Transcription is the DNA → RNA part of the central dogma. It occurs in the nucleus. A copy of mRNA is made that is complementary to a strand of DNA. The sequence of bases in DNA or RNA makes up the genetic code, which is universal, unambiguous, and redundant. Translation is the RNA → protein part of the central dogma. It occurs at a ribosome. All three types of RNA are involved in translation.
- CA.9–12.IE.1.d; CA.9–12.LS.1.d; CA.9–12.LS.4.a, b, e; CA.9–12.LS.5.a, b
- NSES.9–12.A.1.6; NSES.9–12.C.1.1, 2, 3; NSES.9–12.C.2.1
- AAAS.9–12.5.B.3; AAAS.9–12.5.C.4
- Give an overview of transcription.
- Describe the genetic code.
- Explain how translation occurs.
codon: group of three nitrogen bases in nucleic acids that makes up a code “word” of the genetic code and stands for an amino acid, start, or stop
genetic code: universal code of three-base codons that encodes the genetic instructions for the amino acid sequence of proteins
promoter: region of a gene where a RNA polymerase binds to initiate transcription of the gene
protein synthesis: process in which cells make proteins that includes transcription of DNA and translation of mRNA
transcription: process in which genetic instructions in DNA are copied to form a complementary strand of mRNA
translation: process in which genetic instructions in mRNA are “read” to synthesize a protein
Introducing the Lesson
Introduce protein synthesis by discussing the common meanings of transcription (copying words) and translation (changing words from one language into another). Tell students they will read in this lesson how DNA is transcribed into RNA, which is then translated into a protein.
Divide the class into small groups and have each group do the activities RNA Transcription and RNA Translation, which can be accessed at the URL below. Students will develop a model that shows how the sequence of bases in DNA determines the order of bases in mRNA. Then they will determine the amino acid sequence encoded in the mRNA.
Pair English language learners with native English speakers, and ask pairs to create a flow chart of protein synthesis, including both transcription and translation. Tell partners to sketch simple diagrams to illustrate the steps of the flow chart. Give them a chance to share their flow charts with the class. ELL
Provide students with materials such as white yarn or string, colored markers, scissors, and clear tape. Then challenge the students to devise a way to use the materials to demonstrate RNA splicing. Set aside time for the students to present their demonstration to the class.
Assign the activity How Does DNA Determine the Traits of an Organism? (see URL below). Students will analyze DNA data for a fictitious organism named a snork. Then, based on the DNA base sequence, they will determine the organism’s traits. This fun activity can be done as a homework assignment.
A persistent misconception about protein synthesis is that amino acids are products, rather than reactants, of translation. Make sure students know that amino acids come from ingestion and biosynthesis, which are separate from translation.
Reinforce and Review
Copy and distribute the lesson worksheets in the CK-12 Biology Workbook. Ask students to complete the worksheets alone or in pairs as a review of lesson content.
Have students answer the Review Questions listed at the end of the lesson in the FlexBook®.
Points to Consider
When DNA is replicated or transcribed, accidents can happen, leading to a change in the base sequence.
- What do you think could cause such accidents to occur?
- How might the changes affect the reading frame? How might the encoded protein be affected?