ZERO-IN

Italicized font represents information to be shared orally or physically completed with the students at this time.

The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.

ANALYZE IT

Note: Questions marked with a triangle (∆) are included to enrich students’ understanding. These questions do not appear in students’ SDRs but should be used as additional discussion points during the PostLab.

• After student groups complete the Investigation, review the transfer of information from DNA to RNA to protein that was modeled in the Investigation.

• Ask students to think about whether they have understood the basic concepts of the Investigation. Ask students to answer the following questions.

• ∆ How are proteins different from DNA and RNA? Proteins are made up of building blocks called amino acids. DNA and RNA are made up of building blocks called nucleotides (bases).

• ∆ Each gene encodes for a single protein. Genes are made of DNA. How does the information in DNA get converted to proteins? The specific DNA sequences of genes are transcribed into messenger RNA (mRNA) in the nucleus of cells. The mRNA carries the information into the cytoplasm of the cell where it is translated into amino acid sequences on structures called the ribosome.

• ∆ What role does RNA play in the cell? RNA acts as a messenger, carrying the genetic information encoded by DNA in the nucleus to the ribosomes in the cytoplasm. On ribosomes, the code (mRNA sequence) is read and translated into protein. Note to teacher: There are many other types of RNA and functions of RNA in cells, but mRNA is the only type of RNA introduced in this.

• ∆ How does the cell know which amino acids to place in a protein? The mRNA is “read” by the ribosome in groups of three adjacent bases called codons. Each codon specifies a single amino acid that is placed in the protein. Some codons are stop codons that signal the end of the protein amino acid sequence.

• Discuss the impact of mutations in DNA on the structure and function of proteins.

• Ask students to think about the sequences of the four different DNA mutations and the original sequence. How do they compare to one another and to the original sequence? How are they similar and how are they different?

• Ask students to think about the sequences of the mutant proteins and the original protein’s sequence. Ask students to compare the five sequences to each other. How are they similar and how are they different?

• ∆ How can mutations in DNA cause changes in protein function? The function of a protein is directly related to its structure. Structure depends on the amino acid sequence of a protein. Mutations in DNA lead to changes in the mRNA codons that specify which amino acids to place in the protein.

• ∆ Do mutations in DNA always cause a change in amino acid sequence? No. A change in DNA sequence does not always lead to a change in the amino acid sequence. This is due to redundancy built into the genetic code. Some amino acids are coded for by multiple codons. If a mutation causes a change to a different codon that still encodes for the original amino acid, there will be no change in amino acid sequence observed. If students are having trouble with this concept, refer to Mutation 3 in this Investigation which had a change in DNA sequence but no change in amino acid sequence. Have students look at Table B and lead a discussion of how the amino acids serine and valine both have multiple codons. In these cases, different base sequences code for the same amino acids.

• Ask students to decide how the data that they collected in the Investigation fits together. Ask students to review their data and answer the following question:

• Can a change in the amino acid sequence of a protein change the function of the protein? Explain your answer. Student answers will vary. Discuss student suggestions. In this Investigation, all changes in the amino acid sequence led to a change in the function of the protein. Inform students that this is not always the case, as will be demonstrated in the next Investigation. Students should record their conclusions in their Student Data Record.

GET FOCUSED

Instruct students to complete the Focus Questions in their SDRs then discuss them as a class. Use the suggested responses below to guide students’ answers.

• How does DNA control the functions of an organism? Genes contain DNA sequences that encode for proteins. The DNA sequence and its corresponding RNA sequence instruct the cell to build a specific protein. Each set of three nucleotides in the RNA (and DNA) corresponds to one amino acid in the protein. Proteins are responsible for most of the functions of an organism’s cells.

• Can mutations in DNA cause changes in an organism? Explain your answer. Mutations may or may not lead to changes in an organism. If the mutation in DNA does not change the amino acid sequence of the protein, then no change in the function of that protein will occur and no change will be seen in the organism. If the mutation in the organism does cause a change in the amino acid sequence of the protein, then a change in the function of the protein is possible and a corresponding change in the organism would be expected.