Cells: Structure and Varieties

Documents BIO 1140 Cells: Structure and varieties -All living things (organism) are built from cells Cell: a small membrane bound unit filled with a concentrated aqueous solution of chemicals with reproduction capacity. Biology is important for agriculture -Dependence on other organisms -Agriculture began 10 000 years ago -Advance in crop production -Genetics Engineering for climate challenges Cell differs in size E. coli is 1 micrometre Frog egg is 1 micrometre Most cell is 1-100 micrometre Eukaryotic cell is 10-100 micrometre diameter Why are cells small and large organisms made if many small cells? To function, cells must maintain a large surface area to volume ratio -When the cell gets bigger it needs gets more important. If the cell volume is too big, but the surface is not too big to exchange that material, the cell cant function. -Accumulation of waste Cells comes in a variety of shapes Cell also differs in nutritional requirements Cells became visible in the 17th century Robert Hook (put 2 lenses together) (1665) Quark, a plant tissue Anton, Van (1670) observed living organisms Cell biology emerged by the publication of Matthias Shleiden (1838) -all plants are made of cells, Shwann- all living things are made up of cells. The cell Theory (1838) Cells are the fund unit of life All living organisms are composed of cells Original theory Modern cells evolve from a common ancestor In light microscopes glass lenses and visible light are used to form an image Light and electric microscopes Magnification (1000X), resolution 200nm See living cells Bright field microscopy Background is bright, hardly distinguish the cells Phase contrast microscopy Contrast is increased, this enhances light and dark regions in the cell and make it easier to see details Differential interference- contrast microscopy, 2 beams of polarized light Stained bright-field microscopy a stain enhances contrast and reveal details Fluorescence microscopy Electromagnets and electrons are used in electron microscopes Fluorescent screen or a digital camera Resolution is 2nm(100,000x) TEM Principle Similar to a a light microscope Uses a beam of electrons instead of light Uses magnetic coils for focusing instead of glass lenses Specimen requirements Placed in a vacuum Must be very thin Contrast introduction: Achieved by straining with electron-dense heavy metals Metal absorb or scatter electrons, reducing beam passage throught the specimen SEM Principle Uses electrons to scan the surface of a sample Detects emitted electrons to create an image Specimen preparation Coated with a thin film of heavy metal Electron Beam interaction: Focused by magnetic coils Scan the specimen surface Image Formation Builds image on a screen with a good depth of focus Capabilities: Resolve 3nm to 20nm Produce clear 3D surface images Every cell is bounded by a small membrane Cytoplasm, anything that is inside except the nucleus, the cytosol is the fluid Cells are divided in two categories: Prokaryotes and eukaryotes Prokaryotes Eukaryotes No other organelles a cell membrane ribosomes Genetic material nucleoid Membrane enclosing it cytoplasm Some prokaryotic cells have a cell wall (peptidoglycan) Capsule (polysaccharides) : protect from blood cell, helps to attach to each other Some have cytoskeleton (Fts2, MreB) Some have flagella, pilli and fimbrae Nucleus : DNA in the form of chromatin, Nucleolus (genes encoding DNA)