Question

The following statements pertain to the development of the theory of the structure of DNA. Match the statement with the appropriate step (observation, hypothesis, experiment designed to test hypothesis) in the scientific method. (a) Two strands of DNA wind around one another in a helical structure. (b) In a sample of DNA, there are equal amounts of the bases \(\mathrm{A}\) and \(\mathrm{T}\) and equal amounts of the bases \(\mathrm{C}\) and \(\mathrm{G}\). (c) Direct X-rays at a sample of crystallized DNA and interpret the diffraction pattern for structural information.

Short answer

(b) Observation, (a) Hypothesis, (c) Experiment.

Step-by-step solution

Observation

An observation is an initial statement that describes a phenomenon or a pattern that has been seen or discovered. In this exercise, statement (b) "In a sample of DNA, there are equal amounts of the bases \(\mathrm{A}\) and \(\mathrm{T}\) and equal amounts of the bases \(\mathrm{C}\) and \(\mathrm{G}\)" represents data that have been observed.

Hypothesis

A hypothesis is a proposed explanation for an observation, which can be tested. For DNA, the statement (a) "Two strands of DNA wind around one another in a helical structure" is a hypothesis, as it proposes a structural configuration of DNA based on initial observations.

Experiment Designed to Test Hypothesis

An experiment is a procedure carried out to test the validity of a hypothesis. In this case, statement (c) "Direct X-rays at a sample of crystallized DNA and interpret the diffraction pattern for structural information" is the experiment designed to test the helical structure hypothesis of DNA.

Key concepts

DNA Structure

DNA, which stands for deoxyribonucleic acid, is the molecule that carries the genetic instructions for life. Its structure is fundamental to understanding how genetic information is stored and transmitted.

The most well-known feature of DNA is the double helix, a twisting ladder-like structure. This was proposed as a hypothesis based on various observations and eventually proven by experimentation. The structure essentially consists of two strands that wind around each other.

This helix is formed by nucleotide bases: adenine (A), thymine (T), cytosine (C), and guanine (G). These bases pair specifically: A with T and C with G. This complementary base pairing is crucial because it allows DNA to be copied accurately during cell division.

Understanding the DNA structure has been instrumental in fields like genetics, medicine, and forensic science, illustrating its significance in both theoretical and applied sciences.

Observation

Observation in science refers to the process of gathering and noting information, which forms the foundation for further investigation. It often involves using our senses or instruments to collect data about phenomena or patterns.

In the context of DNA research, one critical observation was that in any given sample of DNA, the amount of adenine (A) equals that of thymine (T), and the amount of cytosine (C) equals that of guanine (G). This was a pivotal discovery because it led scientists to question why these pairs occurred in such fixed ratios.

This pattern of base pairing was crucial for proposing further hypotheses about DNA's structure. Observations like these provide the necessary groundwork that drives scientific inquiry and discovery.

Hypothesis

In scientific terms, a hypothesis is an educated guess or a proposed explanation for a phenomenon. It is based on prior knowledge and observations and is a necessary step in the scientific method.

For DNA, the hypothesis that sparked much of modern genetics was that "Two strands of DNA wind around one another in a helical structure." This idea stemmed from understanding the base pairing patterns and the need to explain how genetic information is stored and transferred.

A hypothesis must be testable and falsifiable, meaning that it can be supported or refuted through experiments and observations. Developing a strong hypothesis is crucial, as it guides the design of experiments and the direction of the research.

Experiment

An experiment is a set of planned actions designed to test a hypothesis. It aims to either confirm or refute the proposed explanation through controlled investigation.

Regarding DNA, an experiment to test the hypothesis of the helical structure involved directing X-rays at crystallized DNA. The resulting diffraction pattern gave scientists critical information about DNA's 3-dimensional structure. This technique, known as X-ray crystallography, was instrumental in confirming the double-helix structure.

Conducting experiments is vital in the scientific method, as it provides empirical evidence that supports or further refines hypotheses. Experiments help us transition from mere speculation to evidenced-based conclusions, significantly advancing our understanding of complex topics like DNA.