Cell Structure and Function

Key Terms and Concepts

• Cell theory

• Ribosomes

• Cytosol

• Plasma membrane

• Prokaryote vs. Eukaryote

• Organelle

• Nucleus

• Cytoskeleton

• Microfilaments

• Actin

• Intermediate filaments

• Microtubules

• Tubulin

• Motor proteins (e.g., Myosin, Kinesin, Dynein)

• Microscopes: TEM, SEM, Light microscopy

Learning Goals and Study Notes

Distinguishing Cellular Structures by Microscopy

Microscopy is essential for visualizing cellular structures. Different microscopes provide varying levels of detail and types of information about cells.

• Light Microscopy: Uses visible light to illuminate specimens. Can visualize living cells and larger organelles (e.g., nucleus, cell membrane, chloroplasts).

• Electron Microscopy: Uses beams of electrons for much higher resolution. Two main types:

  • Scanning Electron Microscopy (SEM): Provides detailed 3D images of cell surfaces.

  • Transmission Electron Microscopy (TEM): Reveals internal structures in high detail, such as organelles and macromolecular complexes.

• Major Disadvantage of Electron Microscopy: Cells must be fixed (killed) and cannot be observed alive.

Example: SEM can show the surface of a bacterium, while TEM can reveal the arrangement of ribosomes inside the cell.

Principles of the Cell Theory

The cell theory is a fundamental concept in biology, describing the properties of cells.

• All living organisms are composed of one or more cells.

• The cell is the basic unit of structure and function in living things.

• All cells arise from pre-existing cells.

Cell Size Limitations

Cell size is limited by the relationship between surface area and volume. As a cell grows, its volume increases faster than its surface area, limiting the rate of exchange with the environment.

• Surface Area to Volume Ratio: Smaller cells have a higher ratio, allowing efficient exchange of materials.

• Microvilli: Extensions that increase surface area, aiding absorption (e.g., in intestinal cells).

Equation:

Example: Intestinal epithelial cells have microvilli to maximize nutrient absorption.

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure and organization.

Major Difference: Prokaryotes lack a membrane-bound nucleus; their DNA is in the nucleoid.

Ribosomes: Structure and Function

Ribosomes are molecular machines responsible for protein synthesis in all cells.

• Composed of ribosomal RNA (rRNA) and proteins.

• Found free in the cytosol or bound to the endoplasmic reticulum (in eukaryotes).

• Translate messenger RNA (mRNA) into polypeptide chains.

Example: Ribosomes in bacteria synthesize enzymes needed for metabolism.

Functions of the Cytosol

The cytosol is the fluid component of the cytoplasm, where many metabolic reactions occur.

• Site of glycolysis and other metabolic pathways.

• Contains ions, proteins, and small molecules.

• Supports organelles and provides a medium for molecular transport.

Roles of the Cytoskeleton

The cytoskeleton is a dynamic network of protein filaments that provides structural support and facilitates movement within cells.

• Maintains cell shape.

• Anchors organelles.

• Enables cell movement and division.

• Facilitates intracellular transport.

Cytoskeletal Components: Classification

The cytoskeleton consists of three main types of protein filaments, classified by structure, size, protein subunits, and primary roles.

Motor Proteins and Cytoskeletal Interactions

Motor proteins interact with cytoskeletal filaments to generate movement within cells.

• Myosin: Moves along actin filaments; involved in muscle contraction and cell movement.

• Kinesin: Moves along microtubules, usually toward the cell periphery; transports vesicles and organelles.

• Dynein: Moves along microtubules, usually toward the cell center; powers cilia and flagella movement.

• ATP: Provides the energy for motor protein movement.

Example: Dynein causes cilia to beat, moving mucus in the respiratory tract.

Summary Table: Cytoskeletal Components and Motor Proteins

Additional info: Some details, such as the precise measurements of cytoskeletal elements and the specific examples of motor protein functions, have been inferred from standard biology textbooks to provide a complete and self-contained study guide.