Student Exploration: RNA and Protein Synthesis

Student Exploration: RNA and Protein Synthesis

Name:      Date:

Vocabulary:

amino acid, anticodon, codon, gene, messenger RNA, nucleotide, ribosome, RNA, RNA polymerase, transcription, transfer RNA, translation

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

1. Suppose you want to design and build a house. How would you communicate your design plans with the construction crew that would work on the house?

2. Cells build large, complicated molecules, such as proteins. What do you think cells use as their “design plans” for proteins?

Gizmo Warm-up

Just as a construction crew uses blueprints to build a house, a cell uses DNA as plans for building proteins. In addition to DNA, another nucleic acid, called RNA, is involved in making proteins. In the RNA and Protein Synthesis Gizmo™, you will use both DNA and RNA to construct a protein out of amino acids.

1. DNA is composed of the bases adenine (A), cytosine (C), guanine (G), and thymine (T). RNA is composed of adenine, cytosine, guanine, and uracil (U). Look at the SIMULATION pane. Is the shown molecule DNA or RNA? How do you know?

2. RNA polymerase is a type of enzyme. Enzymes help chemical reactions occur quickly. Click the Release enzyme button, and describe what happens.

Introduction:

The first stage of building a protein involves a process known as transcription. In transcription, a segment of DNA serves as a template to produce a complementary strand of RNA. This complementary strand is called messenger RNA, or mRNA.

Activity A: Transcription

Get the Gizmo ready:

• If necessary, click Release enzyme.

Question: What occurs during transcription?

1. Experiment: Like DNA, RNA follows base-pairing rules. Experiment to find which RNA nucleotide on the right side of the Gizmo will successfully pair with the thymine at the top of the template strand of DNA. (NOTE: The DNA on the right side is the template strand.) Which RNA base bonded with the thymine?

2. Experiment: The next three bases on the DNA template strand are adenine, cytosine, and guanine. Use the Gizmo to answer the following questions:

A. Which RNA base bonds with adenine?

B. Which RNA base bonds with cytosine?

C. Which RNA base bonds with guanine?

3. Analyze: In molecules of RNA, uracil takes the place of the DNA base

4. Build: Continue building the molecule of mRNA until you have used all of the RNA nucleotides. What is the nucleotide sequence of the mRNA strand you built?

5. Apply: Suppose a template strand of DNA had the following sequence:

T A C G G A T A A C T A C C G G G T A T T C A A

What would be the complementary strand of mRNA?

6. Predict: How would a change in the sequence of nucleotides in a DNA molecule affect the mRNA transcribed from the DNA molecule?

Introduction:

After a strand of mRNA has been built, the strand exits the cell’s nucleus. The second stage of protein synthesis, called translation, occurs next. During translation, the strand of mRNA is used to build a chain of amino acids.

Question: What occurs during translation?

1. Observe: Examine the strand of mRNA on the SIMULATION pane. Every group of three bases of mRNA is called a codon. In the table at right, list the nitrogen bases in each codon. (Hint: Start from the top of the strand and read down.) The first mRNA codon is called the universal start codon.

2. Predict: Translation starts when a ribosome binds to a strand of mRNA. Transfer RNA, or tRNA, begins bringing amino acids into the ribosome. Which anticodon do you think would attach to the mRNA’s start codon?

3. Observe: Place the next two anticodons on the mRNA strand. What happens?

4. Describe: UAG (as well as UAA and UGA) is an example of a stop codon. Molecules called release factors bind to stop codons. Place the release factor on the mRNA molecule. What happens?

5. Infer: Why do you think stop and start codon signals are necessary for protein synthesis?

6. Summarize: Describe the processes of transcription and translation in your own words, based on what you have observed in the Gizmo.

Transcription:

Translation:

Introduction: Inside a ribosome, amino acids are linked together to form a protein molecule. As the chain of amino acids grows, it tends to coil and form a three-dimensional shape. The complex shape that results determines the properties of the protein. Proteins have a wide variety of structures and perform many essential functions in living things.

A sequence of DNA that codes for a specific protein is called a gene. By coding for proteins, genes determine an organism’s inherited traits.

Question: How do genes code for specific proteins and traits?

1. Translate: Each codon codes for one of 20 amino acids. This code is universal among all living things. What amino acids do the following codons code for?

AUG:    CUG:    ACC:    UAG:

2. Apply: Suppose you wanted a protein that consists of the amino acid sequence methionine, asparagine, valine, and histidine. Give an mRNA sequence that would code for this protein.

3. Summarize: How do genes determine the traits of an organism? Explain in detail.

4. Extend your thinking: Sometimes errors occur during transcription or translation. How might having several different codons for the same amino acid offset transcription or translation errors?

Extension: Genes and traits

Get the Gizmo ready:

• You will not need to use the Gizmo for this activity.

5. Think and discuss: Consider the two following statements:

• The theory of evolution states that all living things had a single common ancestor.

• The translation between mRNA and amino acids is the same for all living things. (For example, the mRNA codon CAG codes for glutamine in all living things.)

Does the second statement support the theory of evolution? Explain why or why not. If possible, discuss your answer with your teacher and classmates.