BIOL1005 Lecture 7 Mitochondria, Golgi, and Cytoskeleton PDF

B I O L 10 0 5 L E C TU R E 7 Allen Cheung 5 Feb 2025 CEL L ORGANEL LES MAIN FUNC TION OF MITOC HONDRIA As the power factory of the cell Engages aerobic respiration using the following pathways: Glycolysis Krebs Cycle Electron Transport Chain  Occurrence...

B I O L 10 0 5 L E C TU R E 7 Allen Cheung 5 Feb 2025 CEL L ORGANEL LES MAIN FUNC TION OF MITOC HONDRIA As the power factory of the cell Engages aerobic respiration using the following pathways: Glycolysis Krebs Cycle Electron Transport Chain  Occurrence - find in plants & animals (except RBC), not in bacteria MITOCHON DRIA (MT ) - in chemotropic & phototrophic eukaryotic cells - indicates that photosynthetic organisms are capable of respiration Found in both animal (except RBC) and plant cells Not found in bacteria Number of mt is highly variable and depends on the metabolic demands of a cell algae/fungi has one to a few 500-1000 per liver cell Nestled between muscle myofibrils Mt is located throughout the cytoplasm, and clustered where energy is required the most  Structural features - variousStructural shapes features & sizes, depending on the cell type S TRUC TURAL FEATURES - various shapes & sizes, depending on the cell type - appear as spherical, oval, rod, elongated bodies - appear as spherical, oval, rod, elongated bodies Various shapes and sizes - about 0.5 – 1 µm in diameter, 1-2 µm in length (2nd large - about organelle in 0.5 – 1cells), animal µm in size diameter, as a 1-2 µm in length (2nd large bacterium Spherical, oval, rod, elongated organelle in animal cells), size as a bacterium - can change shape & move to area needed energy 0.5 – 1 um in diameter, 1-2 umshape - can change in length (2nd & move largest to area needed energy organelle in -the onecell)onedouble of-the membrane of the double bound membrane boundorganelles organelles Similar size to a -bacterium e.g. chloroplast, nucleus - e.g. chloroplast, nucleus - fundamental - fundamental features features Double membraned organelle 1) outer membrane 1) outer membrane Features: 2) inner membrane 2) inner membrane Outer membrane 3) intermembrane 3) intermembrane space space 4) matrix Inner membrane 4) matrix 5) crista Intermembrane space 5) crista Matrix Cristae 4 - each domain house a distinct set of functions  OUT ER ME MBRA N E Forms a single continuous surface layer around the organelle → encloses the entire organelle Lower protein content than plasma membrane Large number of integral proteins (e.g. porins) to allow transport of small. molecules and ions Large proteins bind to transporters → active transport into mt I N TE R M E M BR A N E S PAC E The space between the outer and inner membranes Contains common ions and sugars similar to cytoplasm Proteins are located in this space that differ to cytoplasm E.g. cytochrome c INNER MEMBRANE Freely permeable to most solutes (e.g. O2, CO2, H2O) Impermeable to most ions & small molecules, which helps to maintain a proton gradient Contains high protein content (~75%) Highly complex and contain many proteins: Specific transport proteins → regulate in & out of different materials from matrix Perform oxidative phosphorylation Generate ATP (energy molecule) Protein import machinery CRIS TA Folds of the inner mt membrane to increase surface area (5x more than plasma membrane) Accommodates large number of protein complexes The prominence of crista reflects the relative metabolic activity of the cell Abundant in the mt in heart, kidney, muscle cells e.g. electron transport chain  MATRIX Semifluidic Contains ~30% of all proteins in mt Contains enzymes for ATP production, oxidation of pyruvate, fatty acid, citric acid cycle (Krebs’ cycle), ribosomes, tRNA, mt DNA genome Cellular Cell cytoplasm Respiration 1 Glucose → 38 ATP Mt matrix Crista  ENDOPLAS MIC RETIC ULUM (ER) Endo = within the cytoplasm Reticulum = net like structure Originates from the outer nuclear membrane Warehouse or manufacturing unit of the cell Eukaryotic organisms Forms an interconnected network of flattened membranes and sacs known as cisternae Provides separate chemical environment which allows for the correct protein folding Rough ER (RER) Smooth ER (SER) FUNCTIONS OF E R Folding and modifications of translated proteins Synthesis of phospholipids and steroids on the cytosolic side of the ER membrane Storage of calcium ion in the lumen and their regulated release into the cytosol Carbohydrate metabolism  SMOOTH ER (SER) It is highly curved and tubular It forms an interconnecting system of pipelines which form a network throughout the cytoplasm Function: synthesizes all major classes of lipids It is involved in the production of steroid hormones Lipid composition of the ER is different to other cell compartment membranes – high abundance of phosphatidyl choline and low conc. of cholesterol Very fluid and disordered due to large proportion of unsaturated fatty acids  ROUGH ER (RER) Flattened sealed sacs that is continuous with the nuclear membrane Studded on its outer surface with ribosomes Found throughout the cell but the density is higher near the nucleus and Golgi apparatus Abundance of pores for ribosomes Ribosomes are free to attach at these sites to synthesize proteins and transport them directly into the ER lumen, after which the ribosomes can detach The presence of ribosomes give the characteristic of roughness FUNCTIONS OF RER Protein folding Assembly of multi-subunit proteins Disulphide bond formation, which requires an oxidizing environment (cytosol is reducing env.); together with disulphide isomerase Glycosylation – the initial stages occur on specific asparagine residues Degradation of misfolded proteins through ubiquitin proteasome pathway Protein secretory pathway GOL GI AP PARATUS GOL GI AP PARATUS Complex collection of membrane Has polarity: cis and trans surfaces Responsible for secretion – very prominent in cells with secretory functions, e.g. epithelial cells Modifies structures previously synthesized in the ER E.g. Modification of carbohydrate groups using enzymes at each cisternae Forming face Maturing face MOVEMENT OF MOLECULES INSIDE THE GOLG I A PPA RATUS For glycoproteins: replace sugar groups Modification of phospholipid acylgroups and head groups Production of vesicles to delivery membrane associated molecules and excreted molecules to cell surface Lysosomes – used in endocytosis and phagocytosis, to degrade the contents Lysosomes Consist of hydrolytic enzymes enclosed in a lipid membrane with glycosylated transport proteins pH 4-5, RNase, DNase, Protease, Lipase, Phosphatase, Carbohydrase Originate from ER but enzymes activated in Golgi Used for phagocytosis, endocytosis, autophagy IMPORTANCE OF GOL GI The Golgi body (apparatus) interacts mostly with the ER, PM, and lysosomes of the cell Glycosylation in the Golgi (besides ER) is the mechanism that directs certain proteins to their proper cellular location Cell will die without Golgi, that is because there would be no lysosomes to breakdown food for the cell Proteins would not be able to go where they should be Exosomes CY TOSKELETON  CY TOSKELETON Structure of the cell consists of fibrous proteins in cytoplasm → shape of the cell Allow movement of molecules 1. Microtubules 2. Actin 3. Intermediate filaments Microfilaments and microtubules can polymerise and depolymerise readily  FUNCTIONS OF THE CY TOSKEL ETON Different functions based on the filaments physical properties Integral strength Cell shape Motility 1. Inside the cell 2. Whole cell 3. Motor proteins associated with 2 filament systems 4. Signal transduction ST RUCTURE OF CY T OSKELE TAL PROT EINS Network of filamentous proteins -filaments formed from a few proteins -monomer protein forms polymer filaments Located in nucleus and cytoplasmic compartments (but not in organelles) Location is based on the cellular function Naming depends on the physical size Cell shape & motility Cilia, mitosis, organelles Tensile strength, cell framework SUMMARY Cell organelles and cytoskeleton have their specific functions Mitochondria – energy ER – protein translation and folding Golgi – protein processing and transport Cytoskeleton – structure of cell and cell movements