Bacteria Introduction

Question 1

What colour do Gram positive bacteria stain?

What colour do Gram negative bacteria stain?

Answer 1

Purple

Red/pink

Question 2

Differentiate Gram positive from negative in terms of membranes

Answer 2

Positive have a plasma membrane and a peptidoglycan

Negative have an additional periplasmic space and a lipopolysaccharide

Question 3

Describe how to carry out Gram staining

Answer 3

Heat fixation of the sample to a glass slide
Add crystal violet and Gram’s iodine (purple, complex formed)
Add acetone (negative decolourise - LPS dissolves)
Add secondary stain (colourless become red/pink)

Question 4

Outline the range of flagellum types a bacterial cell may have

Answer 4

Monotrichous - one
Lopho - many from one point
Amphi - both sides
Peri - all over

Question 5

What is meant by conjugation in term of bacteria?

Answer 5

Plasmid transfer from one bacterium to another

Question 6

What 3 ways does genetic variation occur in bacteria?

Answer 6

Conjugation
Transformation (taken from dead)
Transduction (phage DNA infection)

Question 7

Describe the 2 ways a bacteriophage is formed?

Answer 7

Lysogenic cycle - DNA injection and integration

Lytic cycle - no integration/replication of pathogenic/lysis

Question 8

How does PCR work?

Answer 8

Genetic amplification of bacterial gene sequencing giving a unique pattern of bands
(akin to gel electrophoresis)