1- Cell Physiology-1 (3)

Page 1: Introduction

  • Lecturer: Dr. R. Ahangari

  • University: Central Florida, Orlando

  • Reference Texts: Human Physiology by S.I. Fox, Human Anatomy by Marieb & Mallat

Page 2: Definition of Cell

  • Cells: Basic structural and functional units of life.

  • All organisms are cellular in nature:

    • Unicellular organisms (e.g. amoebas)

    • Multicellular organisms (e.g. humans, animals, large plants)

  • Estimated 50 to 100 trillion cells in the human body.

Page 3: Main Cell Regions

  • Cells consist of three main regions:

    1. Plasma Membrane: Outermost layer.

    2. Cytoplasm: Contains organelles and cytosol.

    3. Nucleus: Information center of the cell.

  • Key structures include:

    • Centrioles

    • Secretion granules

    • Microtubules

    • Microfilaments

    • Nucleolus

    • Microvilli

    • Organelles such as:

      • Rough and smooth endoplasmic reticulum

      • Golgi apparatus

      • Mitochondria

      • Lysosomes

      • Nuclear envelope.

Page 4: Plasma Membrane

  • Plasma membrane (plasmalemma):

    • Outer thin and flexible membrane.

    • Separates intracellular and extracellular compartments.

Page 5: Structure of Plasma Membrane

  • Membrane composed of:

    • Double layer of lipids (phospholipids, cholesterol, glycolipids).

    • Proteins embedded within the lipid bilayer.

Page 6: Phospholipids

  • Phospholipids:

    • Most abundant lipids in plasma membrane.

    • Heads are hydrophilic, facing water on both sides of the membrane.

    • Tails are hydrophobic, orienting towards the center of the membrane.

Page 7: Membrane Proteins

  • Types of membrane proteins:

    1. Integral proteins:

      • Abundant, extend through the membrane (transmembrane) or protrude from one membrane side.

      • Act as receptors.

    2. Peripheral proteins:

      • Positioned mainly on cytoplasmic side.

      • Support the cytoplasmic side through a network of filaments.

  • Glycocalyx:

    • Sugar covering or cell coat from glycoproteins/glycolipids.

    • Functions in cell-to-cell binding and recognition.

Page 8: Glycocalyx in Cornea

  • Glycocalyx on corneal surface:

    • Produced by corneal epithelial cells.

    • Aids in binding mucins onto corneal surface.

Page 9: Functions of Plasma Membrane

  • Functions:

    1. Serves as external barrier against external substances.

    2. External proteins function as receptors for hormones, neurotransmitters, and cell recognition.

    3. Regulates transport of substances in and out of the cell:

      • Selectively permeable barrier.

Page 10: Substance Movement across Plasma Membrane

  • Passive transport:

    • No energy needed.

    • Substances move down their concentration gradient (e.g. diffusion of oxygen, CO2).

  • Active transport:

    • Requires ATP to move substances against their gradient (e.g. glucose, amino acids).

  • Vesicular transport:

    • Bulk transport of large particles and macromolecules (e.g. exocytosis, endocytosis).

Page 11: Exocytosis

  • Exocytosis:

    • Process where vesicles fuse with plasma membrane to release contents outside the cell (e.g. mucus, proteins).

  • Involves proteins called vSNAREs and tSNAREs to facilitate fusion.

Page 12: Endocytosis

  • Endocytosis:

    • Mechanism for bringing large molecules into the cell through infolding of plasma membrane.

    • Involves clathrin proteins that facilitate membrane deformation.

  • Types:

    1. Phagocytosis.

    2. Pinocytosis.

    3. Receptor-mediated endocytosis.

Page 13: Phagocytosis

  • Phagocytosis (cell eating):

    • Plasma membrane forms pseudopodia to engulf large particles like bacteria.

    • Creates phagosomes that fuse with lysosomes for digestion.

    • Common in white blood cells.

Page 14: Pinocytosis

  • Pinocytosis (cell drinking):

    • Process where small portions of plasma membrane engulf extracellular fluid with dissolved molecules.

    • Main function in cells of the small intestine for nutrient absorption.

Page 15: Receptor-Mediated Endocytosis

  • Receptor-mediated endocytosis:

    • Selective transport of specific molecules (e.g. insulin, LDL).

    • Molecules bind to membrane receptors, forming protein-coated vesicles for uptake.

    • Vesicle contents are released in lysosomes; receptors recycle back.

Page 16: Familial Hypercholesterolemia

  • Familial hypercholesterolemia:

    • Genetic disorder leading to lack of LDL receptors.

    • Results in high cholesterol levels in blood, causing hypercholesterolemia and cardiovascular issues (e.g. stroke, myocardial infarction).

Page 17: Cytoplasm Overview

  • Cytoplasm:

    • Area between nucleus and plasma membrane.

    • Contains:

      • Cytosol: Viscous fluid with water, ions, enzymes.

      • Inclusions: Stored nutrients and pigments.

      • Organelles: Functional structures within the cell.

Page 18: Ribosomes

  • Ribosomes:

    • Dark-staining granules; site of protein production.

    • Composed of two subunits (protein and rRNA).

    • Free ribosomes synthesize proteins for cytosol; attached ribosomes synthesize proteins for membranes or export.

    • Protein synthesis dictated by DNA, with instructions delivered by mRNA.

Page 19: Rough Endoplasmic Reticulum

  • Rough Endoplasmic Reticulum (rER):

    • Ribosome-studded membranous network.

    • Involved in protein synthesis and processing.

    • Proteins enter cisternae for secretion or for membrane incorporation.

Page 20: Smooth Endoplasmic Reticulum

  • Smooth Endoplasmic Reticulum (sER):

    • Membranous system without ribosomes.

    • Functions:

      • Lipid and steroid synthesis.

      • Lipid metabolism and detoxification.

Page 21: Golgi Apparatus

  • Golgi Apparatus:

    • Stack of 3-10 membrane-bound cisternae.

    • Functions to sort and package products from rER into vesicles for transport.

    • Source of secretory granules and lysosomes.

Page 22: Mitochondria

  • Mitochondria:

    • Rod-shaped organelles surrounded by two membranes; inner membrane folded into cristae.

    • Primary site for ATP synthesis; crucial for energy generation in the cell.

Page 23: Lysosomes

  • Lysosomes:

    • Spherical sacs containing digestive enzymes (acid hydrolases).

    • Function:

      • Intracellular digestion of waste and damaged organelles.

      • Fuse with phagosomes to digest engulfed materials.

  • Tay-Sachs Disease: Genetic disorder causing enzyme deficiency in lysosomes, leading to glycolipid accumulation and severe neurological issues.

Page 24: Gaucher’s Disease

  • Gaucher’s Disease:

    • Result of glucocerebrosidase enzyme deficiency leading to harmful substance accumulation.

  • Three main subtypes:

    1. Type 1: Most common; involves anemia, bone disease, splenomegaly.

    2. Type 2: Early onset in infancy with severe neurological issues; rapid progression.

    3. Type 3: Can affect liver, spleen, and brain; variable prognosis.

  • Common symptoms include bone pain, enlarged spleen/liver, lung disease, seizures.

Page 25: Peroxisomes

  • Peroxisomes:

    • Membrane-bound sacs containing oxidase and catalase.

    • Function:

      • Breakdown of free radicals and toxins (e.g. alcohol).

      • Contain enzymes for neutralizing harmful substances.

      • Abundant in liver and kidney cells.

Page 26: Cytoskeleton

  • Cytoskeleton:

    • Network of rods providing support and movement for the cell.

    • Composed of:

      • Microtubules: Cylindrical structures made of tubulin, providing cell shape and organelle movement.

      • Microfilaments: Thin filaments of actin involved in contraction and cellular movements.

      • Intermediate filaments: Tough and stable fibers that provide structural support against tension.

Page 27: Centrosome and Centrioles

  • Centrosome:

    • Spherical structure near the nucleus containing matrix and centriole pairs.

    • Matrix involved in microtubule organization during cell division.

  • Centrioles:

    • Paired cylindrical bodies that assist in microtubule network organization during mitosis and form bases of cilia/flagella.