Cell Biology: Microtubules and Centrioles

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Questions and Answers

What is the primary function of ribosomes in a cell?

Synthesis of proteins (correct)

Energy production through respiration

Transportation of molecules

Storage of genetic information

Which type of ribosome is found predominantly in eukaryotic cells?

50S ribosome

70S ribosome

80S ribosome (correct)

90S ribosome

What is the main structural component of microtubules?

Chitin

Actin filaments

Tubulin (correct)

Collagen

What is the shape of mitochondria in most eukaryotic cells?

Oval or rod-shaped Signup and view all the answers

How does the number of mitochondria in a cell relate to its energy requirements?

Higher energy requirement cells have more mitochondria Signup and view all the answers

Which structure is primarily involved in the organization of microtubules in a cell?

Microtubule Organizing Centers (MTOCs) Signup and view all the answers

What is the main component of the ribosomal subunits?

Proteins and rRNA Signup and view all the answers

How are tubulin subunits arranged within a microtubule?

In a helical arrangement Signup and view all the answers

Which of the following best describes the properties of microvilli?

They are short projections that increase cell surface area. Signup and view all the answers

What feature increases the surface area of the mitochondria?

Cristae Signup and view all the answers

What primarily prevents plant cells from forming projections like microvilli?

Cell wall barrier Signup and view all the answers

In which type of cells would you expect to find 70S ribosomes?

In prokaryotic cells and mitochondria Signup and view all the answers

Which of the following describes a primary role of centrioles?

Producing cilia Signup and view all the answers

What is a key function of centrioles in a cell?

Organization of microtubules Signup and view all the answers

What is the significance of the circular DNA molecule found in mitochondria?

It indicates prokaryotic origins Signup and view all the answers

What is the main difference in structure between cilia and flagella?

Cilia are short and numerous, while flagella are long and usually singular. Signup and view all the answers

What structural feature differentiates cilia from flagella?

Cilia are shorter and more numerous. Signup and view all the answers

How do microtubules contribute to intracellular transport?

By facilitating the movement of vesicles within the cell Signup and view all the answers

Which of the following best describes the behavior of microtubules in relation to MTOCs?

They can be easily formed and dismantled based on cellular needs. Signup and view all the answers

What common characteristic do centrioles and cilia share?

Both consist of nine triplets of microtubules Signup and view all the answers

What process allows the release of hydrolytic enzymes from lysosomes outside the cell?

Exocytosis Signup and view all the answers

What role do microtubules play in cell division?

They form spindle fibers for chromosome separation. Signup and view all the answers

What is a unique feature of microvilli in animal cells?

They absorb or secrete substances from the environment. Signup and view all the answers

Which statement accurately describes the composition of a centriole?

Made up of nine triplets of microtubules held by connecting fibers. Signup and view all the answers

Study Notes

Microtubule Functions

Microtubules are important for cell division, forming spindle fibers that help with chromosome separation.
Microtubules are involved in moving vesicles and organelles within the cell, like Golgi vesicles and those involved in exocytosis.
They contribute to cell shape and support, often found near the cell surface membrane.
They are a component of centrioles.
They contribute to the movement of cilia and flagella.

Centrioles

Found only in animal cells.
Occur in pairs, located near the nucleus, at right angles to each other.
Measured at 0.2 micrometers in diameter and 0.3-0.5 micrometers in length, visible only with an electron microscope.
Composed of nine triplets of microtubules held together by connecting fibers.
Tubulin subunits of microtubules are arranged in a helical pattern along the centriole.
Play a role in cilia production.
Located at the base of cilia and flagella as basal bodies.
Act as microtubule organizing centers (MTOCs).

Microvilli

Finger-like projections of the cell surface membrane.
Found only in animal cells, not in plant cells due to the cell wall barrier.
Increase the surface area of the cell membrane.
Involved in the absorption or secretion of substances.

Cilia and Flagella

Short and numerous per cell (cilia) or long and one or two per cell (flagella).
Identical structures, whip-like appendages found in eukaryotic cells.

Lysosomes

Membrane-bound organelles containing hydrolytic enzymes.
Involved in:
- Digestion of worn-out organelles (autophagy): An old organelle is enveloped in a membrane, a lysosome fuses with the vacuole, and the hydrolytic enzymes digest the material.
- Exocytosis: Release of hydrolytic enzymes outside the cell for extracellular digestion.
- Autolysis: Self-digestion of the entire cell by the release of lysosome enzymes resulting in cellular breakdown. This is a normal process in cell turnover.

Cytoskeleton

A network of fibrous protein structures providing support to the cell.
Two types:
- Microtubules
- Microfilaments
Functions:
- Cell support
- Cell shape maintenance
- Organelle movement within the cell

Microtubules

Fine, unbranched, hollow tubes, about 25 nm in diameter and several micrometers in length.
Only visible under an electron microscope.
Composed of tubulin protein (α-tubulin and β-tubulin).
Tubulin molecules form dimers, which assemble into long "protofilaments".
A microtubule contains 13 tubulin subunits in a transverse section, arranged helically.
Assembly and disassembly of microtubules are controlled by microtubule organizing centers (MTOCs).
Involved in a range of cellular functions beyond mechanical support.

Smooth Endoplasmic Reticulum (SER)

A network of interconnected, membrane-bound sacs and tubules.
Functions:
- Synthesis of lipids and steroids.
- Detoxification of drugs and toxins.
- Calcium storage and release.
- In the liver, SER is involved in drug metabolism.

Ribosomes

Tiny organelles, about 20 nm in diameter.
Visible under an electron microscope.
Can be attached to the endoplasmic reticulum (forming Rough ER) or free in the cytoplasm.
Composed of two subunits: a small subunit and a large subunit.
Subunits are made of rRNA molecules and protein molecules.
Two types:
- 70S ribosomes: Found in prokaryotes, smaller and lighter.
- 80S ribosomes: Found in eukaryotic cells, larger and heavier. Mitochondria and chloroplasts contain 70S ribosomes due to their prokaryotic origins.
Function: Site of protein synthesis.

Mitochondria

Present in all eukaryotic cells.
Function: The site of aerobic respiration (energy production).
Number of mitochondria varies depending on the cell's energy requirements.
Structure:
- Oval, rod-shaped, or spherical.
- Surrounded by two membranes forming an envelope.
- Inner membrane is folded into cristae to increase surface area.
- Cristae contain stalked elementary particles (ATPase, stalk, and base).
- Matrix contains:
  - Circular DNA molecule.
  - 70S ribosomes.

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Description

Explore the functions of microtubules and the structure of centrioles in animal cells. This quiz covers their roles in cell division, vesicle transport, and the production of cilia and flagella. Test your knowledge on these essential components of cellular organization.