4. & 5 Cellular Biology

Eukaryotic Cells: Cells that have a nucleus and membrane-bound organelles.
Archaea: A domain of single-celled organisms, distinct from bacteria.
Endosymbiotic Theory: Proposes that eukaryotic cells evolved through the engulfment of ancient bacteria by ancestral eukaryotic cells.
Example: Engulfment of proteobacteria led to the formation of mitochondria.
This theory is supported by evidence:
- Presence of double membranes in mitochondria and chloroplasts.
- Circular DNA reminiscent of bacterial genomes.
- Similarity in 70S ribosomes between mitochondria, chloroplasts, and bacteria.

Neutrophils: Type of white blood cell that hunts and absorbs bacteria.
- Uses vesicle called an endosome to transport bacteria to lysosomes for destruction.
- Endosomes contain hydrolytic enzymes that break down pathogens.

Nucleus: Contains Nuclear Pore Complex (NPC).
Ribosomes: Composed of protein and RNA, featuring a large and small subunit.
Types of Proteins:
- Cytosolic Protein
- Membrane Protein
- Secretory Protein
Endoplasmic Reticulum (ER): Two types:
- Rough ER: Studded with ribosomes, responsible for protein synthesis.
- Smooth ER: Lacks ribosomes, involved in lipid synthesis and detoxification.

Functions as a protein post office, modifying, sorting, and packaging proteins for transport.
Also synthesizes complex carbohydrates.

Provides structure and shape to cells.
- Composed of:
- Actin Filaments: Involved in cell movement.
- Intermediate Filaments: Provide tensile strength.
- Microtubules (tubulin): Maintain cell shape and assist in intracellular transport.

Spherical Bacteria (Coccus): Arrangement based on plane of division:
- Diplococci: Two cells in pairs.
- Streptococci: Chains of bacteria.
- Tetrads: Groups of four.
- Sarcinae: Groups of eight to sixty-four.
- Staphylococci: Clusters resembling grapes.

Coccus shapes include Staphylococcus aureus (clusters) and Streptococcus pneumoniae (chains).
Bacillus: Rod-shaped bacteria with potential arrangements of diplo- and streptobacilli.
Spiral shapes include Vibrio, Spirillum, and Spirochete.

Cell Envelope:
- Chromosomal DNA is compacted, not freely floating.
- Plasmid DNA, separate from chromosomal DNA, plays a role in gene transfer.
- Structural Maintenance of Chromosomes (SMC): Protein responsible for DNA organization.

Bacterial Ribosomes: Have a molecular weight of 2.4 million, composed of ribosomal RNA and proteins.
Target for Antibiotics:
- Chloramphenicol & Erythromycin inhibit 50S subunit.
- Streptomycin & Tetracycline inhibit 30S subunit.

Gram-Positive Bacteria: Feature thick peptidoglycan layer including teichoic acids.
Gram-Negative Bacteria: Possess a thin peptidoglycan layer with an outer membrane of lipopolysaccharides (LPS).
- LPS acts as an endotoxin, causing immune reactions in humans.
Cell wall composed of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).

Involves polymerization of NAG-NAM and crosslinking by Penicillin Binding Proteins (PBPs).
- Penicillin inhibits PBPs, preventing cell wall synthesis.

Endospore: Resistant structure formed by bacteria under adverse conditions, allowing survival.

Capsule: External layer composed of carbohydrates, protects against immune responses by preventing phagocytosis.
Cytoskeleton: Bacterial shape is maintained by filament proteins such as MreB.

Structures include pili, flagella, and stalks.
Flagella: Help with movement; homologous to components of Type III secretion systems (T3SS).
- Flagella structure includes a basal body, hook, and filament (made of flagellin).
Pilus: Involved in attachment and genetic material transfer during conjugation.