option D- medicinal chemistry (D.5)

Question 1

what makes viruses so complex

Answer 1

they lack a cell structure and so are more difficult to target than bacteria

Question 2

describe the differences between viruses and bacteria

Answer 2

while bacteria are living cells that can feed, excrete, grow and multiply, viruses lack cellular structure and do not have their own metabolism.

therefore viruses are not considered to be life forms but rather very complex chemical compounds

Question 3

describe the structure of most viruses

Answer 3

• nucleoproteins containing a nucleic acid surrounded by a capsid (protein coat)
• this consists of multiple protein units (capsomeres) arranged in helical or polyhedral structures

Question 4

describe how viruses function

Answer 4

1. capsid proteins of viruses bind to receptors on the host cell surface
2. they either cross the cell membrane or inject their genome into the cell
3. virus genome is interpreted as a set of instructions for synthesising proteins and nucleic acids, which self-assemble into new copies of the virus
4. replicated viruses are released from the host cell usually by lysis

Question 5

what has the best defence against specific types of virus been in the past few years?

Answer 5

immunisation

Question 6

give the two main ways that antiviral drugs can work

Answer 6

• by preventing the viruses from multiplying by blocking enzymes activity within the host cell (stage 4)
• by altering the cell’s genetic material so that the virus cannot use it to multiply (stage 3)

Question 7

stage 2 antivirals

Answer 7

inhibit the binding of the virus and the injection of its genetic material into the cell (amantadine and rimantadine) but resistance has been developed

Question 8

stage 3 antivirals

Answer 8

biosynthesis of viral compounds by the host cell is targeted by antivirals that mimic the structures of nucleotides (eg acyclovir and zidovudine)

these undergo phosphorylation and produce non-standard nucleotides which are mistakenly incorporated into RNA and DNA sequences. the enzymes produced from these altered nucleic acids are inactive and cannot be used for replicating viral components.

Question 9

stage 4 antivirals

Answer 9

prevent the release of virus copies from the cell by inhibiting neurominidases (viral enzymes), which trigger the process of budding, which allows viruses to bulge through the outer membrane of the host cell. this inhibition therefore keeps viruses trapped within the cell and prevents spread

eg oseltamivir (Tamiflu) and zanamivir (Relenza)

Question 10

give similarities and differences between oseltamivir (Tamiflu) and zanamivir (Relenza)

Answer 10

• both target same enzymes
• both contain a six-membered ring with three chiral carbon atoms
• side chains contain different functional groups (O-COO and Z-COOH)
• cases of resistance in zanamivir more rare
• O inactive in original form, Z active

Question 11

why is oseltamivir inactive in its original form and how is this overcome?

Answer 11

inactive; due to presence of the ester group.

in the body the ester group is hydrolysed into a carboxyl group, producing an active metabolite with enhanced antiviral activity

Question 12

describe HIV and AIDS

Answer 12

human immunodeficiency virus is responsible for acquired immunodeficiency syndrome which is the progressive failure of the immune system and the development of life-threatening opportunistic infections and cancers

Question 13

why is HIV so difficult to tackle?

Answer 13

• fast replication cycle and high mutation rate
• infects lymphocytes/white blood cells that are responsible for righting viral and bacterial infections
• HIV is able to incorporate itself into the host DNA where it can remain dormant for many years

Question 14

what are retroviruses? how can they be fought?

Answer 14

viruses like HIV that use reverse transcriptase enzymes to produce DNA strands from their RNA genomes.

inhibition of reverse transcriptase, which is not used in normal cells.