Funbio 5 2024 PDF - Cell Structure ER, Golgi and Vesicles

Cell Structure: Endoplasmic reticulum (Smooth and Rough), Golgi Class Foundation Year Course Fundamentals of Human Biology Code FUNBIO.5 Lecturer Dr Irene Oglesby Date 3rd October 2024  Learning outcomes At the end of this lecture, the learner will be able to...

Cell Structure: Endoplasmic reticulum (Smooth and Rough), Golgi Class Foundation Year Course Fundamentals of Human Biology Code FUNBIO.5 Lecturer Dr Irene Oglesby Date 3rd October 2024  Learning outcomes At the end of this lecture, the learner will be able to; 1. Discuss the appearance of the endoplasmic reticulum in the cell. 2. Discuss the role of smooth ER in cell activities including lipid production and detoxification. 3. Describe the structure of rough ER and explain its role in protein production. 4. Describe examples of specialised ER such as the sarcoplasmic reticulum. 5. List the four major functions of the Golgi apparatus in the cell including the production of primary lysosomes 6. Describe the structure and function of peroxisomes in the cell. 7. Discuss the presence of secretory and zymogen granules in certain classes of cell. Cell Structure: Endoplasmic reticulum (Smooth and Rough), Golgi 2  Endoplasmic Reticulum An elaborate membrane system which may occupy up to 50% of the total membrane surface of animals cells Called the endoplasmic reticulum from the Greek, rete = a net It extends from the nuclear envelope almost (but not quite) to the plasma membrane The interconnecting channels or tubules may expand in places to form flattened discs called cisternae These may localize the ER into certain cytoplasmic areas  Endoplasmic Reticulum (ER) Two types of endoplasmic reticulum: 1. Rough ER 2. Smooth ER Both are part of one interconnected system and are usually present in the same cell lipids and steroid production protein production After cell division the nuclear envelope is partially reformed from nearby remnants of the ER 1. Rough Endoplasmic Reticulum (RER) Rough (Granular) ER is found abundantly in cells engaged in protein synthesis The granulation which gives the RER its name is due to the attached ribosomes  Rough Endoplasmic Reticulum Function - protein synthesis and transport Two types of protein: 1. Water-soluble proteins, which cross the ER membrane and enter the lumen, for eventual release elsewhere 2. Prospective Transmembrane proteins, which remain embedded in the ER membrane Proteins produced include; Digestive enzymes, Hormones, Plasma membrane proteins, Neurotransmitters, Lysosomal enzymes Proteins may accumulate or be stored for a time in cisternae Post-translational processing also occurs, i.e. modifications made to proteins after translation such as protein folding Impaired protein folding – drastic The proteins are transported to various parts of the cell and in particular consequences to another organelle, the Golgi Apparatus ARIAL 10.5PT Smooth ER 2. Smooth Endoplasmic Reticulum https://www2.estrellamountain.edu/faculty/farab ee/biobk/BioBookCELL2.html  Smooth Endoplasmic Reticulum Agranular or Smooth ER is free of attached ribosomes It is particularly well developed in cells that secrete lipids and steroids and in liver cells For example in cells that secrete steroid hormones such as, Cells of the adrenal cortex Leydig cells in the testis Follicular cells in the ovaries  Smooth Endoplasmic Reticulum Functions: 1. Lipid synthesis 2. Steroid synthesis and secretion 3. Metabolism of carbohydrates 4. Detoxification (including drug breakdown) 5. Ca2+ accumulation e.g. skeletal muscle cells (sarcoplasmic reticulum)  Smooth Endoplasmic Reticulum Two main mechanisms used to keep blood glucose levels from dropping too low (hypoglycemia) 1. Glycogenolysis (Glycogen breakdown) Muscle & liver Glycogen converted to glucose Smooth ER contains glucose-6-phosphatase Converts glucose-6-phosphate to glucose 2. Gluconeogenesis Glucose production from non carbon sources  Smooth ER in rat liver cells https://medcell.org/histology/cell_lab/proliferation_of_smooth_er.php Chemical insult - results in a need for increased activity of detoxification enzymes and the proliferation of the hepatocyte smooth endoplasmic reticulum on which they are located.  Smooth Endoplasmic Reticulum SARCOPLASMIC RETICULUM Specialised form of smooth ER found in smooth & skeletal muscle cells Storage & release of Ca2+ Under the influence of excitable membranes (neurons, muscle cells) Role in Excitation-Contraction Coupling (ECC) Muscle contraction is initiated by transient release of Ca2+ from the sarcoplasmic reticulum in muscle fibers Checkpoint - Endoplasmic Reticulum Summary What other functions can you recall? Smooth Endoplasmic Reticulum Which of the following is NOT true about the smooth ER? 1. Makes lipids 2. Pumps calcium ions 3. Makes steroids 4. Has ribosomes Smooth Endoplasmic Reticulum Smooth ER is responsible for which of the following functions? 1. Lipid production 2. Detoxification 3. Testosterone production 4. All of the above  Smooth Endoplasmic Reticulum Q. Does the sarcoplasmic reticulum have the same function as the smooth endoplasmic reticulum? Discuss……. A. No Functions in Ca2+ storage and release Role in muscle contraction – skeletal muscle Role in excitation-contraction coupling within heart muscle cells Structural differences  Golgi Apparatus This organelle was discovered in 1898 by Camillo Golgi The Golgi apparatus is found in all eukaryotic cells Golgi Apparatus It reaches its greatest size and complexity in secretory and storage cells In some animal cells it is found near the nucleus in an area called the centrosome In plant cells there are many Golgi bodies dispersed through the cytoplasm  Golgi Apparatus - Structure Cisternae Parallel array or stack of curved cisternae or sacs The number of cisternae varies from 3-7 May be interconnected by tubules Each cisternae separated by space up to 30nm wide - Lumen  Golgi Apparatus - Structure The Golgi apparatus is usually located between the ER and the plasma membrane The face that is closest to the ER is known as the cis face The trans face lies at the plasma membrane side  Golgi Apparatus Associated with the cisternae are small vesicles (20-50nm diameter) that… Enter or leave cis-face (receiving face) from/to the ER In the trans-face (releasing face), vesicles containing cargo exit the Golgi Complex Proteins entering the CGN can either move onward in the Golgi apparatus or be returned to the ER Proteins exiting from the TGN move onward and are sorted according to their next destination: endosomes, secretory vesicles, or the cell surface Golgi Apparatus - Function The ‘Post Office’ of the cell Cell factory in which proteins received from the ER are modified, sorted and packaged for transport to their eventual destinations, For example, going to lysosomes, plasma membrane or for secretion  Golgi Apparatus Structure Four major functions: 1. Processing newly synthesized secretory products Proteins, Glycoproteins Mucopolysaccharides 2. To act as a centre for the redistribution of cell membranes e.g. lipid transport 3. Primary lysosome production 4. As a site of carbohydrate synthesis e.g. polysaccharides and glycosaminoglycans (GAGs).  Golgi Apparatus Structure https://www.youtube.com/watch?v=jDadorSbhi4 Golgi apparatus 5min in ARIAL 10.5PT Membrane bound vesicles and secretory granules Membrane Bound 1. Lysosomes Vesicles and 2. Peroxisomes secretory granules 3. Secretory granules  1. Lysosomes Found in all animal cells and some plant cells In most plant cells the vacuole acts as a lysosome Formation & Composition: Originate from Golgi apparatus Contain powerful hydrolytic enzymes o Synthesized in the rough ER o Post-translationally modified in Golgi (Addition of sugar residues mark proteins for dispersion into lysosomes) https://www.youtube.com/watch?v=OZdmaf2R9ys Khan Academy 5 min video lysosomes and peroxisomes Lysosomes – structure and composition Heterogeneous morphology Between 0.4 - 0.5 µm in diameter Single outer limiting membrane o Separates lysosomal components from the cell cytosol o The lysosomal membrane is specially adapted to protect the cell contents Digestive enzymes About 40 enzymes discovered Powerful digestive actions Optimum activity of these enzymes is at a pH of 5.0 Cytosol - pH of ~ 7.2  1. Lysosomes Intracellular digestion/removal of unwanted elements e.g. pathogens and debris Primary lysosomes bud off from the Golgi Apparatus Fuse with phagosomes Fuse with endosomes Secondary lysosomes (contain material to be digested) Fused lysosome = secondary lysosome Digestion occurs in secondary lysosome Undigested or indigestible molecules accumulate as residual bodies  2. Peroxisomes Appear as rounded organelles in the cytoplasm 0.5 - 1.0 µm diameter Bound by a single membrane and contain a fine granular matrix Occasionally contain a core or nucleoid often crystal-like in appearance Sometimes called ‘microbodies’. Fairly numerous with a ratio of 1:4 mitochondria  Peroxisomes - Function Like mitochondria they are a site of molecular O2 use Contain oxidative enzymes involved in oxidation reactions (break down compounds) In the process they remove H+ ions from specific organic substrates (R) RH2 + O2 -----> R + H2O2 One by-product of the reaction is hydrogen peroxide (H2O2) a lethal oxidant in cells and must be removed as rapidly as possible  Peroxisomes - Function Hydrogen peroxide (H2O2) is removed by the enzyme catalase This uses the H2O2 to oxidize a variety of substances (R’) e.g. alcohol, phenols, formaldehyde or produce H2O Peroxisomes also have ß-oxidative enzymes for the breakdown of fatty acids, a process formerly believed to be confined to mitochondria Zellweger syndrome - a defect in peroxisomes. Severe abnormalities in infancy in brain, liver, and kidneys, and they die soon after birth.  3. Secretory Granules Some cells specialize in rapidly secreting products, usually proteins Such cells concentrate and store these products in secretory granules or vesicles The number of secretory granules in the cytoplasm varies Secretory vesicles are always membrane bound  Secretory Granules All secretory vesicles arise from the trans-face of the Golgi Apparatus Chemical messengers signal the vesicles to fuse with the plasma membrane The contents are released by the process of exocytosis e.g. hormone release (insulin from beta cells)  Secretory Granules Insulin contained in granules in the beta cells of the Islets of Langerhans in the pancreatic islets Released in response to elevated glucose in the blood Insulin Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA C T Irene Oglesby EMAIL: [email protected]