Human Anatomy and Physiology: The Cell

3.1 Basic Processes of Cells

• Cell Metabolism: Chemical reactions that a cell carries out to maintain life.

  • Includes:

  • Anabolic Reactions: Build complex molecules from simpler ones.

  • Catabolic Reactions: Break down complex molecules into simpler ones, releasing energy.

  • Oxidation-Reduction Reactions: Involve the transfer of electrons between molecules, facilitating energy production.

• Substance Transport:

  • Compounds may be transported for:

  • Release from a cell.

  • Ingestion into a cell.

  • Movement to different locations within the cell.

• Communication:

  • Cells communicate with themselves, their environment, and other cells in the body through chemical signals and receptors.

• Cell Reproduction:

  • Many cells undergo cell division, allowing for growth, repair, and reproduction.

3.1 Overview of Cell Structure (1 of 4)

• Basic Components of Animal Cells:

  • Plasma Membrane: Encloses the cell.

  • Cytoplasm:

  • Cytosol: Fluid component of cytoplasm.

  • Organelles: Specialized structures with specific functions.

  • Cytoskeleton: Network providing structural support and shape.

  • Nucleus: Contains genetic material and controls cell activities.

3.1 Overview of Cell Structure (2 of 4)

• Functions of the Plasma Membrane:

  • Isolates the cell from surroundings, providing protection and support.

  • Communicates with other cells through receptors.

  • Regulates transport of substances into and out of the cell.

  • Identifies the cell through cellular markers.

• Fluid Compartments:

  • Intracellular Space: Contains intracellular fluid (cytosol).

  • Extracellular Space: Contains extracellular fluid (ECF).

3.1 Overview of Cell Structure (3 of 4)

• Components of the Cytoplasm:

  • Cytosol or Intracellular Fluid (ICF): Watery gel with proteins, dissolved solutes, and RNA.

  • Organelles:

  • Perform specific cellular functions.

  • Cytoskeleton:

  • Network of protein filaments supporting the cell structure.

  • Aids in organelle positioning and transport within the cell.

3.1 Overview of Cell Structure (4 of 4)

• Nucleus:

  • Most cells contain a nucleus, surrounded by a nuclear envelope (double membrane).

  • Contains most of the cell’s DNA, critical for RNA production.

  • DNA and RNA control cellular functions by coding for proteins.

3.1 Cell Size and Diversity

• Cells vary in size and appearance, enabling them to perform specialized functions.

• Examples of cellular diversity can be illustrated through microscopy, highlighting differences in structure and function.

3.2 The Phospholipid Bilayer (1 of 2)

• Phospholipid Bilayer:

  • Forms a barrier between ECF and cytosol.

  • Consists of hydrophilic (polar) regions facing water and hydrophobic (nonpolar) regions that repel water.

3.2 The Phospholipid Bilayer (2 of 2)

• Behavior in Water:

  • Polar heads face water, creating two layers that exclude water from fatty acid tails, forming the phospholipid bilayer.

3.2 The Fluid Mosaic Model of the Plasma Membrane (1 of 9)

• Plasma Membrane Structure:

  • Composed of various proteins, lipids, and carbohydrates creating a mosaic appearance.

  • Membrane components are mobile within the bilayer, contributing to fluidity—a critical function for membrane activities.

3.2 The Fluid Mosaic Model of the Plasma Membrane (2 of 9)

• Fluidity:

  • Essential for the membrane’s function, allowing for movements of proteins and lipids laterally.

3.2 The Fluid Mosaic Model of the Plasma Membrane (3 of 9)

• Membrane Proteins:

  • Perform various functions; types include:

  • Integral Proteins: Span the entire membrane.

  • Peripheral Proteins: Located on one side; may be anchored or freely floating.

3.2 The Fluid Mosaic Model of the Plasma Membrane (4 of 9)

• Functional Types of Membrane Proteins:

  • Channels: Allow substances to pass through.

  • Carriers: Transport substances across the membrane.

  • Receptors: Bind ligands and trigger cellular responses.

  • Enzymes: Catalyze reactions at the membrane.

  • Structural Support Proteins: Provide shape and integrity.

  • Linker Proteins: Connect adjacent cells.

3.2 The Fluid Mosaic Model of the Plasma Membrane (5 of 9)

• COVID-19 Connection:

  • ACE2 Receptor:

  • Integral protein on human cells where SARS-CoV-2 binds, allowing virus entry and replication.

3.2 The Fluid Mosaic Model of the Plasma Membrane (6 of 9)

• Other Components:

  • Cholesterol: Stabilizes plasma membrane integrity against temperature changes.

  • Glycolipids and Glycoproteins:

  • Involved in cell recognition and are found on the external surface of membranes.

3.2 Drugs and Membrane Receptors

• Drug Mechanisms:

  • Agonists: Drugs mimicking ligand actions (e.g., morphine mimics endorphins).

  • Antagonists: Block ligand effects (e.g., antihistamines blocking histamine).

3.3 Transport across the Plasma Membrane

• Selectively Permeable Membranes: Allow specific substances to pass.

• Transport Processes:

  • Passive Transport: No energy required.

  • Active Transport: Requires energy.

3.3 Passive Transport Processes (1 of 11)

• Diffusion: Movement of solute molecules from high concentration to low concentration, driven by concentration gradients which provide potential energy.

3.3 Passive Transport Processes (2 of 11)

• Diffusion Dynamics:

  • Equilibrium is reached when there is no net movement of particles.

3.3 Passive Transport Processes (3 of 11)

• Transport Mechanisms:

  • Simple Diffusion: Nonpolar solutes pass directly through the bilayer.

  • Facilitated Diffusion: Polar/charged solutes use transport proteins (channel/carrier) to cross membranes.

3.3 Passive Transport Processes (4 of 11)

• Osmosis: Movement of water across a membrane from lower solute concentration to higher solute concentration through selectively permeable membranes.

3.3 Passive Transport Processes (5 of 11)

• Water Movement:

  • Can occur via aquaporins or between phospholipids due to its small size.

3.3 Passive Transport Processes (6 of 11)

• Pressures Affecting Osmosis:

  • Osmotic Pressure: Prevents water movement by applying pressure.

  • Hydrostatic Pressure: Force exerted by water on container walls affecting fluid volumes.

3.3 Concept Boost: Osmosis vs. Diffusion

• Fundamental Differences:

  1. Osmosis requires a membrane; diffusion does not.

  2. Osmosis is reversible; diffusion is not.

  3. Solute movement is predictable in diffusion; solvent movement in osmosis is not.

3.3 Tonicity

• Tonicity: Compares solute concentrations between two solutions.

  • Isotonic: No net movement; ECF=same as cytosol.

  • Hypertonic: Cell loses water; shrinks (crenates).

  • Hypotonic: Cell gains water; swells and may burst (lyse).

3.3 Summary of Diffusion and Osmosis

• Key Points:

  • Diffusion: solutes move from high to low concentration.

  • Osmosis: water moves from low to high solute concentration.

3.3 Active Transport via Membrane Proteins (1 of 5)

• Active Transport: Energy-consuming process to move substances against their concentration gradient.

  • Uses carrier proteins called pumps; drives the use of ATP.

3.3 Active Transport via Membrane Proteins (2 of 5)

• Primary Active Transport: Solute is transported using energy from ATP hydrolysis (e.g., sodium-potassium pump).

3.3 Active Transport via Membrane Proteins (3 of 5)

• Sodium-Potassium Pump:

  • Moves 3 sodium ions out and 2 potassium ions into the cell, maintaining critical ionic gradients necessary for functions such as muscle contraction.

3.3 Active Transport via Membrane Proteins (4 of 5)

• Secondary Active Transport:

  • Uses an existing concentration gradient established by primary active transport to move a different substance.

3.3 Active Transport via Membrane Proteins (5 of 5)

• Electrophysiology Introduction:

  • Studies electrical potentials caused by ion imbalances across membranes, including resting membrane potential.

3.3 Active Transport via Vesicles (1 of 5)

• Vesicular Transport: Uses vesicles for transporting large particles or volumes of substances, requiring ATP.

  • Includes endocytosis and exocytosis.

3.3 Active Transport via Vesicles (2 of 5)

• Phagocytosis: Cell ingests large particles (e.g., bacteria) using a specialized vesicle.

3.3 Active Transport via Vesicles (3 of 5)

• Pinocytosis: Cell ingests dissolved substances in small vesicles.

• Receptor-mediated Endocytosis: Specific ligands bind to receptors for selective transport.

3.3 Active Transport via Vesicles (4 of 5)

• Exocytosis: Releases substances from cells, adding components to the plasma membrane.

3.3 Active Transport via Vesicles (5 of 5)

• Transcytosis: Involves endocytosing a substance, transporting it across a cell, and exocytosing it on the opposite side.

3.3 Plasma Membrane Transport Summary (1 of 5)

• Types of Transport:

  • Passive Transport: Movement along concentration gradients without energy.

  • Example: Oxygen and carbon dioxide through simple diffusion.

  • Facilitated Diffusion: Uses transport proteins.

  • Example: Sodium ions, glucose.

  • Osmosis: Water movement across membranes.

  • Example: Water absorption.

3.3 Plasma Membrane Transport Summary (2 of 5)

• Active Transport Methods:

  • Primary Active Transport:

  • Example: Sodium-potassium pump.

  • Secondary Active Transport:

  • Coupled transport with sodium ions used to bring glucose into cells.

3.3 Plasma Membrane Transport Summary (3 of 5)

• Endocytosis:

  • Phagocytosis: “Cell eating.”

  • Pinocytosis: “Cell drinking.”

  • Receptor-mediated Endocytosis: Targeted uptake.

3.3 Plasma Membrane Transport Summary (4 of 5)

• Exocytosis: Release processes.

  • Includes secretion of hormones and enzymes, recycling components of membranes.

3.4 Cytoplasmic Organelles (1 of 2)

• Cytoplasmic Organelles:

  • Organelles are compartmentalized to enhance cellular efficiency.

  • Enclosed by membranes include: Mitochondria, Peroxisomes, Endoplasmic Reticulum, Golgi Apparatus, Lysosomes.

  • Non-membrane-bound organelles include Ribosomes and Centrosomes.

3.4 Cytoplasmic Organelles (2 of 2)

• Organelles: Specialized cellular structures performing distinct functions, enclosed in phospholipid bilayers.

3.4 Mitochondria (1 of 3)

• Mitochondria:

  • Produce most of the cell’s ATP; presence correlates with metabolic activity.

  • Contain DNA, enzymes, and ribosomes; possess a dual membrane structure (outer smooth, inner folded into cristae).

3.4 Mitochondria (2 of 3)

• Outer Membrane: Permeable channels for substances to enter intermembrane space.

• Inner Membrane: Selectively permeable; houses the matrix filled with mitochondrial DNA, proteins, and enzymes for oxidative catabolism.

3.4 Mitochondria (3 of 3)

• Function of Mitochondria: Site of ATP production through various metabolic pathways including the citric acid cycle.

3.4 Peroxisomes

• Peroxisomes:

  • Oxidize organic substrates to produce hydrogen peroxide for metabolism.

  • Involved in detoxifying harmful substances (e.g., alcohol) and breaking down fatty acids.

3.4 Ribosomes

• Ribosomes: Sites of protein synthesis; consist of ribosomal RNA and proteins.

  • Free ribosomes exist suspended in cytosol; bound ribosomes are attached to ER membranes.

3.4 The Endomembrane System (1 of 7)

• Endomembrane System: Organelles that interconnect through vesicular transport—responsible for synthesizing, modifying, and packaging cellular products.

3.4 The Endomembrane System (2 of 7)

• Endoplasmic Reticulum (ER):

  • Continues with the nuclear envelope and is responsible for protein and lipid synthesis.

  • Rough ER: Studded with ribosomes, involved in protein folding and modification.

  • Smooth ER: Lacks ribosomes, plays roles in calcium ion storage and detoxification.

3.4 The Endomembrane System (3 of 7)

• Rough ER Functions:

  • Modifies proteins for secretion; produces components for the cell membrane.

3.4 The Endomembrane System (4 of 7)

• Smooth ER Functions:

  • Involved in lipid synthesis, detoxification processes, and calcium storage.

3.4 The Endomembrane System (5 of 7)

• Golgi Apparatus:

  • Stack of membranous sacs that modify, sort, and package proteins and lipids made by the ER.

3.4 The Endomembrane System (6 of 7)

• Lysosomes:

  • Contain digestive enzymes known as acid hydrolases to degrade macromolecules and damaged organelles.

3.4 The Endomembrane System (7 of 7)

• Function of Lysosomes: Perform autophagy and immune responses by digesting bacteria and cellular debris.

3.3 Lysosomal Storage Diseases (1 of 2)

• Lysosomal Storage Diseases: Result from deficiencies in acid hydrolases, leading to the accumulation of undigested substances.

  • Gaucher’s Disease: Enzyme deficiency leads to glycolipid accumulation, affecting various organs; often fatal in infancy.

3.3 Lysosomal Storage Diseases (2 of 2)

• Other Disease Examples:

  • Tay-Sachs Disease: Missing enzyme for glycolipid breakdown in the brain; fatal by age 4-5.

  • Hurler Syndrome: Accumulation of polysaccharides leading to organ damage.

  • Neimann-Pick Disease: Enzyme deficiency affecting lipid degradation leading to organ dysfunction.

3.4 Review of the Cytoplasmic Organelles (1 of 2)

• Comparison Table:

  • Mitochondrion: Double membrane; ATP synthesis; contains DNA and ribosomes.

  • Peroxisome: Detoxifies harmful substances and metabolizes fatty acids.

  • Ribosome: Non-membrane bound; synthesizes proteins.

3.4 Review of the Cytoplasmic Organelles (2 of 2)

• Comparison of Other Organelles:

  • Rough ER: Modifies/assembles proteins.

  • Smooth ER: Synthesizes lipids; detoxifies substances.

  • Golgi Apparatus: Modifies and sorts proteins for transport.

  • Lysosome: Digests macromolecules and damaged organelles.

3.5 The Cytoskeleton (1 of 2)

• Cytoskeleton: Composed of protein filaments that provide mechanical support, shape, and facilitate movement.

3.5 The Cytoskeleton (2 of 2)

• Types of Filaments:

  • Actin Filaments (Microfilaments): Thin filaments contributing to cell shape and movement.

  • Intermediate Filaments: Provide tensile strength and structural integrity.

  • Microtubules: Hollow tubes involved in organelle transport and cell division.

3.5 Types of Filaments (1 of 9)

• Actin Filaments:

  • Composed of intertangled actin subunits providing tensile support and aiding in motility (e.g., muscle contraction).

3.5 Types of Filaments (2 of 9)

• Intermediate Filaments:

  • Ropelike structures composed of fibrous proteins providing durability and structural support.

3.5 Types of Filaments (3 of 9)

• Microtubules:

  • Hollow tubes of tubulin subunits, allowing dynamic assembly and disassembly, crucial in mitotic processes.

3.5 Types of Filaments (4 of 9)

• Cytoskeletal Functions:

  • Support plasma membrane.

  • Organize cell interior.

  • Enable intracellular transport via motor proteins.

3.5 Types of Filaments (5 of 9)

• Centrosome: Contains centrioles and tubulin proteins necessary for microtubule formation.

3.5 Types of Filaments (6 of 9)

• Cellular Extensions: Includes microvilli (increase surface area), cilia (motile projections), and flagella (propelling movements).

3.5 Types of Filaments (7 of 9)

• Microvilli: Finger-like extensions increasing surface area by 30-40 times, aiding in absorption.

3.5 Types of Filaments (8 of 9)

• Cilia and Flagella:

  • Cilia: Short, coordinated movement; numerous.

  • Flagella: Long, whip-like motion for whole-cell propulsion.

3.5 Types of Filaments (9 of 9)

• Diseases Related to Cilia:

  • Primary Ciliary Dyskinesia (PCD): Genetic disorder affecting cilia functionality causing severe respiratory issues.

3.6 The Nucleus (1 of 2)

• Nucleus: Regulates cellular activities and stores genetic information through DNA.

3.6 The Nucleus (2 of 2)

• Nuclear Envelope: Double phospholipid layer surrounding the nucleus; contains nuclear pores for substance exchange.

3.6 Chromatin and Chromosomes (1 of 3)

• Chromatin: Complex of DNA and proteins allowing compaction within the nucleus; forms nucleosomes throughout.

3.6 Chromatin and Chromosomes (2 of 3)

• Chromosomes: Condensed chromatin during cell division, structured as paired sister chromatids connected at the centromere.

  • Humans have 46 chromosomes.

3.6 Chromatin and Chromosomes (3 of 3)

• Karyotype: Visual representation of chromosomes used to assess genetic information.

3.7 Protein Synthesis (1 of 2)

• Protein Synthesis:

  • Process of creating proteins using DNA as a template; involves transcription and translation.

3.7 Protein Synthesis (2 of 2)

• Gene Expression: Production of proteins based on specific genes.

3.7 Genes and the Genetic Code (1 of 3)

• Genes: DNA segments coding for protein structures; use triplets of nucleotides representing amino acids.

3.7 Genes and the Genetic Code (2 of 3)

• Exons vs Introns: Exons are coding sequences, introns are non-coding that may impact regulation and evolution.

3.7 Genes and the Genetic Code (3 of 3)

• Mutations: Changes in DNA sequences that can lead to disease, including cancer.

3.7 Transcription (1 of 7)

• Transcription Overview: Process of synthesizing mRNA from a DNA template.

  • RNA Polymerase: Enzyme facilitating transcription.

3.7 Transcription (2 of 7)

• Stages of Transcription:

  1. Initiation: Transcription factors assist RNA polymerase in binding to the DNA promoter region.

  2. Elongation: RNA polymerase synthesizes mRNA strand by linking nucleotides.

  3. Termination: Transcription ends at a specific sequence, releasing the mRNA transcript.

3.7 Transcription (3 of 7)

• Initiation Details:

  • Transcription factors recognize the promoter, allowing RNA polymerase to bind.

3.7 Transcription (4 of 7)

• Elongation Details:

  • RNA polymerase catalyzes nucleotide bonding to form the mRNA strand.

3.7 Transcription (5 of 7)

• Termination Details:

  • RNA polymerase detaches upon reaching the termination sequence.

3.7 Transcription (6 of 7)

• RNA Processing: Involves splicing introns and joining exons to form mature mRNA.

3.7 Toxicity of the “Death Cap” Mushroom

• Alpha-amanitin: Toxin that inhibits RNA polymerase, halting protein synthesis, potentially leading to cell death.

3.7 Translation (1 of 10)

• Translation: Converts mRNA sequences into polypeptides using tRNA to bring amino acids to ribosomes.

3.7 Translation (2 of 10)

• Ribosomes: Composed of rRNA, have binding sites for tRNA, facilitating protein assembly.

3.7 Translation (3 of 10)

• tRNA Structure: Single-stranded RNA molecule with an anticodon for complimentary pairing with mRNA and an attached amino acid.

3.7 Translation (4 of 10)

• Stages of Translation:

  1. Initiation: mRNA and initiator tRNA binding to ribosomal subunits.

  2. Elongation: tRNA molecules link amino acids into a growing polypeptide.

  3. Termination: Completed polypeptide is released.

3.7 Translation (5 of 10)

• Initiation Details:

  • Starts with the binding of initiator tRNA to the start codon on mRNA.

3.7 Translation (6 of 10)

• Elongation Details:

  • Ribosome facilitates tRNA amino acid linkage and translocation along the mRNA strand.

3.7 Translation (7 of 10)

• Termination Details: Occurs when a stop codon is reached, signaling release of the polypeptide.

3.7 Translation (8 of 10)

• Posttranslational Modifications: Includes folding and modifications of polypeptides to form functional proteins.

3.7 Translation (9 of 10)

• COVID-19 Vaccine Mechanism: mRNA vaccines introduce viral mRNA, leading to production of spike proteins that trigger an immune response.

3.8 The Cell Cycle

• Cell Theory: All life arises from pre-existing cells; involves cell growth and division.

3.8 Phases of the Cell Cycle (1 of 13)

• Phases:

  • Interphase: G1 (growth/preparation), S (DNA synthesis), G2 (final preparations),

  • M Phase: Mitosis and cytokinesis occur, resulting in cell division.

3.8 Phases of the Cell Cycle (2 of 13)

• Interphase Details:

  • Cells grow, synthesize proteins, duplicate organelles; non-dividing cells enter G0 phase.

3.8 Phases of the Cell Cycle (3 of 13)

• S Phase:

  • DNA replication through semiconservative methods, yielding two identical double helices.

3.8 Phases of the Cell Cycle (4 of 13)

• M Phase: Involves four stages:

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase/Cytokinesis

3.8 Phases of the Cell Cycle (5 of 13)

• Prophase: Chromatin condenses to chromatid, mitotic spindle forms, and chromosome structure stabilizes.

3.8 Phases of the Cell Cycle (6 of 13)

• Metaphase: Chromosomes align at the cell equator, spindle fibers attach.

3.8 Phases of the Cell Cycle (7 of 13)

• Anaphase: Sister chromatids separate and are pulled to opposite poles; begins the cytokinesis process.

3.8 Phases of the Cell Cycle (8 of 13)

• Telophase/Cytokinesis: Nuclear membranes reform, chromosomes decondense, cytoplasmic divisions complete.

3.8 Phases of the Cell Cycle (9 of 13)

• M Phase Details: Ensures two genetically identical daughter cells are formed after division.

3.8 Spindle Poisons

• Spindle Poisons: Inhibit spindle functionality; used in cancer treatment with side effects.

  • Examples: Vinca alkaloids, colchicine, griseofulvin, and taxanes.

3.8 Cell Cycle Control and Cancer (1 of 3)

• Cell Cycle Control: Regulates balanced cell division with cell death through various checkpoints.

3.8 Cell Cycle Control and Cancer (2 of 3)

• Apoptosis: Programmed cell death; prevents malfunctioning cells from proliferating; occurs in fetal development for structural separation.

3.8 Cell Cycle Control and Cancer (3 of 3)

• Tumors:

  • Benign Tumors: Non-invasive growth limited to origin site.

  • Malignant Tumors: Uncontrolled growth that invades surrounding tissues and may metastasize.