An Introduction to Bacteria

Question 1

Describe ways in which bacteria can be identified

Answer 1

Identified by their size, shape, growth requirements and staining characteristics
For gram staining,
gram positive bacteria stain purple while gram negative bacteria stain red.
In terms of shape, cocci are spherical while bacilli are rod shaped

Question 2

List the structural features of gram positive bacteria

Answer 2

Plasma membrane

Periplasmic space

Peptidoglycan

(3 P’s)

Question 3

List the structural features of gram negative bacteria

Answer 3

Plasma membrane

Periplasmic space

Peptidoglycan

Outer membrane (lipopolysaccharide and protein)

Question 4

Give the shape of bacilli

Answer 4

Rod shaped

Question 5

Give the shape of cocci

Answer 5

Spherical

Question 6

Describe the main structures and functions of a typical bacterial cell (13)

Answer 6

• Chromosome (circular and contains genetic information)
• Cytoplasm
• Cell wall (contains peptidoglycan)
• Ribosome (protein synthesis)
• Penicillin binding proteins (enzymes which synthesise peptidoglycans)
• Peptidoglycan (give the cell strength and shape, consist of carbohydrate polymers cross linked with amino acids)
• Lipopolysaccharide (component of gram negative cell wall)
• Capsule (help protect bacteria from phagocytosis/being engulfed)
• Flagella (for motility/locomotion)
• Fimbriae (for adherence)
• Plasmid (small circular DNA)
• Bacteriophage (a virus that infects bacteria)
• Spores (enhance survivability)

Question 7

Describe the 4 types of flagella

Answer 7

Monotrichous (single flagellum on one side)
Amphitrichous (single flagellum on both sides)
Lophotrichous (multiple flagella on one side)
Peritrichous (multiple flagella all over bacterial body)

(REMEMBER MALP)

Question 8

What is the name of the mechanism which transfers plasmids?

Answer 8

The rolling circle mechanism

Question 9

Describe how bacteria replicate and create genetic variation

Answer 9

Replicate by binary fission (ensures identical progeny)
Genetic variation by:
-Spontaneous mutation
-Transfer of DNA

Question 10

Contrast the structure of peptidoglycan in gram positive and negative bacterial cell walls.

Answer 10

Peptidoglycan is thicker in gram positive bacterial cell walls.

Question 11

Describe briefly the detection and culture of bacteria

Answer 11

For individual bacteria:

• They can be seen with a 1000x microscope, using an oil immersion lens
• Staining can be used, such as Gram and fluorescent dyes

For colonies of individual bacteria:

• Cultured on nutrient agar
• Bacterial colonies can be seen by the naked eye

Question 12

The name of bacteria is based on

Answer 12

Genus AND species

genus first then species e.g Staphylococcus aureus