Molecular Tools and DNA Architecture
DNA Features Relevant to Cloning
Essential DNA structure
Cloning depends on the predictable chemistry of DNA: complementary base pairing, antiparallel strands, and a stable sugar-phosphate backbone. Because sequence information is encoded linearly, a copied fragment remains readable and searchable by enzymes and sequencing methods.
Restriction enzymes
Restriction endonucleases recognize specific short DNA sequences and cut at or near those sites. They are often used to generate compatible DNA ends for inserting a fragment into a vector.
DNA ligase and polymerase
DNA ligase joins adjacent DNA ends by forming phosphodiester bonds, while DNA polymerases synthesize new DNA strands. Together, these enzymes support both the assembly and amplification stages of cloning workflows.
Mechanistic insight
Sticky ends created by staggered cuts often improve insertion efficiency because complementary overhangs can base-pair before ligation.
Which enzyme is most directly responsible for sealing DNA fragments together during cloning?
DNA ligase forms the covalent bonds that seal DNA fragments into a continuous molecule.
Correct answer: DNA ligase
What is the main advantage of complementary sticky ends in cloning?
Base pairing between matching overhangs helps align the DNA ends before ligation.
Correct answer: They improve the likelihood and specificity of insert-vector joining.
Common cloning enzymes
| Enzyme | Primary role |
|---|---|
| Restriction enzyme | Cuts DNA at specific sequences |
| DNA ligase | Joins DNA ends |
| DNA polymerase | Synthesizes new DNA |
| Reverse transcriptase | Makes complementary DNA from RNA |