ANTIBIOTICS

Question 1

types of antimicrobials (3)

Answer 1

• antiseptics used on living tissue
• disinfectants used on non-living surfaces
• antibiotics

Question 2

antibiotics (3)

Answer 2

• produced by fungi, act exclusively on bacteria
• narrow-spectrum antiobiotics affect specific species (penicillin)
• broad-spectrum antibiotics affect an array of gram-pos/gram-neg bacteria (tetracycline)

Question 3

antibiotics effect on bacteria metabolism (2)

Answer 3

• bactericidal, kill bacteria

- bacteriostatic, prevent replication but do not kill

Question 4

murein in cell walls (4)

Answer 4

• murein/peptidolycan forms cell walls
• contains polysaccarides & short amino acid chains
• transpeptidase enzymes cross-link polysaccharides by attaching them to side amino acid chains
• cross-linking makes wall strong/keeps shape and resists osmotic pressure

Question 5

gram-positive cell walls (4)

Answer 5

• make of a thick layer of murein (90%)
• pores in murein close during decolorisation of the gram stain so crystal violet is retained in cell
• safranin used as a counter stain and turns it violet
• murein accessible to molecules outside the cell so vulnerable to lysozyme/penicillin attack

Question 6

gram-negative cell walls (4)

Answer 6

• thin layer of murein, surrounded by lipoprotein/lipopolysaccharide
• lipid molecules disrupted by decolorisation and crystal violet leaks out of cell
• safranin stains them red
• lipid-layer protects murein from antimicrobial agents (lyzozyme/penicillin)

Question 7

how does a bacterial cell wall work

Answer 7

• continually breaking/making cell wall

- enzyme DD-transpeptidase catalyses condensation reactions to make cross-links

Question 8

penicillin (6)

Answer 8

• penicillin diffuses into gram-pos and through porins into some gram-neg
• penicilin binds to DD/PBP (penicillin binding protein) and acts as an inhibitor
• hydrolysis of cell wall continues so more is lost than gained
• no peptide cross-links are made
• cell wall is weakened so when osmosis occurs the cell llyses
• penicillin is small enough to penetrate through the murein so the entire wall is effected

Question 9

tetracycline

Answer 9

• inhibits protein synthesis
• diffuses and is pumped into bacteria
• binds to small ribosome subunit & blocks second tRNA position
• binds reversibly

Question 10

why are viruses not affected?

Answer 10

no metabolic pathways

Question 11

types of antibiotic resistance (2)

Answer 11

• bacteria rapidly divide in suitable conditions leading to a high mutation rate
• bacteria can acquire plasmids from environment and pass them on

Question 12

overuse of antibiotics (3)

Answer 12

• accidentally selected for bacterial resistance
• but only advantages when antibiotics are present
• development of new antibiotics paramount to prevent infection following surgery