Q: A researcher is designing primers for a PCR reaction. The forward primer is: $$5'\text{-}ATGCGTACCT\text{-}3'. $$What should the reverse primer be if the target sequence is $$5'\text{-}ATGCGTACCT...AGGATGGCTA\text{-}3'$$?

$$5'\text{-}TAGCCATCCG\text{-}3'$$

Question 1

Which of the following characteristics is MOST important to avoid when designing a DNA primer for PCR amplification?

Accepted Answer

A sequence with long repeats and self-complementarity

Question 2

What is the primary reason dideoxynucleotides (ddNTPs) terminate DNA synthesis in Sanger sequencing?

Accepted Answer

They lack a 3'-OH group required for phosphodiester bond formation

Question 3

A researcher is designing primers for a PCR reaction. The forward primer is: $$5'	ext{-}ATGCGTACCT	ext{-}3'. $$What should the reverse primer be if the target sequence is $$5'	ext{-}ATGCGTACCT...AGGATGGCTA	ext{-}3'$$?

Accepted Answer

$$5'	ext{-}TAGCCATCCG	ext{-}3'$$

Question 4

Which of the following is NOT a required component for a Sanger sequencing reaction?

Accepted Answer

RNA template

Question 5

Why is Sanger sequencing considered less efficient for sequencing very long DNA molecules compared to next-generation sequencing (NGS) methods?

Accepted Answer

It is limited to reading approximately 900 base pairs per reaction

Question 6

In Sanger sequencing, what is the purpose of using fluorescently labeled ddNTPs?

Accepted Answer

To allow visualization and identification of the terminating nucleotide at each fragment

Question 7

A sequencing reaction produces the following gel bands (from bottom to top): G, A, T, C, G, T. What is the sequence of the newly synthesized DNA strand (5' to 3')?

Accepted Answer

$$5'	ext{-}GTCGTA	ext{-}3'$$

Question 8

Which of the following best explains why Sanger sequencing is still used for certain applications despite the availability of NGS technologies?

Accepted Answer

It provides highly accurate, long sequence reads ideal for plasmids and targeted regions

Question 9

A student designs a primer with a melting temperature ($$T_m) of 45$$°C and a GC content of 30%. What is the most likely outcome if this primer is used in a PCR reaction?

Accepted Answer

The primer may not bind efficiently, leading to poor amplification

Question 10

Which of the following statements about the difference between dNTPs and ddNTPs is correct?

Accepted Answer

ddNTPs lack a 3'-OH group, preventing further chain elongation

Question 11

During Sanger sequencing, why is only a single primer used instead of two as in PCR?

Accepted Answer

To generate fragments that all start at the same position and end at different nucleotides

Question 12

A researcher wants to sequence a repetitive region of a plasmid. Which sequencing method would be most appropriate and why?

Accepted Answer

Sanger sequencing, because it provides long, accurate reads suitable for repetitive regions

Question 13

Which of the following best describes the role of Mg$$^{2+} in a $$Sanger sequencing reaction?

Accepted Answer

It acts as a cofactor for DNA polymerase, enabling nucleotide addition

Question 14

A sequencing electropherogram shows overlapping peaks at a single nucleotide position. What is the most likely explanation?

Accepted Answer

There is a heterozygous single nucleotide polymorphism (SNP) at that position

Question 15

Which of the following is a key advantage of capillary gel electrophoresis over traditional slab gel electrophoresis in DNA sequencing?

Accepted Answer

It enables automated, high-throughput detection of fluorescently labeled fragments

Question 16

If a primer is written as $$5'	ext{-}GATTACA	ext{-}3'$$, what direction will DNA polymerase extend the new DNA strand?

Accepted Answer

From 5' to 3'

Question 17

Which of the following is a common application of Sanger sequencing in clinical or research settings?

Accepted Answer

Targeted sequencing of specific genes or plasmids

Question 18

A student observes that their PCR product contains multiple bands after gel electrophoresis. Which primer design issue is most likely responsible?

Accepted Answer

Primers with significant self-complementarity, leading to primer dimers

Question 19

Which of the following best explains why Sanger sequencing is not considered an exponential amplification process like PCR?

Accepted Answer

It uses only one primer, so only one strand is synthesized per template

DNA Sequencing Technologies and Primer Design: Study Notes

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