Kansas College and Career Ready Standards

Disciplinary Core Ideas

• MS-LS1-2 Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.
• HS-LS1-1 Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells.

Science and Engineering Practices

• Developing and Using Models A practice of both science and engineering is to use and construct models as helpful tools for representing ideas and explanations. These tools include diagrams, drawings, physical replicas, mathematical representations, analogies, and computer simulations.

Learning Objectives

• Students will model that DNA is the storage molecule for genetic information in the cell.
• Students will perform transcription of DNA molecules into mRNA.
• Students will translate the mRNA molecules into sentences that represent proteins.
• Students will reverse the process to code a DNA molecule that will produce a given sentence.

Materials

• Printable version of Kansas Corn: Decoding DNA-Modeling Protein Synthesis
• Decoding DNA PowerPoint
• DNA Sequencing Strips and Cards
  • High School (pg. S1-2)
  • Middle School (pg. S3-4)
  • tRNA cards; 1 set for each group (pg. S6-)
  • Blank strips to transcribe mRNA; 1 for each sentence to be transcribed (pg. S5)
• Decoding DNA Student Handout

Procedures for Instruction

Length of Time for Classroom Teaching

Activity 1: Transcription – 30 minutes

Activity 2: Designer DNA – Genetic Engineering -10 minutes

Preparation Procedure

Print out the DNA Sentence Strips, tRNA cards; 1 set for each group, have blank strips to transcribe mRNA; 1 for each sentence to be transcribed. Print enough copied of the Decoding DNA Student Handout and have the Decoding DNA PowerPoint ready.

Instructions

This lab has two activities; Transcription and Designer DNA – Genetic Engineering. Hand out the Decoding DNA Student Handout. The handout includes the instructions for the transcription activity. In addition, the handout provides places for students to write down their sentences for both activities, and also includes reflection and conclusion, as well as assessment questions.

Background Information

Proteins are polymers of amino acids, produced in the cell by structures called “ribosomes”. There are 20 different amino acids that are analogous to letters in the alphabet. We have only 26 letters in our alphabet, but they can be ordered and rearranged to produce thousands of words and a near-infinite number of sentences. Amino acids work similarly in making proteins, where the order and arrangement of these amino acids determines the function of the protein.

DNA is a polymer of four different nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C). It is arranged in long chains that form a double helix. On each side of the helix is a complementary, matching, nucleotide. Adenine (A) always pairs with thymine (T), while cytosine (C) always pairs with guanine (G). This enables DNA to replicate, or copy itself, by “unzipping” and adding complementary nucleotides to each single strand. This allows new cells to be produced with identical copies of the DNA found in the original cell.

Transcription: DNA to mRNA

In plant and animal cells, DNA stays in the nucleus. The instructions in DNA need to be copied into another molecule, RNA, to be carried to the ribosomes where they can be read to make proteins. RNA is another polymer of four nucleotides very similar to DNA. The only nucleotide that is different from those in DNA is uracil (U), which replaces thymine and complements adenine. mRNA is only a single strand that can leave the nucleus and be used by ribosomes as a recipe for making the protein. mRNA is produced in the nucleus in a process called “transcription”. The DNA strand is separated and the enzyme RNA polymerase adds complementary nucleotides to build a matching mRNA strand.

After the mRNA molecule is transcribed, it can leave the nucleus and move out into the cell where the ribosomes can translate the RNA into a protein.

Translation

Translation is the production of a protein from an mRNA strand by a ribosome. During translation, a ribosome uses tRNA molecules to determine the order of amino acids. The tRNA reads sections of mRNA three nucleotides at a time. These three nucleotide sections are called “codons”, and they are complemented by an anticodon on the tRNA molecule. AUG is the “Start” codon. Translation is divided into three parts: initiation, elongation, and termination.

Initiation

A tRNA molecule attaches to the “Start” codon, AUG. This allows a ribosome to attach to the mRNA.

Elongation

The ribosome continues to match antocodons to codons and add amino acids to the protein.

Termination

Occurs when a “Stop” codon is reached. The mRNA, ribosome, tRNA, and protein are all released. The protein folds into its shape and starts to work in the cell. The other components can be reused to make the protein again.

Classroom Discussion

Introduce the topic and assess students for prior understanding.

• Where does transcription occur? (Nucleus)
• Why do the DNA strips have to stay at the original location? (DNA can’t leave the nucleus)
• What is the universal start codon? (AUG)
• Where does translation occur? (Ribosome)
• Which base pairs with A? (U)
• Which base pairs with C? (G)

Procedure for Lab

Activity 1: Transcription- 30 Minutes

Instructions
Hand out the Decoding DNA Student Handout. The handout includes the instructions below and places to write down their sentences.

1. Number group members so that there will be an order to transcribe DNA into mRNA.
2. Group member #1 will go to the nucleus with a blank strip of mRNA strand, and choose a gene to transcribe that the group hasn’t synthesized yet.
3. Write the number of the gene on the mRNA strand.
4. Transcribe the DNA strand into the complementary base pairs. For example:
5. Leave the DNA strip in the nucleus and return to the group with mRNA for translation.

Translation Instructions

1. Once the mRNA strand has reached the group (ribosome), scan for the first “Start” codon, AUG, and highlight it. This is where you will begin translating the protein sentence.
2. Match the complimentary anticodon from the tRNA cards to the codons and record the word on the other end of the card. This represents an amino acid in the protein that is being built. AUG (Start) is not a word to be included in the sentence, but does indicate the next word should be capitalized.
3. Continue until the sentence is complete with punctuation.
4. Group member #2 will move to the nucleus to transcribe another gene.
5. Translate and repeat until all of the group members have transcribed a gene or completed four sentences.

Sentence # ___ ______________________________________________________________
Sentence # ___ ______________________________________________________________
Sentence # ___ ______________________________________________________________
Sentence # ___ ______________________________________________________________

Activity 2: Designer DNA – Genetic Engineering (5-10 minutes)

Overview

With the development of new technologies, such as CRISPR, DNA can be edited more easily inside living cells. This means scientists can design a protein and construct a DNA sequence that will code for that protein. These proteins are made up of the same building blocks as all other proteins, but they can introduce new traits to an organism.

Instructions

1. Each group will be given a sentence to code into a DNA strand.
2. Using tRNA cards, determine and record the order of anticodons that would correlate with the correct sentence. Don’t forget a “start” and “stop” codon.
3. Use complimentary pairs to code for the mRNA strand that would complement the tRNA anticodons, as shown below.
4. Using the following base pairing, perform reverse transcription to produce a DNA strand from the mRNA strand, as shown below.
5. When completed, insert the new gene into the nucleus.

Sentence for students to engineer: Biotechnology can improve our quality of life.

Teacher Resources

1. Set out the genes (DNA strands) in a central location; this will represent the nucleus.
2. Place students in groups of four; each group will synthesize four protein sentences.
3. Give each group a complete set of cards and four blank mRNA strands.
4. Key: Sentences with DNA codes for High School located in printed version of the lesson in the teacher packet (pg. T12)

3D Printer STL File

3D Printer Ribosome Model STL file

Additional Resources

• Howard Hughes Medical Institute DNA Replication Video
  This short animated video demonstrates the intricate process of DNA replication.
• Howard Hughes Medical Institute DNA Transcription Video
  This short animated video demonstrates the intricate process of converting DNA into messenger RNA called transcription.
• BioMan Biology Protein Synthesis Race Interactive
  An interactive website based game that enables students to simulate the processes converting DNA into proteins.
• Scitable by Nature Education  Translation: DNA to mRNA to Protein
  Article describing how cells convert DNA into usable, functioning proteins.  Reading might be best suited to higher level readers.
• CK-12 Foundation Protein Synthesis
  This free online flex book provides easy to ready material covering a difficult topic. In addition there are review questions which accompany the text as well as a video linked within the text.
• DNA Learning Center RNA is an intermediary between DNA and protein.
  This site provides many resources which are often interactive. Be sure to use all of the tabs at the top of the page to find a variety of information on the role of RNA in protein synthesis.

Reflection and Conclusion

Discuss with the students the questions on their handout. Students should understand the processes involved in producing proteins as well as how inserting engineered DNA can enable organisms to produce proteins that are new to that organism.

Science and Agriculture Careers

To learn more about agriculture careers visit agexplorer.com. You can also find career profiles at Careers in Corn.

Sources

• Ohio Corn and Wheat Feed the World 
  This website has a wealth of resources pertaining to corn and it’s emerging uses, additional labs, news articles and many more resources.

Disclaimer

Any educator electing to perform demonstrations is expected to follow NSTA Minimum Safety Practices and Regulations for Demonstrations, Experiments, and Workshops, which are available at http://static.nsta.org/pdfs/MinimumSafetyPracticesAndRegulations.pdf, as well as all school policies and rules and all state and federal laws, regulations, codes and professional standards. Educators are responsible for abiding appropriate legal standards and better professional practices under a duty of care to make laboratories and demonstrations in and out of the classroom as safe as possible. If in doubt, do not perform the demonstrations.