Free Biotechnology MCQs with Answers

1. Recombinant DNA is DNA that

• A. has been copied many times in a test tube
• B. has been joined together from two different sources
• C. has lost one of its two strands
• D. has been broken down into nucleotides

Explanation: A gene cut from one organism is inserted into the DNA of another, usually a bacterial plasmid, so the molecule carries sequences that never occurred together in nature. Because the genetic code is universal, the host reads the foreign gene and makes the protein it codes for. Copying DNA repeatedly in a tube is the polymerase chain reaction, a different technique altogether.

2. A restriction endonuclease is used in genetic engineering to

• A. cut DNA at a specific base sequence, often leaving sticky ends
• B. join two DNA fragments together
• C. translate mRNA into protein
• D. unwind the double helix during replication

Explanation: Each enzyme recognises its own short palindromic sequence and cuts both strands there, and a staggered cut leaves short single stranded overhangs. Because the same enzyme produces complementary overhangs on the gene and on the plasmid, the two pair up by hydrogen bonding when mixed. Bacteria evolved these enzymes as a defence against phage DNA.

3. The enzyme used to seal the gene permanently into the plasmid is

• A. restriction endonuclease
• B. reverse transcriptase
• C. DNA ligase
• D. helicase

Explanation: Sticky ends pair by hydrogen bonds only, which is not strong enough to hold, so ligase forms the covalent phosphodiester bonds in the sugar phosphate backbone and completes the recombinant molecule. Restriction enzymes do the opposite job of cutting, which is why the two are always taught as a pair. Ligase is the same enzyme that joins Okazaki fragments during normal DNA replication.

4. The commonest vector used to carry a gene into a bacterial cell is

• A. a ribosome
• B. a mitochondrion
• C. a molecule of messenger RNA
• D. a plasmid

Explanation: A plasmid is a small circular piece of DNA separate from the bacterial chromosome that replicates on its own and can be taken up from the surrounding medium, which makes it an ideal carrier. Engineered plasmids also carry a marker gene, often for antibiotic resistance, so that transformed cells can be picked out. Viruses are the other common class of vector, especially for animal cells.

5. Human insulin for diabetic patients is now produced mainly by

• A. genetically engineered bacteria carrying the human insulin gene
• B. extraction from the pancreas of cattle and pigs
• C. chemical synthesis from amino acids in a factory
• D. collecting it from the urine of healthy donors

Explanation: The human gene is inserted into a bacterium such as Escherichia coli, which is then grown in a fermenter and makes insulin identical to the human hormone. This avoids the allergic reactions some patients had to insulin extracted from animals, removes any risk of transmitting animal disease and can be scaled to meet demand. Animal extraction was the older method it replaced.

6. The polymerase chain reaction is used to

• A. cut DNA into fragments of known length
• B. make millions of copies of a specific DNA sequence in a few hours
• C. read the amino acid sequence of a protein
• D. insert a gene into a human cell

Explanation: Repeated cycles of heating to separate the strands, cooling so that primers bind, and extension by a heat stable polymerase double the amount of DNA each time, giving exponential amplification. Taq polymerase from a hot spring bacterium is used because it survives the near boiling denaturation step. The technique is what makes forensic work and viral testing possible from tiny samples.

7. In gel electrophoresis, DNA fragments move towards the positive electrode because

• A. they are heated during the run
• B. they carry no charge and drift at random
• C. the phosphate groups of the backbone give DNA a negative charge
• D. the gel pushes them mechanically

Explanation: Every nucleotide carries a negatively charged phosphate, so all DNA fragments move towards the anode, and the gel acts as a sieve in which short fragments travel further than long ones in the same time. This separates a mixture into bands by size alone. Comparing the pattern of bands between samples is the basis of DNA fingerprinting.

8. DNA fingerprinting is possible because

• A. every person has a completely different genetic code
• B. only criminals have unusual DNA sequences
• C. DNA differs between the cells of one person's body
• D. the number of repeats in certain non coding sequences differs between individuals

Explanation: Short tandem repeats in non coding DNA vary greatly in number from person to person, so the pattern of band sizes is effectively unique except in identical twins. Half the bands of a child must match the mother and half the father, which is what makes paternity testing possible. The genetic code itself is the same in all people and indeed in all living things.

9. Gene therapy attempts to treat an inherited disease by

• A. introducing a normal copy of the faulty gene into the patient's cells
• B. removing the affected organ
• C. giving the patient a protein rich diet
• D. vaccinating the patient against the disease

Explanation: A working allele is delivered, usually inside a modified virus or a liposome, so that the patient's own cells can make the missing protein, and cystic fibrosis and severe combined immunodeficiency are the standard examples. Somatic gene therapy treats the patient only, while germ line therapy would alter every descendant and is banned in most countries. Current difficulties are keeping the gene expressed and avoiding an immune reaction to the vector.

10. Dolly the sheep was produced by

• A. fertilising an egg in a test tube
• B. transferring the nucleus of an adult body cell into an enucleated egg cell
• C. inserting a human gene into a sheep embryo
• D. splitting a very early embryo into two

Explanation: Somatic cell nuclear transfer showed for the first time that the nucleus of a fully differentiated adult cell can be reprogrammed to direct the development of a whole new animal. The lamb was genetically identical to the sheep that donated the nucleus rather than to the egg donor or the surrogate mother. Splitting an early embryo also gives clones, but that is how natural identical twins arise, not how Dolly was made.