Introduction to Cell Biology and Cell-I Dr Shahid Akhund.pdf

Introduction to Cell biology & The Cell I Dr. Shahid Akhund MBBS, M Asst &Eval, PhD [email protected] BG 085.D Ext: 8912 Slides are shared by Prof K S Mohammad  Learning Objectives (Cell I and II) ...

Introduction to Cell biology & The Cell I Dr. Shahid Akhund MBBS, M Asst &Eval, PhD [email protected] BG 085.D Ext: 8912 Slides are shared by Prof K S Mohammad  Learning Objectives (Cell I and II)  Define what is cell biology and relate its importance in medical sciences  Define what is cell and differentiate it’s 2 main components  Describe the ultra structures and functions of the plasma membrane and the various cytoplasmic organelles, and inclusions  Relate the structure with the functions of cytoskeleton  Describe the nuclear structure including the nuclear envelopes and nuclear pores, and functions  Distinguish between the euchromatin and heterochromatin  Describe the major steps in cell cycle and cell division Cell Biology Cell biology, also known as cytology, is the branch of biology that studies the structure, function, and behavior of cells. It examines cells in terms of their physiological properties, metabolic processes, signaling pathways, life cycle, interactions with their environment, and their overall role in the organism. Key Areas: Cell structure and organelles Cell function and processes (e.g., cell division, energy production) Cell communication and signaling Cell growth, development, and death Importance of Cell Biology in Medical Sciences Foundation of Medicine: Understanding cellular processes is crucial for comprehending how diseases develop, progress, and respond to treatments. Disease Diagnosis and Treatment: Cell biology provides insights into the molecular mechanisms of diseases like cancer, diabetes, and infections, aiding in the development of targeted therapies and diagnostics. Regenerative Medicine: Research in cell biology underpins the development of stem cell therapies and tissue engineering, offering potential cures for degenerative diseases. Pharmacology: Cell biology helps in understanding how drugs interact with cells, facilitating the design of effective and safe medications.  Cell, Tissue and Organ  During development, cells and their associated matrix become functionally specialized and give rise to fundamental types of tissues with characteristic structural features  Organs are formed by an orderly combination of these tissues, and their precise arrangement allows the functioning of each organ and of the organism as a whole The Cell I  What is the Cell?  It is the basic structural and Cytoplasm functional units of all multicellular organisms  The average adult human body consists of nearly 40 trillion cells Nucleus The cell can be divided into two major compartments The cytoplasm The nucleus  Cell Cytoplasm Cytoplasm  The cytoplasm is the part of the cell located outside the nucleus  It contains organelles (“little organs”) and inclusions in an aqueous gel called the cytoplasmic matrix The cytoplasmic matrix consists of inorganic components Organic components carbohydrates, ions (Na!, K!, Ca2!) lipids, proteins, and RNAs.  The Plasma (Cell) Membrane  It is the interface of the cell with its environment  Composed of an amphipathic lipid bilayer containing (phospholipids and cholesterol) embedded integral membrane proteins with peripheral membrane proteins attached to its surfaces  Around 7.5 to 10 nm in thickness  Visible only in the electron microscope The line between adjacent cells sometimes seen faintly with the light microscope consists of plasma membrane proteins plus extracellular matrix  The Plasma (Cell) Membrane  Membrane phospholipids are amphipathic  Consisting of two nonpolar (hydrophobic or water-repelling) long-chain fatty acids linked to a charged polar (hydrophilic or water attracting) head that bears a phosphate group  Molecules of cholesterol, insert at varying densities among the closely-packed phospholipid fatty acids  The Plasma (Cell) Membrane Glycocalyx  On the extracellular surface of the plasma membrane, carbohydrates may be attached to proteins, forming glycoproteins; or lipids, forming glycolipids Sugar chain of  These surface molecules Glycoprotein constitute a layer at the Cell membrane surface of the cell, referred to as the cell coat or glycocalyx Sugar chain of Glycolipid The Fluid Mosaic Model of the Plasma Membrane & Plasma Membrane Fluidity  Membrane fluidity provides a perfect compromise between a rigid structure absent mobility and a completely fluid, liquid in which the components could not be oriented  Membrane proteins are not bound rigidly in place and are able to move laterally  Membrane fluidity makes it possible for clusters of membrane proteins to assemble at particular sites within the membrane and form specialized structures  The plasma membrane Functions 1. A selective barrier regulating the passage of materials into and out of the cell and facilitating the transport of specific molecules 2. To keep constant the ion content of cytoplasm, which differs from that of the extracellular fluid 3. Membrane proteins also perform a number of specific recognition and signaling functions, playing a key role in the interactions of the cell with its environment  Cytoplasmic Organelles Membranous Non-membranous Has plasma membranes that separate the internal without environment of the organelle plasma membranes. from the cytoplasm Examples: Ribosomes Examples: rough-surfaced endoplasmic reticulum (rER), smooth-surfaced endoplasmic reticulum (sER), Golgi apparatus  Endoplasmic Reticulum (ER)  Is convoluted (twisted/folded) membranous structure  It extends from the surface of the nucleus throughout most of the cytoplasm and encloses a series of intercommunicating channels called cisternae (L. cisternae, reservoirs)  Its membrane surface up to 30 times that of the plasma membrane  Is a major site for vital cellular activities, including biosynthesis of proteins and lipids  Numerous polyribosomes attached to the membrane of ER allow two types of ER to be distinguished, rough and smooth ER Rough Endoplasmic Reticulum (RER)  Is prominent in cells specialized for protein secretion, such as pancreatic acinar cells (making digestive enzymes), and fibroblasts (collagen)  Consists of saclike as well as parallel stacks of flattened cisternae, each limited by membranes that are continuous with the outer membrane of the nuclear envelope  The presence of polyribosomes on the cytosolic surface of the RER confers basophilic staining properties on this organelle when viewed with the light microscope  Free Ribosomes ribosomes  Measure 15 to 30 nm in diameter Mitochondria  The site of protein synthesis RER  Assemble polypeptides from amino acids in a sequence specified by mRNA  Consist of a small and large subunit  Each subunit contains ribosomal RNA (rRNA) of different length as well as numerous different proteins  During protein synthesis many ribosomes typically bind the same strand of mRNA to form larger complexes, called polyribosomes or polysomes  Smooth Endoplasmic Reticulum  Regions of ER that lack bound polyribosomes make up the smooth endoplasmic reticulum (SER), which is continuous with RER but frequently less abundant  Lacking polyribosomes  SER is not basophilic and is best seen with the TEM  Unlike the cisternae of RER, SER cisternae are more tubular or saclike rather than stacks of  Abundant in cells that function in lipid metabolism  Golgi Apparatus  Consists of many smooth membranous saccules, some vesicular, others flattened  Material moves from the RER cisternae to the Golgi apparatus in small, membrane-enclosed carriers called transport vesicles  Has two distinct functional sides or faces, the transport vesicles merge with the Golgi-receiving region, or cis face. On the opposite side of the Golgi network, at its shipping or trans face  Larger vacuoles accumulate, condense, and generate other vesicles that carry completed protein products to organelles away from the Golgi  Golgi Apparatus  Completes posttranslational modifications of proteins produced in the RER and then packages and addresses these proteins to their proper destinations Golgi  Mitochondria  Membrane-enclosed organelles  Elongated structures with diameters of 0.5-1 μm and lengths up to 10 times greater  The number of mitochondria is related to the cell’s energy needs  Specialized for aerobic respiration and production of adenosine triphosphate (ATP), with high-energy phosphate bonds, which supplies energy for most cellular activities  Change their location and undergo transient changes in shape  Mitochondria Mitochondria possess two membranes that delineate distinct compartments 1. Outer mitochondrial membrane: Contains many voltage- dependent anion channels 2. Inner mitochondrial membrane: Arranged into numerous cristae (folds) that significantly increase the inner membrane surface area. The mitochondrial matrix contains a small Surrounds the matrix which contain circular chromosome of DNA, ribosomes, several enzymes mRNA, and tRNA, all with similarities to the corresponding bacterial components Intermembrane space. Located between the inner and outer membranes The environment of the intermembrane space similar to that of cytoplasm with respect to ions and small molecules  Lysosomes Spherical membrane bound, range in diameter from 0.05 to 0.5 μm. Visible with the light microscope Sites of intracellular digestion and turnover of cellular components. It is an animal cell’s digestive organelles Cytosolic components are protected from these enzymes by the membrane surrounding lysosomes and because the enzymes have optimal activity at an acidic pH (~5.0). Any leaked lysosomal enzymes are practically inactive at the pH of cytosol (~7.2) and harmless to the cell  Proteasomes  Non-membranous, cylindrical structure  It has two major structural components: the core (CP) and the regulatory particle (RP)  They function to degrade target proteins down to small peptides  Remove proteins no longer needed by the cell and provide an important mechanism for restricting the activity of a specific protein to a certain window of time  Whereas lysosomes digest organelles or membranes by autophagy, proteasomes deal primarily with free proteins as individual molecules  Peroxisomes Spherical organelles enclosed by a single membrane Containing enzymes that participate in oxidative reactions Oxidases located here oxidize substrates by removing hydrogen atoms that are transferred to molecular oxygen (O2), producing H2O2 Peroxidases such as catalase immediately break down H2O2, which is potentially damaging to the cell  These enzymes also inactivate various potentially toxic molecules, including some prescription drugs, particularly in the large and abundant peroxisomes of liver and kidney cells  Cytoplasmic Inclusions  Cytoplasmic or nuclear structures that are formed from the metabolic products of cells  Unlike organelles have little or no metabolic activity themselves  Some of them, such as pigment granules, are surrounded by a plasma membrane; others (e.g., lipid droplets or glycogen) instead reside within the cytoplasmic or nuclear matrix  Main Types of Cellular Inclusions  Lipid droplets, accumulations of lipid- filling adipocytes (fat cells) and present in various other cells  Glycogen granules, aggregates of the carbohydrate polymer in which glucose is stored, visible as irregular clumps of periodic acid–Schiff (PAS)— positive or electron-dense material in several cell types, notably liver cells.  Main Types of Cellular Inclusions  Pigmented deposits of naturally colored material, including:  Melanin, dark brown granules which in skin serve to protect cells from ultraviolet radiation;  Lipofuscin, pale brown found in many cells, especially in stable nondividing cells (eg, neurons, cardiac muscle), containing a complex mix of material partly derived from residual bodies after lysosomal digestion  Hemosiderin, is an iron-storage complex found within the cytoplasm of many cells  Summary What is cell biology Know the definition of the cell Describe the structure of the plasma membrane and the fluid mosaic model Describe the structure and function of the cytoplasmic organelles (mitochondria, endoplasmic reticulum, Golgi apparatus and ribosomes) and inclusions Thank you! Questions?