1.How does the spiral shape of DNA help it perform its function?
1 mark
AIt allows the two strands to separate during transcription and replication.
Why this is wrongStrand separation during transcription and replication is possible because the two strands are complementary and held by weak hydrogen bonds, not because of the spiral coiling.
BIt ensures the accuracy of the information and facilitates the correction of any errors.
Why this is wrongAccuracy and error correction come from complementary base pairing between the two strands, which is a different property from the coiled shape.
CIt allows for the packing of a huge amount of genetic information Correct answer
DIt provides each strand as a template for the construction of a new strand.
Why this is wrongEach strand acting as a template follows from the double-stranded complementary structure, not from the helical coiling the stem asks about.
Why this is correctHelical coiling helps compact a long DNA molecule so large genetic content can fit in cells.
The concept is how the coiled (helical) shape of DNA serves its job. Winding the very long molecule into a tight spiral lets a huge amount of genetic information be packed into the small space of the cell. The other choices describe features that come from DNA being double-stranded and complementary, not from the spiral coiling itself. Method: separate what the coil does (compaction) from what the two complementary strands do (separation, templating, error checking).
2.All the following statements describes the action of DNA polymerase Except:
1 mark
AAdding new nucleotides to the 5′ end of the new nucleic acid Correct answer
BForms covalent bonds between adjacent nucleotides in the strand of new nucleic acid
Why this is wrongThis is a true action — DNA polymerase forms the covalent bonds linking adjacent nucleotides of the new strand, so it is not the exception.
CHelps in formation of hydrogen bonds between the strand of new nucleic acid and the template strand
Why this is wrongThis is a true action — DNA polymerase helps establish the hydrogen bonds between each new nucleotide and its complement on the template strand, so it is not the exception.
DAdd the 5′ end of new nucleotide to the 3′ end of previous nucleotide
Why this is wrongThis is a true action — the new nucleotide is joined by its 5′ end to the 3′ end of the previous nucleotide, which is exactly how synthesis at the 3′ end proceeds.
Why this is correctDNA polymerase extends a new strand only at its 3′ end, not at the 5′ end.
This is an "Except" question testing the actions of DNA polymerase. DNA polymerase always adds incoming nucleotides to the 3′ end of the growing new strand, never to the 5′ end, so adding to the 5′ end is the action it does NOT perform. It also forms the covalent bonds between adjacent nucleotides of the new strand and assists the hydrogen bonding between the new strand and the template strand. The reusable method: recall the fixed rule "synthesis proceeds 5′→3′ by addition at the 3′ end," then flag any option that contradicts this direction as the exception.
3.Plasmids in bacteria resemble eukaryotic DNA in the following ways:
1 mark
ATheir linear shape and its combination with histone.
Why this is wrongPlasmids are circular and are not combined with histones, so this describes neither plasmids nor the point of similarity.
BTheir high content of non-coding genes.
Why this is wrongPlasmids mainly carry useful genes, not a high proportion of non-coding genes.
CTheir location within a nuclear membrane.
Why this is wrongBacteria have no nuclear membrane, so plasmids are not located inside one — unlike eukaryotic DNA.
DTheir ability to replicate at the same time with the main DNA. Correct answer
Why this is correctBoth plasmids and eukaryotic DNA are capable of DNA replication, unlike the other listed traits for bacterial plasmids.
Plasmids are small circular DNA molecules in bacteria. They are not linear and are not wrapped around histones, they are not enclosed in a nuclear membrane (bacteria have no nucleus), and they are not especially rich in non-coding genes. The one feature they share with eukaryotic DNA is that they can replicate at the same time as the main (chromosomal) DNA of the cell. So the shared property is their ability to replicate together with the main DNA.