Cell Organelles: Structure and Function

Posted on Dec 1, 2024 in Biology

Plasma Membrane

Cell Type: Prokaryotes and Eukaryotes

Structure:

  • Lipid bilayer (phospholipids, cholesterol)
  • Proteins (transmembrane, peripheral)
  • Carbohydrates (oligosaccharides)

Functions:

  1. Acts as a semipermeable barrier.
  2. Provides protection.
  3. Aids subcellular compartmentalization.
  4. Regulates transport to and from the cell.
  5. Serves as receptor for signal transduction.
  6. Enables cell recognition.
  7. Provides anchoring sites for cytoskeletal filaments.
  8. Serves as a site for enzymatic catalysis.
  9. Provides gap junctions for intercellular passage.
  10. Regulates membrane fusion.
  11. Directs cell motility.

Mitochondria

Cell Type: Prokaryotes and Eukaryotes

Structure:
0.5-1 micrometer long, surrounded by a double membrane. The smooth outer membrane is separated from the inner membrane by a liquid film. The inner membrane, folded into cristae, encloses a liquid matrix containing enzymes. Mitochondrial DNA (mtDNA) is within the matrix.

Function:
Generates energy through aerobic respiration.

Golgi Apparatus

Cell Type: Eukaryotes

Structure:
Flattened, discoidal sacs (saccules) with associated vesicles. Cis (proximal) face receives vesicles from the endoplasmic reticulum. Trans (distal) face releases secretory vesicles.

Functions:

  • Glycosylation of proteins and lipids.
  • Secretion and accumulation of substances.
  • Membrane production.
  • Intracellular transport.
  • Lysosome formation.
  • Sperm acrosome formation.

Peroxisome

Cell Type: Eukaryotes

Structure:
Circular, membrane-bound organelles containing a homogeneous matrix. Some contain urate oxidase crystals. Classified by size: microperoxisomes (0.15-0.5 microns) and larger peroxisomes (>0.5 microns).

Function:
Catalyzes the production and decomposition of hydrogen peroxide (H2O2).

Lysosome

Cell Type: Eukaryotes

Structure:
Storage granules containing enzymes produced in the endoplasmic reticulum and processed by the Golgi apparatus. Primary lysosomes contain a single enzyme, while secondary lysosomes contain a complete set.

Functions:

  • Elimination of substances.
  • Participation in endocytosis.
  • Regulation of cell secretion.

Cytoskeleton

Cell Type: Eukaryotes

Structure:
Composed of microfilaments, microtubules, and intermediate filaments.

Functions:

  • Cell stability and shape.
  • Cell locomotion.
  • Cell division.
  • Organelle movement.
  • Metabolic regulation.

Ribosome

Cell Type: Prokaryotes and Eukaryotes

Structure:
Non-membrane-bound organelles composed of a large and small subunit made of RNA and proteins.

Function:
Protein synthesis.

Centriole

Cell Type: Eukaryotic Animal

Structure:
Located within the centrosome, the origin of microtubules. Consists of a pair of centrioles, each composed of nine microtubule triplets arranged in a ring.

Functions:

  • Mitotic spindle formation.
  • Formation of kinetosomes and axonemes in cilia and flagella.

Chloroplast

Cell Type: Eukaryotic Plant

Structure:

  • Outer membrane
  • Inner membrane with selective permeability
  • Membranous sacs (thylakoids) stacked into grana
  • Stroma (colloidal substance containing DNA and ribosomes)
  • Reserve substance (starch)

Function:
Photosynthesis (production of organic matter).

Rough Endoplasmic Reticulum (RER)

Cell Type: Eukaryotes

Structure:
Network of membranes with attached ribosomes.

Functions:

  • Protein synthesis.
  • Protein glycosylation.
  • Membrane formation.
  • Cell secretion.
  • Lysosome enzyme production.

Smooth Endoplasmic Reticulum (SER)

Cell Type: Eukaryotes

Structure:
Network of tubular membranes without ribosomes.

Functions:

  • Lipid synthesis.
  • Steroid hormone synthesis.
  • Detoxification.
  • Muscle contraction.

Vacuole

Cell Type: Eukaryotes

Structure:
Membrane-bound sacs. Plant cells typically have one or few large vacuoles, while animal cells have smaller vacuoles.

Function:
Storage of water, nutrients, waste, and minerals.

Cell Wall

Cell Type: Eukaryotic Plant

Structure:
Composed primarily of cellulose.

Functions:

  • Provides mechanical strength.
  • Bonds with other cells.
  • Controls cell shape.
  • Regulates turgor pressure.
  • Influences plant morphogenesis.
  • Acts as a diffusion barrier.
  • Protects against pathogens.

Nucleus

Cell Type: Eukaryotes

Structure:

  • Nuclear envelope (double membrane with pores)
  • Chromatin (DNA and proteins)
  • Nucleoplasm
  • Nucleolus (involved in ribosome synthesis)

Functions:

  • Directs cell activity.
  • Houses DNA replication and transcription.