Cell theory & Microscopy

Question 1

Who first discovered cells?

Answer 1

Robert Koch

Question 2

What is cell theory?

Answer 2

• All organisms composed of ONE OR MORE CELLS
• Cells are the SMALLEST UNITS of life - form basis of organisation (in all living things)
• Cells arise only by division of a PRE-EXISTING CELL

Question 3

What can we do to understand a cells function?

Answer 3

Based on the COMPONENTS of the cell - VARIATION allows us to understand this

Question 4

How many types of cells are in the human body?

Answer 4

At least 200 cell types

All have the same chromosomes

Question 5

What is the Honey Fungus like?

Answer 5

Largest organism in the world (2,200 acres)

Probably <20 types of cells in this fungus

Question 6

What is microscopy?

Answer 6

Produces enlarged image through magnification

Images can be sensor detected & computer manipulated/enhanced

Question 7

What is resolution?

Answer 7

Ability to discriminate parts of an image

Question 8

What are the two main types of microscopy used?

Answer 8

Light microscopy
Electron microscopy

Question 9

What is light microscopy?

Answer 9

• Broad beam of illuminating light focussed on specimen by condenser lens
• Bright light passes thru img

Requires staining - often involves in cell death

Question 10

What sort of section needs to be used for light microscopy?

Answer 10

Thin section

Question 11

What is the limit of resolution and magnification for light microscopy?

Answer 11

Resolution = 0.2um

Which is 1000x

Question 12

What are the 4 stages to prepare a section for light microscopy?

Answer 12

1. Fixation
2. Embed
3. Section
4. Staining

Question 13

What is the purpose of fixation for light microscopy?

Answer 13

Stops the tissue falling apart, immobilises cells

(use fixative e.g. formaldehyde)

Question 14

What is the purpose of embedding for light microscopy?

Answer 14

This provides mechanical support

Question 15

What is the purpose of sectioning for light microscopy?

Answer 15

You need a thin section for light microscopy

Cut thin section using microtome (with metal, glass or diamond blade)

Question 16

What is the purpose of staining for light microscopy?

Answer 16

Improves the visibility of the thin sections

Question 17

What is the equation for magnification?

Answer 17

Total magnification = magnification of objective lens X magnification of eyepiece lens

Question 18

What are the other types of light microscopy?

Answer 18

1. Phase contrast
2. DIC (Differential Interference Contrast)
3. Fluorescence microscopy
4. Laser scanning confocal light microscopy

Question 19

What is phase contrast microscopy?

Answer 19

Increase ‘contrast’ of images using phase contrast microscopy, cellular components have different refractive indexes

(good for looking at components)

Question 20

What is DIC microscopy?

Answer 20

Rates of change in refractive index = 3D shapes

(Differential Interference Contrast)

Question 21

What is fluorescence microscopy?

Answer 21

Specimen stained w fluorescent dye or protein - UV light excites the specimens, makes high contract img

Contrasts to dark background

Question 22

What protein is often used for fluorescence microscopy?

Answer 22

GFP from jellyfish (Green Fluorescent Protein)

Question 23

What is laser scanning confocal light microscopy?

Answer 23

Imagining of a thin plane with a thicker specimen (non-sectioned)

Focussed laser beam excited fluorescent molecules in cells & tissues, scans at single points in planes (gives sharp images)

Question 24

What is laser scanning confocal light microscopy useful for?

Answer 24

For living cells - can pool images to construct 3D model

Question 25

What are the two types of electron microscopy?

Answer 25

1. Transmission electron microscopy (TEM) 2. Scanning electron microscopy (SEM)

Question 26

How does electron microscopy work?

Answer 26

Uses a beam of electrons rather than light Creates much more powerful images that light

Question 26

How does electron microscopy work?

Answer 26

Uses a beam of electrons rather than light Creates much more powerful images that light

Question 27

How does TEM work?

Answer 27

Electrons pass through a very thin specimen - allows magnification of up to 1,000,000x

Question 28

How must the specimen be prepared for TEM?

Answer 28

Fixed, dehydrated, sectioned & stained with electron dense metals (platinum or gold)

Question 29

What happens to samples for TEM?

Answer 29

The samples could be rapidly frozen (cryofixatton) Freeze-fracture reveals cell structure (knife used) cleaving cell then split surfaces using dense materials

Question 30

How does SEM work?

Answer 30

Electron beam is scanned over the surface - electrons bounce back & strike a detector

Question 31

What kind of image is produced by SEM?

Answer 31

Provides info on the surface details - appears 3D Lower mag than TEM

Question 32

What are the 3 main recent advances in microscopy?

Answer 32

- Cryo-electron microscopy - Super resolution microscorpy - Atomic force microscopy (AFM)

Question 33

What is Cryo-electron microscopy?

Answer 33

Less harsh method, more intricate detail Use deep frozen molecules in solution & gentler electron beams (these are collected on the other side of the cell) Determines structure of biomolecules

Question 34

What is super resolution microscopy?

Answer 34

Fluorescent based techniques Overcomes traditional light resolution limit by various complex interference/tunneling methods Allows resolution to ca. 100nm

Question 35

What is Atomic Force Microscopy (AFM)?

Answer 35

Method to visualise surfaces at a molecular scale uses fine pointed tip linked to cantilever arm, can move up & down as moves across surface Detect fine movement by reflected laser beam