Eukaryotic Organelles Overview

Eukaryotic Organelles

• Nucleus: Organizes DNA into chromosomes, houses nuclear pores, site of transcription (DNA → RNA).
• Nucleolus: Subsection of the nucleus where ribosomal RNA (rRNA) is produced.
• Mitochondria: Site of metabolic processes and ATP production. Inner membrane folds (cristae) contain enzymes for the electron transport chain (ETC). Reproduce independently via binary fission. Can initiate apoptosis.
• Lysosomes: Contain hydrolytic enzymes for substrate breakdown. Enzyme release leads to autolysis (cell self-destruction).
• Endoplasmic Reticulum (ER): Series of interconnected membranes continuous with the nuclear envelope. Synthesizes lipids and modifies proteins.
• Rough ER (RER): Studded with ribosomes; site of protein translation for secretion.
• Smooth ER (SER): Synthesizes lipids, detoxifies, stores calcium ions.
• Golgi Apparatus: Stacked membrane-bound sacs; modifies, packages, and directs cellular products to specific locations.
• Peroxisomes: Contain hydrogen peroxide; break down long-chain fatty acids (beta-oxidation). Involved in phospholipid synthesis, and the pentose phosphate pathway.

Cytoskeleton Proteins

• Microfilaments: Composed of actin; provide structural support, cause muscle contractions via interactions with myosin, form the cleavage furrow during cytokinesis.
• Microtubules: Composed of tubulin; create pathways for motor proteins (kinesin and dynein). Form cilia and flagella, and are part of the mitotic spindle's structure; centrioles (in centrosomes) organize microtubules.
• Intermediate Filaments: Maintain and strengthen the cytoskeleton, anchor organelles, and facilitate cell-cell adhesion. Examples include keratin and desmin.

Microtubular Motor Proteins

• Kinesin: Facilitates anterograde transport (away from the nucleus).
• Dynein: Facilitates retrograde transport (toward the nucleus).

Epithelial and Connective Tissues

• Epithelial Tissue: Covers/lines the body; functions in absorption, secretion, sensation, immunity, desiccation prevention. Parenchyma refers to the epithelial component of an organ (the functional parts).
• Connective Tissue: Supports the body; provides a scaffold for epithelial cells. The stroma refers to the connective tissue component of an organ (the supportive structure). Examples: bone, cartilage, tendons, ligaments, adipose tissue, blood.

Prokaryotic Cells (Bacteria & Archaea)

• Prokaryotic Characteristics: Lacks membrane-bound organelles, single circular DNA, divides via binary fission. Electron transport chain (ETC) occurs on the cell membrane.
• Gram-Positive Bacteria: Thick peptidoglycan cell wall, lipoteichoic acid; stain purple in Gram staining.
• Gram-Negative Bacteria: Thin peptidoglycan layer, outer membrane with phospholipids and lipopolysaccharides; stain pink-red in Gram staining.
• Aerobes, Anaerobes, Facultative Anaerobes, Aerotolerant Anaerobes: Classification based on oxygen requirement for metabolism.

Prokaryotic Genetics

• Plasmids: Extrachromosomal DNA; may carry antibiotic resistance or virulence genes. Episomes can integrate into the bacterial chromosome.
• Transposons: Genetic elements that can move (insert or remove) themselves within the genome (found in both prokaryotes and eukaryotes).
• Bacterial Genetic Recombination Methods:
• Transformation: Uptake of environmental DNA.
• Conjugation: Transfer of DNA between bacteria via a conjugation bridge (sex pilus), often involving plasmids with sex factors in the donor.
• Transduction: Transfer of DNA using a bacteriophage as a vector.

Viruses and Subviral Particles

• Viral Genomes: Can be DNA or RNA, single-stranded or double-stranded.

• Single-Stranded RNA Viruses: Categories include positive-sense (directly translated) and negative-sense (requires complementary strand synthesis by RNA replicase before translation).

• Retroviruses: Single-stranded RNA genomes; use reverse transcriptase to synthesize DNA from RNA, which is then integrated into the host genome.

• RNA Polymerase: Enzyme that synthesizes RNA from DNA during transcription.

• Bacteriophage Life Cycles:

• Lytic Cycle: Virus produces new virions (viral particles), leading to cell lysis; virulent bacteria.

• Lysogenic Cycle: Virus integrates into host genome (provirus or prophage) and replicates with the host cell; provirus may leave the genome.

• Prions: Infectious proteins that cause misfolding of other proteins, impacting solubility and degradation.

• Viroids: Plant pathogens, small circular RNA molecules that can turn off genes and cause metabolic/structural changes.

Prokaryotes vs. Archaea vs. Eukaryotes vs. Viruses

• Archaea: Similar to Bacteria (prokaryotic features) but also similar to eukaryotes (starting translation with methionine, similar RNA polymerases).
• Bacteria, Archaea, Eukaryotes, Viruses: Comparison table provided distinguishing their key characteristics (cell type, nucleus, organelles, cell wall, cellular division, chromosome type, cell membrane, and ribosomes).

Other Cellular Processes

• Cell Membrane: Phospholipid bilayer, proteins, cholesterol, carbohydrates; passive and active transport mechanisms (diffusion, osmosis, facilitated diffusion, primary/secondary active transport). Endocytosis (phagocytosis, pinocytosis), exocytosis.
• Cell Cycle: Stages (G1, S, G2, M phase) including checkpoints, cyclins, and cyclin-dependent kinases (CDKs). Phases of mitosis and meiosis comparison.
• Signal Transduction: Ligand binding to receptors (e.g., G-protein coupled receptors, receptor tyrosine kinases), second messengers (e.g., cAMP, calcium ions, IP3), signal amplification, differing types of cellular signaling (autocrine, paracrine, endocrine, juxtacrine).
• Metabolism: Glycolysis, citric acid cycle (Krebs cycle), oxidative phosphorylation; role of electron transport chains and chemiosmosis in ATP production in mitochondria.
• Gene Expression: DNA transcription to RNA; RNA processing (splicing, capping, polyadenylation); mRNA translation to proteins (role of ribosomes, tRNAs, codons); post-translational modifications and regulation (epigenetics, enhancers, silencers).