2.3: Explain how medicines affect causative agents of infectious diseases (Amoxicillin)

Question 1

What are the 4 different ways we can stop a bacteria from growing and reproducing?

Answer 1

• Stop expansion of cell wall, make holes in cell wall
• Damage membranes
• Stop synthesis of nucleic acids or proteins
• Stop metabolic pathways required by bacteria to survive

Question 2

What are the 4 ways a bacteria can stop drugs from entering its cytoplasm?

Answer 2

1. Barriers to entry:
   - Cell wall
   - Plasma membrane
   - Channel proteins
2. Removing or breaking down toxins (antibiotics)
3. Drug efflux transporters - pump drugs back out
4. Enzymes - break down drugs

Question 3

Inhibition of cell wall synthesis: Amoxicillin (Penicillins) explained:

Answer 3

• Bacteria have cell walls made of peptidoglycans e.g. *Murien / *It’s a mesh-like layer made of sugars and amino acids that surrounds the cytoplasmic membrane of the bacteria.
• Peptidoglycans in bacterial cell walls increase their strength and keep external fluids (e.g. Water) and particles from entering them (e.g. by osmosis) which would cause them to burst.

1. When a bacterium multiplies, small holes open up in their cell walls as the cells divide. These holes are then backfilled with newly produced peptidoglycans, and the wall is reconstructed.
2. Penicillins inhibit the protein struts that link the peptidoglycans together in the wall. This inhibition prevents the bacterium from closing the holes in its wall.
3. Because of the difference in pressure between the inside of the bacterium and the surrounding fluid, water rushes into the hole and osmosis through the plasma membrane into the bacterium causing it to burst (osmolyse).

• Because of their thin but difficult-to-penetrate outer cell membranes, gram-negative bacteria are often resistant to this type of antibiotic and other antibacterial interventions.

Question 4

2 Mechanisms of Amoxicillin

Answer 4

1. Bacterial infections (medicines that inhibit nucleic acid synthesis: e.g. sulphonamides; medicines that inhibit cell wall synthesis, e.g. Penicillins; Medicines that inhibit protein synthesis, e.g. Chloramphenicol and Erythromycin)
2. Viral infections (medicines that stop a virus entering host cells, e.g. Amantadine; medicines that inhibit nucleic acid synthesis, e.g. Acyclovir)

Question 5

Difference between Gram-negative and Gram-positive

Answer 5

• Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide.
• Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives.

Question 6

What are Sulphonamides?

Answer 6

Sulfonamides are bacteriostatic agents that inhibit cell growth by interfering with bacterial biosynthesis of folic acid.

Question 7

Why is Folic acid important?

Answer 7

Folic acid is necessary in the production of purines that are involved in the construction of the backbone of the DNA. Sulfonamides have broad-spectrum activity. They are active against Gram-negative, Gram-positive bacteria, and some protozoa species.

Question 8

Difference between the 2 Grams stain colours under the microscope
Gram stain colour

Answer 8

Gram-positive bacteria appear purple or blue under a microscope after Gram staining.

While Gram-negative bacteria appear pink or red.

Question 9

Mechanism of Sulfonamides

Answer 9

1. Sulfonamides are a type of antibiotic that work by inhibiting the production of folic acid in bacteria, which stops their growth
2. Sulfonamides bind to the enzyme dihydropteroate synthase (DHPS), which is needed for bacteria to synthesize folate.
3. Sulfonamides compete with p-aminobenzoic acid (PABA) for the enzyme DHPS. PABA is a cofactor that bacteria need to make folic acid.
4. The enzymes are “misled” into making a “false” folic acid molecule that can’t perform its normal function.

Question 10

What disease does sulfonamides treat and what is the disease caused by?

Answer 10

• Co-trimoxazole is used to treat certain bacterial infections, such as pneumonia cause by Streptococcus pneumoniae, bronchitis caused by Bordetella pertussis.
• Streptococcus pneumoniae is a gram-positive, lancet shaped bacterium
• Bordetella pertussis is a gram-negative bacterium