Cell Biology And Genetics Short Notes PDF

**🌿 Living Organisms: Unicellular and Multicellular Organisms** **Unicellular Organisms** - Known as single-celled organisms (most primitive form of organisms) - Main groups of unicellular organisms are: - Bacteria - Archaea - Protozoa - Algae - Fungi -...

**🌿 Living Organisms: Unicellular and Multicellular Organisms** **Unicellular Organisms** - Known as single-celled organisms (most primitive form of organisms) - Main groups of unicellular organisms are: - Bacteria - Archaea - Protozoa - Algae - Fungi - Fall into two general categories: prokaryotic and eukaryotic organisms (based on cellular organization) - Oldest form of life, possibly existing 3.8 billion years ago - Mostly microscopic (cannot be seen by naked eyes) and categorized as microorganisms - Examples: - Bacteria like Escherichia coli, Mycobacteria, Bacillus sp. - Protozoans like Amoeba, Paramecium - Algae like Chlorella sp, Chlamydomonas, Diatoms, Euglenophyta, Dinoflagellates - Fungi like yeast **Multicellular Organisms** - Consist of many cells specialized to do different functions for maintaining the complexity of the organism - Most bacteria are unicellular, but some bacterial species are multicellular like Myxobacteria - Some species of cyanobacteria are also multicellular like Spirogyra - Most eukaryotic organisms are multicellular - Multicellular organisms have well-developed body structure and also have specific organs for specific functions - Most well-developed plants and animals are multicellular - All animals are eukaryotic in nature and most of them are multicellular - Examples of unicellular plants are Chlamydomonas (green algae), Chlorella (single-celled green algae) - Acetabularia is the largest unicellular green algae, reaching up to 0.5 to 10 cm in length **Differences between Unicellular and Multicellular Organisms** **Unicellular Organisms** **Multicellular Organisms** ------------------------ ----------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------ Body Structure Made up of single cell Made up of numerous cells Division of Labour May be at cellular level At the organelle level, tissue, organ, and organ system level Operational Efficiency Low level of operational efficiency High degree of operational efficiency Cell Specialization A single cell carries out all life processes Different cells are specialized to perform different functions Cell Exposure The cell body is exposed to the environment on all sides Only outer cells are specialized to face the environment, inner cells are devoted to other functions Injury or Death Injury or death of some cells does not affect the whole organism An injury to the cells can cause death of the organism Cell Size Cell body cannot attain a large size due to the limit imposed by surface area to volume ratio A multicellular body can attain a large size by increasing the number of small cells Lifespan Lifespan is long due to limited load of work for each cell type Lifespan is short due to heavy load of work Regeneration Capacity of regeneration decreases with increasing specialization Power of division is not lost **🌱 Common Features of Unicellular and Multicellular Organisms** - All organisms must accomplish the same functions: - Uptake and processing of nutrients - Excretion of wastes - Response to environmental stimuli - Reproduction - Among others **🔬 Cell: Definitions; Basic Features; Hierarchy** **What is a Cell?** *A cell is a basic structural, functional, and biological unit of all living organisms (unicellular and multicellular).* - Term originated from Latin Word Cellula or Cellus meaning small room or little space - Discovered by Robert Hook in 1665 while studying cork under microscope - Often called building block of life - Study of cell is called cell biology **Cell Theory** - Formulated by Matthias Schleiden and Theodor Schwann in 1838-1839 - Basic principles: 1. All living organisms are composed of one or more cells. 2. The cell is the most basic unit of life. **Essential Features of Cell Theory** - Cells are fundamental units of structure and function in all living organisms. - Cells are physiological units of living organisms. - Cell is the smallest unit of life. All activities of living organisms are the outcome of the activities of its constituent cells. **Exceptions to the Cell Theory** - Viruses are the exception to cell theory because they are made up of proteins and one of the nucleic acid (DNA or RNA), lack protoplasm. - Bacteria lack well-organised nucleus. Nuclear membrane, nucleolus, and nucleoplasm are also absent. **📈 Cellular Hierarchy** - Organism (Human) - Organ-system (Respiratory system) - Organ (Lung) - Tissue (Epithelial tissue, interstitial connective tissue, and lymphoid tissue) - Cells - Cell (Monocyte) **📊 Diversity in Cell Size and Shape** - Diversity exists in the cells as far as size, shape, and number is concerned. - Most cells are microscopic, visible only under the high power of microscope. - Micrometre is usually used to measure the cell-size. - Majority of cells are 5-15 micrometer in size \[RBCs are 5-8 micrometer\]. - Nerve cells are the longest (1-2 m in humans). - Egg of Ostrich is about 175 mm x 135 mm. - In human body, cell size ranges between 3-4 micron (Leukocytes) to over 90-100 cm (nerve cells). - The nucleo-cytoplasmic ratio and surface area are the two important factors that restrict the cell size. - The shape of the cells is related to their functions. Some blood cells and Amoeba change their shape to perform different functions.\#\# Cell Morphology: Cell Size and Shape 📏 Cells come in various shapes and sizes, influenced by several factors. The shape and size of a cell are determined by its function and the environment it inhabits. **Factors Influencing Cell Size and Shape** - **Surface Area to Volume Ratio**: The ratio of a cell\'s surface area to its volume affects its shape and size. A cell\'s surface area must be sufficient to accommodate its internal contents. - **Nucleocytoplasmic Ratio**: The ratio of the nucleus to the cytoplasm is crucial for a cell\'s function. The nucleus must be able to regulate the cytoplasmic activities. - **Rate of Cellular Activity**: Cells with high metabolic rates tend to be smaller and have a higher surface-volume ratio. - **Cell Association**: In multicellular organisms, cell-to-cell attachment plays a significant role in determining cell shape and structure. **Cell Types Based on Morphology 🌿** Cells can be broadly classified into three types based on their morphology: - **Prokaryotic Cells**: These cells lack a true nucleus and membrane-bound organelles. Example: Bacterial cells. - **Eukaryotic Cells**: These cells have a true nucleus and membrane-bound organelles. Example: Plant and animal cells. - **Mesokaryotic Cells**: These cells have a nucleus surrounded by a membrane, but the DNA is not associated with histones. Example: Dinoflagellates, Marine algae. **Structure of Eukaryote and Prokaryote Cells 📊** **Criteria** **Prokaryotes** **Eukaryotes** ---------------------------- ------------------------------------- --------------------------------- Type of Cell Always unicellular Unicellular and multicellular Cell Size 0.1-5.0 μm in diameter 10-100 μm in diameter Cell Wall Usually present, chemically complex When present, chemically simple Nucleus Absent, nucleoid region present Present Ribosomes Smaller, circular Larger, linear DNA arrangement Circular Linear Membrane-bound organelles Absent Present Plasmids Present Rarely found Lysosome Absent Present Cell division/Reproduction Binary fission/Asexual Sexual and asexual **Essential Features of Mesokaryotic Cells 🔍** *Mesokaryotic cells are medium-sized, with a nucleus surrounded by a membrane. They lack a cell wall but have a pellicle or theca. The cell membrane is present, and membrane-bound organelles like mitochondria and plastids are found in the cytoplasm.* - Cell size: Medium-sized, between prokaryotic and eukaryotic cells - Cell wall: Absent, but has a pellicle or theca - Nucleus: Well-organized, surrounded by a membrane - Membrane-bound organelles: Present, including mitochondria and plastids - Ribosomes: 80s type - Histone protein: Absent - Chromosome: Present, formed with acidic proteins - Cell division: Amitosis - Flagella: Present, consisting of filaments **Plant Cell Wall Structure 🌱** The plant cell wall is composed of three layers: 1. **Middle Lamella**: The outermost layer, containing pectins that aid in cell adhesion. 2. **Primary Cell Wall**: The middle layer, formed between the middle lamella and plasma membrane in growing plant cells. It is composed of cellulose microfibrils, hemicellulose fibers, and pectin polysaccharides. 3. **Secondary Cell Wall**: The innermost layer, formed between the primary cell wall and plasma membrane in some plant cells. It is composed of cellulose, hemicellulose, and lignin. **Plasmodesmata 🌿** *Plasmodesmata are cytoplasmic bridges that connect adjacent plant cells, allowing for the exchange of molecules and communication signals.* - Structure: - Plasma membrane lining (plasmalemma) - Cytoplasmic sleeve - Desmotubule - Functions: - Transport of ions and molecules - Cell-to-cell communication - Regulation of growth and development - Types: - Primary plasmodesmata: Formed during cell division - Secondary plasmodesmata: Formed de novo, aided by the enzyme cytokinin **Bacterial Cell Wall Structure 🧬** The bacterial cell wall is composed of peptidoglycan, a polymer of sugars and amino acids. - **Peptidoglycan**: A unique molecule found in bacterial cell walls, composed of sugars and amino acids. - **Gram Staining**: A method used to identify bacterial cell walls, which can be either Gram-positive or Gram-negative.\#\# 🌟 Bacterial Cell Wall Structure and Function 🌟 **Cell Wall Composition** The bacterial cell wall is composed of two main components: - **Peptidoglycan**: a glycopeptide molecule that provides rigidity and shape to the cell - **Teichoic acids**: a type of glycol-polymer that helps maintain the cell wall structure and provides protection against environmental stressors **Peptidoglycan Structure** Peptidoglycan is composed of alternating units of: - **N-Acetyl Muramic acid (NAM)** - **N-Acetyl Glucosamine (NAG)** These units are linked together by a glycosidic bond (-1, 4 linkages), forming a lattice-like structure. **Teichoic Acids** Teichoic acids are a diverse family of cell surface glycol-polymers that contain phosphodiester-linked polyol repeat units. They are found in the outer layer of Gram-positive bacteria and play a role in: - Maintaining cell shape - Regulating ion transport - Providing protection against environmental stressors **Gram-Positive Bacterial Cell Wall** The Gram-positive bacterial cell wall is thick (20-80 nm) and composed of: - **Peptidoglycan**: 40-80% of the dry weight - **Teichoic acids**: present in the outer layer - **Lipoteichoic acids**: covalently linked to the lipid in the cytoplasmic membrane **Gram-Negative Bacterial Cell Wall** The Gram-negative bacterial cell wall is thin (2-7 nm) and composed of: - **Peptidoglycan**: 10% of the dry weight - **Lipopolysaccharides (LPS)**: present in the outer membrane - **Porins**: form passive pores that regulate the entry and exit of molecules **Lipopolysaccharides (LPS)** LPS is a complex molecule composed of: - **O-antigen**: a repetitive glycan polymer attached to the core oligosaccharide - **Core**: contains an oligosaccharide component that attaches directly to lipid A - **Lipid A**: a phosphorylated glucosamine disaccharide decorated with multiple fatty acids **Functions of Gram-Negative Bacterial Cell Wall** - **Porins**: regulate the entry and exit of molecules - **LPS**: acts as an endotoxin and provides protection against environmental stressors - **Outer membrane**: forms a barrier to lysozyme and other toxic microbial agents **Bacterial Gram Staining Protocol** The Gram stain is a differential staining procedure that differentiates organisms according to cell wall structure. **Step** **Description** -------------------- ---------------------------------------------------------------- 1\. Primary stain Apply crystal violet to a heat-fixed smear 2\. Mordant Add Gram\'s iodine 3\. Decolorization Rapidly decolorize with alcohol, acetone, or a mixture of both 4\. Counterstain Counterstain with safranin **Plasma Membrane Structure and Function** The plasma membrane is a dynamic fluid structure that forms the external boundary of cells. *\"The plasma membrane is a selectively permeable membrane that regulates the entry and exit of materials in and out of the cell.\"* **Components of the Plasma Membrane** **Component** **Location** **Function** --------------------- ------------------------------------------------------------ -------------------------------------------- Phospholipid Main fabric of the plasma membrane Provides structure and fluidity Cholesterol Between phospholipids and phospholipid bilayers Regulates fluidity and stability Integral proteins Embedded within phospholipid layers Regulate transport and signaling Peripheral proteins Inner or outer surface of the phospholipid bilayer Regulate transport and signaling Carbohydrates Attached to proteins/lipids on the outside of the membrane Provide cell-cell recognition and adhesion **Fluid Mosaic Model** The fluid mosaic model was proposed by S.J. Singer and Garth L. Nicholson in 1972. *\"The fluid mosaic model describes the plasma membrane as a mosaic of components, including phospholipids, proteins, cholesterol, and carbohydrates, that give the membrane a fluid character.\"* **Timeline of Models to Study the Structure and Function of Plasma Membrane** **Model** **Scientist** **Year** -------------------- ------------------------ ---------- Lipid Nature Overton 1890 Lipid Monolayer Langmuir 1905 Lipid Bilayer E. Gorter & F. Grendel 1926 Unit Membrane Robertson 1960 Fluid Mosaic Model Singer and Nicholson 1972 The plasma membrane contains three classes of lipids: - **Phospholipids**: Examples include Phosphatidylcholine, Phosphatidylserine, and Phosphatidylethanolamine. These lipids are important for cell growth and division. - **Glycolipids**: Examples include Cerebroside and Gangliosides. These lipids are involved in cell recognition and adhesion. - **Sterols**: Examples include Cholesterol and Stigmasterol. These lipids are important for cell growth and viability, and regulate the fluidity and permeability of the membrane. **Lipid Rafts 🌊** Lipid rafts are membrane microdomains enriched with cholesterol and glycosphingolipids, along with proteins. They are involved in: - Signal transduction - Cholesterol trafficking - Endocytosis There are two types of lipid rafts: **Type** **Description** ------------------ --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Caveolar** Flask-shaped invagination with caveolin protein, found in brain, micro-vessels of the nervous system, endothelial cells, astrocytes, oligodendrocytes, Schwann cells, dorsal root ganglia, and hippocampal neurons. **Non-caveolar** Planar lipid rafts found in continuation with plasma membrane, containing flotillin proteins, and found in neurons. **Lipid Aggregates 🌴** Lipid aggregates can interact with water in three forms: - **Micellar structure**: Small spherical structure formed by fatty acid side chains (\< 20 nm) - **Lipid sheets**: Two lipid monolayers forming sheets - **Liposomes**: Closed, solvent-filled vesicles **Function of Lipids in the Plasma Membrane 💡** *Lipids are used for energy storage, and function primarily as anhydrous reservoirs for the efficient storage of caloric reserves.* The matrix of cellular membranes is formed by polar lipids, which consist of a hydrophobic and a hydrophilic portion. The inclination of the hydrophobic moieties to self-associate, and the tendency of the hydrophilic moieties to interact with aqueous environments and with each other, is the physical basis of the formation and stability of membranes. **Plasma Membrane Proteins 🌈** Membrane proteins are responsible for most of the dynamic processes in the plasma membrane. They are classified into two main categories: - **Peripheral proteins**: Bound by electrostatic or hydrogen bonds to the outer layer of the membrane, with no interaction with the hydrophobic core of the lipid bilayer. - **Integral proteins**: Held in the lipid bilayer very tightly, and cannot be released via mild extraction process. **Characteristics of Plasma Membrane Proteins 📊** **Property** **Peripheral Proteins** **Integral Proteins** --------------------------------------------- ------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------- Treatment Mild treatment: extreme pH change, hydrophobic bond breaking agents, exposure to ionic solvents Detergents, organic solvents Association with lipids Usually soluble, free of lipids Usually associates with lipids when solubilized (lipid bilayer also gets disrupted) Solubility after dissociation from membrane Soluble and molecularly dispersed in neutral aqueous buffer Usually insoluble or aggregated in neutral aqueous buffer Examples Spectrin, Ankyrin Glycophorin, Band 3 protein **Classification of Membrane Proteins According to Function 📈** Membrane proteins are classified into three main categories: - **Transport proteins**: Carrier or channel proteins - **Catalytic proteins**: F0F1 ATP synthase in the inner membrane of mitochondria - **Structural proteins** **Transport Proteins 🚚** Transport proteins are classified into two main categories: - **Uniporters**: Transport a single type of molecule - **Co-transporters**: Transport two or more types of molecules **Channel Proteins 🌉** Channel proteins transport solutes down the concentration gradient. They work based on specific signals, including: - Voltage-gated channels - Ligand-gated channels **Biological Importance of Membrane Proteins 🌟** Membrane proteins are interesting scientifically because of their key roles in controlling the processes of life. They are involved in: - Signal transduction - Ion transport - Cell adhesion - Cell recognition - Metabolic processes **Fluid Mosaic Model of Plasma Membrane Structure 🌊** The fluid mosaic model of plasma membrane structure was proposed by Jonathan Singer and Garth Nicolson in 1972. It describes the plasma membrane as a two-dimensional fluid in which proteins are inserted into lipid bilayers. **Postulates of the Fluid Mosaic Model 📝** - Lipids and integral proteins are disposed in a kind of mosaic arrangement. - The biological membrane is a quasi-fluid structure in which both lipids and integral proteins are able to perform translational movements within the bilayer. **Plasma Membrane Fluidity 🌊** Membrane fluidity refers to the fact that lipids have considerable freedom of lateral or transverse movements. **Factors Affecting Membrane Fluidity 🌡️** - Temperature - Lipid composition **Effect of Temperature on Membrane Fluidity ❄️** - Increase in temperature increases membrane fluidity (free-flowing, less viscous) - Decrease in temperature results in the membrane forming a gel-like structure **Effect of Lipid Composition on Membrane Fluidity 🌴** - Lipids with short/unsaturated fatty acyl chains undergo phase transition at lower temperature than lipids with long or saturated fatty acids. - Cholesterol is a major determinant of membrane fluidity. **Bio-techniques Used to Visualize/Study Plasma Membrane 🔍** - Hydropathy plots: Identify the number of alpha-helical protein residues in integral proteins.\#\# Cell Morphology 🧬 **Cytoplasm Basics 🌊** The cytoplasm is a rich, semifluid material present in cells of organisms that are closed off by the cell membrane. It contains various cytoplasmic components, such as: - Cytosol - Cytoplasmic organelles - Inclusion bodies ***Cytoplasm**: The cellular component inside the cell between the cell membrane and the nuclear envelope of the nucleus.* **Theories on Physical Nature of Cytoplasm 🤔** - **Sol-Gel Form**: Cytoplasm is known to behave similarly to that of a sol-gel. A sol-gel is a mixture of molecules that sometimes act like a liquid (sol) and other times acts like a solid (gel) integrated network. - **Glass-like Behavior**: Cytoplasm sometimes have glass-like behavior as well. This is when the cytoplasm acts as though it is approaching the glass transition as a glass-forming liquid. - **Non-Brownian Motion of Cytoplasmic Components**: Constituents of cytoplasm move as a separate entity. These are theorized to be channeled by motor proteins which assist with this non-Brownian motion within the cells. **Structural Features and Composition of Cytoplasm 🌈** **Component** **Description** ------------------------ ----------------------------------------------------------------------------------------------- Cytosol The liquid-like portion of the cytoplasm, making up about 70% of the cytoplasm\'s composition Cytoplasmic Organelles Specialized structures within cells that carry out specific tasks for the cell Inclusion Bodies Small, insoluble particles suspended in the cytosol **Parts and Function of Cell Cytoplasm: Cytosol 💧** - **Cytosol**: The part of the cytoplasm that is the liquid-like portion, making up about 70% of the cytoplasm\'s composition. - **Functions**: - Site of many chemical reactions - Involved in osmoregulation and cell signaling - Generates action potentials in cells, such as nerve and muscle cells **Parts and Function of Cell Cytoplasm: Cell Organelles 🏗️** - **Organelles**: Specialized structures within cells that carry out specific tasks for the cell. - **Examples**: - Nucleus: contains genetic material and controls cellular activities - Chloroplasts: contain green pigments essential for photosynthesis - Mitochondria: synthesize energy for multifarious metabolic processes - Endoplasmic Reticulum: involved in lipid synthesis, carbohydrate metabolism, and intracellular transport **Parts and Function of Cell Cytoplasm: Cytoplasmic Inclusions 📦** - **Cytoplasmic Inclusions**: Small, insoluble particles suspended in the cytosol. - **Examples**: - Lipid droplets: store lipids like fatty acids - Cytoplasmic inclusions in plant cells: store excess glucose during photosynthesis **Overall Functions of Cytoplasm 🌟** - **Support and Structure**: aids with cell structure and turbidity, keeping organelles in place - **Protection**: protects the cell and its components from damage - **Storage**: contains materials such as storage units and enzymes essential for many metabolic activities - **Transport**: assists with the transport of organelles and cytoplasmic inclusions through cytoplasmic streaming **Cytoplasmic Streaming 🌊** - **Cytoplasmic Streaming**: the movement of cytoplasm within the cell membrane, acting as a transportation system to get necessary components to the places they need to be. **Cell Organelles: Definition and Functions 📚** - **Cell Organelles**: cellular components in a cell that are enclosed in structures/compartments, coordinating and functioning efficiently for the normal functioning of the cell. - **Classification**: - Organelles without membrane: Ribosomes, Cytoskeleton - Single membrane-bound organelles: Vacuole, Lysosome, Golgi Apparatus, Endoplasmic Reticulum - Double membrane-bound organelles: Nucleus, Mitochondria, Chloroplast **Nucleus 🌐** - **Nucleus**: a double membrane-bound organelle located centrally in a eukaryotic cell, enclosing the DNA, the genetic material. - **Structure and Characteristics**: - Largest and most prominent organelle in the cell - Accounts for almost 10% of the volume of the entire cell - Average diameter of the nucleus is approximately 6 μm in size - Shape is usually spherical or oblong **Parts and Function of Nucleus 📊** - **Nuclear Envelope and Nuclear Pores**: surrounding the nucleus, made of a phospholipid bilayer, containing tiny openings called nuclear pores. - **Perinuclear Space**: a fluid-filled region between the inner and outer nuclear membranes. - **Functions**: - Controls and coordinates the functioning of the entire cell - Contains genetic material and regulates gene expression\#\# Nucleus 🌐 **Nuclear Envelope** The nuclear envelope is a selectively permeable membrane that separates the nuclear content from the cytoplasm. It regulates the flow of molecules into and out of the nucleus through nuclear pores. **Nuclear Lamina 🌈** The nuclear lamina is a meshwork of protein filaments organized in a net-like fashion that lines the inner nuclear membrane. It is composed of intermediate filament proteins called lamins. ***Definition:** Lamins are a type of intermediate filament protein that provides structural support to the nuclear envelope.* **Nucleoplasm 💧** Nucleoplasm, also known as karyoplasm, is a gelatinous substance found inside the nucleus. It is composed mainly of water with dissolved salts, enzymes, and suspended organic molecules. ***Functions:*** - *Supports the nuclear envelope, maintaining the overall shape and structure of the nucleus.* - *Protects the nuclear content by providing a cushion around the nucleolus and the chromosome.* - *Provides a medium through which enzymes and fragments of genetic materials (DNA or RNA) can be transported throughout the nucleus.* **Nucleolus 🔍** The nucleolus is a non-membrane bound dynamic body that disappears in the late prophase and reappears in the telophase stage of cell division. It is the site of transcription of ribosomal RNA and assembly of ribosomes. ***Structure:*** - *Fibrillar centers: containing rRNA genes in the form of partly condensed chromatin.* - *Dense fibrillar component: surrounds the fibrillar center, which contains RNA molecules in the process of transcription.* - *Granular regions: contains mature ribosomal precursor particles (pre-ribosome assembly).* **Chromatin and Chromosome 📚** Chromatin is an organized structure of DNA and protein found in the nucleus of eukaryotic cells. Chromosomes are highly condensed and extended DNA. ***Definition:** Chromatin is less condensed and extended DNA, while chromosomes are highly condensed and extended DNA.* **Chromatin** **Chromosome** ------------------ ---------------- ------------------ **Condensation** Less condensed Highly condensed **Extension** Extended Extended **Appearance** Light-staining Darkly stained **Centromere 🔗** The centromere is the constricted region of linear chromosomes, usually located exactly in the center of the chromosome. ***Functions:*** - *Serves as the site of association of sister chromatids.* - *Serves as the attachment site for microtubules of the mitotic spindle.* **Telomere 🔝** Telomeres are specialized structures that cap the ends of eukaryotic chromosomes. ***Composition:** Long array of short, tandemly repeated sequences with a high G content in the strand with its 3\' end.* **Origin of Replication 🔁** The origin of replication is a particular sequence in a chromosome at which replication is initiated. ***Note:** One chromosome contains multiple origins of replication.* **Ribosomes 🍴** **Ribosomes (Cell Protein Factories) 🏭** Ribosomes are large ribonucleoproteins that translate genetic information stored in the messenger RNA into polypeptides. ***Composition:** rRNA and r-proteins.* **Prokaryotic Ribosomes** **Eukaryotic Ribosomes** ---------------- --------------------------- -------------------------- **Size** 70S 80S **rRNA** 16S, 23S, 5S 18S, 5.8S, 28S **r-proteins** L and S L and S **Biogenesis of Ribosomes 🔩** Ribosomes are not self-replicating particles. The synthesis of various components of ribosomes, such as rRNAs and proteins, is under genetic control. ***Process:*** - *Synthesis of 18S, 5.8S, and 28S RNAs in the nucleolus.* - *Synthesis of 5S RNA and ribosomal proteins in the cytoplasm.* - *Assembly of ribosomal subunits in the nucleolus.* - *Transport of ribosomal subunits to the cytoplasm.* **Functions of Ribosomes 📈** Ribosomes take part in protein synthesis. ***Functions:*** - *Translation of genetic code.* - *Protection of mRNA strand from nucleases.* - *Protection of nascent polypeptide chains from protein digesting enzymes.* **Ribosomal Protein Targeting and Translocation 🚪** The fate of proteins synthesized by cytosolic ribosomes depends on their amino acid sequence, which can contain specific targeting or sorting signals. ***Types of Protein Translocation:*** - *Gated transport: between the cytosol and nucleus.* - *Transmembrane transport: across a membrane from the cytosol into an organelle.* - *Vesicular transport: between organelles through transport vesicles.* **Endoplasmic Reticulum 📦** **Endoplasmic Reticulum: Basics 📚** The endoplasmic reticulum (ER) is a large organelle made up of an extensive network of closed and flattened membrane-bound structures. ***Functions:*** - *Protein synthesis and transport.* - *Lipid synthesis and transport.* - *Calcium storage and release.\#\# 🌐 Structure of Endoplasmic Reticulum* The **endoplasmic reticulum (ER)** is a network of membranous sheets and tubules that begin near the nucleus and extend across the cell. It creates, packages, and secretes many of the products created by a cell. **Definition of Endoplasmic Reticulum** *The endoplasmic reticulum is a type of organelle found in eukaryotic cells that is involved in several cellular processes, including protein synthesis, folding, and transport, as well as lipid synthesis and detoxification.* **Characteristics of Endoplasmic Reticulum** - The ER is a dynamic structure that can account for more than 50% of the cell in some cases. - It is composed of two types of regions: **rough endoplasmic reticulum (RER)** and **smooth endoplasmic reticulum (SER)**. - The RER is studded with ribosomes on its surface, while the SER is not. - The ER is contiguous with the outer nuclear membrane and interacts with other organelles, such as the Golgi apparatus. **📦 Functions of Endoplasmic Reticulum** **Rough Endoplasmic Reticulum (RER)** - **Protein synthesis**: The RER is the primary location of protein production in the cell. - **Protein folding**: The RER is responsible for folding proteins into their proper conformation. - **Protein modification**: The RER is involved in the modification of proteins, including the addition of carbohydrates (N-linked glycosylation), the formation of disulfide bonds, and the proper folding of proteins. **Smooth Endoplasmic Reticulum (SER)** - **Lipid synthesis**: The SER is the primary location of lipid synthesis in the cell. - **Detoxification**: The SER is involved in the detoxification of xenobiotics. - **Calcium regulation**: The SER acts as a calcium store for the cell. **📊 Comparison of RER and SER** **RER** **SER** ---------------- ---------------------------------------------- --------------------------------------------------------- **Location** Near the nucleus Near the periphery of the cell **Ribosomes** Present Absent **Function** Protein synthesis, folding, and modification Lipid synthesis, detoxification, and calcium regulation **Appearance** Rough Smooth **📈 Essential Functions of Endoplasmic Reticulum** **Protein Synthesis and Folding** - Proteins synthesized in the RER are often destined for secretion. - Proteins are folded within the ER and then moved into the Golgi apparatus for further processing. - Some proteins remain within the endomembrane system itself, such as chaperone proteins that assist in the folding of other proteins. **Lipid Synthesis** - The SER plays an important role in cholesterol and phospholipid biosynthesis. - The SER is enriched in enzymes involved in sterol and steroid biosynthetic pathways. - The SER is necessary for the synthesis of steroid hormones. **Calcium Store** - The SER acts as a calcium store for the cell. - Calcium ions are involved in the regulation of metabolism in the cell. - The ER can interact with the plasma membrane and use Ca2+ for signal transduction and modulation of nuclear activity.