Cell Biology Structure and Function of Cells PDF

CELL BIOLOGY STBP1023 DR.NURUL YUZIANA MOHD YUSOF Structure & Functions of Cells - Organelles, non-organelles & others subcellular components  Structure & Functions of Cells - Organelles, non-organelles & others subcellular compone...

CELL BIOLOGY STBP1023 DR.NURUL YUZIANA MOHD YUSOF Structure & Functions of Cells - Organelles, non-organelles & others subcellular components  Structure & Functions of Cells - Organelles, non-organelles & others subcellular components PART I : Type of Cells – a recap PART II : Cell Structure – The Organelles PART III : Cell Structure – The Non Organelles Nucleus Cell Wall Mitochondrion Cytoskeleton Endoplasmic Reticulum Ribosome Golgi Apparatus Others: cell coats, cell junctions Lysosome & Peroxisome Vacuole Chloroplast  3 different kingdoms – Eukarya, Bacteria and Archaea Type of CELLS Karp 2010; Cell Biology  Prokaryotic Cells pro- “before” karyon- “nucleus”  Bacterial Cell Archaeal Cell (General) http://0.tqn.com/d/biology/1/0/Z/V/prokaryoticcell.jpg http://dbscience3.wikispaces.com/file/view/prokaryote.jpg/ 59566886/prokaryote.jpg Archaeal Cell Structurally similar to prokaryotic cell Several genes and biochemical and metabolism pathways are similar to eukaryotes Examples: Most of them, line in extreme environment - “extremophiles” such as: - methanogens (produce methane) - halophiles (salty) - acidophiles (very low pH) - thermophiles (extreme hot/cold)  Eukaryotic Cells eu- “true” karyon- “nucleus” Animal Cell Plant Cell Eukaryotic Cells Animal Cell Eukaryotic Cells Plant Cell Sub-cellular Components  Organelles and Non-Organelles Components Organelle: – membrane-bound structure – within an eukaryotic cell; have a specific function – contains a specific enzyme complement and chemical composition related to its function – nucleus, mithochondrion, endoplasmic reticulum, chloroplast, Golgi complex, vacuoles, peroxisome, lysosome Non-Organelle - mostly related to structure - non membrane-bound – plasma membrane, cell wall, cytoskeleton, cytosol, ribosome  Sub-cellular Components Organelles Non-Organelles nucleus vacuole plasma membrane cell wall mitochondrion Golgi complex cytoskeleton endoplasmic reticulum lysosome cytosol chloroplast peroxisome ribosome  C A R D – key points NOTE Structure Function Role in Homeostasis What is it? A state of balance among all the body systems needed for the body to survive and function correctly Homeostasis is the maintenance of a stable internal environment within cells and organisms through dynamic regulation and feedback mechanisms, despite external changes or disturbances. It involves coordinated actions of cellular organelles and systems to maintain optimal conditions for life processes, such as pH, temperature, ion concentrations, and metabolic balance. The relationship between homeostasis and cell organelles is crucial because: 1.Organelles are specialized units that maintain specific aspects of cellular balance 2.Each organelle contributes unique functions to overall cell stability 3.The integrated network of organelles allows coordinated responses 4.Understanding these relationships helps in: - Disease treatment - Cell engineering - Biotechnology applications - Medical research THE ORGANELLES  The Nucleus: Control Centre of the Cell Structure Function Role in Homeostasis 1. Nuclear envelope 1. Storage of genetic information (DNA) 1. Coordination of cellular responses - Double membrane structure - Chromosomal organization - Integration of cellular signals - Nuclear pores for controlled transport - DNA replication during cell division - Regulation of gene expression - Connection to endoplasmic reticulum - Protection of genetic material patterns - Adaptation to environmental 2. Nucleoplasm and nucleolus 2. Regulation of gene expression and changes - Gel-like matrix containing genetic material cellular activity - Nucleolus as the site of ribosome - Transcription of genetic information 2. Maintenance of genetic integrity assembly - Processing of RNA molecules - DNA repair mechanisms - Organization of chromatin structure - Control of protein synthesis - Chromosome stability - Quality control of genetic information  Nucleus Outer membrane Inner membrane Nucleoplasm Nucleolus Chromatin Nuclear envelope Pore in nucleus envelope also refer red as g e n o m that deter mine ic DNA (g s the specific DNA) trait/characte r of an organis m Contains the genetic material of an eukaryotic cell Enclosed by two membranes Numerous small openings, nucleopores; allows movement of molecules  Nucleus Contains chromosome – structural unit of genetic material – Consist of DNA molecule and histone – Readily visualised during mitosis – During interphase, dispersed as chromatin this is when the cell actually ‘active’ Nucleus Nucleus Nucleus  Mitochondrion: Powerhouse of the Cell Structure Function Role in Homeostasis 1. Double membrane and inner 1. ATP production through cellular 1. Energy supply for cellular processes membrane folds (cristae) respiration - ATP availability regulation - Outer membrane permeability - Oxidative phosphorylation - Metabolic rate adjustment - Cristae increase surface area - Electron transport chain - Energy distribution - Compartmentalization of respiratory - Proton gradient generation processes 2. Role in metabolic pathways 2. Regulation of apoptosis and metabolic 2. Matrix composition - Citric acid cycle balance - Enzymes for metabolic processes - Fatty acid oxidation - Cell death signalling - Multiple copies of mitochondrial DNA - Amino acid metabolism - Calcium homeostasis - Protein synthesis machinery - Reactive oxygen species management Mitochondrion  Mitochondrion Similar size to a prokaryotic cell Two membranes Contain their own DNA and ribosomes ‘powerhouse’ of the eukaryotic cell – Generates high-energy compound adenosine triphosphate (ATP) – Localises most of the enzymes and intermediates involved in energy-producing pathways  Mitochondrion Number and location within the cell are often related directly to their role in that cell, e.g. muscle cell and sperm cell  Mitochondrion Occurrence of other Localises intermediates chemical reactions, such as involved in the electron Krebs cycle & fat transport chain oxidation  Endoplasmic Reticulum: Protein & Lipid Synthesis Structure Function Role in Homeostasis 1. Smooth ER vs. Rough ER 1. Protein synthesis and folding 1. Quality control of proteins - Structural differences (Rough ER) - Unfolded protein response - Distribution within the cell - Ribosome attachment - Protein trafficking - Membrane composition - Protein translocation - ER stress management - Quality control mechanisms 2. Connection to the nuclear envelope 2. Modulation of lipid levels in the cell - Continuous membrane system 2. Lipid synthesis and detoxification - Membrane composition regulation - Transport mechanisms (Smooth ER) - Lipid distribution - Spatial organization - Membrane lipid production - Cellular stress response - Steroid hormone synthesis - Drug metabolism  Endo = within, plasmic = the plasm, reticulum = network ER is continuous with the outer membrane of the nuclear envelope Rough ER & Smooth ER  Rough ER – Due to the ribosomes – Ribosomes synthesise secretory proteins and membrane proteins – Proteins are transported into or across the ER membrane via RER, Golgi complex or secretory vesicles  Smooth ER – No ribosomes – Responsible for: Packaging of secretory proteins Synthesis of lipids and steroids Metabolism of carbohydrates Inactivation and detoxification of toxic drugs and other compounds  Golgi Apparatus: Modification and Transport Hub Structure Function Role in Homeostasis 1. Stacked cisternae 1. Modification of proteins and lipids 1. Regulation of cellular transport - Structural organization - Glycosylation - Membrane traffic control - Membrane composition - Protein processing - Protein distribution - Vesicle formation - Sorting signals - Vesicle targeting 2. Polarized structure (cis & trans faces) 2. Packaging for secretion or delivery 2. Maintenance of cellular communication ic Asym metr ha e p - Directional processing - Vesicle formation - Secretory pathway regulation cell s - Sorting mechanisms - Protein targeting - Signal molecule processing - Transport regulation - Quality control - Membrane composition control  A stack of flattened vesicles Role in: – Processing and packaging secretory proteins (mostly glycoproteins) – Synthesis of complex polysaccharides https://www.pnas.org/content/105/24/8256 Sub-Organelle: Secretory Vesicles Contains secretory proteins and substances processed by Golgi complex To export the packaged contents from the cell Vesicles move from GC Øto the plasma membrane Øfused with it, Ødischarge their contents to the extracellular space (exocytosis)  Production of Secretory Vesicles by GC 1. Vesicles budding off the ER 2. Accepted by Golgi complex (GC) 3. Contents of the vesicles further 5 modified and processed in the GC 4 4. Vesicles budding off the GC 5. The contents are passed to 3 other compartments of the cell (or being expelled from the cell to 2 1 release secreted proteins)  Lysosomes and Peroxisomes: Waste Management and Metabolism Structure Function Role in Homeostasis 1. Membrane-bound vesicles Function of Lysosomes 1. Cellular cleanup and recycling - Single membrane structure 1. Breakdown of macromolecules - Waste management - Specific protein composition - Protein degradation - Material recycling - Size and distribution - Lipid breakdown - Quality control - Carbohydrate processing 2. Enzymatic content and functions 2. Regulation of metabolic byproducts - Hydrolytic enzymes 2. Role in autophagy - Toxin elimination - Oxidative enzymes - Cellular recycling - ROS management - Substrate specificity - Organelle turnover - Metabolic balance - Stress response Function of Peroxisomes 1. Breakdown of fatty acids - β-oxidation - Hydrogen peroxide production - Metabolic coordination 2. Detoxification processes - ROS neutralization - Specialized metabolism - Cellular protection  0.5-1.0 µm in diameter Single membrane Discovered by Christian de Duve and his colleagues – Discovered a class of particles that contained acid phosphatase and hydrolytic enzymes Means of storing hydrolases, digestive enzyme – To digest food molecules that the cell acquire from the environment – To break down unwanted cellular constituents – To contain the enzyme and use it when required  Synthesised in the RER and transported to GC – inactive form Develop by budding off the ends of the Golgi cristernae – Primary lysosome: contain hydrolytic enzymes but not yet engaged in digestive activity Secondary lysosome: fused with food vacuole containing or vacuole with damaged organelles – The digestion products pass through the membrane and out into the cytoplasm and recycled  Resemble lysosome in size, mode of origin and structure Found in both animal and plant cells Carry several distinctive function according to cell type – Common property of both generating and degrading hydrogen peroxide (H2O2) – H2O2 highly toxic; eukaryotic cell protect themselves by decomposing H2O2 into H2O and O2 by catalase in peroxisomes An example of lysosome-based application Nano Lipid Particle for mRNA Vaccine Delivery  Vacuoles: The Multifunctional Compartments Structure Function Role in Homeostasis 1. Membrane (Tonoplast) 1. Storage 1. Turgor Pressure Regulation - Single membrane system - Water retention - Cell growth control - Selective transport proteins * Turgor pressure maintenance - Structural support - Aquaporins * Cell volume regulation - Guard cell function - Ion channels and pumps * Drought resistance - Movement responses - Nutrient storage 2. Internal Organization * Ions (Ca2+, K+, NO3-) 2. pH and Ion Balance - Aqueous matrix * Sugars - Cytoplasmic pH regulation - Stored compounds * Proteins - Ion concentration control - Protein aggregates * Secondary metabolites - Metal ion sequestration - Crystal structures - Toxic compound sequestration - Salt stress management * Heavy metals * Xenobiotics * Waste products 2. Cell Maintenance - pH regulation - Ion homeostasis - Protein turnover - Waste management 3. Defense Functions - Storage of defense compounds Alkaloids | Tannins | Protease inhibitors - Pathogen resistance - Herbivore deterrence  A membrane-bound organelle In eukaryotic cells and some bacterial cells In animal cells, temporary storage or transport E.g.: Food vacuoles; take up food particles by phagocytosis – phago: eating , cyte: vessel, osis; process – The cellular process of engulfing foreign particles (e.g. food, bacteria etc.) by the cell membrane, followed by a pinching-off process that form vacuoles  In plant cell: – Central Vacuole – Major role in maintenance of the turgor pressure of the cell – ‘pumped up’ with liquid – Pressing the cellular constituents out against the cell wall – \maintaining the turgor pressure of the characteristic of non- lignified plant tissue  Chloroplasts: The Photosynthetic Centers Structure Function Role in Homeostasis 1. Membrane Systems 1. Photosynthetic Processes 1. Energy Balance - Outer membrane - Light-dependent reactions - Glucose production * Permeable to small molecules * Photosystem I and II operation - ATP generation * Protection and structural support * Electron transport chain - NADPH supply * Transport protein channels * ATP synthesis - Energy storage as starch - Inner membrane * NADPH production * Selective permeability 2. Redox State Maintenance * Specialized transport systems - Carbon fixation (Calvin cycle) - ROS management * Protein import machinery * CO2 incorporation - Antioxidant production - Thylakoid membrane system * Sugar synthesis - Electron transport regulation * Grana stacks (appressed regions) * Starch production - Photoprotection mechanisms * Stromal lamellae (non-appressed regions) * Photorespiration * Light-harvesting complexes * Electron transport components 2. Additional Metabolic Roles - Fatty acid synthesis 2. Internal Compartments - Amino acid production - Stroma - Secondary metabolite synthesis * Site of carbon fixation - Nitrogen and sulphur assimilation * Contains DNA, ribosomes * Metabolic enzymes * Starch granules - Thylakoid lumen * Proton accumulation space * Water-splitting components * Plastocyanin transport  Larger than any other organelles except for the nucleus The site of photosynthesis Found in leaves and other photosynthetic tissue http://upload.wikimedia.org/wikipedia/commons/thumb/4/49/Plagiomnium_affine_laminazellen.jpeg/250px- Plagiomnium_affine_laminazellen.jpeg  Third membrane Surrounded by two Outer system membranes membrane Inner membrane Stroma lamellae Thylakoid Situate reactions that Stroma depend directly on solar Situate reactions involved energy in ‘fixing’ CO2 into organic Intermembrane space form, its subsequent reduction and Granum rearrangement into sugar (stack of thylakoids) molecules http://micro.magnet.fsu.edu/cells/chloroplasts/images/chloroplastsfigure1.jpg  Other functions: The process of reducing oxidised form of N (nitrate, NO3-) to ammonia (NH3) An e.g. of a class of plant organelles, plastids Other member – Chromoplasts: pigment-containing plastid, responsible for colour – Amyloplasts: starch storage THE NON-ORGANELLES  Plasma Membrane: The Dynamic Barrier Structure Function Role in Homeostasis 1. Lipid Bilayer Organization 1. Barrier Function A. Ion Balance Regulation B. Osmotic Balance - Phospholipid composition - Selective permeability 1. Ion Channel Control 1. Volume Regulation * Phosphatidylcholine - Ion gradients maintenance - Na+/K+ ATPase regulation - Osmolyte transport * Phosphatidylethanolamine - Cellular integrity * Membrane potential * Compatible solute * Phosphatidylserine - Protection from environment maintenance adjustment * Sphingomyelin * Cell volume control * Volume regulatory ↓ (VRD) 2. Transport Systems * Energy metabolism coupling * Volume regulatory ↑ (VRI) - Cholesterol distribution - Passive Transport - Calcium signalling - Water flux control * Membrane fluidity regulation * Simple diffusion * Ca2+ channel regulation * Aquaporin regulation * Microdomain formation * Facilitated diffusion * Second messenger systems * Osmotic stress response * Structural stability * Ion channels * Signal transduction * Cell volume maintenance - Active Transport 2. Membrane Proteins * Primary active transport 2. pH Regulation 2. Mechanical Stability - Integral Proteins (ATP-driven) - Proton pumps - Membrane tension control * Transmembrane proteins * Secondary active transport * Intracellular pH maintenance * Cytoskeleton interaction * Single-pass proteins * Bulk transport * Acid-base balance * Membrane reservoir * Multi-pass proteins (endo/exocytosis) * Metabolic regulation management * Lipid-anchored proteins - Bicarbonate transporters * Surface area regulation 3. Cell Signalling * pH buffering - Peripheral Proteins - Receptor functions * CO2 transport * Cytoskeletal attachments - Signal transduction * Acid-base homeostasis * Signal transduction components - Cell-cell communication * Regulatory proteins - Environmental sensing  Surrounds every cell, define the boundaries and ensure its contents retained Consists lipids, proteins and carbohydrates Fluid-mosaic model Functions, fluid – dynamic movement within membrane plane, mosaic: protein embedded  Consist of: Lipids Proteins – Phospholipids, – Glycoproteins – Glycolipids, – Transport proteins sphingolipids – Enzymes – Cholesterol – Receptors – ‘anchors’ Carbohydrates – Glycoproteins protein/lipid ratio vary; – Glycolipids amphiphatic (polar/non-polar)  Plasma membrane – The Lipids Phospholipids - a phosphate group attached to fatty acids - Phosphate group - hydrophilic and ‘head’ structure - Fatty acids - hydrophobic and ‘tails’ structure  Plasma membrane – The Lipids Glycolipids – Lipids with a carbohydrate attached – Function as cell- markers and also as a source of energy Cholesterol – Strengthen the cell membrane  Plasma membrane – The Proteins Glycoproteins: – Polypeptide with one or more carbohydrate side chains attached Types: – Transmembrane protein, peripheral protein and surface protein Roles: – Transport proteins, enzymes, hormone-receptors and ‘anchors’ for structural elements  Cell wall: The Protective Framework (Plant/Fungal/Bacterial) Structure Function Role in Homeostasis 1. Plant Cell Walls 1. Structural Support A. Pressure Regulation B. Environmental Protection - Primary Wall - Mechanical strength 1. Turgor Pressure Control Stress Response * Cellulose microfibrils - Shape maintenance - Wall extensibility - Temperature adaptation * Hemicellulose - Growth regulation * Growth regulation * Wall flexibility adjustment * Pectin - Pressure resistance * Pressure adaptation * Thermal protection * Structural proteins * Mechanical feedback * Stress signaling 2. Protection - Stress response - Chemical protection - Secondary Wall - Physical barrier * Osmotic challenge management * Barrier function * Additional cellulose layers - Pathogen defense * Mechanical stress adaptation * Selective permeability * Lignin deposition - Stress resistance * Growth adjustment * Toxin exclusion * Specialized modifications - Environmental protection 2. Structural Integrity 2. Bacterial Cell Walls 3. Cell-Cell Interaction - Wall composition modification - Peptidoglycan layer - Communication * Enzyme regulation - Teichoic acids (Gram-positive) - Adhesion * Polymer cross-linking - Outer membrane (Gram- - Recognition * Wall strengthening negative) - Transport regulation - Repair mechanisms - Surface proteins * Damage response * Remodeling processes 3. Fungal Cell Walls * Integrity maintenance - Chitin framework - β-glucans - Mannoproteins - Specialized polymers  Cell wall; rigid, cellulose-containing, that encases the plant cell (non-motile)  Confine and restrain the cell Chemical composition varies; – Always consists of microfibrils of cellulose embedded in a matrix of polysaccharides and small amount of proteins Neighbouring cells are connected by numerous plasmodesmata – cytoplasmic bridges – Channel is membrane- lined Source: Loix et al. 2017. Frontiers in plant Science 8  Cytoskeletons: The Cellular Framework Structure 1. Microfilaments (Actin Filaments) 2. Microtubules 3. Intermediate Filaments - Structure - Structure - Structure * G-actin monomers * α/β-tubulin dimers * Various protein families * F-actin polymers * Protofilaments * Non-polar assembly * Polarity * Dynamic instability * Stable structures * Dynamic assembly * Polarity * Tissue-specific expression - Associated Proteins - Associated Proteins - Associated Proteins * Motor proteins (myosin) * Motor proteins (kinesin, dynein) * Crosslinking proteins * Crosslinking proteins * MAPs (Microtubule Associated * Anchoring proteins * Capping proteins Proteins) * Regulatory factors * Regulatory factors * +TIP proteins * Regulatory factors  Cytoskeletons: The Cellular Framework Function Role in Homeostasis 1. Cellular Organization A. Structural Homeostasis B. Transport Homeostasis - Organelle positioning 1. Cell Shape Maintenance 1. Vesicular Traffic - Spatial organization - Dynamic remodelling - Organelle positioning - Cell shape maintenance * Tension regulation * Spatial organization - Structural support * Shape adaptation * Transport regulation * Mechanical response * Distribution control 2. Cell Movement - Stability control - Material transport - Cell migration * Scaffold maintenance * Cargo delivery - Muscle contraction * Organelle positioning * Pathway organization - Ciliary/flagellar movement * Structural integrity * Traffic regulation - Cytoplasmic streaming 2. Mechanical Response 2. Molecular Motor Function 3. Transport - Force distribution - Transport regulation - Vesicle trafficking * Stress fibre formation * Speed control - Organelle movement * Tension management * Directional movement - Chromosome segregation * Mechanical adaptation * Energy efficiency - Cytoplasmic organization - Shape recovery - Cargo selection * Deformation response * Specific targeting * Elasticity maintenance * Load distribution * Structure restoration * Transport priority  Portion of cell interior not occupied by the nucleus or other membrane-bound organelles Many cellular activities involved Consist of intricate three-dimensional array of interconnected filaments and tubules called the cytoskeleton : the cytoskeletal network Establish and maintain cellular shape  Important roles in cell movement and cell division – E.g. contraction of muscles cells, beating of cilia and flagella, movements of chromosomes and locomotion of the cell Positioning and actively moving organelles within the cytoplasm – Same for ribosomes and enzymes Water also influence the cytoskeleton dynamics 3 major structural elements – Microtubules – Microfilaments (actin filaments) – Intermediate filaments  Cytoskeleton: Microtubules Role in motiliy – E.g.: axoneme of cilia and flagella Role in chromosome movement – Form spindle fibers needed to separate chromosomes prior to cell division Role in organisation of the cytoplasm – the polarity and overall shape of the cell – Spatial disposition of its organelles – Distribution of microfilaments and intermediate filaments Examples of diverse role: – asymmetric shapes of animal cells, – the plane of cell division in plant cells, – the ordering of filaments during muscle development and – the positioning of mitochondria around the axoneme of motile appendages  Straight, hollow cylinders Wall consists of longitudinal arrays of protofilaments, usually 13 arranged side by side around the hollow centre, or lumen Each protofilament is a linear polymer of tubulin molecules – Dimeric protein; α-tubulin and b- tubulin – Oriented in the same direction, i.e. all subunits face the same end in microtubule, hence uniform orientation – polarity  Role in the contractile fibrils of muscle cells Form connections with the plasma membrane – Influence locomotion, – amoeboid movement, – cytoplasmic streaming (a cyclic flow of cytoplasm seen in variety of algal, animal and plant cells) Produce cleavage furrows that divide the cytoplasm of animal cells after chromosomes have been separated by the spindle fibers Contribute importantly to the development and maintenance of cell shape  Cytoskeleton: Microfilaments Polymers of actin – Synthesised as monomer called G-actin (G = globular) – G-actin monomers polymerise reversibly into long, double- helical strands of F-actin (F for fibrous) Consists of two strands of F-actin wrapped around each other to form a double helix Polar structures, similar to microtubules – Influence the direction of elongation and disassembly  Cytoskeleton: Intermediate Filaments Most stable and the least soluble constituents – Scaffold that supports the entire cytoskeletal network – A tension-bearing role Composition differ from tissue to tissue – Grouped into 5 classes – IFs serves as a diagnostic tool for medicine https://www.ncbi.nlm.nih.gov/pmc/articles/P MC6562751/  Have a central rodlike segment, similar to all 5 classes – The N-terminal and C- terminal segments differ greatly in size and sequence Basic structural unit is a dimer of two intertwined IF polypeptides tetramer Two dimers align laterally to form a tetrameric protofilament Protofilament interact with each other to form an IF – Up to 8 protofilaments – Joined end to end in overlapping manner  Ribosomes: The Protein Factories Structure Function Role in Homeostasis 1. Prokaryotic Ribosomes (70S) 1. Protein Synthesis A. Protein Homeostasis B. Metabolic Homeostasis - Small subunit (30S) - Translation initiation 1. Translation Control 1. Energy Balance * 16S rRNA - Elongation - Protein synthesis regulation - Translation efficiency * 21 proteins - Termination * Rate adjustment * ATP utilization * Decoding center - Quality control * Quality control * Energy conservation * Energy efficiency * Resource allocation - Large subunit (50S) 2. Regulatory Roles - Stress response - Metabolic coupling * 23S and 5S rRNA - Translation regulation * Heat shock response * Energy sensing * 31 proteins - Protein folding * Unfolded protein response * Pathway coordination * Peptidyl transferase center - Cellular stress response * Metabolic adaptation * Resource management - Gene expression control 2. Eukaryotic Ribosomes (80S) 2. Protein Quality Control 2. Stress Adaptation - Small subunit (40S) - Error detection - Response coordination * 18S rRNA * Proofreading * Stress protein synthesis * 33 proteins * Mistake prevention * Repair mechanism * mRNA binding site * Quality assurance activation - Response mechanisms * Protective measures - Large subunit (60S) * Protein folding * 28S, 5.8S, and 5S rRNA * Degradation signaling * 47 proteins * Repair processes * Exit tunnel  Involved in protein synthesis from amino acids Not a true organelle Found in both eukaryotic and prokaryotic cells – Difference in sizes 25nm-30nm in eukaryotic cells, 20 nm is prokaryotic cells – 350,000 ribosomes in a bacterial cell Sedimentation coefficient – Express sizes of small particles – How rapidly the particle sediments in an ultracentrifuge – Svedberg units (S) – Eukaryotic cell; 80S and prokaryotic cell; 70S  2 subunits with differing sizes – In Eukaryotic cell, large and small ribosomal subunits are 60S and 40S, respectively – In Prokaryotic cell; 50S and 30S respectively – Both are synthesised and assembled separately in the cell Eukaryotic cells have more ribosomes than Prokaryotic cells Can also be found in mitochondria and chloroplast – Differ in size and composition from ribosomes in the cytoplasm – Very similar to those found in bacteria and blue-green algae By RIT RAJARSHI - Own work, CC BY-SA 4.0 THE OTHERS Structural components: Cell Coats Structural components: Cell-to-cell junction Strengthen the cell surface and hold cells together Important in cell-cell recognition, due to the unique molecular structure of carbohydrates Intercellular connections: – Gap junctions; transfer of material between the cytoplasms of adjacent cells – Tight junctions; hold cells together and block any transport of substances – Desmosomes; Disc-shaped type of specialised adhesive junction to give structural integrity and function as a unit Example of Cell-to-cell junction  THANK YOU! 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