Antimicrobials

Question 1

Compare the ribosomes in eukaryotic and prokaryotic cells

Answer 1

prokaryotic cells have 70S while eukaryotic have 80S

Question 2

compare the replication mechanism in eukaryotic and prokaryotic

Answer 2

prokaryotic uses binary fission and eukaryotic uses mitosis

Question 3

What are antibiotics

Answer 3

overlapping subset of antimicrobial agents produced naturally

Question 4

Characteristics of gram negative bacteria

Answer 4

gram negative take up less readily as thinner layer

Question 5

what is magic bullet

Answer 5

the concept that chemicals could be designed to bind to and kill specific microbes or tumor cells

Question 6

What are the three classes of targeting biochemical reactions

Answer 6

1. Class I
   - Target the production of metabolic precursors from substrates such as glucose
   - Restrict any downstream processes
   2. Class II
   - Target processes involved in the production of small molecules from metabolic precursors
   3. Class III
   - Target processes involved in production of macromolecules from small molecule substrates

Question 7

What can the antibacterial agents target

Answer 7

cell wall synthesis, bacteria cell membrane ,protein synthesis, nucleic acid synthesis and action

Question 8

Describe the structure of bacterial cell wall

Answer 8

formed from peptidoglycan made of N-acetylglucosamine and N-acetylmuramic acid bonded by beta-1,4-glycosidic linkages

Question 9

what are the function of bacterial cell wall inhibitors - beta-lactam drugs

Answer 9

they act by covalently binding to DD-transpeptidase enzyme which is responsible for crosslinking the peptides between peptidoglycan

Question 10

What are the two types of beta-lactam drugs and their functions

Answer 10

penicillin and vancomycin
penicillin and different functional groups
attached to the core penicillin gives rise to a variety of antibacterial agents.
vancomycin prevent synthesis by forming strong H bond with peptides and prevent formation of normal lattice

Question 11

What are the inhibitors of bacterial cell membrane and their functions

Answer 11

daptomycin and polymixins
daptomycins aggregate and distort the cell membrane by forming holes so depolarises the membrane and chemical gradient cannot be maintained and bacteria cannot carry our critical biochemical functions

polymixins bind to lipopolysaccharide that is highly abundant in gram negative

Question 12

What is folic acid and its role in nucleic acid synthesis

Answer 12

• DNA and RNA are synthesised from folic acid
• Folic acid are produced from precursor molecule p-aminobenzoic acid (PABA) with the action of dihydropteroate synthetase
• Folic acid is also subsequently metabolised to tetrahydrofolate by dihydrofolate reductase
• Targeted by competitive inhibitors - reduce rate of bacterial DNA/RNA production and are bacteriostatic
1. Sulfonamides are structurally similar to PABA
2. Trimethoprim structurally similar to folic acid

Question 13

function of quinolones

Answer 13

they are DNA gyrase inhibitor that prevent bacterial gene translation or replication and bacterial cell division
examples are ciprofloxacin, norfloxacin and nalidixic acid

Question 14

give examples of RNA synthesis inhibitors

Answer 14

rifampicin that inhibits bacterial DNA -dependent RNA polymerase

Question 15

How bacteria can reduce efficacy of antibacterial agents

Answer 15

1. Target modification
   - the target of the antibacterial agent is changed to prevent biochemical interaction between the agent and target
   
   2. Immunity or bypass
      
      • Bacterial targets not sufficiently well target or there is redundancy in system and the bacterial process can still occur
   3. Reducing the internal dose
      
      • Efflux pumps can be expressed on cell membrane to pump out active agent
   4. Chemical inactivation
      
      • Expression of enzymes or creation of an environment that inactivates a drug

Question 16

How are resistance displayed to an antibacterial agent

Answer 16

1. Inherent resistance of cells
   
   • Bacterial species has certain biological characteristics which allow it to be resistant to antimicrobial agent
     1. Cells has existing degradation ability for the drug
     2. Cell is impervious (not allowing fluid to pass through making target inaccessible and cannot be acted upon
     3. Do not utilise the specifi target/mechanism of drug
2. Mutation and selection of resistant cells
   
   • Genetic variations between cells result from spontaneous mutations that could potentially result in resistance to antimicrobial agents
   • If population of bacterial cells is subjected to antibacterial agents that does not kill all the cells
     
     • Those that remain have been selected on the basis of their resistance
   • These individuals will repopulate and cause subsequent generations to have greater resistance to the drug
   • This is caused by incomplete or unecessary use of antibiotics
3. Horizontal gene transfer to confer resistance mechanism on cells
   
   • Genetic material transferred between organisms and between species
   • The recipient of the material gains the functions associated with it such as resistance.

Question 17

What are the mechanisms of horizontal gene transfer

Answer 17

1. Transformation through the uptake and incorporation of DNA containing a resistance gene
   
   2. Transduction - virus (Phage) mediated transfer of a resistance gene
   3. Conjugation - transfer of a resistance gene across a pilus