Chapter 1 - Cell Structure PDF

Chapter 1 – Cell Structure Light Microscopy  Light Microscopy  This is how the light microscope works.  Photomicrographs Plant Cell Cheek Cells Guard Cells  Plant vs. Animal Cell There are many similarities and differen...

Chapter 1 – Cell Structure Light Microscopy  Light Microscopy  This is how the light microscope works.  Photomicrographs Plant Cell Cheek Cells Guard Cells  Plant vs. Animal Cell There are many similarities and differences between animal and plant cells. In order to see and identify certain cell structures under a microscope the specimens need to stained.  Animal vs. Plant Cells  A centriole - near the nucleus cell division, only animal cells, pair @ right angles, area called centrosome  Plant cells much larger  Plant cells cell wall, freely permeable & allows movement of molecules & ions through to cell membrane  Gives definite shape, prevents bursting as water enters cell, increasing osmotic pressure, made of cellulose & sometimes reinforced w/ lignin  Neighboring plant cells connected by plasmodesmata  Animal vs. Plant Cells  Plant cells possess large central vacuole, surrounded by tonoplast, permanent structures  Can store mineral salts, sugars, O2, CO2, pigments, enzymes, & other organic compounds  Chloroplasts - lg green organelles found mainly in leaves, used in photosynthesis, double membrane  Contain chlorophyll, green pigment, needed for light dependent reactions of photosynthesis  Plant & Animal Cells  Partially permeable cell (plasma) membrane  Relatively lg nucleus containing chromatin, a mass of loosely coiled threads  Chromatin condenses forms visible chromosomes during cell division  Loops of DNA form the nucleolus within nucleus, ribosomes made here  Animal vs. Plant Cells –  Similarities Cytoplasm – fluid material between plasma membrane & nucleus  Mitochondria is the most abundant organelle seen w/microscope, aerobic respiration, double membrane  Organelles - distinct functional & structural parts of cell  Each organelle has own membrane (compartmentalisation)  Allows “division of labor”  The Golgi apparatus - complex sorting & distribution system  Measuring in Cell Studies  When measuring objects in the microscopic world, small units of measurement should be used. The basic unit of length using the International System of Units (SI units) is the meter (m).  However, in order to measure some of these microscopic objects we must sometimes use units even smaller than the millimeter (mm). Fraction of a meter Unit Symbol One thousandth = 0.001 = 1/1000 = 10-3 millimeter mm One millionth = 0.000 001 = 1/1 000 000 = 10-6 micrometer μm One thousand millionth = 0.000 000 001 = 1/1 000 000 000 = 10-9 nanometer nm  Magnification and Resolution  Magnification is the number of times larger an image is compared with the real size of the object. Magnification = I (size of image) A (actual size of specimen) AIM  ALL units must be the SAME!!!  Resolution is the ability to distinguish between two separate points. If 2 objects are closer together than the resolution of the apparatus used, then the objects cannot be distinguished as separate.  Light microscope max resolution is 200 nm  Measuring Cells  Eye-piece graticule - used when measuring cells & organelles using microscope, transparent scale which is placed in eyepiece  However, before you can determine size of specimen, the eyepiece graticule must be calibrated  Using (stage micrometer scale) on stage of microscope & focusing  Must be done on each objective used, low or high  Measuring Cells  Once the scales are superimposed, you can find the value of each eyepiece graticule division by: Stage micrometer scale = Eyepiece graticule division Eyepiece graticule scale  Once the measurement for each division is found, then observe how many divisions the specimen measures and you can find the actual diameter of your specimen. Number of X Value (measurement) = Actual diameter of divisions of each division specimen Transmission vs. Scanning Electron Microscope  Electron Micrographs TEM Micrograph SEM Micrograph The Electromagnetic Spectrum  The range of wavelengths is electromagnetic spectrum  The longer the waves, the lower the frequency.  Energy changes wavelengths. The greater the energy, the shorter the wavelength.  Limit of resolution is ½ the wavelength of radiation used to view specimen  If object is smaller than 1/2 the wavelength of radiation used to see it, then object will not be separated from nearby objects.  Ultrastructure of Cell  The ultrastructure of a cell is the detailed structure that is revealed by the electron microscope.  Nucleus  Largest cell organelle that is surrounded by 2 membranes (nuclear envelope).  A rounded structure enclosed in a membrane and embedded in the cytoplasm. Its function is to control the type and quantity of enzymes produced by the cytoplasm.  This allows the nucleus to regulate the chemical changes which take place within the cell and determines WHAT that cell will be.  The nucleus also controls cell division (reproduction). It contains the thread-like chromosomes that play an important role in cell division and inheritance.  Most cells contain one nucleus, but some cells can have many nuclei.  Endoplasmic Reticulum  Extensive system of membranes that run through cytoplasm & can contain ribosomes, flattened sacs (cisternae) that can go on to form Golgi Apparatus  Ribosomes – formed of 2 sub-units made up of RNA & protein, make proteins  Rough ER contains ribosomes, & responsible for transporting proteins made by ribosomes  Smooth ER - no does ribosomes, makes lipids & steroids used by cell  Golgi Body (Apparatus / Complex)  Stack of flattened sacs, constantly being formed at one end from vesicles that bud off the ER  Golgi apparatus is responsible for collecting, processing, & sorting molecules that will be transported to other parts of cell or out (secretion)  Can also form lysosomes  Lysosomes  Spherical sacs, single membrane  Lysosomes contain hydrolytic enzymes  Digest unwanted structures w/in cell like old organelles, entire cells, or digest bacteria  Mitochondrion  Surrounded by double membrane, ~ 1 μm in diameter  Inner membrane forms cristae  Releasing energy from food substances (cellular respiration), transferred into molecules of ATP, can also be involved in synthesis of lipids  Microtubules  Long, rigid, hollow tubes found in cytoplasm, make up cytoskeleton of cell  Made up of tubulin (protein), alpha & beta, form a cylinder with a hollow center  Microtubule organising centres (MTOCs) are special locations within cell  Centrioles  Hollowcylinders formed from ring of microtubules, close to each other near animal cell nucleus  Grow the spindle fibers used for nuclear division  Each centriole contains 9 triplets of microtubules  Cilia, Flagella & Microvilli  Microvilli are finger-like extensions of surface membrane, increase cell surface area for max absorption  Cilia & flagella are long, thin extensions, covered by an extension of plasma membrane & contain microtubules, movement  Few– flagella  Many - cilia  The Endosymbiont Theory  Mitochondria & chloroplasts contain ribosomes that are smaller than those that are found in the cytoplasm and are the same size as the ones found in bacteria.  Mitochondria and chloroplasts also contain small, circular DNA.  Later it was proved that mitochondria and chloroplasts are ancient bacteria that now live inside larger cells.  Two Fundamentally Different Cell Types  Prokaryotes - do NOT contain nucleus, (bacteria), smaller & “primitive”  Eukaryotes - DO contain nucleus, animals, plants, fungi, & protoctists Prokaryotes Eukaryotes Average diameter is 0.5 – 5 μm Cell can measure up to 40 μm Circular DNA DNA is linear w/in a nucleus (double membrane envelope) DNA is naked DNA is associated w/ proteins, forming chromosomes Slightly smaller (70s) ribosomes (approx. Slightly larger (80s) ribosomes (Approx. 25 nm in diameter) 20 nm in diameter ER present; Ribosomes can be attached No membrane bound organelles Has membrane bound organelles Cell wall –contains murein, a Cell wall sometimes present (Not in animals at ALL!!!) in plants & peptidoglycan (polysaccharide and amino fungi – contains cellulose or lignin in plants & chitin (nitrogen- acids) containing polysaccharide similar to cellulose) in fungi  Prokaryotic Cell  Pili – Used for the attachment to other cells or surfaces; involved in sexual reproduction  Cell Wall – contains murein, a type of peptidoglycan  Flagellum – used for locomotion.  Plasmid – Small circle of DNA  Capsule – additional protection  Ribosomes – 70s  Viruses  Viruses are tiny ‘organisms’ that are much smaller than bacteria and are on the boundary between living and non- living.  Viruses do NOT have a cell structure. They mostly consist of:  A self-replicating molecule of DNA or RNA which acts as its genetic code.  A protective coat of protein molecules. (Capsid), capsomere  each protein  Viruses can range in size from 20-300 nm.  Viruses are parasitic since they can only reproduce by infecting and taking over other living cells.