Lecture 1- Bacterial cell structure

Question 1

What are the basic steps in bacterial identificiation? (x5)

Answer 1

1. Size and shape (gram stain)
2. Cell arrangement (chain of cells of cluster?)
3. Motility (flagella)
4. Spores - one per cell
5. Capsules

Question 2

What are the 7 size and shape categories for bacteria?

Answer 2

1. Coccus- circle
2. Rod (also vibrios)
3. Spiral
4. Spirochetes (flexible, helical)
5. Square (flat square)
6. Star shaped -genus Stella
7. Absolutely huge (not sure if that’s an actual category. e.g. fisheloni- 85000 copies of DNA)

Question 3

Why do streptococcus form chains while staphylococcus form clusters? And E.Coli don’t form either?

Answer 3

Streptococcus spp always divide on the same plane so form chains length ways. Staphylococcus spp divide on different planes so form in random directions, forming clusters.

E. Coli split apart after each division so don’t stick together.

Question 4

The Gram stain was invented in 1884 by Christian Gram.

It differentiates bacteria on the bases of cell wall structure into which two groups?

Answer 4

1. Gram positive- purple
2. Gram negative- pink/red

Question 5

Which type of bacteria does penicillin work on? Why?

Answer 5

Gram positive bacteria. Because it attacks the peptidoglycan which Gram +ve has lots of.

Question 6

What’s the difference between gram positive and gram negative bacteria?

Answer 6

Gram positive has a thick peptidoglycan layer of 20nm and no outer membrane.

Gram negative has an outer membrane and a thin peptidoglycan layer underneath of 5-8nm.

Question 7

What are the steps of The Gram Stain?

Answer 7

1. Prepare cells on slide
2. Stain with crystal violet
3. Stain with iodine- (CVI complex forms)
4. Acetone- (dissolves outer membrane)
5. Counter stain with safranin

Gram positive= purple

Gram negative = pink/red

Question 8

How does the Gram stain work?

Answer 8

The CVI (crystal violet-iodine) complex is trapped in the gram positive bacteria because of the thick peptidoglycan layer.

The acetone dehydrates the peptidoglycan layer, sealing the CVI complex into the cell.

In Gram negative bacteria acetone dissolves the outer membrane, releasing the CVI complex.

The CVI stays in the gram positive bacteria but not the gram negative one so gram positive is purple.

Question 9

What are the biological functions of peptidoglycan?

Answer 9

1. Rigid structure of wall
2. Protects from osmotic lysis
3. Withstands a high internal osmotic pressure

Question 10

In gram positive and gram negative bacteria, is it high or low pressure?

Answer 10

Gram +ve= high internal pressure. (thick walls)

Gram -ve = low internal pressure (thinner walls)

Question 11

Pleomorphic cells like *Mycoplasma pneumoniae *have no peptidoglycan and and are surrounded by a membrane. How do they survive the variable conditions?

Answer 11

They are parasitic so always live inside eukaryotic cells. So they don’t need to be adapted to varying conditions because they’ve got such constant conditions. Over time evolution has cause it to lose functions because it doesn’t need them anymore. Lazy.

Question 12

How does penicillin work?

Answer 12

It stops the peptide bridges forming between the polymers in peptidoglycan.

Question 13

What’s peptidoglycan made up of and what give it its strength?

Answer 13

1/2 sugar and 1/2 protein. With peptide bridges joining the mesh. The bridges are the really strong part.