2.04_Introduction to the Eukaryotic cell structure.pptx
Transcript
Introduction to the Eukaryotic cell structure Mrs Cassy Ross Week 2 – Cell Biology SCI1023-N-GJ1-2020 2022 Learning Outcomes • Quickly revision from last week (Eukaryotic cells vs Prokaryotic cells) • Eukaryotic cell structure (organelles and cell membrane) • The cell membrane: structure, models,...
Introduction to the Eukaryotic cell structure Mrs Cassy Ross Week 2 – Cell Biology SCI1023-N-GJ1-2020 2022 Learning Outcomes • Quickly revision from last week (Eukaryotic cells vs Prokaryotic cells) • Eukaryotic cell structure (organelles and cell membrane) • The cell membrane: structure, models, general functions, specialised cell membranes and implications in disease Just to remember…different type of cells Prokaryotic cells Eukaryotic cells Macromolecular assembly of a (eukaryotic) cell …and levels of organisation to form an organism Cell Tissue Organ Organ System Organism All life is made of cells • Cells were discovered by Hooke in 1665 • The word cell means ‘box’ or ‘room’ • He remarked that it looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name Think of a cell… Can you draw on a piece of paper or picture it in your mind Think of a cell… Think of a cell… A lot learn in the coming weeks… “the key to all biological problems is hidden in the cell” …and most, of not all of the fundamental events happening inside the cell are dynamics and highly regulated! Core biochemical reactions in cell KEGG:https://www.genome.jp/kegg/ • About 200 different types of specialised cells carry out a multitude of functions that contribute to keep homeostasis of the entire body • All eukaryotic cells share key structures and functions that support their intense activity • 3 main parts are: 1. Cell membrane. 2. Cytoplasm. 3. Nucleus Bone cell Sperm cell Nerve cell Smooth muscle cell Red blood cell The cell membrane • All cells contain a cell membrane • Surrounds the whole cell as an entirety, separating the interior of the cell from the outside environment • Encapsulate all contents of the cell Ramon Andrade 3DSciencia/Science Photo Library/Science Source (MCB Lodish, 8th ed. 2016) Cell membrane structure • The cell membrane is the outer coating of the cell and contains the cytoplasm, substances within it and the organelle • It is a double-layered membrane composed of 1. Lipids (45-50%) 2. Proteins (45-50%) 3. Carbohydrates (4-8% - outer surface only) Cell membrane structure The lipid molecules on the outer and inner part (lipid bilayer) allow it to selectively transport substances in and out of the cell Cell membrane structure The membrane proteins could be peripheral, soluble or integral (cross the cell membrane) are responsible for most membrane functions molecules Lipids composition of cell membranes Heterogeneity and asymmetrical distribution of lipids: • Phospholipids : the major component, bilayer, semipermeable (allows certain molecules to diffuse across), subtypes: Phosphatidylcholine, Phosphatidylethanolamine, Phosphatidylserine • Cholesterol (35% approx, disperse between phospholipids, prevents phospholipids from being too closely packed, allows fluidity • Sphingosine-based lipid or ceramides (Sphingomyelin, important in signalling pathways, surrounding part of nerve cell axons) Protein composition of cell membranes Main categories are: • Integral membrane proteins (intrisec): permanently embedded within the membrane, Hydrophobic in nature, penetrates the phospholipid bilayer, thus anchors the protein to the membrane • Peripheral membrane proteins (extrinsic): only temporally associated to the membrane. Most are hydrophilic, loosely attached to phospholipid head group. Models for the structure of the cell membrane The Fluid Mosaic Model (1972, Singer and Nicholson) Updated Model: Lipid rafts (1997, Simons) Molecular Cell Biol, Lodish 8th ed. (2016) The fluid mosaic https://www.youtube.com/watch?v=UxvFdW9aO0s 5min Functions of the cell membrane • • • • • • • Barrier (selective permeable) Regulates transport Regulates reactions (maintain homeostasis) Communicates with the environment Detects signals and responds to those Cell recognition (cell identity) Cell adhesion (communication) Cell transport https://www.youtube.com/watch?v=XHES1qwGeII 3.22min Types of active transport regulation Endocytosis: move particles into a cell by enclosing them in vesicle made out of cell membrane Cell membrane invaginates, forms a pocket around that particle(s), the pocket pinch off with the help of specialised proteins, the particle keeps trapped in a newly created vesicle or vacuole inside the cell Types of endocytosis: 1. Phagocytosis (cell eating, large particles are transported into the cell, macrophages engulfing a pathogen) 2. Pinocytosis (cell drinking, cells takes extracellular fluid) 3. Mediated by receptors Phagocytosis Pinocytosis Receptor-mediated endocytosis Types of active transport regulation • Exocytosis: Material from inside to outside of the cell in vesicles that fuse to cell membrane. E.g. Nutrients that need to release other molecules such as signalling or waste products to the outside environment. Cell adhesion • Cells adhere to each other and to the extracellular matrix • Essential for cell communication and regulation • Allows communication and coordination among groups of cells • Integrins and several other adhesive proteins are used to maintain physical contact Cell adhesion molecules (CAMS) • Two types: Cell-cell adhesion molecules and cell matrix adhesion molecules • Three mechanisms by which cell surface molecules can mediate cell to cell adhesion: 1. Binding through a extracellular linker molecule 2. Homophilic binding 3. Heterophilic binding Cell junctions and CAMS Four major cell adhesion molecules: 1. 2. 3. 4. Cadherin Selectin Intergrin IG-SF Cell adhesion – communication Collective cell migration of HUVEC cells (From Arnold Hayer, McGill University) Specialised cell membranes in the small intestine Intestinal lumen Microvilli Nutrients Luminal apical surface Apical proteins Tight junctions Basolateral proteins Basolateral membrane Connective tissue/ blood supply Disruption of cell membrane function Regents of Univ Michigan Med School, 2012 McConnell, R.E., et al. 2009. JCB Food allergy, celiac disease, autoimmune diseases, bowel inflammation Specialised cell membranes in the small intestine Celiac disease – cell membranes are damaged! Problem to absorb nutrients Inflammatory response Autoimmune response Suzuki et al., 2012 Regulation of intestinal epithelial permeability by tight junctions Loss of membrane integrity under physiological and pathological context Worth reading this article from Nature! https://www.nature.com/articles/s41421-02000233-2 Learning Outcomes from today • Eukaryotic cell structure (organelles and plasma membrane) • The plasma membrane: • • • • • structure models general functions specialised cell membranes and implications in disease Test yourself! Multiple choice questions on cell membrane https://forms.office.com/Pages/ResponsePage.aspx? id=WxHSQ16ltkad97AziOz8YHPKVJ7iwLlEi3zi7EZn_8pU N0hBRzhZQTNNUU02NlFTRVhVSEg1NUFaRC4u Any questions? [email protected] Thank you!
