_CELL BIOLOGY: Cytoskeleton Structure & Function
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Questions and Answers

Microtubules are static structures with stable walls composed of polymerized tubulin heterodimers.

False

Microfilaments are responsible for providing mechanical stability to cells.

False

Intermediate filaments are the most dynamic component of the cytoskeleton.

False

Inclusions are metabolically active and have a variety of functions within the cell.

<p>False</p> Signup and view all the answers

Microtubules are involved in the transport of vesicles and organelles by motor proteins such as kinesin and dynein.

<p>True</p> Signup and view all the answers

Myosins are motor proteins that move along microtubules carrying vesicles or producing cytoplasmic movement.

<p>False</p> Signup and view all the answers

Intermediate filaments have an average diameter of 20-25 nm.

<p>False</p> Signup and view all the answers

Cytoskeletal components are only involved in maintaining cell shape and mechanical stability.

<p>False</p> Signup and view all the answers

Mitochondria are single membrane-enclosed organelles.

<p>False</p> Signup and view all the answers

Mitochondrial diseases are a group of genetic conditions that affect how lysosomes produce energy.

<p>False</p> Signup and view all the answers

Microtubules are 5-7 nm in diameter.

<p>False</p> Signup and view all the answers

Intermediate filaments are 25 nm in diameter.

<p>False</p> Signup and view all the answers

Cytoskeleton is composed of only two types of polymers.

<p>False</p> Signup and view all the answers

Mitochondria are responsible for the synthesis of ATP during anaerobic cellular respiration.

<p>False</p> Signup and view all the answers

Ribosomes are typically found in the cell membrane

<p>False</p> Signup and view all the answers

The cytoskeleton determines the shapes of cells and plays an important role in the movement of organelles and cytoplasmic vesicles.

<p>True</p> Signup and view all the answers

The Endoplasmic Reticulum is a network that extends from the surface of the mitochondria throughout most of the cytoplasm

<p>False</p> Signup and view all the answers

Actin filaments are most concentrated at the centrosome area near the nucleus.

<p>False</p> Signup and view all the answers

The cytoskeleton is responsible for determining a cell's shape and motility

<p>True</p> Signup and view all the answers

Ribosomes produce proteins that are incorporated into the cell wall

<p>False</p> Signup and view all the answers

The Endoplasmic Reticulum is composed of a series of non-intercommunicating channels

<p>False</p> Signup and view all the answers

Lysosomes are involved in protein synthesis

<p>False</p> Signup and view all the answers

The Golgi Apparatus is responsible for modifying and packaging proteins for transport out of the cell

<p>True</p> Signup and view all the answers

Cytosol contains hundreds of enzymes involved in cellular metabolism

<p>True</p> Signup and view all the answers

What is the primary function of the Golgi apparatus in protein synthesis?

<p>Posttranslational modification and packaging of proteins</p> Signup and view all the answers

Which organelle is responsible for intracellular digestion and turnover of cellular components?

<p>Lysosomes</p> Signup and view all the answers

What is the Endoplasmic Reticulum responsible for, aside from protein synthesis?

<p>Biosynthesis of proteins and lipids</p> Signup and view all the answers

What is the main function of the mitochondria in cellular metabolism?

<p>Generating energy for the cell through cellular respiration</p> Signup and view all the answers

What is the primary function of lysosomes in cellular metabolism?

<p>Breaking down and recycling cellular waste and foreign substances</p> Signup and view all the answers

What is the main component of the cytoskeleton involved in providing mechanical stability to cells?

<p>Intermediate filaments</p> Signup and view all the answers

What is a primary function of microtubules in maintaining cell shape?

<p>Serving as tracks for motor proteins</p> Signup and view all the answers

What is a key characteristic of intermediate filaments?

<p>Most stable component of the cytoskeleton</p> Signup and view all the answers

What is the primary function of microfilaments in the cytoskeleton?

<p>Regulating cytoplasmic viscosity and movement</p> Signup and view all the answers

What is the average diameter of intermediate filaments?

<p>8-10 nm</p> Signup and view all the answers

What is the role of motor proteins in the cytoskeleton?

<p>Moving vesicles and organelles along microtubules</p> Signup and view all the answers

What is the primary function of the cytoskeleton?

<p>Maintaining cell shape and mechanical stability</p> Signup and view all the answers

What type of protein subunits make up intermediate filaments?

<p>Various protein subunits</p> Signup and view all the answers

What is a key difference between microfilaments and microtubules?

<p>Microtubules are semirigid tubular structures</p> Signup and view all the answers

What is the primary function of microtubules in the cytoskeleton?

<p>Involved in the transport of vesicles and organelles by motor proteins</p> Signup and view all the answers

What is the diameter of intermediate filaments?

<p>8-10 nm</p> Signup and view all the answers

What is the function of the cytoskeleton in the cell?

<p>Determining the shape of cells and playing an important role in the movement of organelles and cytoplasmic vesicles</p> Signup and view all the answers

What is the diameter of microfilaments?

<p>5-7 nm</p> Signup and view all the answers

What is the role of actin filaments in the cell?

<p>Most concentrated at the centrosome area near the nucleus</p> Signup and view all the answers

What is the composition of the cytoskeleton?

<p>Three types of polymers: microtubules, actin filaments, and intermediate filaments</p> Signup and view all the answers

What is the function of microtubules in the transport of vesicles and organelles?

<p>Involved in the transport of vesicles and organelles by motor proteins</p> Signup and view all the answers

What is the characteristic of microtubules in terms of their diameter?

<p>25 nm in diameter</p> Signup and view all the answers

Study Notes

Cytoskeleton

  • Microtubules: semi-rigid tubular structures composed of polymerized tubulin heterodimers, dynamic with steady addition and dissociation of tubulin.
  • Microtubules are important for maintaining cell shape and as tracks for transport of vesicles and organelles by motor proteins kinesin and dynein.

Microfilaments

  • Short, flexible, highly dynamic filaments of actin subunits.
  • Changes in length and interactions with binding proteins regulate cytoplasmic viscosity and movement.
  • Myosins are motor proteins that bind and move along actin filaments, carrying vesicles or producing cytoplasmic movement.

Intermediate Filaments

  • Most stable cytoskeletal component, conferring strong mechanical stability to cells.
  • Composed of various protein subunits in different cells, including vimentin, nuclear lamins, neurofilament proteins, and keratins.
  • Average diameter of 8-10 nm, between that of actin filaments and microtubules.

Inclusions

  • Not metabolically active, primarily storage sites, such as lipid droplets, glycogen granules, pigment granules, or residual bodies (also called lipofuscin).

Mitochondria

  • Double membrane-enclosed organelles with arrays of enzymes specialized for aerobic respiration and production of ATP.
  • Synthesize most ATP during aerobic cellular respiration by digestion of fuel molecules in the presence of oxygen.
  • Mitochondrial diseases are a group of genetic conditions that affect how mitochondria produce energy.

Cytoplasmic Organelles

  • Metabolically active structures inside the cell membrane, such as mitochondria, ribosomes, and proteasomes.
  • Positioned in the cytoplasm by movements along the polymers of the cytoskeleton, which also determines a cell's shape and motility.

Ribosomes

  • Macromolecular machines that assemble polypeptides from amino acids on molecules of transfer RNA (tRNA) in a sequence specified by mRNA.
  • Functional ribosome has two subunits of different sizes bound to a strand of mRNA.
  • Engage in protein synthesis, with bound ribosomes producing proteins that are secreted or incorporated into the plasma membrane.

Endoplasmic Reticulum

  • Convoluted membranous network that extends from the surface of the nucleus throughout most of the cytoplasm.
  • Encloses a series of intercommunicating channels called cisternae (reservoirs).

Endoplasmic Reticulum

  • ER is a major site for vital cellular activities, including biosynthesis of proteins and lipids.
  • Responsible for various cellular activities.

Golgi Apparatus

  • Completes posttranslational modifications of proteins produced in the RER.
  • Packages and addresses proteins to their proper destinations.
  • Consists of many smooth membranous saccules, containing enzymes and proteins being processed.
  • Named after histologist Camillo Golgi who discovered it in 1898.

Lysosomes

  • Sites of intracellular digestion and turnover of cellular components.
  • Spherical-shaped membrane-bound organelles formed from the Golgi apparatus.
  • Contain about 40 different hydrolytic enzymes.
  • Particularly abundant in cells with great phagocytic activity (e.g., macrophages, neutrophils).
  • Digest microbes or materials, including ingested by the cell, worn out cellular components, or the entire cell.

Mitochondria

  • Double membrane-enclosed organelles with arrays of enzymes specialized for aerobic respiration and production of ATP.
  • Synthesize most ATP during aerobic cellular respiration by digestion of fuel molecules (e.g., glucose) in the presence of oxygen.
  • Mitochondrial diseases are a group of genetic conditions that affect how mitochondria in the cells produce energy.
  • Can affect almost any part of the body, including cells of the brain, nerves, muscles, kidney, heart, liver, eyes, pancreas, etc.

Cytoskeleton

  • A complex array of microtubules, microfilaments (also called actin filaments), and intermediate filaments.
  • Determines the shapes of cells, plays an important role in the movements of organelles and cytoplasmic vesicles, and allows the movement of entire cells.
  • Microtubules and actin microfilaments can be clearly distinguished by TEM.
  • Immunocytochemistry using antibodies against their subunit proteins can demonstrate arrays of microfilaments and microtubules.
  • Actin filaments are most concentrated at the cell periphery.
  • Microtubules are oriented in arrays that generally extend from the centrosome area near the nucleus into the most peripheral.

Microtubules

  • Semi-rigid tubular structures with walls composed of polymerized tubulin heterodimers.
  • Structure is often very dynamic, with steady addition and dissociation of tubulin.
  • Important in maintaining cell shape and as tracks for transport of vesicles and organelles by the motor proteins kinesin and dynein.
  • Diameter of 25 nm.

Microfilaments

  • Short, flexible, highly dynamic filaments of actin subunits.
  • Changes in length and interactions with binding proteins regulate cytoplasmic viscosity and movement.
  • Myosins are motor proteins that bind and move along actin filaments, carrying vesicles or producing cytoplasmic movement.
  • Diameter of 5-7 nm.

Intermediate Filaments

  • The most stable cytoskeletal component, conferring strong mechanical stability to cells.
  • Composed of various protein subunits in different cells, including vimentin, nuclear lamins, neurofilament proteins, and keratins.
  • Display an average diameter of 8-10 nm, between that of actin filaments and microtubules.
  • Serve to provide mechanical strength or stability to cells.

Inclusions

  • Not metabolically active and are primarily storage sites.
  • Examples include lipid droplets, glycogen granules, pigment granules, or residual bodies (also called lipofuscin).

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