The cytoskeleton
The cytoskeleton is a network of protein filaments and tubules that provide structural support, shape, and organization to a cell. It also plays essential roles in cell movement, division, intracellular transport, and maintaining the cell’s integrity. The cytoskeleton is highly dynamic and constantly changes in response to the cell’s needs. It is composed of three main components:
- Microfilaments (Actin filaments):
- These are the thinnest filaments of the cytoskeleton.
- Made of actin protein, they are involved in cell movement, shape changes, and muscle contraction.
- They also play a role in cell division and the formation of the contractile ring during cytokinesis.
- Intermediate Filaments:
- These filaments are thicker than microfilaments but thinner than microtubules.
- They provide mechanical strength and help maintain the shape of the cell.
- They are made of various proteins, including keratins, vimentin, and lamins.
- These filaments are particularly important in cells that undergo mechanical stress (e.g., skin cells, neurons).
- Microtubules:
- These are the thickest filaments of the cytoskeleton.
- Made of tubulin protein subunits, they form a rigid structure that helps maintain cell shape.
- They are involved in intracellular transport (such as vesicles and organelles) and form the mitotic spindle during cell division.
- Microtubules are also key components of cilia and flagella, enabling movement in certain cells.
Functions of the Cytoskeleton:
- Structural Support: It provides the cell with its shape and mechanical strength.
- Cell Motility: Microfilaments and microtubules help in processes like cell migration, muscle contraction, and flagella/cilia movement.
- Intracellular Transport: The cytoskeleton acts as a track for transporting organelles, vesicles, and other cargo within the cell.
- Cell Division: During mitosis, microtubules form the mitotic spindle that ensures the accurate distribution of chromosomes.
- Signal Transduction: The cytoskeleton interacts with various signaling pathways, affecting how the cell responds to its environment.
MCQs on Cytoskeleton
- Which of the following is the thinnest filament of the cytoskeleton?
- A) Microtubules
- B) Intermediate filaments
- C) Microfilaments
- D) Actin
- What is the main protein component of microtubules?
- A) Actin
- B) Tubulin
- C) Keratin
- D) Collagen
- Which cytoskeletal structure is involved in the formation of the mitotic spindle?
- A) Microfilaments
- B) Intermediate filaments
- C) Microtubules
- D) Lamins
- Intermediate filaments are primarily involved in which of the following?
- A) Cell movement
- B) Providing mechanical strength
- C) Intracellular transport
- D) Muscle contraction
- Which of the following is NOT a function of microfilaments?
- A) Muscle contraction
- B) Cell division
- C) Intracellular transport
- D) Providing structural support to the nucleus
- Which cytoskeletal component forms the “tracks” for vesicle and organelle transport within the cell?
- A) Microfilaments
- B) Intermediate filaments
- C) Microtubules
- D) None of the above
- What is the primary function of actin filaments in the cell?
- A) Intracellular transport
- B) Cell shape and movement
- C) Formation of the mitotic spindle
- D) Providing mechanical strength
- Which of the following is a characteristic of intermediate filaments?
- A) They are involved in intracellular transport.
- B) They are composed of tubulin protein.
- C) They provide structural stability and resist mechanical stress.
- D) They are the thinnest filaments in the cytoskeleton.
- What structure is made of microtubules and is responsible for the movement of cells with flagella or cilia?
- A) Mitotic spindle
- B) Centrioles
- C) Basal body
- D) Axoneme
- Which of the following is NOT a function of the cytoskeleton?
- A) Maintenance of cell shape
- B) Facilitation of cell division
- C) Synthesis of proteins
- D) Intracellular transport
- Which of the following is a major function of microfilaments in muscle cells?
- A) DNA replication
- B) Muscle contraction
- C) Protein synthesis
- D) Ribosome formation
Answer: B) Muscle contraction
- Which of the following cytoskeletal components is involved in the mechanical strength of the nuclear envelope?
- A) Microfilaments
- B) Intermediate filaments
- C) Microtubules
- D) Actin filaments
Answer: B) Intermediate filaments
- The formation of the contractile ring during cytokinesis is primarily due to which cytoskeletal element?
- A) Microtubules
- B) Intermediate filaments
- C) Microfilaments
- D) Centrioles
Answer: C) Microfilaments
- Which of the following proteins is most commonly associated with intermediate filaments?
- A) Actin
- B) Tubulin
- C) Keratin
- D) Collagen
Answer: C) Keratin
- Which of the following cytoskeletal structures is responsible for cell motility via flagella and cilia?
- A) Microfilaments
- B) Intermediate filaments
- C) Microtubules
- D) Endoplasmic reticulum
Answer: C) Microtubules
- Which of the following best describes the role of actin filaments in the cell?
- A) They form the tracks for motor proteins in the cell.
- B) They contribute to the structural rigidity of the cell.
- C) They play a key role in cell shape and movement.
- D) They organize and align chromosomes during mitosis.
Answer: C) They play a key role in cell shape and movement.
- Which structure is composed of 9 triplets of microtubules and is found in the centrosome?
- A) Centrioles
- B) Microfilaments
- C) Cilia
- D) Actin filaments
Answer: A) Centrioles
- Which of the following is true about the cytoskeleton’s role in cell signaling?
- A) The cytoskeleton has no role in cell signaling.
- B) The cytoskeleton can alter cell signaling pathways by changing its structure.
- C) The cytoskeleton only plays a role in structural support, not signaling.
- D) The cytoskeleton directly transmits electrical signals in nerve cells.
Answer: B) The cytoskeleton can alter cell signaling pathways by changing its structure.
- Which cytoskeletal component is most involved in forming the structure of the mitotic spindle?
- A) Microfilaments
- B) Intermediate filaments
- C) Microtubules
- D) Ribosomes
Answer: C) Microtubules
- Which of the following is a primary function of microtubules during mitosis?
- A) Formation of the cleavage furrow
- B) Movement of chromosomes during cell division
- C) Formation of the nuclear envelope
- D) Protein synthesis
Answer: B) Movement of chromosomes during cell division
- Which cytoskeletal structure is responsible for maintaining the shape and mechanical stability of the nuclear membrane?
- A) Microfilaments
- B) Intermediate filaments
- C) Microtubules
- D) Golgi apparatus
Answer: B) Intermediate filaments
- What is the role of the actin filament in the process of endocytosis?
- A) Actin filaments help to form the vesicle during endocytosis.
- B) Actin filaments prevent vesicle formation.
- C) Actin filaments disassemble to release the vesicle.
- D) Actin filaments do not participate in endocytosis.
Answer: A) Actin filaments help to form the vesicle during endocytosis.
- Which of the following is true about the dynamic nature of the cytoskeleton?
- A) The cytoskeleton is rigid and does not change.
- B) The components of the cytoskeleton are constantly being assembled and disassembled.
- C) Only microtubules are dynamic.
- D) Only intermediate filaments are dynamic.
Answer: B) The components of the cytoskeleton are constantly being assembled and disassembled.
- Which structure is involved in the attachment of the cell to the extracellular matrix and is composed of actin filaments?
- A) Desmosomes
- B) Focal adhesions
- C) Tight junctions
- D) Hemidesmosomes
Answer: B) Focal adhesions
- Which of the following cytoskeletal proteins form a network that helps organize the structure of the cell’s interior and is a key player in the formation of the nuclear lamina?
- A) Actin
- B) Tubulin
- C) Lamin
- D) Collagen
Answer: C) Lamin
- Which of the following structures is responsible for controlling the movement of motor proteins along microtubules?
- A) Centrosome
- B) Actin filaments
- C) Kinesins and dyneins
- D) Golgi apparatus
Answer: C) Kinesins and dyneins
- Which cytoskeletal filament is involved in the formation of the contractile ring that separates the daughter cells during cytokinesis?
- A) Microtubules
- B) Actin filaments
- C) Intermediate filaments
- D) Myosin filaments
Answer: B) Actin filaments
- Which of the following is a primary function of microtubules in a non-dividing cell?
- A) Cell movement
- B) Maintaining cell shape and internal organization
- C) Cytokinesis
- D) Protein synthesis
Answer: B) Maintaining cell shape and internal organization
- Which of the following describes a function of the centrosome in relation to microtubules?
- A) The centrosome serves as the site where microtubules are synthesized.
- B) The centrosome breaks down microtubules.
- C) The centrosome serves as the anchor point for microtubule organization.
- D) The centrosome transports microtubules within the cell.
Answer: C) The centrosome serves as the anchor point for microtubule organization.
- Which type of motor protein moves along microtubules and is responsible for moving organelles such as mitochondria?
- A) Kinesins
- B) Dyneins
- C) Myosin
- D) Actin
Answer: A) Kinesins
- Which of the following is true regarding the composition of microtubules?
- A) Microtubules are composed of actin filaments.
- B) Microtubules are composed of tubulin dimers.
- C) Microtubules are composed of keratin protein.
- D) Microtubules are composed of collagen fibers.
Answer: B) Microtubules are composed of tubulin dimers.
- During cell division, which structure helps organize and separate the chromatids?
- A) Intermediate filaments
- B) Actin filaments
- C) Microtubules
- D) Ribosomes
Answer: C) Microtubules
- Which protein is responsible for binding to actin filaments and facilitating muscle contraction?
- A) Tubulin
- B) Keratin
- C) Myosin
- D) Dynein
Answer: C) Myosin
- Which of the following is the primary function of the microtubules in the axon of neurons?
- A) Facilitating neurotransmitter synthesis
- B) Serving as tracks for intracellular transport
- C) Forming the myelin sheath
- D) Regulating protein synthesis
Answer: B) Serving as tracks for intracellular transport
- Which cytoskeletal component is most responsible for the stability and structural integrity of muscle cells?
- A) Microfilaments
- B) Intermediate filaments
- C) Microtubules
- D) Actin filaments
Answer: B) Intermediate filaments
- Which of the following motor proteins moves along microtubules toward the cell’s periphery?
- A) Kinesins
- B) Dyneins
- C) Myosin
- D) Actin
Answer: A) Kinesins
- Which of the following is true about the process of cilia and flagella movement?
- A) Cilia and flagella movement is powered by myosin.
- B) Microtubules in cilia and flagella are arranged in a 9+0 pattern.
- C) The movement is driven by the sliding of microtubules against each other.
- D) The movement is controlled by intermediate filaments.
Answer: C) The movement is driven by the sliding of microtubules against each other.
- Which of the following cytoskeletal components is involved in the formation of stress fibers?
- A) Microtubules
- B) Actin filaments
- C) Intermediate filaments
- D) Dyneins
Answer: B) Actin filaments
- What is the role of the centrosome during the cell cycle?
- A) It regulates gene expression.
- B) It is the site where ribosomes are synthesized.
- C) It organizes microtubules and helps in the formation of the mitotic spindle.
- D) It stores genetic material.
Answer: C) It organizes microtubules and helps in the formation of the mitotic spindle.
- Which cytoskeletal structure is primarily responsible for anchoring the cell to its extracellular matrix?
- A) Actin filaments
- B) Microtubules
- C) Intermediate filaments
- D) Focal adhesions
Answer: D) Focal adhesions
- Which cytoskeletal element is primarily responsible for the cell’s ability to change shape and move in response to external signals?
- A) Microtubules
- B) Intermediate filaments
- C) Microfilaments
- D) Golgi apparatus
Answer: C) Microfilaments
- Which of the following is a key structural component of the centrosome?
- A) Actin filaments
- B) Centrioles
- C) Lamin filaments
- D) Ribosomal subunits
Answer: B) Centrioles
- Which of the following structures is responsible for the movement of the cell during processes like amoeboid movement?
- A) Microtubules
- B) Actin filaments
- C) Intermediate filaments
- D) Dyneins
Answer: B) Actin filaments
- Which cytoskeletal component is responsible for organizing the components of the cell’s internal skeleton during cell division?
- A) Microtubules
- B) Actin filaments
- C) Intermediate filaments
- D) Endoplasmic reticulum
Answer: A) Microtubules
- What is the primary function of the nuclear lamina, which is composed of intermediate filaments?
- A) Protecting the cell from external forces
- B) Supporting and maintaining the shape of the nucleus
- C) Facilitating cell division
- D) Transporting materials into the nucleus
Answer: B) Supporting and maintaining the shape of the nucleus
- Which of the following motor proteins is responsible for moving cargo along microtubules toward the cell’s center?
- A) Kinesins
- B) Dyneins
- C) Myosin
- D) Actin
Answer: B) Dyneins
- Which structure is formed by the assembly of microtubules in the form of a “9+2” arrangement?
- A) Centrosome
- B) Axoneme of cilia and flagella
- C) Mitotic spindle
- D) Stress fibers
Answer: B) Axoneme of cilia and flagella
- Which protein subunit is the building block of microtubules?
- A) Actin
- B) Tubulin
- C) Collagen
- D) Keratin
Answer: B) Tubulin
- What role do intermediate filaments play in the structure of the skin?
- A) They are involved in the formation of cell membranes.
- B) They provide mechanical strength and protect cells from stress.
- C) They help in protein synthesis.
- D) They transport nutrients inside the cell.
Answer: B) They provide mechanical strength and protect cells from stress.
- Which of the following is NOT a function of the cytoskeleton?
- A) Intracellular transport
- B) Cell movement and shape
- C) DNA replication
- D) Maintenance of cell integrity
Answer: C) DNA replication