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Microscopes provide windows to the world of the cell.

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Presentation on theme: "Microscopes provide windows to the world of the cell."— Presentation transcript:

1 Microscopes provide windows to the world of the cell

2 Cellular Diversity The average adult has nearly 100 trillion cells There are about 200 different types of cells Cells come in a variety of shapes and sizes Cellular diversity permits organization of cells into more complex tissues and organs

3 History of the Microscope 1665, Robert Hooke described cells using a light microscope Magnification vs resolution Highest magnification of l.m. = 1000x 1950, Electron microscope allowed researchers to clearly identify organelles There are 2 types: –Transmission –Scanning

4 Transmission Electron Microscope (TEM) e- transmitted through specimen are focused image magnified by electromagnetic lenses to bend trajectories of charged e- –Used to study internal cell structure –Image is focused onto a viewing screen/film


6 Scanning Electron Microscope (SEM) e- beam scans surface of specimen that is coated with a thin film of gold Beam excites secondary e- on sample’s surface Secondary e- are collected & focused on viewing screen –Useful for studying surface of specimen –SEM has great depth of field & produces 3D image

7 SEM images

8 Disadvantages of Electron microscopes Can usually only view dead cells because of the elaborate preparation required May introduce structural artifacts

9 Cell Fractionation Technique that enables researchers to isolate organelles without destroying their function –Disrupted cells are centrifuged to isolate components of different sizes, densities, and shapes

10 Surface area: volume ratio Place in order depending on which will dissolve fastest  slowest granulated sugar Powdered sugar Sugar cube Fine sugar Why do you cut up potatoes to boil them?

11 Cells Prokaryotic vs Eukaryotic Cell sizes ( um) –What limits a cell from being too large? –Too small? Eukaryotic cells have 1000x volume of prokaryotic cells, but only 100x the surface area. How can they compensate for the small surface area to volume ratio?

12 Prokaryote “before nucleus” Eukaryote “true nucleus”

13 A Generalized Cell Cytoplasm - all the cellular contents between the plasma membrane and the nucleus - cytosol - the fluid portion, mostly water *site of many chem. Rx. - organelles - subcellular structures having characteristic shapes and specific functions

14 The cytoskeleton - network of protein filaments throughout the cytosol -provides structural support for the cell -three types according to increasing size: microfilaments (cables), intermediate filaments (cables), and microtubules (support beams) Resist tension Bearing tension Resist compression


16 Organelles Centrosome - located near the nucleus, consists of two centrioles

17 Cilia and Flagella Cilia - short, hair-like projections from the cell surface, move fluids along a cell surface Flagella - longer than cilia, move an entire cell; ex. sperm cell’s tail

18 Internal Membranes Partitions cell into compartments Have unique lipid & protein compositions depending upon their specific fx. Participate in metabolic reactions (enzymes)

19 1. Nuclear envelope - a double membrane that separates the nucleus from the cytoplasm –Nuclear pores - numerous openings in the nuclear envelope, control movement of substances between nucleus and cytoplasm –Nucleolus - spherical body that produces ribosomes Class I: membrane derived

20 2. Endoplasmic reticulum - network of membranes in the shape of flattened sacs or tubules - Rough ER - connected to the nuclear envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins -Smooth ER - a network of membrane tubules, does not have ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs

21 3. Golgi complex - consists of 3-20 flattened, membranous sacs called cisternae - modify, sort, and package proteins for transport to different destinations - proteins are transported by various vesicles

22 4. Vesicles Sacs made of membrane Transport substances throughout cell and to/fro membrane

23 5. Vacuoles Food vacuole  formed by phagocytosis (protists & macrophages) Contractile vacuole  pumps excess water from cell (protozoans) Central vacuole  enclosed by membrane (tonoplast); stores organic compounds, ions, poisons, provides turgor pressure (plants)

24 6. Lysosomes Sequesters destructive enzymes from cytosol Maintains optimum acidic environment for enzyme function

25 Peroxisome Bound by a single membrane derived from lipids w/i cell Contains enzymes that transfer Hydrogen atoms from various substrates to oxygen (H 2 O 2 ). Contains catalase that converts H 2 O 2 to water. Breaks down fatty acids Detoxification of alcohol & other poisons (liver)

26 Class II: bacteria like organelles (energy production) Mitochondria - the “powerhouses” of the cell –Generate ATP –More prevalent in physiologically active cells: muscles, liver and kidneys –Inner and outer mitochondrial membranes –Cristae - the series of folds of the inner membrane –Matrix - the large central fluid- filled cavity –Self-replicate during times of increased cellular demand or before cell division

27 Class III: Involved in Gene Expression

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