RNA and Protein Synthesis Answer Key
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.)
[Note: The purpose of these questions is to activate prior knowledge and get students thinking. Students are not expected to know the answers to the Prior Knowledge Questions.]
- 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?
Answers will vary. Sample answer: I would draw plans for the house and make copies of the plans for the crew.
- Cells build large, complicated molecules, such as proteins. What do you think cells use as their “design plans” for proteins?
Answers will vary. [DNA contains the instructions for building 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.
- 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?
It is DNA. It contains thymine instead of uracil.
- RNA polymerase is a type of enzyme. Enzymes help chemical reactions occur quickly. Click the Release enzyme button, and describe what happens.
The two strands of the DNA molecule are separated.
Get the Gizmo ready: If necessary, click Release enzyme.
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.
Question: What occurs during transcription?
- 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? Adenine
- 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? Uracil
B. Which RNA base bonds with cytosine? Guanine
C. Which RNA base bonds with guanine? Cytosine
Analyze: In molecules of RNA, uracil takes the place of the DNA base thymine.
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?
A U G C U G A C C U A G
- 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?
A U G C C U A U U G A U G G C C C A U A A G U U
- Predict: How would a change in the sequence of nucleotides in a DNA molecule affect the mRNA transcribed from the DNA molecule?
Any change would be reflected in the mRNA molecule.
Activity B (continued from previous page)
- Infer: Why do you think stop and start codon signals are necessary for protein synthesis?
Without start and stop codon signals, there would be no way to begin or end the process of translation.
- Summarize: Describe the processes of transcription and translation in your own words, based on what you have observed in the Gizmo.
Transcription begins when the enzyme RNA polymerase splits the DNA molecule into two strands. Complementary mRNA nucleotides attach to the DNA template, forming an mRNA molecule. The mRNA molecule is similar to the DNA molecule except that uracil replaces thymine. The completed mRNA strand then detaches from the DNA molecule.
The mRNA molecule moves to the ribsome. The first mRNA codon, called the start codon (AUG), lines up with the ribosome. A corresponding tRNA molecule (UAC) attaches to the start codon. The tRNA molecule is also attached to an amino acid. A second tRNA molecule and its accompanying amino acid attach to the second mRNA codon. The two amino acids form a bond. More amino acids are added to the molecule as tRNA molecules attach to the mRNA codons until the strand is complete.
Extension: Genes and traits
Get the Gizmo ready:
You will not need to use the Gizmo for this activity.
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?
- Translate: Each codon codes for one of 20 amino acids. This code is universal among all living things. For example, the mRNA codon GGU codes for the amino acid glycine in every living thing, from a bacteria to an elephant.
Examine the codon chart below. The amino acid coded for by a specific mRNA codon can be determined by finding the first base of the codon along the left side of the table, the second base along the top of the table, and the third base along the right side of the table.
What amino acids do the following codons code for?
AUG: Methionine (Start) CUG: Leucine ACC: Threonine UAG: Stop
(Extension continued on next page)