Biochemistry Chapter 9 Exam – DNA Technology, Restriction Enzymes & Molecular Analysis |Verified Questions Complete with A+ Graded Rationales Latest Updated 2026

Biochemistry Chapter 9 Exam – DNA Technology, Restriction Enzymes & Molecular Analysis |Verified Questions Complete with A+ Graded Rationales Latest Updated 2026 What are restriction endonucleases and why were they pivotal in biotechnology? Restriction endonucleases are bacterial enzymes that recognize and cut specific DNA sequences, enabling scientists to fragment and recombine DNA. Their discovery made modern biotechnology possible by allowing precise manipulation of genes. Differentiate between endonucleases and exonucleases. Endonucleases cut internal phosphodiester bonds within a DNA strand, while exonucleases remove nucleotides from the terminal ends of DNA. What are blunt ends versus sticky ends, and why are sticky ends important? Blunt ends result from cuts at the same position on both DNA strands. Sticky ends are staggered cuts leaving single-stranded overhangs, which can easily hydrogen bond with complementary sequences for recombinant DNA formation. How do host bacterial cells protect their DNA from their own restriction enzymes? They methylate their own DNA at restriction sites, preventing endonucleases from recognizing and cleaving those sequences. Describe the key properties of Type I and Type II restriction endonucleases. Type I enzymes both methylate host DNA and cleave unmethylated DNA at recognition sequences (usually far from the site). Type II enzymes cut double-stranded DNA at or near specific recognition sites without methylation activity — these are the primary tools used in molecular biology. What is a palindromic sequence, and why is it significant for restriction enzymes? A palindromic sequence reads the same on both DNA strands in the 5'→3' direction; restriction enzymes often recognize these symmetrical sites, ensuring precise and reproducible cutting. How do ligases complement restriction enzymes in molecular cloning? DNA ligases rejoin DNA fragments by catalyzing the formation of phosphodiester bonds between sticky or blunt ends, sealing recombinant DNA. What is the purpose of gel electrophoresis in DNA technology? It separates DNA fragments by size when subjected to an electric field; smaller fragments migrate faster toward the positive electrode due to DNA's negative charge. What are the two main types of gels used and what are they for? Agarose gels are used for separating DNA, while polyacrylamide gels are used for separating proteins or small nucleic acids. How can DNA fragments be visualized in gels? By staining with dyes (e.g., ethidium bromide) that intercalate into DNA and fluoresce under UV light, or by autoradiography when radioactive isotopes are incorporated into DNA. What is autoradiography and when is it used? A detection method using radioactive DNA; exposed X-ray film reveals the position of DNA bands that emit radiation. What is the function of ethidium bromide in electrophoresis? It binds to DNA and fluoresces under UV light, allowing the visualization of DNA bands in the gel. What is a restriction map and how is it used? A diagram showing specific cleavage sites for restriction enzymes within a DNA molecule, used to identify, characterize, or compare DNA sequences. How does DNA fingerprinting utilize restriction enzymes? By analyzing the unique pattern of restriction fragments produced from variable DNA regions, enabling individual identification or genetic comparison. Why are DNA fingerprints unique to individuals? Highly variable noncoding regions differ between individuals, producing distinct fragment patterns when cut by restriction enzymes. Explain the purpose of the Southern blot technique. To identify specific DNA sequences among many fragments using complementary labeled probes that bind to their target sequences after transfer to a membrane. How do