Question

In the United States, a major cause of death of babies during the first year is sudden infant death syndrome (SIDS). One study showed a strong corrclation for an increased risk of SIDS with a prolonged \(\mathrm{QT}\) interval in their electrocardiograms. In one child, a gene associated with the Long \(\mathrm{QT}\) syndrome had a substitution of AAC for TCC. This gene codes for a protein associated with the sodium channel. The mutation was detected by single-strand conformation polymorphism \((\mathrm{SSCP})\) In order to get enough DNA to analyze, DNA is amplified by a polymerase chain reaction (PCR). In a PCR, A. the nucleotide sequence of the DNA to be amplified must be known. B. the sample is protected from heat which would denature the DNA. C. the role of oligonucleotides in the reaction mixture is to act as primers for the synthesis of new DNA. D. the final product is single-stranded DNA. E. the original DNA can be amplified only about 10 -fold.

Short answer

A. The nucleotide sequence of the DNA to be amplified must be known. B. The sample is protected from heat which would denature the DNA. C. The role of oligonucleotides in the reaction mixture is to act as primers for the synthesis of new DNA. D. The final product is single-stranded DNA. E. The original DNA can be amplified only about 10-fold. Answer: A, C

Step-by-step solution

Statement A: the nucleotide sequence of the DNA to be amplified must be known.

This statement is correct. In PCR, the DNA sequence of interest must be known beforehand, as this information is necessary to design specific primers that will bind to the DNA during the amplification process.

Statement B: the sample is protected from heat which would denature the DNA.

This statement is incorrect. During PCR, the DNA sample is subjected to high temperatures (typically around 95°C) in order to denature the DNA and separate the two strands. This allows the primers to bind to the target DNA sequences and initiate the amplification process.

Statement C: the role of oligonucleotides in the reaction mixture is to act as primers for the synthesis of new DNA.

This statement is correct. Oligonucleotides are short, single-stranded DNA sequences that are designed to bind specifically to the target DNA sequence. They act as primers in PCR and help initiate the synthesis of new DNA strands by providing a starting point for the DNA polymerase enzyme.

Statement D: the final product is single-stranded DNA.

This statement is incorrect. The final product of PCR is double-stranded DNA, as each newly synthesized strand of DNA complements one of the original template strands.

Statement E: the original DNA can be amplified only about 10-fold.

This statement is incorrect. PCR is capable of amplifying the target DNA sequence by more than a million-fold, depending on the number of amplification cycles conducted during the reaction.

Key concepts

Sudden Infant Death Syndrome (SIDS)

Sudden Infant Death Syndrome (SIDS), often referred to as 'crib death', remains a critical concern as it is a leading cause of death among infants aged one month to one year old. The syndrome involves the unexplained passing of a baby, typically during sleep, with no warning signs or a clear reason identified even after a thorough examination.

SIDS deaths are tragic events that leave many questions unanswered. To unravel these mysteries, researchers explore various risk factors from genetics to environmental influences. Studies have shown that genetic variations, like those affecting the heart's electrical system, can increase the risk of SIDS. A prolonged QT interval, which can be a symptom of Long QT syndrome, has been linked to this syndrome, indicating that cardiac arrhythmias could play a key role in these unexpected deaths.

Understanding the relationship between genetics and SIDS is essential to developing preventive strategies and providing peace of mind to parents. The connection between SIDS and genetic factors such as Long QT syndrome is an ongoing area of research, emphasizing the need for further molecular investigations.

Long QT Syndrome

Long QT syndrome (LQTS) is a disorder of the heart's electrical activity that can result in sudden, uncontrollable, and dangerous heart rhythms. This condition causes a delay in the time it takes for the heart to recharge between beats, which is depicted as a prolonged QT interval on an electrocardiogram (EKG or ECG).

Genetic mutations affecting ion channels, particularly those involving potassium and sodium, are often the cause of this syndrome. Such mutations can disrupt the heart's electrical system and lead to arrhythmias, increasing the risk of fainting, seizures, and even sudden death. As the case study from the original exercise suggested, a mutation where AAC substitutes TCC in a gene coding for a sodium channel protein can lead to LQTS, signifying a concrete genetic alteration that might increase the risk for SIDS.

Since LQTS can be hereditary, understanding one's genetic makeup through DNA analysis is crucial, especially for those with a family history of the syndrome. Modern medical interventions and lifestyle changes can help manage the condition and mitigate risks of complications.

DNA Amplification

DNA amplification is a laboratory technique used to make multiple copies of a specific DNA segment. This process is at the heart of many genetic investigations, including those related to SIDS and Long QT syndrome. A common method of DNA amplification is the Polymerase Chain Reaction (PCR), an efficient and rapid technique to multiply a specific DNA sequence exponentially.

In PCR, the DNA to be amplified must be known so that specific primers can be designed. These primers flank the DNA region of interest and are crucial for the initiation of DNA synthesis. Each PCR cycle consists of three steps: denaturation, annealing, and extension. In the denaturation phase, the DNA sample is heated to a high temperature to separate the DNA strands. Next, during annealing, the temperature is lowered to allow primers to attach to their complementary sequences on the DNA strands. Finally, in the extension step, the DNA polymerase enzyme extends the primers, creating new strands of DNA.

Through multiple cycles of PCR, the quantity of the DNA target can be amplified by more than a million-fold, making it an indispensable tool in genetic research, diagnostics, and forensics.

Oligonucleotide Primers

Oligonucleotide primers are short strands of nucleotides that are designed to be complementary to the specific sequences at the start and end points of the DNA segment to be amplified in PCR. The selection of primers is based on the nucleotide sequence of the DNA target, and their specificity is crucial as they dictate the accuracy of the amplification.

The role these primers play in PCR is pivotal. After the DNA strands are separated by heat during the denaturation step, the primers anneal to their matching sequences on the single-stranded DNA during the cooling phase. This provides a foothold from which the DNA polymerase can begin to synthesize new DNA strands. Each new strand becomes a template in subsequent cycles, allowing exponential amplification of the DNA segment.

Precise primer design is essential for successful PCR, as mismatched primers can lead to non-specific amplification or failed reactions altogether. Efficient primer design, followed by accurate DNA amplification, paves the way for further genetic analysis, such as investigating genetic markers associated with Long QT syndrome and potentially SIDS.