After wrapping up the discussion from the previous day’s lesson, we launched into an investigation of the process of Central Dogma. Students learned how DNA codes for RNA which codes for protein. We drew out the processes of transcription and translation, using a guided worksheet approach to help students understand what happens at each step of the process. Whiteboard notes from two different classes are shown below:
Updated: February 5, 2016
We completed the DNA base-pairing worksheet that we began yesterday. We reviewed how DNA codes for RNA and RNA codes for protein. We learned how RNA is read by ribosomes, with 3-base RNA sequences (codons) coding for specific amino acids. Students were surprised to learn that that for many amino acids, there are more than one codons. This was emphasized in questions 22 and 23 of the worksheet, where students learned to work backwards from a sequence of amino acids to figuring out one possible RNA sequence encoding that amino acid sequence, and finally figuring out the DNA sequence coding for the chosen RNA sequence.
Question 26 of the worksheet asked students to notice how amino acids with multiple codons often “wobble” at the third position (click here for a brief summary, or here for a not-so-brief summary). The picture below attempts to add some context to the discussion.
The final lesson of Unit 2 explores how amino acids connect to make proteins. The Lesson 48 PowerPoint includes the vocabulary terms of amino acid and protein. Lesson 48 connects with Lesson 47, as amino acids are chiral molecules. Notably, all of the 20 different amino acids in human proteins are “left-handed” (as opposed to the mirror-image “right-handed” isomers), meaning they all have the L conformation (L for laevus, Latin for “left”) rather than the D conformation (D for dexter, Latin for “right”). Students will work in pairs to complete the Lesson 48 Worksheet, learning about the properties of amino acids and how they bind together to form proteins. For more on the D and L convention, click on the picture below.
As noted previously, there are 20 different amino acids. All amino acids share the same base structure of a central carbon atom bound to a carboxylic acid (-COOH), an amino group (-NH2), and a hydrogen (H). The central carbon is also bound to an R group, with R indicating any one of the 20 different amino acid structures. The structures each have different physical properties. When individual amino acids link together, a polypeptide chain is formed (and a molecule of water is removed as each new amino acid is linked to the chain). The polypeptide chain, composed of a string of amino acids, folds into a particular shape determined by the interactions of all of the amino acids. The shape of a protein determines its function in the body. Mr. Anderson of Bozeman Science has a fantastic video explaining the nature of proteins:
For students looking for a good review of Central Dogma (DNA > RNA > Protein > Trait), the Crash Course Biology video DNA, Hot Pockets, & The Longest Word Ever is a good resource:
Finally, for students with access to a home computer, the Fold.It website will have you folding proteins in no time!