Restriction Enzymes

Correct answer: B. DNA

Restriction enzymes primarily cut DNA at specific recognition sequences, so DNA is the correct answer. Glucose, fats and cellulose are carbohydrates or lipids, not targets of restriction enzymes. Exam tip: when you see “restriction endonuclease,” recall that it recognises and cuts a specific DNA sequence.

Correct answer: A. A specific DNA sequence recognized by a restriction enzyme

A restriction site is a specific nucleotide sequence in DNA that is recognized by a particular restriction enzyme. The enzyme cuts the DNA at this sequence or very close to it. The site where DNA replication starts is a different concept, called the origin of replication. Exam tip: associate a restriction site with a DNA recognition sequence.

Correct answer: A. Palindromic sequences

Many restriction enzymes recognize palindromic DNA sequences. This increases their usefulness in gene cloning.

Correct answer: A. It reads the same on both strands in opposite directions

A palindromic sequence shows directional similarity on both strands. In exams link it with restriction enzyme recognition.

Correct answer: A. Restriction enzyme

EcoRI is a restriction enzyme, which is a protein enzyme that recognizes and cuts DNA at a specific sequence. It commonly recognizes the sequence 5′-GAATTC-3′ and produces sticky ends. A hormone acts as a chemical messenger in the body, so it is not EcoRI. Exam tip: Names beginning with Eco, Hind, or Bam often refer to restriction enzymes.

Correct answer: A. Escherichia coli

The governing concept is restriction-enzyme nomenclature. EcoRI was isolated from the bacterium Escherichia coli, specifically the strain traditionally represented in its name. The first letter, E, refers to the genus Escherichia; the next two letters, co, refer to the species coli; the Roman numeral I indicates that it was the first restriction enzyme identified from the relevant strain or source system. Therefore option A, Escherichia coli, is correct. Rhizopus and Agaricus are fungi, while Spirogyra is a green alga; none is the bacterial source associated with EcoRI. The name is therefore a useful example of how restriction enzymes are named from their organisms of origin.

Correct answer: A. It was an early example of controlled DNA cutting

HindII strengthened the idea of cutting at specific DNA sequences. In exams link it with early restriction enzymes.

Correct answer: A. Type II

Type II enzymes cut clearly at or near recognition sites. Therefore they are most useful in cloning.

Correct answer: A. Joining complementary DNA fragments

Direct answer: Option A, joining complementary DNA fragments. A restriction enzyme may leave short single-stranded overhanging ends called sticky ends. The exposed bases can temporarily pair with matching bases on another DNA fragment. This pairing brings the fragments close and in the correct alignment. DNA ligase then seals the sugar-phosphate backbone to make a stable recombinant DNA molecule. Option A is correct because complementary sticky ends assist joining, although ligase performs the final sealing. Option B, photosynthesis, uses light, pigments, carbon dioxide, and water; sticky ends are not involved. Option C, blood clotting, depends on platelets and clotting proteins, not DNA ends. Option D, starch digestion, is performed by amylase and related enzymes, not sticky ends. Common mistake: sticky ends help alignment and pairing; they are not themselves DNA ligase.

Correct answer: A. Blunt ends have no overhang

Blunt ends are straight cut and have no single stranded overhang. This difference is often asked in easy exam questions.

Correct answer: A. Restriction enzyme

The direct answer is option A: restriction enzyme. In cloning, a vector is a DNA molecule used to carry a desired gene into a host cell. To insert the gene, scientists first cut the vector at a suitable restriction site. A restriction enzyme recognises a specific DNA sequence and cuts the DNA there, producing ends that can be joined with the insert, often with matching sticky ends. This is why the enzyme is often called molecular scissors. Option A is correct because it directly cuts the vector DNA at a planned site. Option B, a ribosome, reads messenger RNA and helps make proteins; it does not cut DNA. Option C, a chloroplast, is a photosynthetic cell organelle, not a DNA-cutting tool used for opening a vector. Option D, a lysosome, contains digestive enzymes that break down materials inside cells; it is not the specialised laboratory tool for cutting a cloning vector. After cutting, DNA ligase is commonly used to join the insert and vector, but ligase is not one of the options and is not the cutting tool. Memory cue: restriction enzyme cuts; DNA ligase joins.

Correct answer: A. Gel electrophoresis

Gel electrophoresis separates DNA fragments by size. In exams remember it as analysis after cutting.

Correct answer: A. Protecting self DNA by methylation

The modification part is the protective component of a restriction-modification system. It recognizes the organism’s own DNA and adds methyl groups to particular bases at the system’s recognition sites. This chemical marking does not destroy the DNA or change its information. Instead, it tells the restriction enzyme that this DNA belongs to the host and must be spared. Therefore, option A is correct. The other choices describe unrelated processes: coloring DNA is not a biological role here, making protein from RNA is translation, and changing sugar into fat is a metabolic process.

Restriction enzymes can cut DNA that lacks the protective methyl mark, including incoming foreign DNA. The modification enzyme acts before such cutting becomes a problem by methylating the host’s corresponding sites. Thus, methylation protects self DNA while allowing the restriction component to attack suitably unmodified foreign DNA. The wording “protecting self DNA by methylation” accurately states the main function, so the supplied answer is consistent.

Correct answer: A. Antiviral genetic protection

Cutting phage DNA is part of bacterial genetic defense. Remember it as an example of biological protection.

Correct answer: A. Sugar-phosphate backbone

Restriction enzymes recognize specific DNA sequences and cleave phosphodiester bonds in the sugar-phosphate backbone. Hydrogen bonds between nitrogenous bases hold the two strands together, but the actual permanent cut is made in the phosphodiester linkage between sugar and phosphate. Exam tip: associate the DNA backbone (sugar + phosphate) with phosphodiester bonds.

Correct answer: A. Restriction enzyme cuts and ligase joins

The governing concept is the division of enzymatic roles in recombinant-DNA technology. Restriction enzymes recognise specific DNA sequences and cleave the phosphodiester backbone, thereby producing defined DNA fragments with blunt or sticky ends. DNA ligase performs the opposite construction step: after compatible fragments are aligned, it catalyses phosphodiester-bond formation and seals the backbone. Thus option A accurately states that the restriction enzyme cuts and ligase joins. Option B incorrectly assigns both enzymes a lipid-digesting function. Option C reverses the relevant roles and adds an incorrect staining claim, while option D describes neither enzyme. The distinction is essential for understanding cloning workflows.

Correct answer: A. Compatible ends

Cutting with the same enzyme gives similar compatible ends. This makes joining the gene into the vector easier.

Correct answer: A. Cutting DNA at selected sites

Restriction enzymes make cuts at selected DNA sites. This is a first important step in recombination.

Correct answer: A. Nucleotide sequence

The direct answer is A: nucleotide sequence. Restriction-enzyme specificity means that an enzyme cuts only when it finds a particular arrangement of DNA bases at its recognition site. DNA is made from nucleotides containing bases such as A, T, G, and C. Step by step: the enzyme encounters DNA; it checks the base pattern; only the matching sequence fits its binding site; the enzyme attaches there; cutting occurs at a defined position. A different base order may not fit, so the enzyme does not cut there. Option A is correct because the nucleotide order forms the molecular information recognized by the enzyme. Option B, cell colour, is a visible characteristic and does not determine a DNA cutting site. Option C, leaf shape, may be a plant feature but is not the sequence read by the enzyme. Option D, soil smell, is unrelated to DNA recognition. The enzyme does not cut randomly throughout the molecule; its target sequence gives it selectivity. Memory cue: restriction enzymes read DNA letters, not colours, shapes, or smells.

Correct answer: A. DNA fragments

The governing concept is the result of restriction digestion. When a restriction enzyme cleaves a long DNA molecule at specific recognition sites, the original molecule is divided into shorter pieces. Each resulting piece is called a DNA fragment. The fragments may differ in nucleotide sequence and length, and their lengths can later be estimated by separating them through gel electrophoresis. Therefore option A is the correct scientific term. Green particles, fat droplets, and water molecules are different kinds of biological or chemical entities and do not describe pieces produced by cutting DNA. The word fragment refers to a portion of a larger DNA molecule, not to a new non-DNA substance.

Correct answer: A. DNA fragments from different sources

Recombinant DNA joins DNA fragments from different sources. Restriction enzymes help cut these fragments properly.

Correct answer: A. Bacteria

The direct answer is A: bacteria. Restriction enzymes were first identified in bacteria, where they form part of a defence system against foreign DNA, such as DNA introduced by bacteriophages. Step by step: a bacterium may encounter foreign genetic material; the enzyme recognizes a suitable foreign DNA sequence; it cuts that DNA; this can help protect the bacterial cell. Bacteria also have their own protective pattern, commonly involving methylation, so their important DNA is not normally cut by their own restriction system. Option A is correct because bacteria are the original biological source of these enzymes used in biotechnology. Option B, sand, is an inorganic material and does not produce enzymes. Option C, metal, can be a chemical element or material but is not the living source of restriction enzymes. Option D, glass, is an artificial non-living material and cannot synthesize proteins. Scientists may now produce or use enzymes through laboratory methods, but their natural discovery and source are bacterial organisms. Memory cue: bacteria use restriction enzymes as defence scissors against foreign DNA.

Correct answer: A. Fixed recognition site

The governing concept is sequence-specific recognition. A restriction enzyme does not cut DNA randomly; its active site recognises a particular short nucleotide sequence called the recognition site, often a palindromic sequence, and cleaves at a defined position within or near that site. Because the same sequence can be located and cut reproducibly, researchers can excise a selected gene or open a vector in a controlled manner. Therefore option A, fixed recognition site, is correct. Loud sound, sweet taste, and round shape are physical descriptions unrelated to the catalytic specificity of an enzyme. This sequence-directed action is what makes restriction enzymes valuable tools in cloning.

Correct answer: A. Sticky end

The governing concept is the structural difference between sticky and blunt DNA ends. A staggered restriction-enzyme cut leaves a short region of one strand unpaired at the end of the fragment. This single-stranded overhang is called a sticky or cohesive end because it can temporarily anneal with a complementary overhang. Such pairing helps align DNA fragments before ligase seals them. A blunt end, in contrast, is produced when both strands are cut at the same position and has no single-stranded projection. Closed end and mineral end are not standard DNA-end categories. Therefore option A is the only correct answer.

Correct answer: A. Restriction digestion

The direct answer is option A: restriction digestion. In laboratory biotechnology, digestion means cutting a DNA molecule with a suitable enzyme. Therefore, when a restriction enzyme cuts DNA at its recognition site, the procedure is called restriction digestion or restriction enzyme digestion. The steps in the idea are simple: first identify the target DNA sequence, then add the matching restriction enzyme under suitable conditions, and finally observe the resulting DNA fragments. Option A is correct because it names this exact laboratory operation. Option B, water distillation, separates substances according to differences in boiling points and is unrelated to cutting DNA. Option C, light emission, describes production or release of light, not enzyme treatment of DNA. Option D, soil mixing, is a physical agricultural activity and has no connection with molecular cloning. Do not confuse digestion here with digestion of food: in molecular biology it means enzyme-controlled cleavage of a molecule. The exact cut may produce blunt ends or sticky ends, depending on the enzyme. Memory cue: restriction digestion means DNA is “digested” by a restriction enzyme, that is, cut at selected sites.