1. RNA
Read the lesson title aloud to students.

2. Learning Objectives Contrast RNA and DNA.
Explain the process of transcription.
Click to show each of the learning objectives.
Students may already have some basic knowledge of RNA.
Give students a few minutes to complete a quick write of whatever they know, or think they know, about RNA. Then, ask volunteers to come forward and write their responses on the board.
Tell students that at the end of this lesson, they should be able to compare and contrast RNA and DNA and explain the process of transcription.

3. Comparing RNA and DNA
The sugar in RNA is ribose instead of deoxyribose.
RNA is generally single-stranded, not double-stranded.
RNA contains uracil in place of thymine.
Remind students that each nucleotide in DNA is made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base.
Explain that this is true for RNA as well, but that there are some important differences between RNA and DNA.
Click to reveal the first difference.
Tell students: The difference in the sugar is the distinction in the abbreviations RNA and DNA.
Click to reveal the second difference.
Tell students: This lesson will explain why RNA is single-stranded.
Click to reveal the third difference.
Explain that for every “T” in the DNA code, RNA has a “U.” This means if forming a complimentary code, where there is an “A” in DNA, RNA would pair it with a “U”.
Explain that these chemical differences make it easy for enzymes in the cell to tell DNA and RNA apart.

4. The Role of RNA
The roles played by DNA and RNA molecules in directing protein production are like the two types of plans builders use:
A master plan
A blueprint
Explain to students that the first step in decoding these genetic instructions is to copy part of the base sequence from DNA into RNA.
RNA then uses these instructions to direct the production of proteins, which help determine an organisms’ characteristics.
Make the analogy that the roles DNA and RNA molecules play in directing the production of proteins are like the two types of plans builders use.
Click to reveal the first bullet point.
Ask: What is a builder’s master plan used for?
Answer: A master plan is the original information needed to construct a building.
Tell students: Builders never bring a valuable master plan to the job site because it might be damaged or lost. Instead, they use a blueprint.
Click to reveal the second bullet point.
Ask: Why do you think builders work from blueprints?
Answer: because they are inexpensive, disposable copies of the master plan and multiple copies can be made
Tell students: An RNA molecule is like a disposable copy of a segment of DNA.

5. Types of RNA The three main types of RNA are: Transfer RNA
Ribosomal RNA
Messenger RNA
Explain to students that there are several types of RNA and most of them are involved in protein synthesis.
Tell students: RNA controls the assembly of amino acids into proteins. Each type of RNA molecule specializes in a different aspect of this job.
Tell students: There are three main types of RNA.
Click to reveal each type.
Read each name.
Address misconceptions: Emphasize the importance of RNA. Explain to students that DNA is the inherited genetic material, but RNA is the genetic material that carries out the instructions encoded in DNA. Without RNA, the instructions in DNA could not be used by cells.

6. Messenger RNA
An mRNA molecule is a copy of the portion of DNA that will be used to make a protein.
After being made in the nucleus, mRNA travels to the cytoplasm, the site of protein synthesis.
Tell students: Many DNA genes contain instructions for assembling amino acids into proteins.
The RNA molecules that form as copies of these instructions are called messenger RNA.
Ask: Where would the instructions for polypeptide synthesis be carried from and to?
Answer: For polypeptide synthesis, messenger RNA moves from the nucleus to ribosomes in the cytoplasm.
Click to reveal this answer.

7. Ribosomal RNA
Protein synthesis occurs on ribosomes, which are made up of two subunits.
These subunits consist of several molecules of ribosomal RNA (rRNA) and as many as 80 different proteins.
Explain to students that proteins are assembled on ribosomes, small organelles composed of two subunits.
Click to reveal the image and information.
Tell students: These subunits are made up of several ribosomal RNA (rRNA) molecules and as many as 80 different proteins.
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8. Transfer RNA
During protein synthesis, transfer RNA molecules (tRNA) carry amino acids from the cytoplasm to the mRNA.
Explain that when a protein is built, a third type of RNA molecule transfers each amino acid to the ribosome as it is specified by the coded messages in mRNA. These molecules are known as transfer RNA.
Click to reveal the image and information.
Ask students to come up with analogies for transfer RNA and have a class discussion in which they share their ideas.

9. RNA Synthesis: Transcription
In transcription, segments of DNA serve as templates to produce complementary mRNA molecules.
Ask: How does the cell make mRNA?
Answer: Most of the work of making RNA takes place during the process of transcription.
Tell students that, in prokaryotes, RNA synthesis and protein synthesis take place in the cytoplasm.
In eukaryotes, RNA is produced in the nucleus, as shown in this illustration, and then moves to the cytoplasm for the purpose of protein synthesis.
Explain that transcription requires an enzyme, known as RNA polymerase, that is similar to DNA polymerase.
Click to highlight RNA polymerase.
RNA polymerase binds to DNA during transcription and separates the DNA strands.
Click to highlight the DNA strands.
Tell students: This is like unzipping the two strands of DNA.
RNA polymerase then uses one strand of DNA as a template from which to assemble nucleotides into a complementary strand of mRNA.
Click to highlight the strand of RNA.
The ability to copy a single DNA sequence into RNA makes it possible for a single gene to produce hundreds or even thousands of RNA molecules.

10. RNA Synthesis: Promoters
RNA polymerase binds only to regions of DNA that have specific base sequences. These regions are called promoters.
Ask: How does RNA polymerase know where to start and stop making a strand of RNA?
Answer: RNA polymerase doesn’t bind to DNA just anywhere. The enzyme binds only to promoters.
Explain that promoters, which have specific base sequences, tell the enzyme where to start transcribing DNA.
Tell students: Transcription is just the first stage of RNA synthesis.

11. RNA Synthesis: RNA Editing
New RNA molecules sometimes require a bit of editing before they are ready to be read.
Exons
Introns
Ask: What happens to the newly made mRNA before it leaves the nucleus?
Answer: RNA editing
Make the analogy that new mRNA molecules are like a writer’s first draft―they sometimes require editing before they are ready to be read.
Tell students: The pieces of pre-mRNA molecules that are cut out, or “edited out,” and discarded are called introns.
Ask for a volunteer to point out the introns in the pre-mRNA.
Click to highlight the introns.
Tell students: The remaining pieces are known as exons.
Ask for a volunteer to point out the exons in the pre-mRNA.
Click to highlight the exons.
Point out that the remaining exons are spliced together.
Click to highlight the exons spliced together.
Tell students: Then, an RNA cap and tail are added to form the final mRNA molecule.
Click to show labels and highlight the cap and tail.
Ask: What is the purpose of making a large RNA molecule and then throwing parts of that molecule away?
Answer: That’s a good question, and biologists still don’t have a complete answer.
Some pre-mRNA molecules may be cut and spliced in different ways in different tissues, so a single gene can actually produce several different mRNA molecules.
Introns and exons may also play a role in evolution, making it possible for very small changes in DNA sequences to have dramatic effects on how genes affect cellular function.
Cap
Tail