9/15/14 ! BIOLOGY 1408 Chapter 4 : A Tour of the Cell First Pioneers "  The first basic microscope was developed by Robert Hooke (England) in 1665 "  He looked at slices of dried cork and proposed the fact that cork was made out of compartmentalized units, which he called “cells”. "  This was the first use of the term “cell”. "  What is cork actually ? 1 9/15/14 First Pioneers Hooke’s publicaQon “Micrographia”, showing the page where he drew the cork cell observaQons. First Pioneers Drawing by Hooke of an insect head 2 9/15/14 First Pioneers "  Antoni van Leeuwenhoek ( ~ 1675, Netherlands) later created beYer microscopes that were up to 10x beYer in resoluQon and capable of magnificaQon up to 400 x. "  He was to first to experience the existence of microscopic life forms. Imagine not knowing these things existed and then come across this whole new universe we take for granted now. First Pioneers –  He viewed proQsta , discovered red blood cells and even bacteria with his own hand-­‐cra_ed microscopes –  He was also the first to observe the finer details of mammalian anatomy e.g. the opQc nerve of a cow 3 9/15/14 First Pioneers First Pioneers "  Van Leeuwenhoek was the first to describe bacteria in tooth plaque. (some of his wri;ngs are below) "  "In the morning I used to rub my teeth with salt and rinse my mouth with water and aAer ea;ng to clean my molars with a toothpick.... I then most always saw, with great wonder, that in the said maCer there were many very li#le living animalcules, very pre2ly a-­‐moving. The biggest sort had a very strong and swi< mo=on, and shot through the water like a pike does through the water; mostly these were of small numbers.” "  “I took in my mouth some very strong wine-­‐Vinegar, and closing my Teeth, I gargled and rinsed them very well with the Vinegar, aAerwards I washt them very well with fair water, but there were an innumerable quant'ty of Animals yet remaining in the scurf upon the Teeth,.. “ 4 9/15/14 First Pioneers "  Van Leeuwenhoek was the first to describe ;ny criCers living in pond Drawings by Van Leeuwenhoek and modern microscopic picture of a roQfer Miscroscope Evolution "  From Hooke to the middle of the 1950’s, microscopes were just beYer instruments of the ones before. "  But all were sQll light microscopes; they are all limited in magnificaQon by the wavelength of visible light, which is ~ 500 nano-­‐meters. "  No maYer how expensive the light microscope, magnificaQon is limited to ~ 1000 x ! "  The advancement was in the quality of the lenses and glassware : this improved the resolu'on ( the clarity of the image… like having dirty or clean sunglasses). 5 9/15/14 What can we See ? "  Our healthy, un-­‐aided eye has a resoluQon of 0.1 milli-­‐meter ( mm). "  Most cells are smaller than 0.1 mm. Thus , unQl the arrival of microscopes, people had no clue about the world at the micro level. "  Since the discovery of these small sized items, scienQfic terminology had to adjust in order to express smaller sizes . What can we See ? "  Science works with the metric system. Why ? Because everything is either 10 Qmes or a mulQple of 10 Qmes larger or smaller. Much easier to calculate…. "  Common prefixes for smaller items are the following : "  Kilo – means 1 thousand of a unit ( 1000) "  Milli-­‐ means 1 thousandth of a unit (1/1,000) "  Micro-­‐ means 1 millionth of a unit (1/1,000,000) "  Nano-­‐ means 1 billionth of a unit ( 1/1,000,000,000) 6 9/15/14 What can we See ? Microscopes "  Since most cells cannot be seen with the naked eye, microscopes were the ulQmate tool to unravel the secrets of life. "  Without microscopes, understanding the finer details of the inside of a cell would never have been possible "  Bacteria are the smallest of all cells ( 10 x smaller than normal eukaryoQc cells) and require magnificaQons of at least 1,000X 7 9/15/14 10 m Chicken egg 10 mm (1 cm) 100 µm 10 µm 1 µm 100 nm 10 nm 1 nm 0.1 nm In the 1950’s a new instrument was developed that used a beam of electrons to highlight structures: the electron microscope ! Frog egg Most plant and animal cells Nucleus Most bacteria Mitochondrion Mycoplasmas (smallest bacteria) Viruses Ribosome Proteins Lipids Small molecules Atoms Electron microscope 1 mm Electron Microscopes Light microscope 100 mm (10 cm) Human height Length of some nerve and muscle cells Unaided eye 1 m It increased magnificaQon down to the nano-­‐meter scale. This allowed even finer structures (ultra-­‐
structure) to be discovered inside the cells. A special technique called , called scanning electron microscopy, provides almost 3 dimensional structures. Some Examples Difference between an Scanning Electron Microscope (SEM) image (le_) and Light Microscope image of Paramecium, a unicellular proQst (size ~ 200 micro-­‐meters). The ‘hair’ on the this animal are called cilia, which create movement. 8 9/15/14 Examples SEM image and light microscope picture of a Tardigrade, a microscopic animal that goes by the name of ‘water bear’. Examples 9 9/15/14 Examples The light microscope is sQll the tool of choice for immediate observaQon and diagnosis. For example, this blood is ‘contaminated’ with a unicellular organism called Plasmodium… the agent that causes malaria. Cell Size "  So why are cells small ? "  Cells need to do a variety of funcQons, most of which include interacQons across the surface ( uptake of nutrients, oxygen,…) ! "  There is a certain advantage of being smaller, since it increases the surface to volume raQon and allows to diffusion to proceed at a very fast rate. 10 9/15/14 Surface to Volume Ratio Who has the beYer surface to volume raQo ? 1 3 Surface area of one large cube = 54 units2 (3 x 3 x 6 sides) Total surface area of 27 small cubes = 162 units2 3 1 Volume of one large cube = 27 units3 (1 x 1x 6 sides x 27 cubes) Volume of all cubes = 27 units3 (1 x 1 x 1 x 27 cubes) (3 x 3 x 3) Surface to Volume Ratio "  Having more smaller cells while keeping the volume constant increases the surface to volume raQo "  In the previous example, one ‘cell’ has a S/V raQo of 54/27= 2 "  Dividing that cell up into 27 smaller ‘cells’ provides a S/V raQo of 162/27 = 6 "  Thus a 3 fold increase in S/V raQo ! "  Thus it’s good to be Qny for a cell.. more surface to interact with the outside and obtain goodies ! 11