Course: Biology Agricultural Science & Technology Unit: DNA State Standard: Students will understand that genetic information coded in DNA is passed from parents to offspring by sexual and asexual reproduction. The basic structure of DNA is the same in all living things. Changes in DNA may alter genetic expression. State Objectives: Explain how the structure and replication of DNA are essential to heredity and protein synthesis. a. Use a model to describe the structure of DNA. b. Explain the importance of DNA replication in cell reproduction. c. Summarize how genetic information encoded in DNA provides instructions for assembling protein molecules. e. Relate the historical events that lead to our present understanding of DNA to the cumulative nature of science knowledge and technology. Unit Objectives: A. Describe the structure of a DNA molecule and the history of its discovery. B. Explain the process of DNA replication and understand its relevance to cell division. C. Describe the structure of RNA and identify the steps associated with protein synthesis. Materials Needed (Equipment): Pre-cut paper nucleotide bases for DNA activity Print or copy enough so that each person in the class has one nucleotide base (Click here for nucleotide activity cards) Red and black licorice sticks, colored marshmallows or gummy bears, toothpicks and string. (Click here for the Candy DNA Lab Activity) The following supplies are for the DNA Extraction Lab (Optional) Split green peas Table Salt Cold water Blender Strainer Detergent (Dawn) Meat tenderizer Rubbing alcohol Test tube Wooden skewers Mixing bowl Beaker
Facilities: Classroom PowerPoint Projector Interest Approach: A: Take a stack of books and have students imagine how much information is held in the stack of books. Explain how small a molecule of DNA is. (You need a microscope to see a cell). Explain that a molecule of DNA has much more information on it than in the stack of books on the table and that DNA is what makes living organisms what they are. B: Demonstrate or have groups do a DNA Extraction Lab o Click here to follow the link to the DNA Extraction Lab
Objective A: Identify the structure of a DNA molecule. Curriculum (Content) (What to teach) Instruction (Methodology) (How to teach) What is DNA? Have a class discussion on what students know about DNA and list on board. What is DNA made of and what does it look like? A1 A2 Deoxyribonucleic Acid Have a class discussion about what DNA is made up of. Have a student draw a diagram of DNA on the board. A1. PPT Slide 1 A2. PPT Slide 2 DNA is the molecule responsible for controlling the activities of the cell It is the hereditary molecule DNA directs the production of protein A3 Structure of DNA In 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases. Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring. A3. PPT Slide A3
A4 Structure of DNA Because DNA is composed of two strands twisted together, its shape is called double helix. A double helix resembles a twisted ladder. A5 Nucleotides A4. PPT Slide A4 A5. PPT Slide 5 DNA is made up of subunits called nucleotides Nucleotides consist of the backbone, which is made of sugar (deoxyribose) and phosphate, as well as a nitrogenous base A6 Nucleotide A6. PPT Slide 6 Discuss the diagram of the nucleotide and help students identify each component. A7 How Did DNA Get its Name? A7. PPT Slide 7 Either have students write an answer to this question in their notes or on a sheet of paper, or discuss as a class.
Based on what you just learned, how do you think deoxyribonucleic acid (DNA) got its name? (Because of the sugar in the backbone of the DNA molecule called deoxyribose) A8 Nucleotides A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen. In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). A9 Nucleotide Sequence The four nucleotides are represented by the first letter in their name A Adenine G Guanine T Thymine C Cytosine A10 Nucleotide Sequence In DNA, Adenine always pairs with Thymine Cytosine always pairs with Guanine A8. PPT Slide 8 A9. PPT Slide9 A10. PPT Slide 10
A11 Nucleotides Nucleotides stack on top of one another forming the double helix, or twisted ladder A11. PPT Slide 11 A12 A12. PPT Slide 12 On the view of the DNA diagram, have students identify the individual components of the DNA molecule A13 DNA Building Click here to link to a DNA building activity online! A13. PPT Slide 13 On this link, have students create a DNA molecule and practice matching nucleotide bases Do Candy DNA Activity (See below) Activity: How to Make a DNA Model Using Candy Here's How: 1. Gather together red and black licorice sticks, colored marshmallows or gummy bears, toothpicks and string. 2. Assign names to the colored marshmallows or gummie bears to represent nucleotide bases. There should be four different colors each representing either adenine, cytosine, guanine or thymine.
3. Assign names to the colored licorice pieces with one color representing the pentose sugar molecule and the other representing the phosphate molecule. 4. Cut the licorice into 1 inch pieces. 5. String half of the licorice pieces together lengthwise alternating between the black and red pieces. 6. Repeat the procedure for the remaining licorice pieces to create a total of two stands of equal length. 7. Connect two different colored marshmallows or gummy bears together using the toothpicks. 8. Connect the toothpicks with the candy to either the red licorice segments only or the black licorice segments only, so that the candy pieces are between the two strands. 9. Holding the ends of the licorice sticks, twist the structure slightly. Tips: 1. When connecting the base pairs be sure to connect the ones that pair naturally in DNA. For example, adenine pairs with thymine and cytosine pairs with guanine. 2. When connecting the candy base pairs to the licorice, the base pairs should be connected to the licorice pieces that represent the pentose sugar molecules.
A14 Go Get It Moment! When you hear Move it! you will have 30 seconds to come get one piece of paper with an A, G, T, or C on it. Then find someone else in the room whose letter correctly matches with your nucleotide letter and stand by that person. What are the questions? Move it! A28 Go Get It Moment! When you hear Double Helix, you will have 1 minute to make a classroom DNA strand by standing next to another pair of nucleotides What questions are there? Double Helix A14. PPT Slide 14 Place your pre-cut nitrogen base papers somewhere in the room where students can access them easily and follow the prompt on the PPT slide 14. When you are ready for the students to get started, click onto the next slide and there is an automatic 30 second timer. A28. PPT Slide 28 Follow the prompt on the PPT slide 28 and when you are ready for the students to get started, click onto the next slide and there is an automatic timer for 1 minute. Have the students keep their nucleotide paper letter and remember their partner and their place in the DNA strand for a future activity. How can people benefit from understanding the structure of a DNA molecule? (Understanding the structure of a DNA molecule can help us understand genetic disorders, solve crimes, paternity testing, genetic engineering, cloning, etc.) Objective B: Explain the process of DNA replication and understand its relevance to cell division.
Why is DNA replication necessary in living organisms? Students should have already learned about mitosis and meiosis. Answers should refer back to Interphase in cell division where DNA replication occurs in order for the cell to divide with the appropriate amount of DNA. B45 DNA Replication B45. PPT Slide 45 In order for cells to divide, DNA must be able to make exact copies of itself This process is known as DNA Replication B46 DNA Replication B46. PPT Slide 46 DNA Replication occurs before mitosis and meiosis Replication results in two identical DNA daughter strands from one mother strand B47 Process of DNA Replication B47. PPT Slide 47 The DNA strand is unzipped at the hydrogen bonds by an enzyme named helicase. Nucleotides in the nucleus then find their corresponding nucleotides on each of the two open DNA strands and produce two new DNA double helixes. B48 Link to DNA Replication Animation Click here to see how DNA Replication works B48. PPT Slide 48 Show Internet animation to illustrate the process of DNA replication
Objective C: Identify the steps associated with protein synthesis. Interest Approach for Objective C: What have you eaten today that contained a lot of protein? Why should you eat protein? Where does protein come from? Discuss or write on the board foods high in protein. (Eggs, meat, beans, etc.) Discuss or write on the board reasons why protein is an important nutrient. (Good for muscles, hair, nails, etc.) Discuss where protein comes from. (Likely, students have never considered this question before now. Some may say that they get protein from the food they eat. Follow this with the question, where did the plant or animal get the protein from? ) C49 Protein Synthesis The main job for DNA is to direct the production of protein Protein makes tissues and organs and carries out the organism s metabolism Proteins are polymers (chains) of amino acids C50 Protein Synthesis The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein C51 RNA RNA is a nucleic acid composed of nucleotides that is crucial in making protein There are three differences between DNA and C49. PPT Slide 49 C50. PPT Slide 50 C51. PPT Slide 51 On the board, make two columns. Write DNA on top of one column and RNA at the top of the other column. List the following characteristics of DNA and then write the characteristics of RNA and note comparisons
RNA RNA is a single strand The sugar in RNA is called Ribose instead of DNA s Deoxyribose Like DNA, RNA has 4 nitrogenous bases, but instead of Thymine, Uracil is the 4 th base among the two. (Sample of what this may look like) DNA RNA Double helix Sugar is called Deoxyribose Single stranded molecule Sugar is Ribose Bases are T, A, C, and G Uracil replaces thymine C52 RNA as a Single Strand You recall that DNA looks like a twisted ladder and is referred to as a double helix RNA looks like half a ladder There is only one side to RNA C52. PPT Slide 52 C53 RNA Contains Ribose Remember how DNA got its name? It is a nucleic acid with deoxyribose as the sugar on the backbone Hence the name Deoxyribonucleic acid Ribonucleic acid (RNA) has the sugar ribose on it s backbone C54 RNA Has Uracil Remember the base pairs in DNA? Adenine pairs with Thymine Guanine pairs with Cytosine C53. PPT Slide 53 C54. PPT Slide 54
C55 RNA Has Uracil In RNA Adenine pairs with URACIL Guanine pairs with Cytosine C56 Making Protein Protein production starts with DNA DNA passes instruction to RNA RNA carries out the work of linking together chains of amino acids C57 Three Types of RNA There are three types of RNA involved in Protein Synthesis Messenger RNA (mrna) Ribosomal RNA (rrna) Transfer RNA (trna) C58 Messenger RNA Messenger RNA (mrna), brings instructions from DNA in the nucleus to the cell s factory floor, the cytoplasm On the factory floor, mrna moves to the assembly line, a ribosome Remember that a ribosome is either a freefloating small dot in the cell or is attached to the endoplasmic reticulum making it rough ER C59 Ribosomal RNA The ribosome, made of Ribosomal RNA (rrna) binds to the mrna and uses the instructions to assemble the amino acids in the correct order C60 Transfer RNA Transfer RNA (trna) is the supplier C55. PPT Slide 55 C56. PPT Slide 56 C57. PPT Slide 57 You may give the types of RNA names for the story given below at slide 61. DNA = Deena mrna = Myrna trna = Trina C58. PPT Slide 58 C59. PPT Slide 59 C60. PPT Slide 60
Transfer RNA delivers the amino acids to the ribosome to be assembled into a protein C61 Transcription The production of messenger RNA (mrna) is known as Transcription DNA acts as a template for the RNA molecule To View a Link to Transcription Animation Click Here. C62 Transcription The main difference between DNA Replication and transcription is that transcription results in one single strand of RNA rather than an exact duplicate of a double stranded DNA molecule Much of the information on the mrna strand codes for specific amino acids to make protein C63 The Genetic Code A code is necessary to turn the language of RNA into the language of amino acids and proteins The four nitrogenous bases make up the code The code letters are A, G, T, and C A set of three letters makes a word called a Codon There are 64 possible codons C61. PPT Slide 61 The Protein Synthesis Story Myrna, the messenger girl(mrna) is at work one day and her boss Deena (DNA) calls her into her office (the nucleus). Deena tells Myrna that she is going to give her a specific recipe for a new protein needed elsewhere in the city (the organism). She gives her the secret recipe code and Myrna writes it down. (This is known as transcription). (This occurs when the DNA molecule is unzipped like in replication, except the free floating nucleotides that fill in on the DNA molecule are RNA nucleotides and when it releases itself from the DNA the resulting product is a single stranded mrna molecule) (Story continued on slide 69) C62. PPT Slide 62 C63. PPT Slide 63
C64 Codon C64. PPT Slide 64 C65 Amino Acids There are 20 different amino acids that make up proteins C66 The Genetic Code C67 The Genetic Code As you could see on the chart of amino acids, there are more than one codon that code for certain amino acids This results in fewer errors in protein synthesis C68 The Genetic Code All organisms use the same genetic code This provides evidence that all life on earth may have evolved from the same origin C69 Ribosomes The newly produced strand of mrna travels from the nucleus to the cytoplasm where it attaches to a ribosome The ribosome is the actual site for protein synthesis C65. PPT Slide 65 C66. PPT Slide 66 Take time to briefly discuss the 20 different amino acids and the codons that code for them at the side of each one. C67. PPT Slide 67 C68. PPT Slide 68 C69. PPT Slide 69 Protein story continued Remember that Myrna got the secret recipe for a specific type of protein? Now Myrna leaves the office (Nucleus) and goes into the cytoplasm to find a ribosome (where the protein is made).
C70 Translation: From mrna to Protein The process of reading the three letter words, or codons, is known as translation Translation takes place at the ribosomes in the cytoplasm The amino acids are free-floating in the cytoplasm and congregate at the ribosome during protein synthesis C70. PPT Slide 70 Protein story continued Myrna is now at the ribosome where the protein will be created. She finds Trina (trna), who is the cook who puts the ingredients together, and gives the secret protein recipe code from Deena, the boss. Trina then translates the code using a special tool called anticodons. (This process is called translation) C71 The Process of Protein Synthesis The first codon is usually A-U-G, methionine, which starts the production of a new protein Following the start codon, the remaining codons call for amino acids in the order in which they appear on the mrna strand C72 Transfer RNA (trna) At the ribosome, Transfer RNA (trna) identifies the code through translation and finds the appropriate amino acid matching the codons Each trna molecule only attaches to one specific amino acid The Anticodon on the bottom of the trna molecule corresponds with the codons on the mrna strand C73 Protein Synthesis Animation Click Here to Link to An Animation Assessment Assess students understanding of DNA C71. PPT Slide 71 C72. PPT Slide 72 Protein story continued Trina, who has the recipe now and has translated the code using anticodons, starts taking ingredients (amino acids) off of the shelf and chaining them together at the ribosome to produce the final product, the protein molecule. C73. PPT Slide 73 This link will show an animation of the process of protein synthesis and should give students a good review of the process. Sample Test Click here to link to a sample DNA test