Cell Biology: Major Organelles and Structures

Major Organelles and Sub-Cellular Structures

• Nucleus: Contains DNA, site of DNA replication and transcription, surrounded by nuclear envelope.
• Ribosomes: Site of protein synthesis, composed of rRNA and proteins, found in the cytoplasm or attached to the ER.
• Endoplasmic Reticulum (ER): Network of interconnected membranes, Rough ER (RER): site of protein synthesis and modification, Smooth ER (SER): site of lipid and steroid synthesis, detoxification.
• Golgi Apparatus: Stack of flattened sacs, involved in protein modification, sorting, and packaging.
• Lysosomes: Membrane-bound organelles containing enzymes for degradation of cellular waste.
• Mitochondria: Powerhouse of the cell, responsible for ATP production through cellular respiration.
• Peroxisomes: Membrane-bound organelles containing enzymes for detoxification and lipid metabolism.
• Centrioles: Involved in cell division, formation of microtubule organizing centers.

Cytoskeleton

• Microtubules: Composed of tubulin dimers, provide structural support, involved in cell movement and transport.
• Microfilaments (Actin filaments): Composed of actin monomers, provide structural support, involved in cell movement, muscle contraction.
• Intermediate filaments: Composed of various proteins, provide structural support and maintain cell shape.

Cell Contacts

• Cell-Cell Junctions:
  • Tight junctions: Prevent leakage of fluids between cells, found in epithelial tissues.
  • Adherens junctions: Link cells together, provide structure and support, involve cadherin proteins.
  • Desmosomes: Anchoring junctions that provide strong cell-to-cell adhesion.
  • Gap junctions: Channels that allow communication between cells, permit passage of small molecules.
• Cell-ECM Junctions:
  • Focal adhesions: Anchoring junctions between the cell and ECM, involve integrins, mediate cell signaling.
  • Hemidesmosomes: Strong anchoring junctions between cells and the basal lamina, involve integrins.

Protein Targeting and Modification

• Protein Targeting:
  • Signal sequences: Amino acid sequences that direct proteins to their specific destination.
  • Chaperone proteins: Assist in protein folding and prevent aggregation.
  • Translocation: Movement of proteins across membranes.
• Post-Translational Modifications:
  • Glycosylation: Addition of sugar moieties, affects protein folding, stability, and cellular function.
  • Phosphorylation: Addition of phosphate groups, can activate or inactivate proteins.
  • Farnesylation: Addition of a farnesyl group, involved in protein-membrane interactions.

Protein Degradation

• Ubiquitin-Proteasome System:
  • Ubiquitin: Small protein tag that marks proteins for degradation.
  • Proteasome: Large protein complex that degrades ubiquitinated proteins.
• Lysosomal Degradation:
  • Lysosomes: Sacs containing enzymes for digesting cellular waste.
  • Autophagy: Process of engulfing cellular components for degradation in lysosomes.

Test your knowledge on the major organelles found in cells and their functions. This quiz covers structures such as the nucleus, ribosomes, and mitochondria, explaining their roles in cellular processes. Challenge yourself to see how well you understand these essential components of cell biology.