DNA Discovery Practice Questions
20 free DNA Discovery practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
In 1869, which Swiss chemist was the first to isolate 'nuclein' (now known as DNA) from the nuclei of white blood cells?
- A Friedrich Miescher
- B Frederick Griffith
- C Albrecht Kossel
- D Phoebus Levene
Correct answer: Friedrich Miescher
Friedrich Miescher isolated a phosphorus-rich substance from pus-soaked bandages. He named it nuclein because it was found within the cell nucleus, marking the very first discovery of DNA.
Frederick Griffith's 1928 experiment with Streptococcus pneumoniae demonstrated a process where harmless bacteria became lethal. What is this process called?
- A Bacterial conjugation
- B Transcription
- C Transduction
- D Transformation
Correct answer: Transformation
Griffith discovered that a 'transforming principle' from heat-killed virulent bacteria could change non-virulent bacteria into virulent ones. This laid the groundwork for identifying DNA as the genetic material.
Which team of scientists performed the 1944 experiment that chemically proved DNA, rather than protein, was the 'transforming principle' described by Griffith?
- A Avery, MacLeod, and McCarty
- B Watson, Crick, and Franklin
- C Hershey and Chase
- D Meselson and Stahl
Correct answer: Avery, MacLeod, and McCarty
Avery and his colleagues used enzymes to selectively destroy proteins, RNA, and DNA. They found that only the destruction of DNA prevented the transformation of bacteria, identifying it as the carrier of genetic information.
The 1952 'Blender Experiment' used radioactive isotopes of sulfur and phosphorus to confirm DNA is the genetic material of viruses. Who conducted this study?
- A Watson and Crick
- B Meselson and Stahl
- C Franklin and Wilkins
- D Hershey and Chase
Correct answer: Hershey and Chase
Hershey and Chase labeled bacteriophage protein with radioactive sulfur and DNA with radioactive phosphorus. They observed that only the radioactive phosphorus entered the bacteria, proving DNA carries the viral genes.
Erwin Chargaff's rules, discovered in the late 1940s, state that in any DNA sample, the amount of adenine is always equal to the amount of:
- A Guanine
- B Cytosine
- C Uracil
- D Thymine
Correct answer: Thymine
Chargaff's analysis revealed a 1:1 ratio of purines to pyrimidines. Specifically, the amount of Adenine (A) equals Thymine (T), and Guanine (G) equals Cytosine (C), which was essential for determining DNA's base-pairing structure.
What technique did Rosalind Franklin use to produce 'Photo 51', the image that revealed the helical structure of DNA?
- A Electron Microscopy
- B X-ray Crystallography
- C Nuclear Magnetic Resonance
- D Mass Spectrometry
Correct answer: X-ray Crystallography
X-ray crystallography involves directing X-rays at crystallized molecules and recording the diffraction pattern. Franklin's high-quality images provided the mathematical evidence for DNA's double-helix dimensions.
In which year did James Watson and Francis Crick publish their landmark paper describing the double-helix structure of DNA?
- A 1944
- B 1950
- C 1953
- D 1962
Correct answer: 1953
Published in the journal 'Nature' in April 1953, the paper proposed the anti-parallel double helix. This model immediately suggested a mechanism for how genetic information is copied.
Which nitrogenous base is found in RNA but is replaced by thymine in DNA?
- A Adenine
- B Guanine
- C Cytosine
- D Uracil
Correct answer: Uracil
DNA contains Adenine, Thymine, Guanine, and Cytosine. RNA contains Uracil instead of Thymine, which is a key structural difference between the two types of nucleic acids.
The DNA backbone is composed of alternating units of a phosphate group and which 5-carbon sugar?
- A Ribose
- B Deoxyribose
- C Arabinose
- D Deoxyglucose
Correct answer: Deoxyribose
DNA stands for Deoxyribonucleic Acid, named after its sugar component, deoxyribose. This sugar lacks one oxygen atom compared to ribose, which makes DNA more chemically stable than RNA.
Who shared the 1962 Nobel Prize in Physiology or Medicine with Watson and Crick for their work on the structure of DNA?
- A Rosalind Franklin
- B Maurice Wilkins
- C Linus Pauling
- D George Beadle
Correct answer: Maurice Wilkins
Maurice Wilkins provided the initial X-ray diffraction data and worked alongside Franklin at King's College London. Rosalind Franklin was not eligible for the prize as she had passed away in 1958, and the Nobel is not awarded posthumously.
The 1958 experiment by Matthew Meselson and Franklin Stahl proved that DNA replication is:
- A Conservative
- B Dispersive
- C Semiconservative
- D Semi-discontinuous
Correct answer: Semiconservative
By using heavy and light nitrogen isotopes, Meselson and Stahl showed that each new DNA molecule consists of one original strand and one newly synthesized strand. This confirmed the 'semiconservative' model predicted by Watson and Crick.
Which chemist incorrectly proposed a triple-helix model for DNA shortly before Watson and Crick's discovery?
- A Linus Pauling
- B Arthur Kornberg
- C Sydney Brenner
- D Max Delbruck
Correct answer: Linus Pauling
Linus Pauling, a double Nobel laureate, published a model with three strands and the phosphate groups in the center. His model was chemically unstable due to the negative charges of the phosphates repelling each other.
In the DNA double helix, the two strands are held together by what type of chemical bond between the nitrogenous bases?
- A Ionic bonds
- B Covalent bonds
- C Hydrogen bonds
- D Metallic bonds
Correct answer: Hydrogen bonds
Hydrogen bonds provide enough stability to hold the two strands together while being weak enough to allow the strands to 'unzip' for replication and transcription.
Who discovered the first DNA polymerase, the enzyme responsible for synthesizing new DNA strands?
- A Francis Crick
- B Arthur Kornberg
- C Marshall Nirenberg
- D Severo Ochoa
Correct answer: Arthur Kornberg
Arthur Kornberg isolated DNA polymerase I from E. coli in 1956. He demonstrated that the enzyme could string together nucleotides to mirror a template strand, for which he won a Nobel Prize.
What is the term for the 5' to 3' orientation of the two strands in a DNA molecule relative to each other?
- A Parallel
- B Anti-parallel
- C Perpendicular
- D Circular
Correct answer: Anti-parallel
Anti-parallel means the two strands run in opposite directions. This orientation is crucial for base pairing and for the directionality of enzymes that read and copy the DNA.
Which scientist won two Nobel Prizes, the second of which was for developing a method to sequence the bases in DNA?
- A James Watson
- B Frederick Sanger
- C Walter Gilbert
- D Har Gobind Khorana
Correct answer: Frederick Sanger
Frederick Sanger developed the 'dideoxy' method for DNA sequencing, often called Sanger Sequencing. This technology was the gold standard for decades and allowed scientists to read the genetic code.
Phoebus Levene is credited with identifying the three components of a nucleotide. These are:
- A Sugar, Phosphate, and Base
- B Sugar, Protein, and Lipid
- C Phosphate, Acid, and Base
- D Carbon, Hydrogen, and Oxygen
Correct answer: Sugar, Phosphate, and Base
Levene correctly identified that DNA is made of repeating units called nucleotides. However, he incorrectly believed in the 'tetranucleotide hypothesis,' thinking the bases occurred in equal, repetitive amounts.
In 1983, who invented the Polymerase Chain Reaction (PCR), a discovery that allows scientists to make millions of copies of a DNA segment?
- A Francis Collins
- B Craig Venter
- C Paul Berg
- D Kary Mullis
Correct answer: Kary Mullis
Kary Mullis realized that using a heat-stable polymerase and thermal cycling could exponentially amplify DNA. PCR has since become one of the most important tools in forensic science and medical diagnostics.
According to the Watson-Crick model, how many hydrogen bonds form between Guanine and Cytosine?
- A One
- B Two
- C Three
- D Four
Correct answer: Three
Guanine and Cytosine form three hydrogen bonds, while Adenine and Thymine form only two. This makes G-C rich regions of DNA more thermally stable and harder to separate.
What was the primary goal of the Human Genome Project, which was completed in 2003?
- A To build a synthetic human chromosome in the laboratory
- B To develop gene therapies for inherited diseases
- C To clone a human being from adult donor cells
- D To sequence all the base pairs in the human genome
Correct answer: To sequence all the base pairs in the human genome
The project was an international effort to identify all 20,000-25,000 genes in human DNA and determine the sequence of the 3 billion chemical base pairs that make up the human genome.