling?

At the front of the cell Signup and view all the answers

What happens to old anchorage points as a cell crawls forward?

They are released Signup and view all the answers

Which of the following describes the movement of a crawling cell?

Stepwise and coordinated Signup and view all the answers

What type of filaments primarily make up the actin cortex in cells?

Actin and spectrin filaments Signup and view all the answers

What is the structure of human red blood cells primarily maintained by?

A network of fibrous proteins Signup and view all the answers

Which event initiates the movement of a cell's front during crawling?

Actin polymerization Signup and view all the answers

Study Notes

Cytoskeleton Overview

Composed of three types of protein filaments: intermediate filaments, microtubules, and actin filaments, found in nearly all animal cells.
Each filament type has unique mechanical properties and is formed from different protein subunits.

Intermediate Filaments

Provide tensile strength; composed of long strands twisted together.
Each strand is made of fibrous proteins with a central elongated rod domain and unstructured domains.
Rod domain contains an extended α-helical region that allows intermediate filament proteins to form stable dimers through coiled-coil configuration.
Dimer pairs associate to form staggered tetramers, which further combine side-by-side to form the final ropelike structure.

Microtubules

Organize cell interior and maintain polarity within differentiated cells like nerve cells.
In neuron axons, all microtubules orient with plus ends toward axon terminals, allowing directional transport of organelles and substances.
Two families of motor proteins, kinesins and dyneins, facilitate transport along microtubules; kinesins move toward plus ends, while dyneins move toward minus ends.

Motor Proteins

Composed of dimers with two globular ATP-binding heads and a single tail for cargo binding.
The heads bind to microtubules directionally, controlling transport directionality.
Tails attach to various cell components, determining the type of cargo transported.

Cilia and Flagella

Function in cell movement or fluid movement over cell surfaces; cilia exhibit coordinated whiplike beating.

Actin Filaments

Interact with various actin-binding proteins for diverse cellular functions, including building stable structures (e.g., microvilli) and facilitating movements (e.g., cell crawling).
Actin polymerization relies on ATP hydrolysis, leading to a phenomenon known as treadmilling, where monomers add at one end (plus) and disassemble at the other end (minus).

Actin in Human Red Blood Cells

Fibrous protein networks, including actin and spectrin, support the plasma membrane, maintaining the cell's discoid shape.

Cell Crawling Mechanisms

Involves coordinated actions: protrusion at the leading edge, adhesion to the substratum, and cell body contraction.
Actin polymerization pushes the plasma membrane forward, with myosin-mediated contraction drawing the cell forward through traction on anchor points.

Muscle Contraction

Sarcomeres shorten due to the sliding of actin against myosin filaments, facilitated by myosin heads attaching and detaching.
This sliding mechanism does not change filament lengths, driving the contraction of muscle cells.

Calcium’s Role in Muscle Contraction

Muscle contraction is triggered by a rise in cytosolic Ca²⁺, initiated by signals from motor nerves.
Signals cause action potentials, spreading through transverse (T) tubules and initiating the release of Ca²⁺ from the sarcoplasmic reticulum, crucial for muscle contraction.

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Description

Explore the structure and function of the cytoskeleton in animal cells. This quiz covers the three main types of protein filaments: intermediate filaments, microtubules, and actin filaments, highlighting their unique properties and roles. Perfect for students studying cell biology and anatomy.