🦠Regenerative Medicine Engineering Unit 2 – Cell Biology Fundamentals

Key Concepts and Terminology

• Cell theory states all living organisms are composed of cells, the basic unit of life
• Prokaryotic cells lack a membrane-bound nucleus and organelles (bacteria)
• Eukaryotic cells contain a membrane-bound nucleus and organelles (animals, plants)
• Cellular differentiation process by which a less specialized cell becomes more specialized
• Totipotency ability of a cell to give rise to all cell types of an organism
• Pluripotency capacity of a cell to differentiate into multiple cell types
• Multipotency ability of a cell to differentiate into a limited number of cell types
• Unipotency capacity of a cell to differentiate into only one cell type

Cell Structure and Organization

• Plasma membrane separates the cell interior from the external environment
  • Composed of a phospholipid bilayer with embedded proteins
  • Regulates the transport of molecules in and out of the cell
• Cytoskeleton provides structural support and enables cell movement
  • Consists of microfilaments, intermediate filaments, and microtubules
• Nucleus contains the cell's genetic material (DNA) and controls cellular activities
• Endoplasmic reticulum (ER) site of protein and lipid synthesis
  • Rough ER studded with ribosomes for protein synthesis
  • Smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification
• Golgi apparatus modifies, packages, and sorts proteins for secretion or transport
• Mitochondria generate energy (ATP) through cellular respiration
• Lysosomes contain digestive enzymes that break down cellular waste and foreign particles

Cellular Processes and Functions

• Metabolism encompasses all chemical reactions that occur within a cell
  • Catabolism breaks down complex molecules to release energy
  • Anabolism synthesizes complex molecules from simpler ones, requiring energy
• Cellular respiration process that converts glucose into ATP in the presence of oxygen
  • Glycolysis breaks down glucose into pyruvate in the cytoplasm
  • Citric acid cycle oxidizes pyruvate to produce NADH and FADH2 in the mitochondria
  • Electron transport chain creates a proton gradient to drive ATP synthesis
• Photosynthesis process by which plants convert light energy into chemical energy
• Protein synthesis involves transcription (DNA to RNA) and translation (RNA to protein)
  • Ribosomes serve as the site of protein synthesis
• DNA replication process by which a cell duplicates its genetic material before division
• RNA processing includes splicing, capping, and polyadenylation to produce mature mRNA

Cell Communication and Signaling

• Cells communicate through direct contact or by secreting signaling molecules
• Ligands (hormones, neurotransmitters) bind to specific receptors on the target cell
• Receptors can be located on the cell surface or within the cell (intracellular receptors)
• Signal transduction pathways relay the signal from the receptor to effector molecules
  • G protein-coupled receptors (GPCRs) activate intracellular signaling cascades
  • Receptor tyrosine kinases (RTKs) initiate signaling through phosphorylation
• Second messengers (cAMP, calcium) amplify and propagate the signal within the cell
• Cell signaling regulates various cellular processes (proliferation, differentiation, apoptosis)
• Dysregulation of cell signaling can lead to diseases (cancer, autoimmune disorders)

Cell Division and Reproduction

• Cell cycle consists of interphase (G1, S, G2) and mitosis (M)
  • G1 phase cell grows and prepares for DNA replication
  • S phase DNA replication occurs
  • G2 phase cell prepares for mitosis
  • M phase cell divides into two daughter cells
• Mitosis division of the nucleus into two genetically identical nuclei
  • Prophase chromosomes condense, nuclear envelope breaks down
  • Metaphase chromosomes align at the equatorial plane
  • Anaphase sister chromatids separate and move towards opposite poles
  • Telophase nuclear envelopes reform around the separated chromosomes
• Cytokinesis division of the cytoplasm to form two separate daughter cells
• Meiosis cell division that produces haploid gametes (sperm, egg) for sexual reproduction
  • Meiosis I homologous chromosomes separate, resulting in two haploid cells
  • Meiosis II sister chromatids separate, resulting in four haploid cells

Stem Cells and Differentiation

• Stem cells unspecialized cells capable of self-renewal and differentiation
• Embryonic stem cells (ESCs) derived from the inner cell mass of a blastocyst
  • Pluripotent can differentiate into all cell types of the body
• Adult stem cells found in various tissues (bone marrow, skin, gut)
  • Multipotent can differentiate into a limited number of cell types
• Induced pluripotent stem cells (iPSCs) generated by reprogramming somatic cells
• Stem cell niche specialized microenvironment that regulates stem cell behavior
• Differentiation triggered by specific signals (growth factors, cytokines)
  • Lineage commitment process by which a stem cell becomes restricted to a specific fate
• Transcription factors (Oct4, Sox2, Nanog) maintain pluripotency in ESCs

Cellular Applications in Regenerative Medicine

• Stem cell therapy involves transplanting stem cells to repair or replace damaged tissues
  • Hematopoietic stem cell transplantation treats blood disorders (leukemia)
  • Mesenchymal stem cells (MSCs) used for tissue regeneration (cartilage, bone)
• Tissue engineering combines stem cells, scaffolds, and growth factors to create functional tissues
• Organoids three-dimensional, miniaturized organs grown from stem cells
  • Used for disease modeling, drug screening, and personalized medicine
• Cell reprogramming converts somatic cells into iPSCs or directly into other cell types
• Gene therapy introduces functional genes into cells to correct genetic defects
• Genome editing (CRISPR-Cas9) precisely modifies the genome of cells for therapeutic purposes

Challenges and Future Directions

• Ethical concerns surrounding the use of embryonic stem cells and gene editing
• Immunogenicity and rejection of transplanted cells or tissues
• Tumorigenicity potential of stem cells to form tumors after transplantation
• Scalability and cost of producing large quantities of high-quality cells for therapy
• Delivery and integration of cells or tissues into the target site
• Long-term safety and efficacy of cell-based therapies
• Regulatory hurdles and clinical translation of regenerative medicine approaches
• Personalized medicine tailoring therapies to individual patient needs and genetics
• Combination therapies integrating stem cells, biomaterials, and growth factors for optimal regeneration