130 ❯ STEP 4. Review the Knowledge You Need to Score High
ampicillin resistance gene will survive, while those that have not will perish. The medium
also contains a special sugar that is broken down by the galactose enzyme present in the
vector to form a colored product. The cells containing the gene of interest will remain white
since the galactose gene has been interrupted and rendered nonfunctional. This allows the
experimenter to isolate cells that contain the desired product. Now, it is time for us to quit
cloning around and move onto another genetic engineering technique.Polymerase Chain Reaction
Think of this technique as a high-speed copy machine. It is used to produce large quantities
of a particular sequence of DNA in a very short amount of time. If the cloning reaction is
the 747 of copying DNA, then polymerase chain reaction (PCR) is the Concorde. This
process begins with double-stranded DNA containing the gene of interest. DNA poly-
merase, the superstar enzyme of DNA replication, is added to the mixture along with a
huge number of nucleotides and primers specific for the sequence of interest, which help
initiate the synthesis of DNA. PCR begins by heating the DNA to split the strands, fol-
lowed by the cooling of the strands to allow the primers to bind to the sequence of inter-
est. DNA polymerase then steps up to the plate and produces the rest of the DNA molecule
by adding the nucleotides to the growing DNA strand. Each cycle concludes having dou-
bled the amount of DNA present at the beginning of the cycle. The cycle is repeated over
and over, every few minutes, until a huge amount of DNA has been created. PCR is used
in many ways, such as to detect the presence of viruses like HIV in cells, diagnose genetic
disorders, and amplify trace amounts of DNA found at crime scenes.❯ Review Questions
- Which of the following statements is incorrect?
A. Messenger RNA must be processed before it
can leave the nucleus of a eukaryotic cell.
B. A virus in the lysogenic cycle does not kill its
host cell, whereas a virus in the lytic cycle
destroys its host cell.
C. DNA polymerase is restricted in that it can
add nucleotides only in a 5′-to-3′direction.
D. During translation, the A site holds the
tRNA carrying the growing protein, while
the P site holds the tRNA carrying the next
amino acid.
E. Viroids are plant viruses that are only a few
hundred nucleotides in length. - The process of transcription results in the forma-
tion of
A. DNA.
B. proteins.
C. lipids.
D. RNA.
E. carbohydrates.
3. Which of the following codons signals the begin-
ning of the translation process?
A. AGU
B. UGA
C. AUG
D. AGG
E. UAG
4. Which of the following is an improper pairing of
DNA or RNA nucleotides?
A. Thymine-adenine
B. Guanine-thymine
C. Uracil-adenine
D. Guanine-cytosine
E. Pyrimidine-purine
5. Which of the following is responsible for the
type of diseases that includes “mad cow” disease?
A. Viroids
B. Plasmids
C. Prions
D. Provirus
E. Retrovirus