Introduction to bacteria

Question 1

What is the function of ribosomes?

Answer 1

Related to protein synthesis involving RNA

Question 2

What is the function of the plasma membrane?

Answer 2

Allows quick diffusion

Question 3

What is the function of a cell wall?

Answer 3

Provides structure and support

Question 4

What is the function of a capsule? (2)

Answer 4

-Used as a defence mechanism
(virulent factor and enhances bacteria to cause disease)
- cause stickiness when they stick to host cells

Question 5

What is the function of a flagellum?

Answer 5

involved in movement and mobility of the cell

Question 6

What is the function of fimbriae? (e.g. in strep throat)

Answer 6

• Involved in attachment to host cells (“attachment pilus”)

- cause adherence in gram positive and negative bacteria

Question 7

What is the colour of gram positive and gram negative cells in gram staining?

Answer 7

Gram positive = purple

Gram negative = red

Question 8

What is the gram positive cell wall composed of? (3)

Answer 8

• plasma membrane
• periplasmic space
• peptidoglycan

Question 9

What is the gram negative cell wall composed of?

Answer 9

• plasma membrane
• periplasmic space
• peptidoglycan
• lipopolysaccharides

Question 10

What are the shapes of; cocci, bacilli and strepto bacteria?

Answer 10

cocci = spherical 
bacilli= rod shaped 
strepto= chains of bacteria

Question 11

What is the primary stain used in gram staining?

Answer 11

Crystal violet

Question 12

Why are gram negative bacteria red and not purple like gram positive?

Answer 12

Gram negative lose its colour because acetyl alcohol is a decolouriser and lipopolysaccharide will dissolve in a solvent such as acetone alcohol (secondary stainer). This will create a faded purple colour which is red

Question 13

What is found on cell wall surfaces of bacteria? (4)

Answer 13

1. plasma/cytoplasmic membrane
2. penicillin binding proteins (PBSs) and cross links (
3. peptidoglycan/murein
4. lipopolysaccharides (elicit strong immune responses in animals and humans)

Question 14

Why do bacteria have spores?

E.g. present in bacillus subtillis found in GI tract

Answer 14

• vital for bacteria’s survival as spores are resistant to environmental stress
• more resistant in harsh conditions
• as it changes from one state to anther, bacteria divide asymmetrically when little nutrients present to increase its chance of survival

Question 15

What is the function of plasmids?

Answer 15

• circular double stranded DNA molecule (separate from chromosomes)
• bacteria can lose its plasmid but not its chromosome

Question 16

What is the function of pillus?

Answer 16

• join 2 bacteria together for plasmid transfer (plasmid becomes mobilised)
• usually between -ve and -ve or +ve and +ve bacteria

Question 17

What are the 3 process involved in DNA transfer which cause genetic variation?

Answer 17

1. conjugation
2. transformation
3. transduction

Question 18

What process do bacteria use to replicate?

Answer 18

Binary fission (identical progeny)

Question 19

What is a bacteriophage?

Answer 19

• viruses which attack bacterial cells

Question 20

How do bacteriophages infect viruses and what cycles are involved?

Answer 20

1. phages inject its genetic material into bacteria (lipid cycle) and become integrated on the host chromosome in the bacteria
2. it can utilise bacterial resources to make copies of itself and split open the bacteria to infect other surrounding cells (lysogenic cycle)

Question 21

How can we detect individual bacteria and colonies of individual bacteria?

Answer 21

• Individual: can only be seen with a microscope and stain (e.g. gram, fluorescent dyes)
• Colonies: cultured on solid medium (agar) and can be seen by naked eye

Question 22

What does MacConkey agar have? (used only for gram negative bacteria)

Answer 22

• lactose
• bile salts (promote growth of -ve bacteria)
• crystal violet
• pH indicator (pink in acidic and yellow in alkali conditions)
  e. g. e.coli will ferment lactose to lactic acid= acidic)

Question 23

What technique is used to identify bacteria strains?

Answer 23

DNA typing technique; incldues gene sequences to distinguish between two similar or different strains of same bacteria. Involves extraction of bacterial DNA using polymerase chain reaction

Question 24

What are some common characteristics between bacteria that would require DNA typing?

Answer 24

non-lactose fermentor, size, shape, morphology (allows easier identification)