Lesson Title: From gene to protein
Level: Grade 10
Strand: Living Things and Their Environment
Content: Heredity: Inheritance and Variation
Learning Competency: Explain how protein is made using information from DNA
This video is best played using a VLC player.
Below are tips on how to use this video in explaining the synthesis of protein from DNA. These suggested tips follow the sequence of the slideshow.
1) The title screen (00:00) shows a representation of a gene and a protein. As drawn, you will notice that a portion of the DNA overlaps a portion of the protein, suggesting that a gene becomes a protein. You may ask the students to identify which represents the gene and which represents the protein.
2) As you continue to play the slideshow, you may reiterate the main focus of this material, i.e., the story of how a gene becomes a protein. As you pause at 00:07, you will find another figure that suggests this idea. You may focus them on the picture of a gene at the narrow portion of the arrow and a picture of the protein in the pointed portion of the arrow.
3) The first part of the slideshow (00:00 to 00:32) involves concepts that were taken up in Grade 9. Being so, this part may be used as you review your students and prepare them for the ideas to be learned from this material.
a) At 00:07, the word “gene” is shown on the screen. You may pause the slideshow and elicit students’ prior ideas about genes. The students know that genes are made up of DNA. However, allow students to give out any idea about genes. This may also serve as an opportunity to check if the students’ ideas on genes are correct. Do correct the ideas as necessary.
b) Among the answers given by the students, focus on the answer that mentioned DNA. You may continue to play the slideshow. As it plays, the word “DNA” will appear on the screen (00:10) aligned with the word “GENE”. This suggests that DNA corresponds to the gene. Again, you may pause and ask the students about DNA. You may continue to play the slideshow until the full diagram for the protein synthesis is projected on the screen (00:31). You may opt to pause and elicit students’ ideas about RNA and polypeptides.
4) Focus the students on the 2 main processes involved in protein synthesis, i.e., transcription and translation.
5) As you play the slideshow, you will notice that the protein synthesis diagram can still be seen on the screen but reduced in size and situated at the leftmost corner. At 00:37, the second portion of the diagram fades away. At this point, you can start discussing the first main process of protein synthesis, i.e., transcription. Emphasize that the process of transcribing DNA to RNA is facilitated by the enzyme RNA polymerase (00:42). You may ask the students the function of the RN
A polymerase. They can deduce the enzyme function by its name. Take the keyword “polymer” as a springboard that a molecule of RNA (or a polymer of nucleic acids) is the product of transcription, which is complementary with DNA (00:46). However, only a portion of the DNA is transcribed, as seen in the slideshow (00:48 to 1:14).
6) At 1:17, the word “complementary” is boxed in for emphasis. After which, a coding region of a DNA strand is shown together with its complementary RNA strand (1:19). Let the students compare these two strands and give them enough time to come up with a description of what “complementary” is. You may guide them as they try to figure it out. You may need to orient them with the letters they see in the strands. These are the first letters of the bases. Have them enumerate the names of the bases. Ask them if they see a certain pattern. Guide them to notice that there are bases that always go together. As such, they are called as base pairs. For instance, they can focus on one base first such as “G” or guanine in the DNA strand, then from the RNA strand, they can look at the base directly below it. Some students, if not all, may notice that it is always “C” that is “directly below” the letter “G”. This is in accordance with the base-pairing rule which pairs up the bases guanine and cytosine. Let them identify the other base pairs.
7) From 1:19 to 2:03, you may pause it as necessary to reiterate the ideas from the preceding discussion. Also, in case the students have not noticed that thymine is only found in DNA and uracil is only in RNA,throw in a question that will make them realize that. You may direct their attention to the red-filled table and let them compare the bases under the DNA and RNA columns. Emphasize as well that this base-pairing starts from the left end (5’) going to the right end (3’). This direction is called as upstream, as seen in the slide show. Moreover, since it is the sequence in the anti-sense strand of the DNA that is being followed, this strand is also referred to as the template (2:20).
8) At 2:23, the upper portion of the DNA strand appears once more on the screen and the lower portion fades away. At this point, you may ask the students to compare this part of the DNA strand and the complementary RNA strand. Guide them to notice that they exactly have the same sequence except that when thymine is present in the DNA strand, it would be uracil that is in the RNA strand.
9) At this point, you may ask the class to describe in their own words what happens during transcription. Help them put together in one single statement all the ideas about transcription that they have learned, especially if they just gave in phrases or keywords or incomplete ideas. Once the class has reached a single statement in describing the transcription of DNA to RNA, continue to play the slideshow. At 2:39, a suggested description and an image/figure are shown that summarizes all the ideas about transcription that are expected to be remembered by the students at this level. You may also want to show a video clip from YouTube© (https://www.youtube.com/watch?v=ztPkv7wc3yU) for reinforcement.
10) At 2:41, a small letter “m” will appear beside the acronym RNA (in red font). This small “m” stands for messenger. The product of transcription is a messenger RNA, so-called due to its function of “carrying the message or information” transcribed from the DNA. This mRNA serves now as the template in the second phase of the protein synthesis which is referred to as translation.
11) Continue to play the slideshow as you reiterate the transcription process to link/introduce translation (2:50). At 3:01, a description of what happens during translation is shown. The terms “codon” and “tRNA” may be new to the students. You may want to go slow in pointing them out as they are shown in the mRNA figure. You may pause the slideshow at 3:13. Emphasize that a codon is simply a sequence of 3 bases, like the AUG, as seen from the slideshow. On the other hand, a tRNA carries a codon that matches a certain codon in the mRNA, like the one shown wherein the tRNA with the UAC codon matches the AUG codon in the mRNA. You may ask the students to infer why these codons are considered a match. Guide them to relate it with the base-pairing rule. In essence, these codons are also complementary. Similarly, the bases must pair; but this time, even the sequence of the bases should match. This codon from the tRNA is referred to as the anti-codon (3:17). The anti-codon practically is the one that decodes an mRNA codon to create the protein. Essentially, translation happens during the decoding of mRNA. The codon that is in the language of nucleic acids can be translated to the language of amino acids as each tRNA has a corresponding amino acid attached to its end.
12) The entire molecule (tRNA with the amino acid) is referred to as aminoacyl tRNA. You may point out the “Met” attached to the first tRNA in the image. At 3:19, a reference for translation, like a dictionary, is shown. In this tool you can find the translation of a codon to an amino acid. You may ask the students to find AUG from the reference table and find its equivalent amino acid. Do the same with the next sequence of codons in the mRNA strand shown in the slideshow, until the students reach UAA. From the table they will find STOP, which means that the translation STOPS at this point. If there is a STOP, the students should infer that there must be a START. At 3:32, you may point out that typically it is the AUG that is the START codon. You may also add that translation happens at the ribosome (3:35).
13) At this point, it is imperative to show a video clip to see the “process in action”. From the preceding discussion, the students only learned the translation of the nucleic acid to an amino acid, but they were not presented on how these amino acids link together to form the protein. We suggest you let them watch this YouTube© video clip (https://www.youtube.com/watch?v=5bLEDd-PSTQ) and annotate as necessary. The first part of this video is essentially a review of what has been discussed, however, there are key molecules mentioned that were not yet introduced. Let it be. These key molecules are not expected to be known by the students, at this grade level. Besides, the students may be able to deduce their functions as they finish watching the video clip. But do make sure that the students give their complete attention, as this is where they will see how the protein is formed from the linking of amino acids through peptide bonds. Moreover, the students should be able to realize at this point why protein is sometimes referred to as a polypeptide.
14) You may end the discussion by showing them again the full diagram (3:42). At this point, the students should be able to describe what happens during transcription and translation. Also, they should be able to make sense of the image shown beside transcription and translation. Ask some students to share their description to the class, and perhaps use the image on the screen as they share their description.
15) You may reinforce the ideas learned by showing another video which presents the entire protein synthesis. You may use the suggested YouTube© video clip (www.youtube.com/watch?v=erOP76_qLWA). Please note though that the video also shows how the synthesized protein is “chaperoned” to avoid premature folding. At this grade level, this idea is not essential but may come only as interesting. Use this part of the video as necessary.
The video may be downloaded upon sending a request e-mail to firstname.lastname@example.org.