FFP1_TheEukaryoticCell - 2022-23 (3).pptx

RCSI Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn The Eukaryotic Cell Class MedYear 1 Course Foundations for Practice 1 (FFP1) LecturerDr Paul O’Farrell Date September 21 2022 1 LEARNING OUTCOMES • Outline the structure of cell • Describe the structure and function of...

RCSI Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn The Eukaryotic Cell Class MedYear 1 Course Foundations for Practice 1 (FFP1) LecturerDr Paul O’Farrell Date September 21 2022 1 LEARNING OUTCOMES • Outline the structure of cell • Describe the structure and function of cell junctions • Describe cell adhesion and cell recognition THE HIERARCHY OF BIOLOGICAL ORGANISATION Atom Organ Biosphere Tissue Organism Molecule Organ System Ecosystem Cell Population Organelle Macromolecule THE CELL • All living things have a basic building block in common – the cell • Humans contain about 30 trillion cells* - 70 billion die and are replaced every day • Cells only arise from pre-existing cells, by cell division • Growth and development result from the increase in the number of cells, and their differentiation into different types *Sender et al . PLoS Biol. 2016 Aug; 14(8) BASIC STRUCTURE OF THE EUKARYOTIC CELL The cell: Not a simple “bag of molecules” A complex internal structure Many different specialised “organelles” Different internal microenvironments THE CELL (PLASMA) MEMBRANE SEE LECTURE ON THE STRUCTURE OF THE CELL MEMBRANE LATER IN THE MODULE Structure • Made up of a lipid bilayer • Proteins are inserted into the lipid bilayer • Carbohydrates are attached to proteins and lipids Functions • Acts as a barrier: physical isolation • Holds molecules inside in the cell • Regulation of the movement of molecules into and out of the cell • Maintains a unique intracellular pH environment • Responds to changes in the outside and inside of the cell THE CYTOPLASM Structure • A viscous, aqueous solution inside the cell • Fills the space between the cell membrane and the nucleus • It forms a suspending medium for other subcellular organelles • The fluid part of the cytoplasm outside all the organelles is known as the cytosol Functions • Suspends and solubilizes organelles and cellular molecules • Many cellular processes occur in the cytoplasm, e.g. : - synthesis of many proteins - the first stage of cellular respiration (glycolysis) - the events of mitosis and meiosis • Allows molecules to move around the cell and ‘find’ each other Squamous Cells With Visible Nucleus and Cytoplasm. National Cancer Institute THE CYTOSKELETON Structure • consists of filaments and tubules • filaments are double strands of actin that form a mesh below the plasma membrane • They link with proteins embedded in the membrane • These in turn may connect with molecules present in the extracellular matrix (ECM) Function • It is the protein scaffolding of a cell • It preserves the shape of the cell • It also allows the cell to change shape if needs be • It provides a frame for movement of the cell • Provides a framework for transport of materials http://scienceblogs.com/transcript/2007/01/cytoskeleton.php THE NUCLEUS Structure • surrounded by a double layer of membrane called the nuclear envelope • The inner nuclear membrane is smooth • The outer membrane may be linked to the endoplasmic reticulum (ER) • Nuclear pores regulate the passage of molecules through the nuclear envelope • Proteins and RNA can pass these pores • It contains chromatin, a mixture of DNA and proteins that form the chromosomes • It also contains one or more dark-staining spherical areas called nucleoli; these are the place of assembly of the ribosomes and contain large amounts of RNA and proteins • Surrounding the chromatin and the nucleoli is a gel-like substance called the nucleoplasm Endoplasmic reticulum Nucleus WHAT HAPPENS TO DNA IN THE CELL? • DNA is stored in chromosomes in the nucleus • The fate of the DNA depends on signals that the cell receives • The signals can allow DNA • • • To remain quiescent or To translate to RNA for new protein synthesis or Replicate for cell division See lectures on cell cycle, DNA replication, transcription, translation FROM DNA TO PROTEIN Taken from http://www.actigenomics.com/wp-content/uploads/2013/03/TransRegul2.jpg THE ENDOPLASMIC RETICULUM (ER) Structure • It is a network of interconnected membranous tubules and sacs • These extend from the nucleus into the cytoplasm • two types of ER within the cell: the smooth ER and the rough ER • The rough ER membranes are covered with ribosomes • The smooth ER is continuous with the rough ER but does not have ribosomes Function • The rough ER is involved in protein synthesis. • The smooth ER is involved in lipid metabolism THE GOLGI APPARATUS Structure • It consists of stacks of flattened containers called cisterns or sacs • It is located in the cytosol, in the space extending from the ER towards the cell membrane • The parts close to the nucleus are known as the cis -Golgi • The parts closest to the cell membrane are the trans -Golgi • The system remains in contact with cytoskeletal filaments Function • Modification of proteins and lipids, through the attachment of carbohydrates (glycosylation) • Their sorting and distribution to other organelles within the cell • Their packaging for subsequent secretion from the cell THE MITOCHONDRION Structure • sausage-shaped, approximately 1 µm wide and 7 µm long • double membrane separated by the intermembrane space • The outer membrane is permeable to small molecules • The inner membrane has multiple folds (cristae) projecting inwards • The interior of the mitochondrion is called the matrix Function • It contains the enzymes of the electron transport chain, the Krebs cycle and the pathway of the betaoxidation of fatty acids • It generates most of the cellular ATP through oxidative phosphorylation • They are plentiful in cells that use large amounts of energy THE LYSOSOME Structure • They are spherical or oval organelles • They have a single-layer membrane • They contain acid hydrolases (degradative enzymes) • These enzymes digest most biological molecules • The pH inside is approximately 5.0 • This is optimal for the activity of the enzymes • The pH differential with the cytosol has a protective function Function • The lysosomal membrane compartmentalises intracellular degradative enzymes • The pH 5 environment denatures proteins facilitating their degradation • Vesicles from the Golgi apparatus fuse with lysosomes delivering their contents for degradation • Lysosomes also destroy aged cell organelles • These are first engulfed by the ER, forming vesicles, that are subsequently fused with the lysosome PROTEASOME • • • • • • This is a multi-subunit enzyme (protein) complex The protein complexes are arranged in four rings around a central hollow core. It degrades cytosolic proteins It is also involved in the control of the cell cycle and apoptosis Proteins destined for destruction are labelled with a small protein called ubiquitin This directs them into the core of the proteasome, where they are broken down by enzyme action PEROXISOME • Similar to the lysosome • They have a single lipid bilayer • They contain many enzymes, mainly oxidases and catalases • They are involved in – Lipid metabolism eg breakdown of VLCFA – Chemical detoxification of the cell CELL JUNCTIONS • Cells adhere to each other, forming tissues and organs • The most common types of junctions between cells are: – Tight junctions – Anchoring/adhesive junctions (desmosomes) – Gap/communicating junctions Naish Fig 2.40 THE TIGHT JUNCTION • • • • This is a protein complex between two cells It creates a seal to prevent any leakage of the content through the cell membrane It leaves no space between plasma membranes of adjacent cell In polarized cells, they prevent movement of membrane proteins from one side to the other THE ANCHORING/ADHESIVE JUNCTIONS • Attach the cytoskeleton to a neighbouring cell or to the extracellular matrix • Junction is made between intracellular anchor proteins and transmembrane adhesion proteins THE GAP/COMMUNICATING JUNCTIONS • • • • • Made from proteins that form a tunnel between cells (called connexins) Connexin proteins form a pore in the cell membrane called the connexon Allows cells to communicate with each other To share nutrients such as water, ions, sugars and amino acids Transfer chemical and electrical signals CELL ADHESION • • • • • This is the ability of one cell to stick to another cell or an extracellular matrix Adhesion is important for cell communication and regulation It is essential for the maintenance and development of tissue Adhesion stimulates signals that regulate cell differentiation, cell cycle, cell migration and cell survival Adhesion occurs through the action of proteins called CAMs (Cell Adhesion Molecules) CELL RECOGNITION • • • • Some proteins on the surface of cells have short chains of sugars attached to them These proteins are called glycoproteins They act as identification tags These tags are specifically recognised by other cells Cell Membrane Cell 1 Cell Membrane Cell 2 Sugars Cell recognition protein: glycoprotein OTHER RESOURCES Reading: “Medical Sciences” Naish. Chapter 2 Viewing: Overview of cell structure Inner life of the cell Short and Long VR tour of cell Other: Online histology course on VLE Identifying organelles OTHER RESOURCES Check out chapter 2 in this textbook online through the library