Cell Pathology: Core Concepts and Mechanisms

Cells: The fundamental, basic unit of the body.
Tissues: Groups of similar cells working together to perform similar functions.
Organs: Tissues are grouped together in varying proportions to form organs.
Organ System: Multiple organs functioning in concert.
Functioning Organism: Integrated organ systems working collectively.
Disease Implication: An abnormality at any level of this organization can lead to disease.

Function: Contains genetic information and directs the metabolic functions of cells.
Content:
- Nucleoli: Structures within the nucleus.
- Nucleic Acids: Two types combined with protein:
  - DNA (Deoxyribonucleic acid): Contained within chromosomes, holds the genetic code.
  - RNA (Ribonucleic acid): Primarily contained in nucleoli, involved in gene expression.

DNA Structure: A DNA molecule consists of two strands.
Base Pairing: The two strands are held together by weak chemical attractions between their bases. Specific pairing rules apply due to the chemical structure:
- Adenine (A) always pairs with Thymine (T).
- Guanine (G) always pairs with Cytosine (C).

The process by which information from a gene is used in the synthesis of a functional gene product, such as a protein.
Transcription: Occurs in the NUCLEUS.
- DNA is transcribed into an RNA transcript (messenger RNA or mRNA).
Translation: Occurs in the CYTOPLASM.
- The mRNA transcript moves to the cytoplasm.
- mRNA binds to ribosomes.
- Ribosomal subunits and tRNA molecules (carrying amino acids) facilitate the process.
- Codons on the mRNA (sequences of three bases) are read.
- Amino acids are assembled into proteins.
- Proteins destined for export or membrane integration are synthesized on ribosomes attached to the RER.
- The Golgi apparatus then packages these proteins for their final destination.

Definition: The mass of protoplasm, including various cytoplasmic organelles, enclosed by the cell membrane.
Hyaloplasm: The jello-like substance within which organelles float; it has no definite shape.
Cytoplasmic Organelles: Include mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, and lysosomes.
Plasma Membrane: Separates the cytoplasm from the extracellular fluid.

Location: The outer surface of the cell.
Properties:
- Selectively permeable: Controls what enters and leaves the cell.
- Possesses an electric charge.
Structure: Composed of lipid bilayers with embedded glycolipids and glycoproteins.
Regions: Contains both hydrophobic (water-fearing) and hydrophilic (water-loving) regions, crucial for its function as a barrier.

Membranes: Surrounded by a double membrane.
Internal Structure: Inner membrane is folded into structures called cristae, which increase surface area.
Function: The primary site for generating energy in the form of ATP (Adenosine Triphosphate) through cellular respiration.
Enzymes: Rich in oxidative enzymes, such as cytochrome oxidase, which are vital for energy production.

Ribosomes (Polysomes):
- Function: Synthesize proteins that are intended for internal cellular purposes (e.g., enzymes used within the cytoplasm).
Rough Endoplasmic Reticulum (RER):
- Structure: Characterized by ribosomes attached to its surface.
- Function: Primarily responsible for the synthesis of proteins destined for export from the cell, or for insertion into membranes (e.g., hormones, immune proteins).

Functions: Has a variety of complex metabolic roles:
- Catabolism: Involved in the metabolic degradation (breakdown) of various substances, including drugs, hormones, and nutrients.
- Synthesis of Steroid Hormones: Key site for the production of hormones such as female estrogen and male testosterone.
Prominence: Especially abundant and prominent in cells with high metabolic activity related to these functions, such as:
- Liver cells (for detoxification).
- Adrenal cells (for hormone synthesis).
  Leydig cells (in the testes, for testosterone synthesis).

Structure: Membrane-bound digestive organelles within the cell.
Contents: Contain various powerful enzymes that are acidic in nature.
Types:
- Primary lysosome: An inactive lysosome budding off from the Golgi apparatus.
- Secondary lysosomes: Formed when a primary lysosome fuses with a vesicle containing material to be digested.
Residual Bodies: Give rise to residual bodies, also known as lipofuscin, which are undigested materials.
Function: Act as the cell's "recycling centers," digesting waste materials and cellular debris, and foreign invaders like bacteria or viruses. They are involved in autophagy (digesting worn-out organelles) and heterophagy (digesting external substances).