Medical Biology and Genetics for Pharmacy 2020-2021 Lecture 2 PDF
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Medipol University
Berrak Çağlayan
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This document is a lecture on medical biology and genetics for pharmacy students. It covers the subject of cellular structure and organelles. The lecture notes provide information on the features of life, the origin of life, prokaryotes, eukaryotes, and the cell theory.
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Medical Biology and Genetics for Pharmacy 2020-2021 Lecture 2: Cellular structure and organelles Assist. Prof. Berrak ÇAĞLAYAN [email protected] Learning Objectives ✓ To explain the features of life ✓ To describe the origin of life on Earth ✓ To explain the differences o...
Medical Biology and Genetics for Pharmacy 2020-2021 Lecture 2: Cellular structure and organelles Assist. Prof. Berrak ÇAĞLAYAN [email protected] Learning Objectives ✓ To explain the features of life ✓ To describe the origin of life on Earth ✓ To explain the differences of prokaryotes and eukaryotes ✓ To describe the cell theory ✓ To understand the evolution of organelles ✓ To explain the function of organelles Features of life 1. Are highly organized compared to natural inanimate objects. 2. Display homeostasis, maintaining a relatively constant internal environment. 3. Reproduce themselves. 4. Grow and develop from simple beginnings. 5. Take energy and matter from theenvironment and transform it. 6. Respond to stimuli. 7. Show adaptation to their environment. There are 4 theories about the origin of life on Earth 1. Cosmic theory 2. Creation theory 3. Abiogenesis (Miller-Urey experiment) 4. Heterotroph teory Origin of modern human (Homo sapiens) Single origin hypothesis: Modern human first appeared in Africa, then spread from East Africa to North America, Europe and Asia. Lower-level organisms do not have a tissue-level organization. Viruses Kingdom Monera Bacteria Blue-green algae Kingdom Fungi Fungi Kingdom Protista Protozoa Sarcodina/Rhizopoda Flagellata/Mastigofora Sporozoa Ciliata Viruses Viruses were discovered by Pasteur in 1881. They are neither live nor dead. They don’t have their own metabolic enzymes. They require host cell materials and enzymes to reproduce. Outside of a living host, viruses are motionless and in a crystal-like structure. They can have either DNA or RNA as their genetic material. Kingdom Monera Single-celled prokaryotic organisms. Bacteria and blue-green algae belong to Kingdom Monera. They have DNA, RNA and ribosomes. Nucleus or membrane-bound organelles do not exist. Bacteria are the most abundant microorganism on Earth. There are more bacteria cells in a human’s body than his/her own cells! Blue-green algae also contain chlorophils and they can photosynthesize. Kingdom Fungi Fungi kingdom involves yeast (unicellular), mushrooms and molds (multicellular). These are eukaryotic organisms, but they are not capable of photosynthesis. Their bodies consist of long, thread-like structures called hyphae. Their cells have cell walls made up of tough polysaccharide complexes called chitin. Fungi have many commercial applications. Kingdom Protista Protists are a very diverse group of unicellular eukaryotic cells. Protist cells may contain a single nucleus or many nuclei; they range in size from microscopic to thousands of meters in area. Protists may have animal-like cell membranes, plant-like cell walls, or may be covered by a pellicle. Kingdom Protista Some protists are heterotrophs and ingest food by phagocytosis, while other types of protists are photoautotrophs and store energy via photosynthesis. Some are motile and generate movement with cilia, flagella, or pseudopodia. Some live inside the bodies of vertebrates as parasites. Hierarchical organization of life New cells form by growth and division of existing cells (Cell theory) Cell theory was first described in 1839 by Matthias Schleiden and Theodor Schwann In 1858, Rudolf Wirchow showed that a cell can only arise from a pre-existing cell. Modern Cell Theory states that: All known living organisms are made up of cells. The cell is structural and functional unit of all living things. All cells come from pre-existing cells by division. (Spontaneous Generation does not occur) Cells contains hereditary information which is passed from cell to cell during cell division. All cells are basically the same in chemical composition. All energy flow (metabolism & biochemistry) of life occurs within cells. Cells vary enormously in appearance and function All organisms are constructed from cells The hereditary information in the fertilized egg cell determines the nature of the whole multicellular organism Shapes or structures are dependent on the cells’ function Cells are transparent, but some of the internal structures of a living cell can be seen with a light microscope Staining (labelling or dyeing) cells enable us to examine intracellular and extracellular components of cells in tissues Prokaryotic Cells vs Eukaryotic Cells Prokaryotes vs. Eukaryotes Prokaryotes : Eukaryotes : “truly nucleated,” from without/before a The words eu, “well” or “truly,” and defined nucleus. karyon, “kernel” or “nucleus”. Eukaryotes vs Prokaryotes Eukaryotes : “truly nucleated,” from The words eu, “well” or “truly,” and karyon, “kernel” or “nucleus”. Prokaryotes : without/before a defined nucleus. Prokaryotes do not have a defined nucleus In prokaryotic cells (bacteria and blue- green algae) do not contain a nucleus with a defined membrane. Prokaryotes have a cell wall made up of peptidoglycans and underneath the cell wall there is a cell membrane. Genetic material of prokaryotes is a circular DNA known as chromosome. Prokaryotes also contain small circular DNA fragments called plasmids Eukaryotic cells are typically larger than prokaryotic cells and have a “true” nucleus, membrane-bound organelles, and linear chromosomes. Cells have 2 major parts: nucleus and cytoplasm Nucleus is separated from the cytoplasm by a nuclear membrane Cytoplasm is separated from the surrounding fluids by a cell membrane, (plasma membrane). Different substances that make up the cell are collectively called protoplasm. Protoplasm = nucleus + cytoplasm The cytosol is a concentrated aqueous gel of large, small molecules and organelles The nucleus is the information store of the cell Nucleus is the first discovered organelle Nucleus is relatively larger than the other organelles. Typically all cells have one nucleus. However, liver cells, skeletal muscle cells and adrenal cortex cells have more than 1 nucleus. Mature red blood cells do not have any nuclei. Nucleus is composed of: nucleoplasm, nuclear envelope, nucleolus and chromatin (DNA). Size of the nucleus is dependent on the size of the cell that it stays in. During cell division, nucleus undergoes some structural changes. Nucleoplasm is the semi-solid fluid inside the nucleus. The main function of nucleoplasm is to store DNA and create an isolated environment inside the nucleus and contains various proteins, lipids, inorganic materials and RNAs. Nuclear envelope is a double-membrane structure that consists of two phospholipid bilayers: an outer membrane and an inner membrane Nuclear envelope separates the cytoplasm and nucleus from each other. Nuclear envelope is punctuated with pores that control the passage of ions, molecules, and RNA between the nucleoplasm and cytoplasm. Nuclear pores regulate the passage of molecules between the nucleus and cytoplasm Nuclear pores are the sites where the outer membrane and inner membrane of the nuclear envelope are fused together. Due to this fusion, the membranes can be considered continuous with one another although they have different biochemical characteristics and can function in distinctive ways. Since the outer nuclear membrane is also continuous with the membrane of the endoplasmic reticulum (ER), both it and the inner nuclear membrane can exchange membranous materials with the ER. This capability enables the nuclear envelope to grow bigger or smaller when necessary to accommodate the dynamic contents of the nucleus. Nucleolus composed of RNA and proteins which form around specific chromosomal regions Nucleolus is seen as a bright round structure inside the nucleus. It participates in the formation of ribosomes. Number and size of nucleus changes during cell division. A cell cannot divide without its nucleolus. Ribosomes are large macromolecule complexes made from dozens of small proteins and several crucial RNA molecules (rRNAs) and is involved in protein synthesis. Ribosomes are found in both eukaryotic and prokaryotic cells, but they are slightly different Every cell has a cell membrane that encircles the cytoplasm Cell membrane separates individual cells from each other and from their environment. Cell membrane is a very thin pliable, elastic structure only 7.5 to 10 nanometers thick. Plant cells have an additional cell wall that is made up of cellulose. Cell membranes act as selective barriers Cell membrane is a lipid bilayer Cell membrane is a thin, double-layered film of lipids that is continuous over the entire cell surface. Lipid barrier of the cell membrane impedes water penetration. Cell membrane is composed almost entirely of proteins and lipids The approximate composition is proteins, 55 %; phospholipids, 25 %; cholesterol, 13 %; other lipids, 4 %; and carbohydrates, 3 %. Cell Membrane is composed of phospholipid molecules Phospholipids are amphipathic molecules One end of each phospholipid molecule is soluble in water; that is, it is hydrophilic. The other end is soluble only in fats; that is, it is hydrophobic. Lipid molecules in membranes are very disordered and mobile in a lipid bilayer Hydrophobic interactions hold the lipid bilayer together The phosphate end (head) of the phospholipid is hydrophilic, and the fatty acid portion (tail) is hydrophobic. Because the hydrophobic portions of the phospholipid molecules are repelled by water but are mutually attracted to one another, they have a natural tendency to attach to one another in the middle of the membrane. Hydrophilic phosphate portions then constitute the two surfaces of the complete cell membrane, in contact with intracellular water on the inside of the membrane and extracellular water on the outside surface. Cholesterol is found in large amounts in eukaryotic plasma membranes The cholesterol molecules orient themselves in the bilayer with their hydroxyl group close to the polar head groups of adjacent phospholipid molecule Cholesterol is important in membrane permeability Because cholesterol molecules are oriented in the lipid bilayer with their hydroxyl groups close to the polar heads of phospholipids, they enhance the permeability-barrier of the lipid bilayer. Because cholesterol fills the space between phospholipids, it decreases the permeability of the bilayer to small water-soluble molecules. Although cholesterol tends to make the lipid bilayers less fluid, it also prevents the hydrocarbon chains from coming together and crystallizing. The fluidity of a lipid bilayer depends on its composition A shorter chain length reduces the tendency of the hydrocarbon tails to interact with one another. Double bonds produce kinks in the hydrocarbon chains that make them more difficult to pack together, so that the membrane remains fluid at lower temperatures. Bacteria, yeasts, and other organisms whose temperature fluctuates with that of their environment adjust the fatty acid composition of their membrane lipids to maintain a relatively constant fluidity. For instance, as the temperature falls, fatty acids with more double bonds are synthesized, so the decrease in bilayer fluidity that would otherwise result from the drop in temperature is avoided. Functions of cell membrane Gives their shape to the cells. Defines the borders of a cell and functions as a selective barrier. Regulates intracellular molecule and ion concentrations by using membrane proteins (pumps and channels). Is involved in cellular communication. Transmits the chemical and electrical stimuli. Excretes the intracellular secretion molecules to the outside. Fluid-Mosaic Model of Cell Membrane Cell Membrane Proteins Most of the cell membrane proteins are glycoproteins There are 2 types of membrane proteins: 1) integral proteins that protrude all the way through the membrane, and 2) peripheral proteins that are attached only to one surface of the membrane and do not penetrate all the way through. Membrane proteins have diverse functions Channels or transporters: transportation of water-soluble molecules across the membrane. Enzymes: Located in the membrane to regulate metabolic functions. Receptors: involved in signal transduction between cells, sensitive to hormones or other signaling molecules. Membrane proteins have diverse functions Intercellular joining: membrane proteins can make connections with other proteins. Antigens: involved in recognition of cells. Structural proteins: are connected to cytoskeletal proteins and proteins of extracellular matrix to maintain the shape of the cell. The cytoskeleton is a network of protein filaments that are responsible for movement of cells and compartments in the cell Cytoskeleton is the intricate network of protein filaments that extends throughout the cytoplasm. Cytoskeleton gives a cell its shape and allows the cell to organize its internal components and move. Endoplasmic reticulum (ER) Endo: «within», Plasmic: «the cell», reticulum: «net» Smooth ER in steroid (testesterone)- Rough ER in a pancreatic exocrine cell ER from a living plant cell hormone-secreting cell (Leydig cell) that secretes digestive enzymes About half the total area of membrane in a eukaryotic cell encloses the labyrinth of branching tubules and flattened sacs of ER. Have central role in protein and lipid (plasma membrane, mitochondrial, peroxisome, nuclear and other membranes) biosynthesis. Provides the space for Ca++ storage. Almost all transmembrane proteins and secreted proteins pass through the ER lumen. Polypeptide chains are folded and assembled in the lumen of rough ER (disulfide bonds are formed, incorrectly folded proteins are recognized…). Endoplasmic Reticulum (ER) produces many of the components of a eukaryotic cell ER is functionally and structurally diverse Rough ER (ER+ribosome) Smooth ER (specialized in lipid metabolism) Transitional ER: areas of smooth ER from which transport vesicles carrying newly synthesized proteins and lipids bud off for transport to Golgi. Golgi complex is typically comprised of a series of five to eight cup-shaped, membrane-covered sacs called cisternae. Golgi is responsible for manufacturing, warehousing, and shipping certain cellular products, particularly those from the endoplasmic reticulum (ER). Depending on the type of cell, there can be just a few complexes or there can be hundreds. Cells that specialize in secreting various substances typically have a high number of Golgi. Mitochondria generate usable energy from food to power the cell A mitochondrion is organized into 4 seperate compartments Mitochondria are remarkably mobile and often associate with cytoskeleton elements. Microtubules can determine the unique orientation and distribution of mitochondria in cells. A mitochondrion can divide like a bacterium Mitochondria most likely evolved from engulfed bacteria A lysosome contains a large variety of hydrolytic enzymes, which are only active under acidic conditions and is involved in digestion of cellular macromolecules. Next Class Next lecture: DNA, chromosomes and genome