The central dogma of molecular biology can be summed up as DNA → RNA → Protein. Starting in the early 1900s, several researchers made important discoveries about DNA and how it codes for proteins. Three types of RNA are also involved in protein synthesis: mRNA, rRNA, and tRNA.
- CA.9–12.IE.1.d, k; CA.9–12.LS.1.d; CA.9–12.LS.4.a; CA.9–12.LS.5.a
- NSES.9–12.A.1.6; NSES.9–12.A.2.1, 2, 5; NSES.9–12.C.1.1, 3; NSES.9–12.C.2.1; NSES.9–12.G.1.1; NSES.9–12.G.3.2, 3, 4
- AAAS.9–12.1.A.2; AAAS.9–12.5.B.3; AAAS.9–12.5.C.4
- McREL.9–22.214.171.124, 2, 3; McREL.9–126.96.36.199, 2; McREL.9–188.8.131.52, 3, 4; McREL.9–184.108.40.206, 4; McREL.9–220.127.116.11, 2
- State the central dogma of molecular biology.
- Outline discoveries that led to knowledge of DNA’s structure and function.
- Describe the structure of RNA, and identify the three main types of RNA.
central dogma of molecular biology: doctrine that genetic instructions in DNA are copied by RNA, which carries them to a ribosome where they are used to synthesize a protein (DNA → RNA → protein)
Chargaff's rules: observations by Erwin Chargaff that concentrations of the four nucleotide bases differ among species; and that, within a species, the concentrations of adenine and thymine are always about the same and the concentrations of cytosine and guanine are always about the same
messenger RNA (mRNA): type of RNA that copies genetic instructions from DNA in the nucleus and carries them to the cytoplasm
ribosomal RNA (rRNA): type of RNA that helps form ribosomes and assemble proteins
transfer RNA (tRNA): type of RNA that brings amino acids to ribosomes where they are joined together to form proteins
Introducing the Lesson
By taking the Tour of the Basics at the URL below, students can review genes and chromosomes and get an introduction to the structure of DNA.
Have students build an edible model of DNA. This will help them learn the structure of DNA and how DNA bases pair. The URL below provides everything you and your students need for the activity.
Pair less proficient readers with more proficient readers, and ask pairs to make a table comparing and contrasting the structure and function of DNA and RNA. A sample table is shown below (Table below). LPR
RNA vs. DNA
C, G, A, U
C, G, A, T
nucleus and cytoplasm
Ask your advanced students to do the online genetics tutorial at the URL below. It uses multimedia to present principles of molecular genetics at a more sophisticated level than the text.
Have small groups of students do the activity Where Do Genes Begin? (see URL below). In the activity, students will build a simple model of DNA and use it to investigate Chargaff’s rules and DNA sequencing.
Common student misconceptions about DNA include:
- DNA, genes, and chromosomes are interchangeable concepts.
- DNA is the only genetic material in the genome.
- Simple organisms such as bacteria do not have DNA.
- All DNA sequences code for proteins.
Work with students to restate each misconception so it is true.
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
All three types of RNA are needed by cells to make proteins.
- Can you develop a model in which the three types of RNA interact to make a protein?
- How do you think mRNA copies the genetic instructions in DNA? How are these instructions encoded in the DNA molecule?