Cytoskeleton and Microtubules Quiz

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Questions and Answers

What is the primary role of connexins in cellular communication?

They interact with cadherin to stabilize cell adhesion.

They provide structural support to the cell membrane.

They serve as the major protein component of gap junctions. (correct)

They help create tight junctions between cells.

What occurs when tight junctions fail to function properly?

Catenin levels increase significantly.

Materials can pass freely between cells. (correct)

Substances are prevented from leaking across the free surface.

There is increased electrical coupling between cardiac cells.

What major protein interacts with the cytoskeleton in tight junctions?

Catenin

Connexin

ZO-1 (correct)

Occludin

Which statement about cadherins is true?

Cadherin interacts with actin filaments through catenin. Signup and view all the answers

What is the approximate molecular weight of small proteins that can pass through gap junctions?

Approximately 10 kDa Signup and view all the answers

What is the primary structural difference between microtubules and microfilaments?

Microtubules are made of tubulin, microfilaments are made of fibrous proteins. Signup and view all the answers

Which of the following functions is NOT associated with microtubules?

Muscle contraction Signup and view all the answers

What composition do centrioles have in their structure?

9 sets of 3 attached microtubules Signup and view all the answers

How do motile cilia function on a cell's surface?

They beat in coordinated waves. Signup and view all the answers

What role does the centrosome play in relation to microtubules?

It organizes microtubules in the cytoplasm. Signup and view all the answers

Which statement regarding primary cilia is true?

They serve as sensory organelles. Signup and view all the answers

Which type of protein subunit forms intermediate filaments?

Fibrous proteins Signup and view all the answers

What is the approximate outer diameter of a microtubule?

25 nm Signup and view all the answers

What is the primary function of tight junctions in epithelial membranes?

Create impermeable or semipermeable barriers between cells Signup and view all the answers

Which type of junction primarily allows for cell-cell communication in tissues?

Gap junctions Signup and view all the answers

What role do cadherins play in adherens junctions?

Provide strong adhesion between adjacent cells Signup and view all the answers

What happens to cell-cell interactions involving cadherins when calcium ions are removed?

Interactions are disrupted and cells dissociate Signup and view all the answers

Which junction type is responsible for preventing lateral tearing of tissues?

Desmosomes Signup and view all the answers

What is the primary cytoskeletal anchor associated with adherens junctions?

Actin Signup and view all the answers

Which proteins are major components of cadherins involved in cell adhesion?

Cadherins and catenins Signup and view all the answers

Which characteristic best defines the apical surface of epithelial cells?

It faces the lumen of an organ Signup and view all the answers

What is the primary function of actin filaments in the cell?

They are involved in cell motility and division. Signup and view all the answers

Which end of the microtubule grows more rapidly?

The plus end Signup and view all the answers

What characterizes intermediate filaments compared to microtubules and microfilaments?

They vary in protein composition. Signup and view all the answers

Which of the following statements about microtubules is true?

Microtubules exhibit dynamic instability. Signup and view all the answers

What is the primary role of the nuclear lamina formed by intermediate filaments?

To support the structure of the nucleus. Signup and view all the answers

What feature distinguishes microfilaments from microtubules?

Microfilaments are composed of actin protein. Signup and view all the answers

Which of the following is NOT a function of actin filaments?

Providing genetic information Signup and view all the answers

How do intermediate filaments enhance the mechanical strength of epithelial tissues?

By spanning the cytoplasm between cell-cell junctions. Signup and view all the answers

Study Notes

Cytoskeleton

Microtubules are long, hollow cylinders made of the protein tubulin, they are more rigid than actin filaments
Microfilaments (actin filaments) are two-stranded helical polymers of the protein actin, they are less rigid than MT
Intermediate filaments are ropelike fibers made of intermediate filament proteins, they do not participate in cell motility

Microtubules

Microtubules are long, hollow cylinders made of the protein tubulin (alpha tubulin and beta tubulin), with an outer diameter of 25 nm
Microtubules have one end attached to a single microtubule-organizing center (MTOC) called a centrosome
Microtubules are involved in cell division, organization of intracellular structure, and intracellular transport, as well as ciliary and flagellar motility
Centrosomes organize microtubules in cytoplasm
Centrioles are made up of tubulin, two centrioles form a centrosome, which is the major microtubule-organizing center (MTOC) in human cells
Centriole consist of 9 sets of 3 attached microtubules arranged to form a hollow cylinder
Microtubules form cilia and flagella
Cilia are short, hair-like structures that beat rhythmically to move fluid or particles past the cell
Flagella are long, whip-like structures that propel cells through a fluid environment
Microtubules are constantly adding and subtracting tubulin dimers at both ends of the filament, this is known as dynamic instability

Microfilaments

Actin filaments are highly concentrated in the cortex, just beneath the plasma membrane
Actin filaments are involved in muscle contraction, cell motility, cell division and cytokinesis, vesicle and organelle movement, cell signaling, and the establishment and maintenance of cell junctions and cell shape
Actin filament and myosin work together for muscle movement

Intermediate Filaments

Intermediate filaments are ropelike fibers with a diameter of around 10 nm, they are made of intermediate filament proteins, they do not participate in cell motility
One type of intermediate filament forms a meshwork called the nuclear lamina just beneath the inner nuclear membrane
Other types extend across the cytoplasm, giving cells mechanical strength
In an epithelial tissue, they span the cytoplasm from one cell-cell junction to another, thereby strengthening the entire epithelium

Specialized Junctions

Tight junctions produce impermeable or semipermeable barriers between cells, especially in epithelial membranes
Gap junctions allow electrolytes and other molecules to pass between cells, also known as communicating junctions, found in epithelial tissues, cardiac and smooth muscle, nervous and certain connective tissues
Adherens junctions provide strong mechanical attachment between adjacent cells, holding cardiac muscle cells tightly together as the heart expands and contracts, and holding epithelial cells together
Desmosomes are like spot welds which hold cells together and help prevent lateral tearing of tissues

Adherens Junction

Major transmembrane protein: cadherin
Major peripheral proteins: catenin
Cytoskeletal anchor: actin

Cadherins

Cadherins are a group of membrane proteins, the extracellular segments with 5 domains that form dimers in the same cell in a Ca2+-dependent manner, which interacts with cadherin dimers from another cell
The intracellular domain of cadherin interacts with catenin which adhere the cadherin to intracellular cytoskeleton

Gap Junctions

Gap junctions allow the transfer of small molecules and ions between adjacent cells
Major protein component: connexin
Connexon is made up of 6 connexins

Tight Junctions

Tight junctions prevent the passage of materials through spaces between cells
Major transmembrane proteins: occludin, claudin
Major peripheral protein for interaction with cytoskeleton: ZO-1

True or False

Actin filament is more rigid than microtubules ( False )
Cilia are made of microtubules ( True )
Calcium ion controls the interaction between cells via adherens junctions. ( True )
Major transmembrane protein in gap junction is claudin. ( False)
Gap junction permits the free passage of small proteins of ~10kDa between the cells ( False )

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Description

Test your knowledge on the structure and function of the cytoskeleton, focusing on microtubules, microfilaments, and intermediate filaments. This quiz will cover the roles these structures play in cell division, organization, and motility.