Centrioles in Eukaryotic Cells
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Questions and Answers

What are centrioles?

Centrioles are cylindrical, rod-shaped structures found in the cytoplasm of eukaryotic cells. They are composed of microtubules.

Centrioles have their own DNA and RNA.

False

What is the function of centrioles in cell division?

Centrioles form spindle microtubules, which are essential for the separation of chromosomes during cell division.

What are basal bodies?

<p>Basal bodies are modified centrioles that form the base of cilia and flagella.</p> Signup and view all the answers

In which type of cells are centrioles absent?

<p>All of the above</p> Signup and view all the answers

What is the approximate diameter of a centriole?

<p>0.15 to 0.25 micrometers</p> Signup and view all the answers

What is the approximate length of a centriole?

<p>0.3 to 0.7 micrometers</p> Signup and view all the answers

What is the most striking feature of the ultrastructure of a centriole?

<p>An array of nine triplet microtubules arranged around the perimeter of an imaginary cylinder.</p> Signup and view all the answers

What is the space between and around the triplet microtubules filled with?

<p>An amorphous, electron-dense material.</p> Signup and view all the answers

The triplets in a centriole are arranged in a spiral pattern like blades of a turbine.

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

How are the microtubules within each triplet arranged?

<p>They twist from one end to another, forming a helical structure.</p> Signup and view all the answers

Centrioles have a defined outer membrane.

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

What connects the 'A' tubule of each triplet to the 'C' tubule of the next triplet?

<p>Protein linkers.</p> Signup and view all the answers

What is the function of the linkers in a centriole?

<p>They hold the cylindrical array of microtubules together and maintain the radial tilt of the triplets.</p> Signup and view all the answers

Centrioles have central microtubules and special arms.

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

What pattern do protein spokes radiate out from in a centriole?

<p>A central core.</p> Signup and view all the answers

What does the cartwheel configuration in a centriole determine?

<p>The proximal end of a centriole.</p> Signup and view all the answers

What is the functional significance of the cartwheel configuration in a centriole?

<p>It provides a structural and functional polarity to the centriole.</p> Signup and view all the answers

From which end of a centriole does growth occur?

<p>The distal end.</p> Signup and view all the answers

Where do cilia and flagella grow from in basal bodies?

<p>The distal end.</p> Signup and view all the answers

What are the two types of ciliary rootlets that originate from basal bodies?

<p>Tubular root fibrils and striated rootlets.</p> Signup and view all the answers

What are basal feet?

<p>Dense processes that are arranged perpendicular to the basal body.</p> Signup and view all the answers

What do basal feet impose on the basal body?

<p>Structural asymmetry.</p> Signup and view all the answers

What are satellites in relation to centrioles?

<p>Electron-dense structures lying near the centriole.</p> Signup and view all the answers

What is the primary function of a pair of centrioles in the centrosome?

<p>They organize the array of cytoplasmic microtubules.</p> Signup and view all the answers

What do centrioles do during mitosis?

<p>They duplicate and nucleate the two poles of the mitotic spindle.</p> Signup and view all the answers

Basal bodies can form centrioles prior to cell division.

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

What is one function of cilia and flagella?

<p>Locomotion for cells or organisms.</p> Signup and view all the answers

How do cilia contribute to feeding in lower aquatic animals?

<p>They create food currents.</p> Signup and view all the answers

What is the function of cilia in the respiratory tracts?

<p>They help to eliminate solid particles.</p> Signup and view all the answers

What role do cilia play in the oviduct of amphibians and mammals?

<p>They drive eggs out of the oviduct.</p> Signup and view all the answers

Match the following terms with their correct definitions:

<p>Centrioles = Cylindrical structures composed of microtubules, involved in cell division and cilia/flagella formation. Basal bodies = Modified centrioles that form the base of cilia and flagella. Ciliary rootlets = Structural components that connect basal bodies to the cell cytoskeleton, anchoring cilia and flagella. Basal feet = Dense processes that are arranged perpendicular to the basal body, contributing to structural asymmetry. Satellites = Electron-dense structures near the centriole, thought to be nucleating sites for microtubules.</p> Signup and view all the answers

Centrioles are found in both plant and animal cells.

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

What role do centrioles play in the formation of cilia and flagella?

<p>They form the basal bodies, which are essential for the assembly and anchoring of cilia and flagella.</p> Signup and view all the answers

What is the difference between cilia and flagella?

<p>Cilia are shorter and more numerous than flagella, and they beat in a coordinated, wave-like motion. Flagella are longer and fewer in number, and they typically propel cells in a whip-like fashion.</p> Signup and view all the answers

Study Notes

Centrioles

  • Eukaryotic cells contain cylindrical, rod-shaped microtubular structures called centrioles.
  • Centrioles lack a limiting membrane, DNA, and RNA.
  • They form spindle microtubules.
  • Centrioles sometimes arrange beneath the plasma membrane, forming basal bodies for cilia or flagella.

Occurrence

  • Present in most algal cells, moss cells, fern cells, and most animal cells.
  • Absent in red algae, prokaryotes, yeast, cone-bearing and flowering plants (conifers and angiosperms), and amoeba.

Structure

  • Cylindrical structures.
  • Diameter is approximately 0.15 to 0.25 μm.
  • Length is approximately 0.3 to 0.7 µm; length in some cases varies from 0.16 to 8 µm.
  • All centrioles possess a consistent ultrastructure.

Ultrastructure

  • Cylinder wall: Composed of nine triplets of microtubules arranged around an imaginary cylinder. The space between and around triplets is filled with an amorphous, electron-dense material. The tubules twist, forming a spiral/helical structure. The triplets themselves are arranged like blades of a pinwheel, angled inward toward a central axis.
  • Triplets: Three subunit microtubules (A, B, C). A is complete, while B and C are incomplete. They share walls with each other (200 – 260 Å= 20-26nm). Triplet microtubules are generally similar to other microtubules. They nearly run parallel to each other along the cylinder, but that's not always the case. The microtubules are in close proximity at the proximal end (end closer to the center).
  • Spokes, Cartwheel, Linkers, Ciliary rootlets: Other components found within the centriole structure.
  • Basal feet and satellites: Dense processes that are perpendicular to the basal body. In some cells, structures arise from the basal end of the centriole. Satellites are dense structures near the centriole.

Linkers

  • 'A' tubule is linked to the 'C' tubule of the next triplet by protein linkers, running the entire length.
  • Linkers hold the cylindrical array of microtubules, maintaining radial tilt.

Cartwheel

  • No central microtubules or special arms are present.
  • Protein spokes radiate from a central core to each triplet, forming a cartwheel pattern.
  • Cartwheel configuration provides structural and functional polarity to the centriole (proximal end vs. distal end).
  • Growth occurs from the distal end (away from the center).

Ciliary rootlets

  • From basal ends of basal bodies
  • Two types: Tubular root fibrils and striated rootlets

Basal Feet and Satellites

  • Basal feet are dense processes perpendicular to the basal body.
  • They create structural asymmetry related to ciliary beat direction.
  • Satellites are electron-dense structures near the centriole, possibly nucleating sites for microtubules.

Functions of Centrioles

  • Formation of basal bodies and cilia.
  • Centrosome: Pair of centrioles act as a focal point, organizing cytoplasmic microtubules during interphase and duplicating at mitosis to create the mitotic spindle poles.
  • Basal bodies can form centrioles prior to cell division.
  • Involved in ciliary or flagellar beat.

Cilia and Flagella

  • Flagella: Present in Class Flagellata, sponges, gametes of plants and algae, and gametes of animals.
  • Cilia: Present in Class Ciliata, larvae of certain Platyhelminthes, Echinodermata, Mollusca, and Annelida, and respiratory tracts of animals.

Functions of Cilia and Flagella

  • Locomotion in cells or organisms.
  • Create food currents in lower aquatic animals.
  • In respiratory tracts, ciliary movement helps eliminate solid particles.
  • Eggs of amphibians and mammals are expelled from the oviduct due to ciliary movement.

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Centrioles PDF

Description

Explore the fascinating world of centrioles, the cylindrical microtubular structures found in eukaryotic cells. This quiz covers their structure, occurrence, and ultrastructure, highlighting their crucial role in cell division and motility. Test your knowledge about the different types of cells that possess or lack centrioles.

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