Welcome to Your New Model for DNA !!!
After many delays, a downloadable version of this model is finally available.
Please peruse the Learning Segment Table and materials below. This version is significantly different than the previous version posted in July 2017 (which can be found here).
There are a couple of optional learning segments at the end of the table. Optional Segment B contains many of the detailed protein synthesis materials associated with the last posted edition. This exploration goes beyond the scope of what NGSS calls us to develop in classrooms and has therefore been replaced with the activities in Learning Segment 6.
If you have questions about the new materials, please post to the forum!
Phenomenon
In our families we saw that proteins were causing problems yet DNA—not protein—is passed from parent to offspring.
Question
What is the connection between DNA and protein?
What is the connection between DNA and traits?
(There are also ideas in our model that more directly address related questions that are really more about inheritance such as, "How can the cell make an exact copy of the DNA sequence when it divides?")
Model Ideas
Note: The Teacher Notes included in the PowerPoint (available in the compressed Downloadable Resources files at the bottom of the page) present a couple of different versions of the model in terms of wording. The key ideas, however, are the same. Be sure to read both before you start and decide how you will honor student ideas and student language when building the model together.
- DNA is the hereditary material and it codes for the protein.
- DNA is in a code and it is read by the base pairing rules: A pairs with T and C pairs with G. This base pairing allows the cell to make an exact copy of DNA to pass along to daughter cells.
- Because DNA is in the cell’s nucleus and ribosomes (where proteins are made) are found in the cytoplasm, a messenger RNA molecule transports the code from the nucleus to the ribosomes where translation of the code occurs.
- The messenger RNA is read in groups of 3 bases, that corresponds to an amino acid, the ribosome then strings the amino acids together to make a protein.
- Depending on the function of the protein, you will see different patterns of phenotypes (dominance versus codominance) in heterozygotes.
- When multiple genes are involved in determining a trait, patterns of inheritance are more complex.
- Errors in the processing of DNA can lead to changes in the genetic material and are called mutations.
- Mutations are a source of genetic variation.
- Not all DNA codes for a protein. (The reason behind this is left open for the moment and is picked up in other models.)
Overview
Transition in: We've been tracking family traits across generations in order to make sense of the patterns of inheritance. Now we dive into an examination of the molecule of inheritance, DNA.
We have figured out that each parent contributes genes to their offspring and that those genes interact to cause the offspring to look or behave a certain way. Basically, we inherit traits from our parents—a concept we’ve had a handle on for a while. But now we begin to wonder what the link might be between the genes we inherit and the traits that make us who we are. We recognize through examination that a number of the traits we’ve studied thus far can be linked back to a protein, spurring us to ask the more immediate question: how is DNA linked to protein?
We do a bit of review about Chromosomes, genes, and DNA , we track the historical data that led to Watson and Crick’s model for DNA. With this we can reason first about how the cell makes an exact copy of the DNA every time it divides (in mitosis or meiosis) and then how it might be a code for assembling proteins. After working through some of those details, we spend some time thinking about the role mutations play in generating variation and how that variation may or may not affect the protein structure and function. We pull together our ideas about the links between DNA, proteins and traits by trying to understand more completely what is happening at the molecular level in achondroplasia and PKU, two heritable diseases we explored in Classical Genetics.
Finally we wonder about the link between mutation, variation in traits, and evolution by natural selection. The unit ends with a bit of a new mystery: it turns out that most of our DNA (over 98% in humans) doesn’t directly code for protein at all. So what is it all for!?! We take up this phenomenon in Growth and Development, though not right away.
Transition out: Now that we have a broad understanding of how the instructions encoded in DNA are a recipe for building us trait by trait, we wonder how that process unfolds during growth and development.
Advanced Planning
Check "Advanced Planning" for Growth and Development.
Though the materials for this unit require little preparation (unless you choose to engage in Optional Learning Segment B - see details), you will need to start generating the phenomenon for the next unit, Growth and Development. The wet labs require you order animals and start observations in the unit ahead of G&D. For most classrooms, the unit leading to G&D will be this one.
Download Resources
| Attachment | Size |
|---|---|
| DNA Structure and Function vFeb2019.zip | 25.51 MB |
| Optional Learning Segment B Materials vDec2018.zip | 7.95 MB |