Organelles and cellular structures

Plasma Membrane

• Functions: Serves as a barrier to cell contents, physical isolation, regulation of exchange, communication, cell-cell adhesion, and selective permeability.

• Location: Outermost boundary surrounding the cell.

• Characteristics: Flexible, elastic phospholipid bilayer embedded with proteins, cholesterol, and glycoproteins. (Selective Permeability)

Nucleus

• Functions: Houses the genetic material (DNA) and acts as the control center of the cell.

• Location: Typically centrally located within the cytoplasm.

• Characteristics: Enclosed by a double-layered nuclear membrane containing nuclear pores; contains nucleoplasm, chromatin (DNA and proteins), and a nucleolus where ribosomes are synthesized.

Rough Endoplasmic Reticulum (RER)

• Functions: Functions in protein synthesis.

• Location: Attached to the nucleus.

• Characteristics: Composed of membrane-bounded flattened sacs (cisternae) and fluid-filled vesicles; studded with ribosomes on its outer surface.

Smooth Endoplasmic Reticulum (SER)

• Functions: Contains enzymes important for lipid synthesis, drug and alcohol metabolism, and may be modified depending on the cell type.

• Location: Suspended in the cytoplasm, continuous with the Rough ER.

• Characteristics: Lacks ribosomes on its surface.

Ribosomes

• Functions: Protein synthesis.

• Location: Found freely in the cytoplasm or bound to the surface of the Rough ER.

• Characteristics: Made of RNA and proteins; non-membrane-bound structures.

Golgi Apparatus

• Functions: Modifies, packages, and ships proteins in vesicles to various locations inside the cell or for secretion outside the cell.

• Location: Located in the cytoplasm, usually near the Endoplasmic Reticulum and nucleus.

• Characteristics: Composed of stacks of flattened membranous sacs.

Mitochondria

• Functions: Produces energy molecules (ATP) and synthesizes cholesterol.

• Location: Distributed throughout the cytoplasm.

• Characteristics: Elongated, fluid-filled sacs with a double membrane; feature extensive folding of the inner membrane (cristae) and have the ability to reproduce independently.

Lysosomes

• Functions: Contain enzymes to break down nutrients or foreign particles. (protein degradation)

• Location: Dispersed within the cytoplasm.

• Characteristics: Tiny membranous sacs.

Peroxisomes

• Functions: Contain enzymes to speed up chemical reactions and detoxify alcohol.

• Location: Found throughout the cytoplasm; highly abundant in liver and kidney cells.

• Characteristics: Membranous sacs.

Centrosome

• Functions: Plays an important role in cell division.

• Location: Positioned in the cytoplasm near the nucleus.

• Characteristics: Non-membrane-bound structure consisting of two hollow cylinders called centrioles.

Cytoskeleton (Microfilaments & Microtubules)

• Functions: Microfilaments provide cell motility; microtubules provide structural strength and facilitate the movement of materials within the cell.

• Location: Extends throughout the cytoplasm.

• Characteristics: Composed of thin strands in the cytoplasm.

  • Microfilaments: Tiny rods composed of actin proteins, highly abundant in muscle cells.

  • Microtubules: Long, slender tubes with a larger diameter.

Cilia

• Functions: Cilia move fluids on surface of cells (made of microtubules)

• Location: Protrude from the outer surface of the cell membrane.

• Characteristics: Structural extensions made of microtubules.

  
  

Flagellum

• Functions: flagella enable an entire cell to move (e.g., sperm cells). (made of microtubules)

• Location: Protrude from the outer surface of the cell membrane.

• Characteristics: Structural extensions made of microtubules.