Welcome to Cell Biology!
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Transcript of Welcome to Cell Biology!
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Cell Theory
• 2.1: Outline the Cell Theory• 2.1.2: Discuss the Evidence for Cell Theory
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Cell Theory
1. Living organisms are composed of cells2. Cells are the smallest unit of life3. Cells come from pre-existing cells, by division
(so that new cells cannot be constructed from non living substance)
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The History of Cell Theory
Let’s meet who discovered cells…Meet the Scientists...
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1. All living things are made of cells…
Digestive Tissue Goblet Cells http://www.olympusmicro.com/galleries/abramowitz/index.html 6.11.12
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How do we know that all living things are made of cells?
Because we can SEE them through microscopes….
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When we we first start talking about ‘Cells’?
Robert Hooke coined the term ‘cells’ since he felt that the space-filled chambers of dead cork resembled a monk’s empty cell…
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Cell Theory: Robert HookeMicrographia, 1665:
. . . I could exceedingly plainly perceive it to be all perforated
and porous, much like a Honey-comb, but that the pores of it
were not regular. . . . these pores, or cells, . . . were indeed the first microscopical pores I ever saw,
and perhaps, that were ever seen, for I had not met with any Writer
or Person, that had made any mention of them before this. . .
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The Father of Microscopy: Van Leeuwenhoek
The first man to visualise single-celled animals (he called protists animacules): 1674Microscopy bytes
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Nothing smaller can survive independently
If a cell is broken down into its individual components, its
subunits cannot survive independently
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3.All cells come from pre-existing cells: ‘Omnis Cellula e cellula ‘
• Disproving spontaneous generation
• Pasteur
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Limitations to cell theory
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Limitations 1: There are many unicellular organisms
• Mobile amoeba
Primitive unicellular organisms carry out all of the functions of life• Prostista • Paramecium• Amoebae• Giant amoebae!
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Limitations to cell theory: multinucleated cells (syncytiae)
• Skeletal and cardiac muscle
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Limitations to cell theory: multinucleated cells (syncytiae)
Fungal hyphae (phase contrast microscopy)
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Cell Biology: Magnification and Illumination
Or…how to win a Nobel prize….
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Cell Biology: Magnification and Illumination
• Let's take a look at the secret life inside our cells...
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IB Cell Theory 2.1.4
‘Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria,
organelles and cells, using the appropriate SI unit.’
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How large are cells?
Let's put things into perspective....
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What units do we use to measure cells and cell components?
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Size is relative….
Organism Size
Prokaryotic cell 1 – 10 μm
Animal Cell 10 – 30 μm
Plant Cell 10 – 100 μm
Virus < 100 ηm
DNA molecule 2 ηm
Phospholipid membrane 10 ηm
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Is magnification all that matters?Magnification versus Resolution
• Is there a limit to magnification?• Does magnification improve resolution?• Resolution of a microscope is its ability to separate small
objects which are cose together• Resolution is determined by light/(electron) wavelength;
the shorter the wavelength, the higher the resolution• Light microscope resolution is 0.2 μm• Electron microscope resolution is 1 ηm• Scanning Tunnel microscope resolution is 0.01 ηm length
0.01 ηm depth
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Light microscope: Magnification
Normal maximum magnifications of
ocular and objective lenses are 10X and 100X respectively,
giving overall maximal
magnification of X 1000
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How do microscopes work (I)?
• Anatomy of vision
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How do microscopes work (2)?• Objective lens (high powered magnifying glass)• Very short focal length (very close to the specimen)• Inverted image at high magnification• Second weak lens (eyepiece) produces a real image
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Why do modern microscope images look so beautiful?
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Modern Illumination techniques used in light microscopy
These techniques modify the light path to generate improved contrast:• Phase contrast micrcoscopy• Cross-polarised light microscopy• Dark field microscopy• Fluorescent microscopy
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Phase contrast microscopy• Improved contrast,
allowing identification of structures in living cells
• Allowed us to understand cell division
• Won its inventor, Franz Zernike, the NOBEL PRIZE in 1951
• Nobel Prize link to Phase microscope:
• Phase Nobel
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Contrast Microscopy
• Fluorescence contrast techniques
• Immunofluorescence techniques
• Here is a whole gallery of beautiful images:
• Fluorescence Gallery• Cell fluorescence
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Electron Microscopy!• Follows the same
principles as light microscopy, but shines a beam of electrons rather than light particles
• The lower ‘wavelength’ of the electron beam allows incredible resolution
• Can visualise particles to the order of a few angstom (10-10m)
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Transmission Electron Microscopy
• Image gallery • Designed by Ernst Ruska (Heidelberg) in 1938
• He won the Nobel Prize just before his death, in 1986
• First electron microscope was built in Toronto in 1938
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Scanning Electron Microscope
• a tour of the scanning electron microscope
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Scanning Tunneling Microscope
• Sharing a Nobel Prize• Scanning tunneling m
icroscopes
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IB 2.1.5
Calculate the linear magnification of drawings and the actual size of specimens in images of
known magnification
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Magnification and scale bars
• You will often need to calculate the actual size of a specimen/ component of a cell from a microscope image, or a photograph/micrograph
• The first step is to ensure that all parts of your calculation have the same units!!
Magnification = size of imageactual size of
specimen
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Calculating size/ Magnification
Graticules can be used to help estimate organelle/
sample size
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Calculating size/ Magnification: Worked examples
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On Monday, we will learn about:1. What limits cell size?
2. Why and how do cells ‘specialise’?3. What are stem cells and why are they
controversial?
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