Nucleotide and nucleoside analogues are therapeutic drugs that have a similar structure to nucleotides or nucleosides of RNA and DNA. A nucleoside is composed of a nitrogenous organic base (base) and a pentose sugar. Abacavir is an analogue drug used in the treatment of some viral diseases. It enters a cell infected by a virus and is metabolised to the analogue carbovir triphosphate. Fig. 5.1 shows the molecular structure of abacavir and carbovir triphosphate. Carbovir triphosphate can be inserted into an elongating polynucleotide chain instead of a nucleotide. This interferes with the action of DNA polymerase during the synthesis of viral DNA. Suggest and explain how carbovir triphosphate interferes with the action of DNA polymerase and how this may prevent the synthesis of viral DNA.

Biology

IGCSE&ALevel

CAIE

Exam No：9700_s23_qp_22 Year：2023 Question No：5(b)(iii)

Answer:

Knowledge points:

10.2.1 outline how penicillin acts on bacteria and why antibiotics do not affect viruses

10.2.2 discuss the consequences of antibiotic resistance and the steps that can be taken to reduce its impact

6.1.1 describe the structure of nucleotides, including the phosphorylated nucleotide ATP (structural formulae are not expected)

6.1.2 state that the bases adenine and guanine are purines with a double ring structure, and that the bases cytosine, thymine and uracil are pyrimidines with a single ring structure (structural formulae for bases are not expected)

6.1.3.1 the importance of complementary base pairing between the 5' to 3' strand and the 3' to5' strand (antiparallel strands)

6.1.3.2 differences in hydrogen bonding between C–G and A–T base pairs

6.1.3.3 linking of nucleotides by phosphodiester bonds

6.1.4.1 the roles of DNA polymerase and DNA ligase (knowledge of other enzymes in DNA replication in cells and different types of DNA polymerase is not expected)

6.1.4.2 the differences between leading strand and lagging strand replication as a consequence of DNA polymerase adding nucleotides only in a 5 to 3 direction

6.1.5 describe the structure of an RNA molecule, using the example of messenger RNA (mRNA)

Answer:

Knowledge points:

Solution:

Related Question