Lecture 1 - Cell Theory PDF

BIOL 1017- Cell Biology Lecture 1: Cell Theor y  Characteristics of Living Organisms  Living organisms must be able to carry out all these seven functions of life simultaneously and independently: 1. Feeding 2. Energy transduction 3. Growth 4. Reproduction 5. Excretio...

BIOL 1017- Cell Biology Lecture 1: Cell Theor y  Characteristics of Living Organisms  Living organisms must be able to carry out all these seven functions of life simultaneously and independently: 1. Feeding 2. Energy transduction 3. Growth 4. Reproduction 5. Excretion 6. Irritability 7. Locomotion  Characteristics of Living Organisms Living organisms carry out the following functions: 1. Homeostasis. 2. Organization. 3. Metabolism. 4. Growth. 5. Adaptation. 6. Response to stimuli. 7. Reproduction.  Life & the environment  Entropy – the tendency toward disorder that exists in the natural world ▪  Enclosing biochemical reactions inside a cell: 1. Key event in the origin & maintenance of life. 2. Concentrated the reactions within a given space (& time). 3.  The Cell Theory ▪ Formulated in 19th century. ▪  The theory has three critical components: 1. All living things are composed of cells. 2. The cell is structural and functional unit of living things. 3. All cells come from division of pre‐existing cells; ▪ i.e.,  All living organisms are composed of cells: 1. Single-celled organisms are unicellular. 2. Many-celled organisms are multicellular.  The cell as the basic unit of life  The cell is the vehicle for the hereditary information that defines the species.  Specified by this information, the cell includes the machinery to:  Nothing less than a cell has this capability.  Cells → tissues → organs → systems → organism   Cells therefore are the closest thing to an autonomous biological unit that exists  The cell as the basic unit of life 1. All cells store their hereditary information in the same linear chemical code (DNA) 2. All cells replicate their hereditary information by templated polymerization 3. All cells transcribe portions of their hereditary information into the same intermediary form (RNA) 4. All cells translate RNA into protein in the same way 5. The fragment of genetic information corresponding to one protein is one gene 6. All cells use proteins as catalysts 7. All cells function as biochemical factories dealing with the same basic molecular building blocks − 8. All cells are enclosed in a plasma membrane across which nutrients and waste materials must pass  Cell size  The lower limit of cell size is determined by the smallest volume within which the essential components may be fitted for cell integrity & function to be perpetuated.  The upper limit is determined by several factors: 1. 2. 3. 4.  Cell function  As a self‐perpetuating system, the cell must have appropriate mechanisms to optimize its functioning through the management of the: 1. flow of energy 2. flow of information  The cell, as an ordered biological system, must attain this level of order (→ metabolism) while existing within an environment that is full of disorder / entropy  Life & environment energy balance ‘Entropy’ Order Disorder (Cell) (Environment) Cell integrity Life & environment energy balance  Life & environment energy balance  Life exists in disequilibrium with the physical environment  Constraints and Solutions: 1. Living organisms have a purposeful existence 2. They depend on the physical world for: a. b.  Cells will:  affect and alter the physical world  function within limits set by physical laws  Cell function: Energy requirement  Cell integrity & function is heavily dependent on a constant supply of free energy  The source of this energy is the environment and is accessed directly or indirectly through autotrophic mechanisms  This energy is harnessed by the cell in the form of ATP that is generated within the cell itself:  The cell must: 1. have mechanisms for the input of energy 2. possess energy transducers, capable of harnessing this energy to perform work (e.g., chloroplasts and mitochondria) 3. resist the general increase in entropy in the physical environment 4. successfully compete with other life forms Energy Relations of Cells  Cell function: Energy requirement  Types of work at the cellular level: 1. Chemical work  synthesis of cellular material  cell replication  repair & replacement of cellular components 2. Osmotic work  control of appropriate concentration gradients within the cell & in relation to its environment  Cell function: Energy requirement  Types of work at the cellular level: 3. Electrical work  movement of charged particles across membranes  nerve impulses 4. Mechanical work (locomotion & movement)  Locomotion - cilia & flagella  Movement - cyclosis, movements involved with cell division, cilia in the trachea 5. Regulatory work  regulation of synthesis & interaction between macromolecules  entropy‐decreasing mechanisms Cell function: Energy cycling  Cell Theory: Central Dogma of Biology  All cells: 1. Are enclosed in a plasma membrane through which nutrients and wastes pass. 2. Employ the Central Dogma of Molecular Biology:  Central Dogma of Molecular Biology 1. Hereditary information is stored in a coded sequence of nucleotides in DNA → 2. DNA copies itself via replication → 3. DNA transcription produces an intermediate nucleotide-coded molecule, RNA → 4. Translation converts RNA’s nucleotide code into an amino acid sequence in a protein→ 5. The fragment of DNA that corresponds to one protein is one gene. Transcription & Translation  Universal Features of Cells  All cells use proteins: 1. Cycling of materials, i.e. in the transformation of matter 2. To manage the flow of energy.  Information flow within a cell Viruses Viruses: ▪ Are not cells: ▪ Contain protein and nucleic acid; but ▪ Lack membranes, nucleus and protoplasm. ▪ Alive only while reproducing after infecting a host cell. tail fibres  Types of cells Unicellular Multicellular Bacteria Protist (Paramecium) Flowering Plant Mammal (Dolphin)  Universal Features of Cells ▪ Even the largest creatures are made of cells. ▪ But cells themselves are usually very small.  Universal Features of Cells  Most cells are within a fairly narrow size range ▪ 1 – 100 µm  Small cell size is practical necessity: 1. Numerous chemical reactions occur in cells. 2. Substances must move from one site to another within the cell. ▪ The smaller the cell: 1. The shorter the distances that substances must move; and 2. The faster the movement of substances within cells.  Universal Features of Cells ▪ Cell size is largely influenced by surface area to volume ratio. ▪ Adequate concentrations of reactants for chemical reactions ▪ Rates of movement: 1. Passive means - diffusion and facilitated diffusion 2. Active means - Active transport ▪ As an object increases in volume: − Surface area also increases, but at much slower rate → Surface area to volume ratio decreases SA:V ratio and size  SA/V and cell life ▪ Biological significance of SA:V ratio 1. Volume affects the rate at which chemical activity can proceed within the cell. 2. Surface area determines the rates of: a. Access of raw materials: i. Passive entry – diffusion, osmosis, facilitated diffusion ii. Active entry – active transport b. The exit of cellular products from the cell: a. Secretion b. Excretion  Microscopy Microscopes are: 1. Instruments used to view objects that are too small to be seen with the unaided eye. 2. Are used to reveal the features of cells. 3. Allow cellular details to be seen by: 4. Increasing the apparent size of the object (magnification). 5. Making the magnified object sharp, or clear (resolution).  Microscopy  Two basic types of microscopes, based on the wavelength of the part of the EM spectrum that is used: 1. Light microscope. 2. Electron microscope.  Microscopy  Resolution: − The smallest distance two objects can be apart and still be seen as two objects, cf. magnification − Limit for the unaided human eye is 200 µm. − Limit for the light microscope is 0.2 µm: − Allows visualisation of cell size, shape and some internal structures. − Limit for the electron microscope is 2 nm (= 0.002 µm): − Allows many cellular structures to be distinguished in fine detail. Microscopy  Light Microscopy  Several different types of light microscopy: 1. Bright-field microscopy 2. Stained bright-field microscopy 3. Dark-field microscopy 4. Fluorescence microscopy 5. Phase-contrast microscopy  Light Microscopy 1. Bright-field microscopy: ▪ Light passes directly through the cells. ▪ Unless natural pigments are present, there is little contrast and little detail.  Light Microscopy 3. Stained bright-field microscopy: ▪ Stains are used that: − Enhance contrast, revealing details not otherwise visible. − May bind to specific cell materials.  Light Microscopy 2. Stained bright-field microscopy:  Light Microscopy  Stained bright-field microscopy  Some commonly used stains Stains Uses 1. Iodine Starch grains (blue) 2. Haemotoxylin Nuclei (violet-brown) 3. Eosin Cytoplasm & membranes (red-pink) 4. Crystal Violet Cell walls of Gram +ve bacteria (dark purple) 4. Phloroglucinol-HCl Stains sclerenchyma (red)  Light Microscopy 2. Dark-field microscopy ▪ The light source is blocked by an opaque object in the condenser ▪ Light passes through the specimen from oblique angles and is diffracted, refracted, and reflected into the microscope objective to form a bright image of the specimen superimposed on a dark background. Ideal candidates for darkfield illumination include − Minute living aquatic organisms, (e.g., diatoms) − Small insects − Bone or hair fibres − Micropropagation − Protozoa  Light Microscopy 4. Fluorescence microscopy: ▪ A natural substance in the cell, or a fluorescent dye that binds to a specific cell material, is stimulated by light. ▪ The stimulated dye/substance emits longer-wavelength fluorescent light. ▪ The light energy source is used to “excite” the fluorophores in a sample. ▪ This light can include the visible spectrum, ultraviolet (UV) and infra-red (IR) ▪ The source in a microscope can range from a mercury or xenon arc lamp to lasers. ▪ The fluorophores are chemical compounds in the sample which have special properties of re-emitting higher wavelength light/photons upon excitation by light energy Light Microscopy Fluorescently labelled cells visualized by fluorescence microscopy  Light Microscopy 5. Phase-contrast microscopy: ▪ Contrast is increased by emphasising differences in the refractive index (capacity to bend light) between cell structures. ▪ Enhances light and dark regions in the cell.  Microscopy Types compared Light microscopy Electron microscopy 1. Source of illumination – Light rays, longer λ 1. Source of illumination – beam of electrons, much shorter λ 2. Image may be coloured 2. Image is in black & white 3. Specimen preparation is relatively quick (~ 3. Specimen preparation is much more minutes to hours) detailed (usually over a few days) 4. Live or dead specimens may be observed 4. Specimens are always dead 5. All lenses are made up of glass 5. All lenses are electromagnetic 6. Lower resolving power 6. ~ 250x higher resolving power 7. Magnification: 500 – 1500x 7. Magnification: 100,000 – 300,000x 8. No need for high voltage electricity 8. High voltage electricity required 9. Image observed directly by the eye 9. Image observed from a screen or photo 10. Radiation risk negligible 10. Risk of radiation leakage