Genetic Engineering

Genetic engineering changes or transfers genes. For exams remember it as a method to add desired traits.

Recombinant DNA is formed by joining DNA from different sources. It is the basis of gene cloning in exams.

Direct answer: Option A is correct. Restriction enzymes are biological enzymes used to cut DNA at particular recognition sequences. They act like molecular scissors: an enzyme recognises a specific short DNA sequence and breaks the DNA backbone at or near that site. In genetic engineering, this allows scientists to remove a selected fragment, open a vector such as a plasmid, and join compatible DNA pieces using other enzymes. Option A gives the essential use. Option B is wrong because converting DNA information into protein is mainly the work of gene expression, involving transcription and translation, not restriction enzymes. Option C is wrong because restriction enzymes do not give light to cells; light production, when engineered, involves different genes and proteins. Option D is wrong because ribosomes are made through cellular processes involving ribosomal RNA and proteins, not by cutting DNA with restriction enzymes. Memory cue: restriction enzymes recognise and cut; they are molecular scissors, not protein-making machines.

DNA ligase forms bonds between DNA fragments. For exams remember it as the enzyme that joins after cutting.

Plasmids are small circular DNA molecules and act as vectors. Remember plasmid as a common cloning vector.

In gene cloning, a vector is a DNA molecule used to carry a desired foreign DNA fragment into a suitable host cell. Common vectors include plasmids, bacteriophages and specially designed viral or artificial chromosomes. A useful vector generally has an origin of replication so it can be copied in the host, a selectable marker to help identify transformed cells, and a cloning site where the target DNA can be inserted. Once inside the host, the inserted gene can be replicated and, in an appropriate system, expressed. Therefore option A is correct because it states the vector’s transport and delivery role. It does not mix genes with soil, perform photosynthesis by itself or simply colour proteins.

Direct answer: Option A is correct. A recognition site is a particular DNA sequence that a specific enzyme can identify by its molecular structure. In genetic engineering, restriction enzymes are especially important examples. Step by step: DNA contains a long sequence of bases; a restriction enzyme checks the sequence as it moves along DNA; when it finds its matching recognition sequence, it binds there; it may cut the DNA at that site or at a nearby defined position; this allows scientists to remove, join, or insert DNA fragments in a planned way. Therefore Option A is correct. Option B is wrong because a cell’s outer shape is a physical feature, not a DNA sequence recognized by a restriction enzyme. Option C is wrong because protein color is not the enzyme’s DNA address. Option D is wrong because nucleus size is a cell-structure feature, not a recognition sequence. Recognition sites are often short and may show special symmetry, but the essential exam idea is a specific DNA sequence recognized by an enzyme. Memory cue: recognition site = the enzyme’s DNA address for finding and cutting.

A blunt end is a DNA end produced when a cutting enzyme cuts both complementary strands at the same position. Because the cuts line up, neither strand extends beyond the other. There is therefore no single-stranded overhang or sticky, complementary projection. This is why blunt ends are often described as straight or flush ends.

Removing sugar does not create the defined end produced by a restriction cut, and deleting a gene is a much larger genetic event. A change in plasmid colour is unrelated to DNA-end structure. Thus the process described in option A is the correct formation of blunt ends. The answer is appropriate for the expected school-level explanation.

A host cell is a living recipient cell into which the desired foreign DNA is introduced. It can replicate the introduced DNA or express the inserted gene; Escherichia coli is a common example used in genetic engineering. Option B describes a donor cell, while a dead cell cannot express the foreign gene. Exam tip: remember that the host cell receives the foreign DNA.

During transformation, a competent host cell takes up foreign DNA, often recombinant DNA, from outside the cell. Option B describes restriction-enzyme digestion, while option C describes phage-mediated transduction. Exam tip: remember transformation as DNA uptake and transduction as DNA transfer by a bacteriophage.

A selectable marker shows which cell has taken the vector. Antibiotic resistance is a common exam example.

Only resistant transformed cells survive on antibiotic medium. This is a simple selection method for exams.

A cloning site is the vector region where the desired gene is inserted. In exams it is also called insertion site.

The direct answer is A: the origin of replication is needed for replication of the vector. In genetic engineering, a vector such as a plasmid carries useful foreign DNA into a host cell. The origin of replication, written as ori, is a particular DNA sequence where copying of the vector begins. Step by step: the vector enters the host; the host's copying machinery recognises ori; the vector DNA is copied; daughter cells can receive vector copies. Thus ori helps maintain and multiply the vector, although its exact copy number depends on the vector and host. Option A is correct because it states this function. Option B is wrong because protein digestion is done by digestive enzymes such as proteases, not ori. Option C is wrong because cell colour is not the basic function of an origin of replication; colour may be used in some markers, but ori itself starts DNA copying. Option D is wrong because water absorption is a physiological process unrelated to vector replication. Memory cue: ori means the starting point for copying DNA.

PCR is an in vitro technique that uses primers, nucleotides and DNA polymerase to produce many copies of a selected DNA segment. Therefore, its main use is DNA amplification. Option B is incorrect because cutting DNA is performed by restriction enzymes, not by PCR. Exam tip: Remember PCR as the rapid amplification of a specific DNA segment.

Primers are short nucleotide sequences that start the new strand. For exams remember them as starting points.

Taq polymerase tolerates heat so it remains active in PCR cycles. For exams remember its source as a hot spring bacterium.

The direct answer is A, Denaturation. PCR copies a chosen DNA region through repeated temperature cycles. DNA normally has two complementary strands held together by weak hydrogen bonds. In the denaturation step, the mixture is heated, and this heat breaks those weak attractions, so the two strands separate. Next, during annealing, short primers attach to the single strands. During extension, DNA polymerase adds nucleotides and makes new strands. Option A is correct because denaturation specifically means separation of the DNA strands. Option B, ligation, joins DNA pieces with DNA ligase; it does not separate the strands. Option C, transformation, means introducing DNA into a cell, not a PCR temperature step. Option D, selection, means identifying cells with a desired genetic feature and is not the strand-separation step. Remember: in PCR, heat first separates, primers then attach, and polymerase then extends.

During annealing primers bind to complementary DNA parts. Remember that primers bind when the temperature is lowered.

In extension DNA polymerase adds new nucleotides. For exams understand it as the synthesis step.

When an electric field is applied, negatively charged DNA fragments move toward the positive electrode through the agarose gel. Smaller fragments pass through the gel more easily, so they travel farther than larger fragments and become separated by size. DNA replication and direct sequence modification are not the primary functions of this technique. Exam tip: In agarose gel electrophoresis, smaller DNA fragments migrate farther.

DNA has negative charge due to phosphate groups. Remember that DNA moves toward the positive electrode.

In elution the desired DNA fragment is taken from the gel. It is a step to obtain purified DNA.

In gene gun DNA coated micro particles are delivered into cells. Remember it as a useful plant method.

Agrobacterium can transfer DNA into plants. In exams it is called a natural genetic engineer of plants.