AP BIOLOGY

Detailed explanation-1: -The SmaI and XmaI endonucleases are imperfect isoschizomers that recognize the sequence CCCGGG. SmaI cleaves between the internal CpG to produce blunt end scissions whereas XmaI cleaves between the external cytosines to produce a four base, five prime overhang.

Detailed explanation-2: -Examples of neoschizomers are SmaI (5′-CCC↓GGG-3′) and XmaI (5′-C↓CCGGG-3′), which both recognize 5′-CCCGGG-3′ but cleave them differently and thus generate different types of ends (in this case, blunt ends for SmaI and 5′ protruding ends for XmaI).

Detailed explanation-3: -An enzyme that recognizes the same sequence but cuts it differently is a neoschizomer. Neoschizomers are a specific type (subset) of isoschizomer. For example, SmaI (CCC/GGG) and XmaI (C/CCGGG) are neoschizomers of each other. Similarly KpnI (GGTAC/C) and Acc65I (G/GTACC) are neoschizomers of each other.

Detailed explanation-4: -XmaI is an isoschizomer of SmaI. XmaI produces a 5´ extension whereas SmaI produces blunt-ended fragments. Impaired by CpG methylation.

Detailed explanation-5: -Two or more restriction enzymes that recognize the same DNA sequence and cleave it with exactly the same specificity are called isoschizomers. Neoschizomers are similar to isoschizomers in that they recognize the same DNA sequence; however, they generate different cleavages at the recognition sequence.