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Transcript of DNA Structure
What is the structure of DNA?
DNA takes the form of a double helix, with two sugar phosphate chains bound to each other by hydrogen bonds between complementary nucleotide bases.
Justification of Evidence
Model of DNA Structure
Analysis Questions (continued)
1. Do you agree or disagree with the following statement: All scientific knowledge, including the findings from studies that have been published in peer-reviewed journals, is subject to ongoing testing and revision. Explain your answer, using information from your investigation about DNA structure.
2. Do you agree or disagree with the following statement: When conducting a new investigation, scientists can use data previously gathered by other scientists. Explain your answer, using examples from your investigation about DNA structure.
3. Scientists often attempt to identify patterns in nature. Explain why the identification of patterns is useful in science, using an example from your investigation about DNA structure.
4. Scientists often need to look for proportional relationships when analyzing data. Explain why it is often useful to look for these relationships in science, using an example from your investigation about DNA structure.
5. Scientists often attempt to determine the structure of molecules that are too small to see. Explain why this is important for scientists to do, using an example from your investigation about DNA structure.`
Sugar: brown connector
Phosphate group: short purple stick
Adenine: short black stick
Thymine: short silver stick
Guanine: short white stick
Cytosine: short turquoise stick
Hydrogen bond: yellow half-sun
DNA is composed of 6 different subunits:
1. deoxyribose (a sugar)
2. phosphate group
3. adenine (a base)
4. thymine (a base)
5. guanine (a base)
6. cytosine (a base)
DNA consists of 2 chains, bonded together. A subunit from one strand bonds to a subunit on the other.
The diameter of DNA is the same along its entire length (4 subunits wide).
Sugar can only bind w/ 2 other subunits: base and phosphate.
Base can only bind w/ 2 other subunits: sugar and base.
Phosphate can only bind w/ sugar.
The relative proportion of adenine is approximately equal to that of thymine, and the relative proportion of guanine is approximately equal to that of cytosine in a variety of organisms.
The relative proportion of adenine is not necessarily equal to that of guanine.
Agree; Not only can scientists use data previously gathered by other scientists, but rather it is necessary that they do so. If scientists do not build upon previous achievements in the field, and must start from the very beginning in every investigation, it would have been impossible to get anything done. Cell theory is a combination of the work of three scientists, each building upon others' ideas. Although repeating experiments is useful when trying to validate ideas, scientists can build upon previous ideas without validating everything by themselves.
Identification of patterns is useful in science because analysis of trends is crucial to the organization and interpretation of data. Data sets include many individual data points and values, making it difficult to take them all into account at once. By finding patterns, one is able to see past these individual data points to the relationship between them. DNA, even when compared to other macromolecules, is highly complex, with thousands of genes, each with hundreds of nucleotides. To take into account so much information in a single model is difficult, which is why patterns are necessary. By examining patterns, we can determine the number and type of basic subunits, the bonds they form, and their relative positions.
In science, it is important for scientists to model the structures of molecules to small to see because structure is essential to function. Understanding how something is built greatly aids in the understanding of how it works and vice versa. Looking specifically at DNA structure, the fact that DNA has two helices leads to its functions of replication and gene expression because each helix provides a backbone for nucleotides to be arranged in a specific order and complementary base pairing is what allows DNA to be replicated, transferred, and translated.
Agree; Science is a field that attempts to discover and understand the workings of the universe. Due to the vastness of the field and the extremely limited amount that we understand in comparison, new discoveries and ideas constantly challenge those previously established. Therefore, even the most widely accepted knowledge may be reexamined and expanded upon. As a scientist, it is crucial to keep an open mind and the consideration that knowledge is subject to modification. In the case of modeling DNA structure, the evidence provided serves as a basis, which if not revised, can be improved. As new technology aids in the understanding of how DNA leads to gene expression, our understanding of DNA structure may become more detailed as well.
It is important to look for proportional relationships within data because as a type of pattern, proportional relationships simplify the task of analysis. For example, it's given that the relative proportion of adenine is approximately equal to that of thymine, and the relative proportion of guanine is approximately equal to that of cytosine in a variety of organisms. By examining the proportional relationships of the four nucleotide bases, it is easy to associate bases into pairs. Knowing that DNA consists of two chains bonded together, one can deduce that base pairs bond to each other and are found on opposite chains. Hence through learning about the proportional relationship between the bases, a key element to the structure of DNA can be inferred.
Chains suggests linear, while diameter suggests circular. A combination of the two suggests a double helix.
Relative proportions of nucleotide bases suggests that they are paired (adenine to thymine and guanine to cytosine). Since the chains are also a pair, it follows that for each base on one chain, there is a complementary base on the other.
Since phosphate can only bind with sugar, it is illogical for the phosphate to be located at the widest point along the DNA structure, where 4 subunits are bound together.
The remaining option is for phosphate to be a part of the chains. Therefore, the 2 chains would be alternating sugars and phosphates, while bases are bound to sugars and their complements on the other chain.
By examining accurate data achieved with a replicable methodology, scientists build upon previously gathered information. In order to construct the structure of DNA, it was necessary to examine evidence from other scientists.