AP BIOLOGY

Detailed explanation-1: -A bacterium uses a restriction enzyme to defend against bacterial viruses called bacteriophages, or phages. When a phage infects a bacterium, it inserts its DNA into the bacterial cell so that it might be replicated. The restriction enzyme prevents replication of the phage DNA by cutting it into many pieces.

Detailed explanation-2: -In vivo, these enzymes are involved in recognizing and cutting up foreign DNA entering the cell; their most likely role is thus protecting the bacteria against phage infection.

Detailed explanation-3: -Bacteria protect their DNA by modifying their own recognition sequences, usually by adding methyl (CH3) molecules to nucleotides in the recognition sequences and then relying on the restriction enzymes’ capacity to recognize and cleave only unmethylated recognition sequences.

Detailed explanation-4: -Restriction enzymes cut DNA bonds between 3′ OH of one nucleotide and 5′ phosphate of the next one at the specific restriction site. Adding methyl groups to certain bases at the recognition sites on the bacterial DNA blocks the restriction enzyme to bind and protects the bacterial DNA from being cut by themselves.

Detailed explanation-5: -Like all enzymes, a restriction enzyme works by shape-to-shape matching. When it comes into contact with a DNA sequence with a shape that matches a part of the enzyme, called the recognition site, it wraps around the DNA and causes a break in both strands of the DNA molecule.