GH travels through bloodstream, reaching various body cells
Cells respond based on presence of appropriate receptors
Similar to using an intercom system
Summary
Key Takeaway: Cells use various methods to communicate, involving direct contact, short distances, local groups, and wide-reaching signals.
Lecture Notes: Mitochondria and Apoptosis
Overview of Mitochondria
Known for metabolic pathways like the Krebs cycle and the electron transfer chain.
Produces ATP, earning it the name "energy powerhouse of the cell".
Apoptosis (Programmed Cell Death)
Definition: Programmed cell death with significant roles in development and homeostasis.
Necrosis vs. Apoptosis:
Necrosis: Uncontrolled cell death due to extreme stress (infection, trauma).
Apoptosis: Controlled, purposeful cell death with advantages for the organism.
Importance of Apoptosis
Embryological Development: Example of fingers and toes; apoptosis helps shape digits by removing tissue.
Advantages: Helps in removing damaged cells, infected cells, and cells under stress.
Triggers of Apoptosis
DNA Damage: Cells with irreparable DNA damage undergo apoptosis to prevent passing on mutations.
Infection: Immune cells signal infected cells to undergo apoptosis.
Environmental Stress: Deprivation of oxygen, nutrients, and cell-to-cell connections.
Lack of Growth Factors: Absence of signals for cell proliferation can trigger apoptosis.
Reactive Oxygen Species (ROS): Unstable oxygen species (e.g., superoxide anion, hydroxide radical, hydrogen peroxide) can induce apoptosis if damage is extensive.
Role of Mitochondria in Apoptosis
Outer Membrane Permeability: Becomes more permeable in response to apoptotic signals.
BCL2 Family of Proteins: Regulate membrane permeability.
Pro-apoptotic proteins: Promote apoptosis.
Anti-apoptotic proteins: Inhibit apoptosis.
Cytochrome c Release: Increased permeability releases cytochrome c from the intermembrane space into the cytoplasm.
Function: Activates caspases.
Caspases and Apoptosis
Caspase Activation: Cytochrome c activates caspase enzymes in the cytoplasm.
Caspase Function: Proteases that break down proteins after aspartate residues using cysteine in their active site.
Cascade Effect: Initial caspases activate other caspases, leading to widespread protein degradation.
Recycling: Degraded cellular components can be phagocytosed and reused by neighboring cells.
Key Differences: Apoptosis vs. Necrosis
Apoptosis: Caspase-mediated, controlled, and allows recycling of cellular components.
Necrosis: Non-caspase mediated, uncontrolled, and usually results in cell lysis without recycling.
Lecture on Stem Cells and Cell Differentiation
Introduction to Stem Cells
Stem Cells: The origin of all specialized cells in the body (muscle, nerve, skin, red blood cells, etc.)
Specialized Cells: Muscle cells, nerve cells, skin cells, red blood cells all originate from unspecialized stem cells
Analogy with a Library
Library of DNA: The nucleus of each cell contains DNA, which acts like a library with all genetic instructions
Books/Genes: Segments of DNA called genes; these give specific instructions for making proteins
Gene Expression: When a cell uses certain genes, it is said to express those genes (turned on or off)
Differentiation Process
Pluripotent Stem Cells: Stem cells that can turn into any somatic adult body cell
Specialization: Process of turning on specific genes to become specialized cells (e.g., muscle cell genes for muscle cells)
Irreversibility: Once specialized, cells cannot de-differentiate back into stem cells naturally
Cues for Differentiation
Internal and External Cues: Cells decide specialization based on internal or external signals
Transcription Factors: Proteins that activate certain genes; crucial for differentiation
Mechanisms of Differentiation
Asymmetric Segregation of Cellular Determinants
Initial Distribution: Transcription factors cluster in one area of the zygote
Division Outcome: Resulting cells have different transcription factors, leading to different gene activation and specialization
Signaling Methods: Diffusion, direct contact, and gap junctions (connexons)
Importance: Key for the formation of body parts (limbs, ears, eyes) during embryological development
Summary
Goal of Differentiation: Change gene expression to turn on/off specific genes, leading to specialized cell formation
Lecture Notes: Types of Cells and Cellular Senescence
Types of Cells in the Body
Mitotic Cells
Definition: Cells capable of dividing through mitosis.
Examples:
Epithelial cells (skin)
Fibroblast cells (organ scaffolding like kidneys and liver)
Endothelial cells (line blood vessels)
Function: Replenish and regenerate tissues.
Include: Some stem cells (precursors).
Key Feature: Undergo mitosis.
Post-Mitotic Cells
Definition: Cells incapable of undergoing mitosis; also called non-mitotic cells.
Examples:
Neurons (brain and nervous system)
Heart muscle cells
Function: Limited ability to repair or regenerate tissues.
Regeneration: Slow, relies on tissue-specific stem cells.
DNA Replication and Telomeres
Mitosis and DNA Replication: DNA must be copied for daughter cells.
Eukaryotic DNA: Linear strands with telomeres at both ends.
Telomeres: Caps that protect DNA from damage during replication (don’t code for proteins).
DNA Polymerase Limitation: Does not copy DNA to the end, causing telomeres to shorten with each replication.
Telomere Shortening: Limits cell divisions to around 60-70 cycles (Hayflick limit).
Cellular Senescence
Definition: State where a cell stops dividing due to short telomeres or DNA damage.
Replicative Senescence: When a cell reaches its Hayflick limit due to telomere shortening.
Features: Changes in gene expression, appearance, and response to surroundings.
Purpose: Prevents DNA damage from being passed on, reducing cancer risk.
Triggers: Telomere dysfunction, DNA mutations, toxin damage.
Implications of Senescent Cells
Pros: Helps prevent tumors and cancer by stopping cell division.
Cons: Reduced tissue regeneration with age, possible link to age-related diseases (e.g., cataracts).
Active Research: Ongoing studies to better understand these cells.
Senescence in Different Cell Types
Mitotic Cells: Can undergo replicative senescence.
Post-Mitotic Cells: Do not replicate but can become senescent due to DNA damage.
Cell Division Capacity Graph
Y-Axis: Cell division capacity.
X-Axis: Number of doublings.
Somatic Cells: High initial capacity, decreases with each division due to telomere shortening.
Stem Cells
High Division Capacity: Maintains high capacity regardless of doublings.
Reason: Presence of enzyme telomerase, which replenishes telomeres.
Cancer Connection: Somatic cells can mutate to express telomerase, evade senescence, and potentially form tumors.
Lecture Notes: Cell Movement and Migration
Introduction
Cells move around in our bodies to perform various functions.
Red blood cells are pumped by the heart; they don't swim.
Other cells can move independently, both in the bloodstream and through tissues.
Cell movement is vital for development (forming tissues/organs) and immune function in adults.
Sperm Cells Movement
Sperm cells move using a flagellum (tail).
Flagellum made of microtubule proteins and dynein proteins.
Importance: Sperm needs to move to reach the egg for fertilization.
Flagella in bacteria and archaea differ in structure and function.
White Blood Cells Movement
Example: Neutrophils (a type of white blood cell).
Neutrophils travel in the bloodstream and respond to infection signals.
Movement involves sticking to endothelium, rolling along, and moving between endothelial cells to reach tissues.
Movement driven by the cytoskeleton (cell skeleton).
Theories of Cell Movement
1. Cytoskeletal Model of Movement
Actin Polymerization: Actin proteins rapidly polymerize at the cell's leading edge, pushing it forward.
Microtubules: Located at the back, acting as a rudder (steering) or anchor (stopping movement).
Flexible microtubules: steer the cell.
Fixed microtubules: anchor the cell.
2. Membrane Flow Model
Endocytosis and Exocytosis: Plasma membrane bits internalized as vesicles, then move to the front and exocytose.
Types of Vesicles:
Plasma membrane vesicles: extend the leading edge.
Integrin-containing vesicles: anchor the cell membrane to help it crawl.
Net effect: Cell moves in a specific direction by alternating between extending and anchoring.
Conclusion
Understanding cell movement mechanisms is crucial for insights into development, immune response, and potential disease treatment (e.g., infertility due to immotile sperm).