Lecture #2 - Basics of Cell Bio

Question 1

What is a cell?

Answer 1

Simplest collection of matter that can be alive (all organisms are made of cells)

Question 2

Species are classified based on their…..

Answer 2

Structure and DNA sequence

Question 3

The highest classification are called …… and what are the three?

Answer 3

Domains

1. Bacteria prokaryotes
2. Archaea prokaryotes
3. Eukarya eukaryotes

Question 4

Eukarya have 4 kingdoms - name them

Answer 4

1. Plantae
2. Fungi
3. Animalia
4. Protist (single cell)

Question 5

Diameter of plant/animal cell

Answer 5

Between 10 to 100 micrometer

Question 6

Diameter of typical bacteria cell

Answer 6

Between 1 to 5 micrometers

Question 7

1000micrometers = ?mm

Answer 7

1mm

1e-9 (nano)
1e-6 (micro)
1e-3 (milli)

Question 8

Why are cells limited to size range?

Answer 8

Larger cells have a reduced SA:V ratio - this ratio limits the exchange with environment

Smaller cells have a better SA:V ratio bc SA prop to diameter squared but V prop to diameter cubed

Question 9

Light microscopy

1. Magnification about….
2. Greater magnification limited by….
3. What recent advances have enhanced the power of EM?
4. Can you image living cells?

Answer 9

1. Mag is 1000x
2. Greater magnification limited by RESOLUTION (0.2microm)
3. Recent advances have used STAINING and IMAGING techniques
4. SOME FORMS of LM may be used to image living cells

Question 10

Electron Microscopy

1. Focus what rather than light?
2. Resolution is 𝝰 or inversely 𝝰 to wavelength?
3. More than ?-fold improvement on LM?
4. What are the two types?

Answer 10

1. Focus ELECTRONS
2. Resolution is INVERSELY PROPORTIONAL to ƛ
   (if ƛ ↑ then res ↓)
3. More than 100-FOLD improvement
4. TEM and SEM

Question 11

Scanning Electron Microscopy

1. How does it work?
2. Images are grey-scale or coloured?

Answer 11

1. Scans the surface of the specimen which has been coated in a thin film of gold - electrons excite the gold atoms to generate a 3-D image of the surface of a specimen.
2. Images are grey-scale but can be artificially coloured to highlight structures.

Although this microscope gives lower magnifications than the TEM, the SEM permits three‐dimensional views of microorganisms and other objects

Question 12

Transmission Electron Microscopy (TEM)

1. Used to examine what?
2. How does it work?

Answer 12

1. Used to examine cell’s internal structure
2. Electron beam passes through a thin section of a specimen that has been stained with heavy metals. The scattered electrons are focused by electromagnets to generate an image.

Question 13

Which of the four (LM, EM, SEM and TEM) can only be used on processed DEAD cells?

Answer 13

SEM and TEM - dead only

Question 14

Describe the Endosymbiont theory

Answer 14

1. Prokaryotic cells were engulfed by early eukaryotic cells and established a stable relationship of benefit to both parties
2. Engulfed prokaryotes evolved into mitochondria
   (similar proposal for chloroplasts arising from photosynthetic prokaryotes)

Evidence: Two membranes (inner resembles bateria and outer is more eukaryotic. Also, they have their own DNA but they aren’t fully independent - main cell makes some of the proteins so table relationship.

Question 15

Three imp parameters in microscopy are

1. Magnification
2. Resolution
3. Contrast

Answer 15

1. Magnification - RATIO of image size to real size
2. Resolution - refers to CLARITY of image
3. Contrast - the difference between light and dark areas of the image…enhanced by STAINING