Introduction of Cell, Cell Theory and History Chapter 1

TOPIC: INTRODUCTION OF CELL, CELL THEORY AND HISTORY CHAPTER: 1 (CELL; FUNDAMENTAL UNIT OF LIFE) ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Cell biology: Study of structure, function and behavior of cell. Questions to which Cell biology provides answers are: Where did we come from? How do we develop from a single fertilized egg cell? How is each of us similar to—yet different from—everyone else on Earth? Why do we get sick, grow old, and die? What do you mean by living organism? What does differentiate between living and non-living organisms? Characteristics of living organisms – Have life. Life? Characteristics of life: 1- Cells (fundamental unit of life) small, membrane enclosed units filled with a concentrated aqueous solution of chemicals and endowed with the extraordinary ability to create copies of themselves by growing and then dividing in two. 2- Unicellular/ multicellular (intricate pattern of communication from cell to cell). 3- Reproduction 4- Respiration 5- Metabolism 6- Coordination 7- Inheritance 8- Growth Diversity among cells: Diversity in size: Lactobacillus _ few micrometers in length _ 25 times smaller than the width of human hair. General range of bacterial cells is 0.2 to 2.0 micrometer. Eukaryotic cells: 10- 100 um Frog egg _ a cell _ about 1 millimeter in diameter Neurons_ transmit impulses with the help of long fibers _ several meters long Diversity in shape: Shapeless _ amoeba _ Rod shape or elongated, spherical, filament like, cube like, star shape, spiral shape etc. Diversity in chemical requirements: Some require O2 but for other its deadly. Some use light, water and CO2 but some require complex nutrients. Diversity in functions: Some cells produce special compounds like: hormones, fats, starch, latex, or pigments. Some do mechanical work like muscles. Some do electrical work like neurons, modified muscles in eel. * some cells are so specialized that they do not even divide and spend solitary life. Similar chemistry of cells: Despite of many physical differences, fundamentally all cells have similarities. All cells _ same sort of chemicals _ Similar reactions. All cell _ Genetic information _ Genes or DNA _ Same chemical code with same building blocks (nucleotides)_ Same machinery for replication and reproduction. All cells _ Genetic information _ Expression _ Transcription and translation _ proteins. (fundamental process to life called central dogma). Proteins → Structural role, perform catalysis, motor function etc. All cells _ Proteins _ same 20 types of amino acids _ join in a specific order to produce specific proteins. *Nothing less the cell is living. ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Viruses: Nucleic acid packed in capsid / no ability to reproduce / Require living host / Chemical zombies _ inert and inactive outside the cell but becomes active in cell and take the control of it. Evolution of Cell All cells _ replicate DNA _2 cells _ passing the same copy of genetic information _ same cells _ mutations _ sometimes the copies are not exact. Mutations _ Variations 1- Worse _ changes those threat the survival of an organism 2- Good _ changes those help in better survival and reproduce 3- Neutral _ changes in genetical material but physically same or viable Struggle for existence eliminates the first, favor the second and tolerate the 3rd type. Sexual reproduction _ Lead to variations due reshuffling of genes during crossing over and mixing of genome from different members of same species _ selection of better combinations. Simple principles _ Changes and Selection _ Repeated over billions of years _ Evolution. Evolution: “the process by which living species become gradually modified and adapted to their environment in more and more sophisticated ways.” Present day cell _ inherit information from common ancestor. 1st ancestral cell existed about 3.5 to 3.8 billion years ago → General prototype of all cells existed today → Mutations and variations → descendants will diverge gradually Instructions for cell functioning A cell’s genome—that is, the entire sequence of nucleotides in an organism’s DNA—provides a genetic program that instructs the cell how to behave. Example: Embryo → Genome _ development of an adult organism with different types of cells i.e. fat cells, neurons, muscle cells, epithelial cells. Different cells_ expression of different genes _ produce only specific proteins _ depending on the internal and external signals. CELL AND MICROSCOPY 17th century → microscope _ Cell become visible All information about cell _ by using microscope Light microscope _ use light as a source of illumination _ limitations Light microscope development associated with advances in lenses. Robert Hooke _ Uses lenses _ Self made microscope _ examined a piece of cork _ composed of mass of minute chambers _ Called them cells Hooke and Antoni van Leeuwenhoek – observe living cells Matthias Schleiden _ 1838 _ Botanist and Theodor Schwann _ 1839 _ Cell theory A) Cell consist of cell membrane, cytoplasm and nucleus B) Cell is the fundamental unit of all living organisms C) New cells arise by the division of previous cells Louis Pasteur: experiments _ evidences in favor of biogenesis. First cell? Charles Darwin: Theory of evolution _ Explain the process of random variations and natural selection which give rise to the diversity among the organism that share common ancestry. Combination of cell theory and theory of evolution _ lead us to the history of emergence of cell Electron microscope _ Beam of electrons _ source of illumination _ increase the abilities to see the details of cells Importance of Light microscope Plant or Animal tissue _ under light microscope _ Closely packed or separated cells with extracellular space (a dense material made up on collagen/protein fibers embedded in polysaccharide gel) Range of cells _ 5-20 um in diameter Inside components are also visible to some extent. Cell division can also be observed *visualization of internal structures is difficult _ due to small size and they are transparent. *dyes are used for staining Anatomy of Cell: ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Cell boundary/ cell membrane A large nucleus _ prominent _ in the middle A transparent substance present between membrane and nucleus _ Cytoplasm With good light microscope _ larger components (>0.2um) _ can distinguish and classify them. Sample preparation for light microscope: Tissue _ fixed (persevered in a reactive chemical solution) _ embedded in solid wax or resin _ cut or sectioned into thin slices _ staining before visualization. Fluorescence microscopes: Use for illumination of fluorescently labeled cell components Some Fluorescence microscopes can push the limits of resolution down to 20nm (size of the ribosomes). Electron microscope: Highest magnification and resolution Can reveal the details down to few nm. Sample preparation for electron microscope: Similar procedure as for light microscope but: - section must be much thinner - no possibility of looking at living, wet cells Section cut, stained and placed under electron microscope _ cell components _ resolved into distinct organelles *A delicate membrane, only of 5nm thick, is visible enclosing the cell and similar membranes form the boundary of many of the organelles. *Plasma membrane _ the membrane that separate the interior of the cell form its external environment is called plasma membrane. *Internal membrane _ the membranes surrounding the organelles. Transmission electron microscope: Similar to electron microscope but it transmits a beam of electron rather then light from the thin section of sample. Scanning electron microscope: Scatter the electrons from the surface of sample and use to look at the surface details of cell and other structures. ▪ ▪ X-Ray Crystallography: use to study the 3D structure of molecules and atomic details. ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Cell and its components: PROKARYOTIC CELLS: → A-nucleated/ primitive cells All bacteria and Archaea _ simplest structure _ essentially no organelles _No nucleus Presence or absence of nucleus _ fundamental difference between prokaryote and eukaryote cell. Major shapes of prokaryotes _ Rod like, spherical or corkscrew-shaped. Cell wall _ enclose _cell membrane, cytoplasm and DNA Under electron microscope _ cell interior _ No obvious internal structure ▪ ▪ ▪ ▪ Prokaryotic cell _ plentiful food _ divide to produce daughter cells in just 20 minutes. 11 hours _ repeated division _ 8 billion progenies _ more than humans on earth General properties: Large number, rapid growth, ability to exchange genetic material, high rate of evolution, ability to use new food source and have resistance against many antibiotics. Some single celled and some make chains, clusters or other organizations. Survive in enormous range of habitat (hot puddles of volcanic mud, interior of living cells) Aerobic (use oxygen to oxidize the food molecules) and anaerobic Endosymbiotic hypothesis _ aerobic bacteria _ Mitochondria. Photosynthetic organelle in plants _ chloroplast _ photosynthetic bacteria ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Nutrition modes: 1- Food _ all type of organic compounds _ from wood to petroleum. 2- Some bacteria survive on _ inorganic substances like C form CO2 in air, N form N2 in atmosphere, and O2, H, S and P from air, water and inorganic minerals. 3- Autotrophs: photosynthesis _ sunlight + H2O + CO2 _ organic molecules 4- chemosynthetic _ derive energy from the chemical reactivity of inorganic substance. Domains of prokaryotes: 1- Bacteria 2- Archaea They have large differences at molecular level Bacteria _ well known _ survive in normal habitat Archaea _ survive under very hostile environment _ concentrated brine, hot acidic or volcanic springs, airless depths of marine sediments, sludge of sewage treatment plant, pools beneath the frozen surface of antarctica and acidic, oxygen free environment of cow’s stomach where they break down cellulose and generate methane gas. EUKARYOTIC CELL: nucleated cells Largest and more complex then bacteria or archaea Single celled i.e. amoeba, yeasts. Multicellular _ plants, animals, fungi and algae. More complex: membrane enclosed organelles and complex functioning. Nucleus: Store house of information Most prominent organelle of cell _ double membranous _ nuclear envelope _ DNA _ genetic information _ chromosome (condensed form) Energy production: Mitochondria _ all eukaryotic cells_ under microscope _ worm like with branching network _ double membranous _ inner membrane formed infoldings. Could be separated by cell fractionation technique Source of chemical energy for cell which is produced by oxidation of food. ATP _ adenosine triphosphate _ basic chemical fuel Use oxygen _ release CO2 _ called cellular respiration/ cellular breathing Own DNA _ self-replicating ▪ ▪ Chloroplast ▪ ▪ Largest, green organelle, double membranous _ only in plants and algae Internal stacks of membrane bounded sacs called thylakoid _ contain chlorophyll. ▪ ▪ ▪ ▪ ▪ Grana: Pile of thylakoid Carryout photosynthesis _ Trapped sun energy in chlorophyll + CO2 + H2O → Energy rich sugar molecules. Extract that energy from sugar _ Mitochondria _ cellular respiration _ ATP. Own DNA _ self-replicating ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Internal Membranes Develop compartments which perform different functions Single membrane organelles also present along with Nucleus, chloroplast and mitochondria. Most of them function to import raw material and export both the useful substances and waste material. Endoplasmic Reticulum (ER): Irregular maze of interconnected spaces enclosed by a membrane. Large organelle Functions: Form cell membrane components and components for export Golgi Apparatus Stacks of flattened, membrane bounded sacs constitute the Golgi apparatus Modify and package molecules synthesized on ER and transport them out of the cell or to anther compartment of cell. Lysosomes: Small, single membranous, irregular shaped organelles involved in intracellular digestion. Ingested food particle will be broken down for either recycling within the cell or for excretion. Peroxisomes: Small, single membranous vesicles Provide a safe environment far variety of reactions including reactions in which hydrogen peroxide is use to inactivate toxic molecules. *A continuous exchange of material takes place between ER, GA and lysosomes and outside of cell. * The exchange between vesicles is mediate by small vesicles which pinch off form one organelle and transported towards the other. Animal cells: Endocytosis: large particles fuse with membrane and entire particle engulfed in the form of vesicle ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Exocytosis: vesicle from inside the cell fuse with plasma membrane and release its contents into the external environment. Most of the hormones and signal molecules transported by this method. Cytoplasm: Insoluble part → contain organelles Cytosol: Concentrated aqueous gel of large and small molecules The soluble part of cytoplasm which do not contain cell organelles. Thick solution of large and small molecules which space close together and give them a gel like appearance. It is the site of may chemical reactions. CYTOSKELETON System of protein filaments in cell is called cytoskeleton. Filaments: 1- Actin filaments (microfilaments): thinnest, most abundant in eukaryotic cells, involve in muscle contraction in muscle cells, 2- Microtubules: thickest, minute hollow tubes, help in movement of chromosomes during cell division. 3- Intermediate filaments: Intermediate thickness, strengthen the cell. * These filaments along with attached other proteins form a system in the cell that provide mechanical strength, controls the shape and derive and guide its movement. * Cytoskeleton use to develop separate compartment in the cell to separate the organelles into daughter cells. * it also plays its role in cell division. ▪ HISTORICAL PERSPECTIVE OF CELL STRUCTURE ▪ ▪ ▪ ▪ ▪ EMERGENCE OF EUKARYOTIC CELL Eukaryotic cell: 10x greater in length and 1000x greater in volume from prokaryotic cell. Possess: Cytoskeleton, Double membranous organelles and single membranous organelles. Bacteria, Archaea and eukaryotic cell have emerged from common ancestor According one theory: Eukaryotic cell was predator that fed itself by capturing other cells. For this cell has to develop cytoskeleton, flexible membrane and large size. Nuclear compartment may have evolved to keep DNA segregate it from its physical and chemical reactions. Such cells _with nucleus and cytoskeleton _ engulf free living, oxygen consuming bacteria _ likely ancestor of mitochondria _ Release oxygen _ O2 rich atmosphere. Lager _ engulf _ photosynthetic bacteria _ Chloroplast. Resultant organism _ single celled / free living / actively motile micro-organisms _ Protozoans. Some protozoans _ Motile/ sedentary / photosynthetic / carnivorous. ▪ ▪ ▪ ▪ ▪