Dusty Carroll Lesson Plan 6: DNA to RNA How Protein Synthesis Works

Transcription

1 Dusty Carroll Lesson Plan 6: DA to RA ow Protein Synthesis Works Target Audience AP chemistry class. I ll be assuming they have the appropriate background knowledge of the structure of DA and RA and proteins from their previous biology course. This lesson will focus on the more chemical aspects of the protein synthesis process. bjectives Recall the basic mechanisms of protein synthesis Explain the chemistry of the translation mechanism Introduction to the Lesson Use the Reference for ucleic Acids handout Review the basic structure of nucleic acids Recall that DA and RA are similar in structure, but differ in one of their bases Review the basic structure of nucleotides Show the phosphodiester link Point out that continued polymerization causes a backbone of alternating sugars and phosphates with bases as side chains Use the worksheet verview of Protein Synthesis Review structure of DA Recall the 5 bases from previous handout Students draw proposed orientation of the bases for optimum hydrogen bonding Show overhead with correct orientation Review basic steps of protein synthesis o ote that the complementary bases are such because of the chemical structure Use the transparency Translation: Chemical Aspects I Show how the DA stays in the nucleus and the mra takes the information out of the nucleus to the ribosome. otice how the mra has bases exposed (single strand, not double like DA) The ribosome moves over the mra Each time this happens, a new amino acid is added to the peptide chain These amino acids are brought to the mra by tra The slide says, Every amino acid is coded by a sequence of three bases What does this mean? Use the transparency Translation: Chemical Aspects II A codon is a set of three nucleotide bases. Just as DA has complementary bases, the three bases in the mra codon will have a complementary codon that can interact with them. This is called the anticodon. The anticodon is found on tra o tra binds to specific amino acids on one end and contains an anticodon on the other end o Show transparency tra structure note the anticodon and the site of the amino acid

2 When tra brings a new amino acid, an enzyme helps to form a peptide bond, attaching it to the polypeptide chain Use the transparency Translation: Chemical Aspects III This process is more clearly seen diagrammatically in this transparency Explain the process again and answer any questions that arise Use the transparency Translation: Chemical Aspects IV This transparency shows the same process, but the diagram has some chemical structure to give students an idea of how the amino acids continue to add to the polypeptide chain. ote that the bases are still drawn in cartoon form here, but remind students what they look like (from handout and worksheet) and that they are complementary because of the hydrogen bonding seen earlier Summarize and Close Students previously accepted the explanation that the two strands of DA stuck together because of paired bases. They also accepted the explanation that mra magically copies the DA information and takes it away to make a protein. They now have a better understanding of the chemistry behind the magic! References Garrett, R.., and Grisham, C.M., Principles of Biochemistry With a uman Focus. Brooks/Cole & Thomson Learning, McMurry, J. and Castellion, M.E., Fundamentals of General, rganic, and Biological Chemistry, 4 th ed. Pearson Education, Inc., Image references noted within

3 Reference for ucleic Acids Remember that nucleic acids are polynucleotides. A nucleotide is composed of three parts: A sugar (5-membered monosaccharide) C 2 C 2 or ribose 2-deoxyribose A phosphate group P - - A nitrogen-containing cyclic compound that is a base The 5 bases in DA and RA Adenine Guanine Cytosine Thymine Uracil The nucleotides polymerize in a specific way 2 Two nucleotides connected through a phosphodiester link - P - P - 2 Long chains of nucleotides form DA and RA Thymine is only found in DA; Uracil is only found in RA The other three bases are found in both

4 verview of Protein Synthesis DA exists as a double helix. Each strand contains a backbone of alternating sugars and phosphates. The bases of the nucleotides stick out from the backbone. In DA, the bases on opposite strands are complementary because they form hydrogen bonds which hold the strand together. Image from The complementary bases are oriented in such a way as to maximize the hydrogen bonding capabilities. Using the structures in the Reference for ucleic Acids handout, determine the orientation that each pair of bases must assume in order to maximize hydrogen bonding. Use the following parameters to assist you: Guanine and Cytosine pair to form 3 hydrogen bonds Thymine and Adenine pair to form 2 hydrogen bonds Draw your structures in the space below: Guanine and Cytosine Thymine and Adenine Steps for protein synthesis An enzyme breaks the hydrogen bonds between some base pairs in DA in order to separate the two strands Messenger RA (mra) is assembled by enzymes to carry the DA information out of the nucleus and into the ribosome where protein synthesis can occur mra and transfer RA (tra) work together along with enzymes to translate the DA information into a chain of amino acids (protein)

5 verview of Protein Synthesis Answer Key DA exists as a double helix. Each strand contains a backbone of alternating sugars and phosphates. The bases of the nucleotides stick out from the backbone. In DA, the bases on opposite strands are complementary because they form hydrogen bonds which hold the strand together. Image from The complementary bases are oriented in such a way as to maximize the hydrogen bonding capabilities. Using the structures in the Reference for ucleic Acids handout, determine the orientation that each pair of bases must assume in order to maximize hydrogen bonding. Use the following parameters to assist you: Guanine and Cytosine pair to form 3 hydrogen bonds Thymine and Adenine pair to form 2 hydrogen bonds Draw your structures in the space below: Guanine and Cytosine Thymine and Adenine sugar sugar sugar sugar Steps for protein synthesis An enzyme breaks the hydrogen bonds between some base pairs in DA in order to separate the two strands Messenger RA (mra) is assembled by enzymes to carry the DA information out of the nucleus and into the ribosome where protein synthesis can occur mra and transfer RA (tra) work together along with enzymes to translate the DA information into a chain of amino acids (protein)

6 Transparency Translation: Chemical Aspects I

7 Transparency Translation: Chemical Aspects II

8 Transparency tra

9 Transparency Translation: Chemical Aspects III

10 Transparency Translation: Chemical Aspects III