2. Magnification

Electron Microscope - how does it magnify a specimen more?

• A beam of electron can accurately illuminate the specimen

Advantages of an Electron Microscope

• It produces images with a higher magnification and a clear resolution

Disadvantages of an Electron Microscope

• It is an expensive equipment and it can only be used in a carefully controlled environment

• Specimens can be damaged by an electron beam 

• Artefacts are shown (unneeded)

Scanning Electron Microscope

• Scans across the surface of a specimen and provides a 3D image of surfaces

Transmission Electron Microscope

• A beam of electrons transmitted in to the specimen and produces a 2D image

Types of Preparation for a Slide (Electron Microscope)

• Fixation (using chemicals)

• Staining (heavy metals)

• Dehydration (solvents)

Comparing a Light and Electron Microscope (Light)

• Inexpensive and portable

• Simple sample preparation

• Vacuum is not required

• Up to 2000x magnification

Comparing a Light and Electron Microscope (Electron)

• Expensive and larger

• Complex sample preparation

• Vacuum is required

• Up to x500,000 magnification

Artefact

• Unneeded structures forming on a specimen e.g, empty spaces in the cytoplasm, bubble spaces under the cover slip - these distort organelles

Mesosomes

• Inward foldings produced by chemicals used in the fixation process by electron microscopy found on cell membranes

Laser-Scanning Confocal Microscopy

• Moves a single spot of focused, concentrated light across a specimen - point illumination

Laser-Scanning Confocal Microscopy steps

• Light emitted from the specimen - filtered through a pinhole

• Only light source radiated closely to the focal plane is detected (focal plane - distance providing the sharpest focus)

• Thin sections of specimen are examined - high resolution images are obtained

• Spot illuminating the specimen moves across to form a 2D image

Advantages of Laser-Scanning Confocal Microscopy

• Non-Invasive (can visualise samples without damaging them)

• Can diagnose long-term diseases such as forms of cancer

Fluorescent Tags

• Antibodies with fluorescent tags to target specific features with precision to study the production of proteins in a specimen sample

Fluorescent Tag - what does it show?

• It indicates that a protein is being made and shows where the protein goes - e.g, to cell or to organelle