Cell Biology: Microtubules and Actin Filaments

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Questions and Answers

What role do microtubules play during cell division?

They assist in the formation of the nuclear envelope.

They create structural integrity by forming the cell membrane.

They transport nutrients throughout the cytoplasm.

They help separate chromosomes. (correct)

Which protein interacts with actin filaments to facilitate cell movement?

Kinesin

Tubulin

Myosin (correct)

Dynein

How do eukaryotic flagella differ from bacterial flagella in structure?

Eukaryotic flagella rotate continuously like a propeller.

Eukaryotic flagella contract like muscle cells.

Eukaryotic flagella are made of microtubules. (correct)

Eukaryotic flagella are made of protein filaments called flagellin.

What is the primary component that forms actin filaments?

Actin proteins Signup and view all the answers

What distinguishes cilia from flagella in terms of cellular structure?

Cilia are shorter and often found in large numbers. Signup and view all the answers

What role do dynein arms play in the movement of cilia and flagella?

They act as motors that facilitate bending by moving along microtubules. Signup and view all the answers

What is the key structure that powers the movement of cilia and flagella?

Axoneme Signup and view all the answers

Which components form the basic structural unit of the axoneme?

Microtubule doublets Signup and view all the answers

How does the addition of ATP affect dynein activity?

It causes dynein to walk towards the minus end, facilitating bending. Signup and view all the answers

What is the arrangement of microtubules in the axoneme?

Nine doublets surrounding a central pair. Signup and view all the answers

What is the primary function of phagocytosis in a cell?

Uptake of smaller cells or food particles for digestion Signup and view all the answers

Which component of the cytoskeleton is primarily responsible for providing structural support?

Intermediate filaments Signup and view all the answers

What characterizes microtubules in terms of their structure?

They are large, hollow tubes made of tubulin dimers Signup and view all the answers

In which process does a damaged organelle become enclosed within a membrane to be digested?

Autophagy Signup and view all the answers

How do actin filaments contribute to the cell's plasma membrane?

They shape the plasma membrane Signup and view all the answers

What roles do microtubules serve within the cell?

Organize organelles and provide pathways for transport Signup and view all the answers

Which structure serves as the organizing center for microtubules in animal cells?

Centrosome Signup and view all the answers

What initiates the formation of a phagosome during phagocytosis?

Engulfing foreign particles or cells Signup and view all the answers

Study Notes

Microtubules

Microtubules are hollow tubes made of tubulin.
Microtubules can act as “highways”, transporting vesicles via the protein kinesin.
Microtubules are involved in separating chromosomes during cell division.
Microtubules originate from the microtubule organizing center, such as the centrosome in animal cells.
Microtubules are directional - they have a “-” end and a “+” end.

Actin filaments

Actin filaments are the smallest cytoskeletal elements, formed by polymerization of actin proteins.
Actin filaments are directional - they have a “-” end and a “+” end.
Actin filaments are arranged in bundles that are typically found near the plasma membrane, helping to define the cell’s shape.
Actin filaments interact with the protein myosin, resulting in movements such as cell crawling, cytokinesis, and cytoplasmic streaming.
Actin is essential for muscle tissue contraction.

Moving Whole Cells: Cilia & Flagella

Flagella and cilia are hair-like projections from the cell that allow the cell to move.
Flagella are long and move like a propeller, while cilia are shorter and wave back and forth.
Bacterial flagella are composed of flagellin, while eukaryotic flagella are composed of microtubules.
Cilia are involved in moving substances like mucus and nutrients in the airways and digestive tracts.
Cells usually have one or two flagella, but may have many cilia.

Receptor-mediated endocytosis

This process uses receptors to bind to macromolecules outside the cell.
The plasma membrane pinches inwards, forming a vesicle that delivers cargo to the lysosome.
Recycling of receptors allows for continuous uptake of molecules.

Phagocytosis

This is a process that engulfs smaller cells or food particles into the cell, forming a phagosome.
The phagosome is then delivered to the lysosome for digestion.

Autophagy

This process encloses damaged organelles within a membrane to form an autophagosome.
The autophagosome is then delivered to the lysosome for digestion.

The Cytoskeleton: Moving down the roads

The cytoskeleton is a network of protein fibers that give the cell shape, organizational stability, and facilitates movement.
The cytoskeleton helps to organize organelles and cellular structures.
The three main components of the cytoskeleton are: Microtubules, Intermediate Filaments, and Actin filaments.
Microtubules act as the "interstates" of the cell, providing a pathway for molecule delivery.
Intermediate filaments provide structural support.
Actin filaments help to shape the plasma membrane.

Cytoskeletal Structures

Microtubules are made of tubulin.
Actin filaments are made of actin.
Intermediate filaments are made of various proteins.

Axoneme: A complex machine

The axoneme is a complex structure that powers the movement of cilia and flagella.
It is composed of microtubule doublets and central microtubules.
Dynein arms, located on the microtubule doublets, “walk” along the microtubules, causing the axoneme to bend.
ATP is required for dynein to “walk” along the microtubules.

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Description

Explore the crucial roles of microtubules and actin filaments in cell structure and movement. This quiz covers their properties, functions, and the mechanisms of cellular transport and division. Test your understanding of these essential cytoskeletal components in cell biology.