The restriction enzymes XhoI and SalI cut their specific sequences as shown below:

Can the sticky ends created by XhoI and SalI sites be ligated? If yes, can the resulting sequences be cleaved by either XhoI or SalI?

Verified step by step guidance

1. Step 1: Understand the concept of sticky ends. Sticky ends are single-stranded overhangs created when restriction enzymes cut DNA at specific recognition sites. These overhangs can pair with complementary sequences, allowing DNA fragments to be ligated together.
2. Step 2: Analyze the sequences cut by XhoI and SalI. XhoI cuts at 5'-CTCGAG-3' and leaves a sticky end with the sequence 5'-TCGA-3'. SalI cuts at 5'-GTCGAC-3' and leaves a sticky end with the sequence 5'-TCGA-3'. Notice that both enzymes produce identical sticky ends (5'-TCGA-3').
3. Step 3: Determine if ligation is possible. Since the sticky ends produced by XhoI and SalI are identical, they can pair and be ligated together using DNA ligase. This is because complementary base pairing occurs between the overhangs.
4. Step 4: Examine the resulting sequence after ligation. When the sticky ends are ligated, the resulting sequence will contain the joined DNA fragments. However, the ligation may disrupt the recognition sites for XhoI and SalI, depending on the orientation of the ligated fragments.
5. Step 5: Assess cleavage by XhoI or SalI. After ligation, check if the recognition sites for XhoI (5'-CTCGAG-3') or SalI (5'-GTCGAC-3') are restored. If the ligation alters the sequence such that the recognition sites are no longer present, the resulting DNA cannot be cleaved by either enzyme.

Key Concepts

Restriction Enzymes

Restriction enzymes, or restriction endonucleases, are proteins that cut DNA at specific sequences, known as recognition sites. Each enzyme recognizes a unique sequence of nucleotides and cleaves the DNA, often producing 'sticky' or 'blunt' ends. Understanding how these enzymes work is crucial for genetic engineering, as they allow for the manipulation of DNA fragments for cloning or other applications.

Sticky Ends

Sticky ends are short, single-stranded overhangs that are created when restriction enzymes cut DNA in a staggered manner. These overhangs can easily anneal with complementary sequences, facilitating the ligation of different DNA fragments. The ability to ligate DNA fragments with sticky ends is fundamental in recombinant DNA technology, allowing for the creation of new genetic combinations.

Ligation and Cleavage

Ligation is the process of joining two DNA fragments together, typically using the enzyme DNA ligase, which forms covalent bonds between the sugar-phosphate backbones. After ligation, the resulting DNA can be tested for susceptibility to cleavage by the original restriction enzymes. If the ligated sequence contains the recognition sites for either enzyme, it can be cleaved again, which is important for verifying successful cloning or modification.