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The CENTRAL DOGMA in Biology: Introduction to Transcription & Translation Review: One of the key discoveries in biology is that DNA is the genetic material that codes for traits. But exactly HOW does it code for traits? The ‘central dogma in biology’ states that DNA provides a code for synthesizing proteins. Ultimately, it is the proteins in our body that determine all of our traits! In other words: Proteins are highly complex molecules comprised of chains of amino acids. Amino acids are compounds containing carbon, hydrogen, oxygen, nitrogen and occasionally sulphur. There are _____ different amino acids (the human body can make some amino acids, others must be obtained from food). Amino acids link to form polypeptide chains which make up the primary structure of a protein. A typical protein may contain ____________ or more amino acids. Each protein has its own unique _______________ & ________________of amino acids which determine its particular ________________________ & ______________________. THE ROLE OF DNA and RNA in making proteins DNA is the genetic material that we inherit, but proteins are actually responsible for determining our traits. DNA provides our cells with the information on what proteins should be synthesized. DNA provides a code, in the language of base pairs ( ____ ) that instructs the cells to make specific proteins. DNA stores the ‘codes’ in the ________________ of a cell, but a messenger is needed to take the information to the sites where proteins are actually assembled. The information from nucleus is carried to the _____________________ in the form of RNA. The messenger of this information is called mRNA or messenger-RNA (RNA stands for RiboNucleic Acid). The process of reading a DNA strand and creating RNA is called transcription. The process of using the code of RNA to assemble a protein is called translation. DNA mRNA Protein 1 RNA: RNA is made from the DNA and has a fairly similar structure to DNA, with a few differences we can summarize below in a Venn Diagram: TRANSCRIPTION: creating mRNA from DNA First, the 2 strands of DNA ‘unzip’ exposing the gene (section of DNA holding the code for that particular protein) Using one strand of DNA as a template, a complimentary strand of RNA is produced. Wherever a thymine (T) would have been used for DNA, uracil (U) is used instead. Messenger RNA (mRNA) carries the message to a ribosome, where the protein is then manufactured. Inside the nucleus, the 2 strands of DNA rejoin and recoil. EXAMPLE: Double stranded DNA molecule: One strand of DNA is used as a template to make the mRNA molecule: …T A C C C T A G G A G C A T G… …T A C C C T A G G A G C A T G … …A T G G G A T C C T C G T A C… mRNA: …A U G G G A U C C U C G U A C… 2 Translation: Creating a Protein from RNA Translation is the process that creates, or synthesizes, proteins from the genetic code, which is now in mRNA form. The mRNA is read in triplet, _________ base pairs at a time. Each triplet, called a ________________, codes for a specific amino acid that will be added to the protein. For example: consider the following sequence of mRNA: AUGGAUCCUCGU… This sequence would be read, 3 bases at a time, as - - - The codons above represent the following different amino acids. - - - We use the following chart to determine which amino acids are coded for each of the ______ possible triplet combinations of A, U, C, and G. Note that some triplet combinations code for the same amino acids! 3 NOTE: The ribosome begins adding amino acids when it finds a ‘start’ codon: _______ The protein is ‘complete’ when the ribosome reaches one of the 3 STOP codons: __________ ____________ & ___________ This synthesis employs another set of RNA, known as transfer RNA, or tRNA. Each tRNA has 2 ends: an _________________________________(which is complementary to a codon) and the corresponding _________________________________________ The Steps of PROTEIN SYTHESIS 1. The ribosome starts at the start codon AUG. It attracts the tRNA with the correct anticodon & corresponding amino acid (in the case of the start codon, it would be methionine). 2. The tRNA binds its anticodon to the start codon. 3. The ribosome then reads the next codon, and attracts the corresponding tRNA, which binds to the corresponding codon. 4. The two amino acids form a peptide bond – the beginning of a protein. 5. The ribosome releases the first tRNA, then reads next codon. 6. The ribosome continues this process, growing a chain of amino acids. The resulting chain of amino acids is the primary structure of the protein. 7. The process ends once the ribosome reaches one of the 3 STOP codons – UGA, UAA or UAG. 8. The protein folds to obtain its secondary, tertiary, and quaternary structure. 9. The protein is complete! 4 Central Dogma Analysis Questions (also reference text chapter 12-3 (pages 300-306) 1. Summarize the ‘Central Dogma’ of biology. 2. Describe the structure of a protein (what are the sub-components of a protein? What makes proteins different from each other? How is its final structure formed?) 3. Differentiate the places in a cell where DNA is stored in a cell and where proteins are manufactured in a cell. What molecule delivers the ‘message’ between those 2 places? 4. Compare and contrast RNA and DNA (give both similarities and differences) Use the following base sequence of ONE strand of a DNA molecule to answer 5-9: …T A C A A T G C C A G T G G T T C G C A C … 5. Draw the complete DNA molecule – provide both the strand given above and its complementary strand. 6. Give the base sequence of the strand of mRNA that will be read from the original DNA strand. 7. What sequence of amino acids (protein fragment) would this mRNA code for? Why do you think I only had you do a fragment rather than a whole protein? 8. If the seventh nucleotide in the original DNA strand was replaced with a cytosine, what would the resulting mRNA look like? 9. What would the resulting protein fragment (sequence of amino acids) look like? 10. What is the start codon? What then is always the first amino acid of any protein? 11. Which 3 codons cue the ribosome to stop adding more amino acids (stop codons)? Central Dogma Analysis Questions (also reference text chapter 12-3 (pages 300-306) 1. Summarize the ‘Central Dogma’ of biology. 2. Describe the structure of a protein (what are the sub-components of a protein? What makes proteins different from each other? How is its final structure formed?) 3. Differentiate the places in a cell where DNA is stored in a cell and where proteins are manufactured in a cell. What molecule delivers the ‘message’ between those 2 places? 4. Compare and contrast RNA and DNA (give both similarities and differences) Use the following base sequence of ONE strand of a DNA molecule to answer 5-9: …T A C A A T G C C A G T G G T T C G C A C … 5. Draw the complete DNA molecule – provide both the strand given above and its complementary strand. 6. Give the base sequence of the strand of mRNA that will be read from the original DNA strand. 7. What sequence of amino acids (protein fragment) would this mRNA code for? Why do you think I only had you do a fragment rather than a whole protein? 8. If the seventh nucleotide in the original DNA strand was replaced with a cytosine, what would the resulting mRNA look like? 9. What would the resulting protein fragment (sequence of amino acids) look like? 10. What is the start codon? What then is always the first amino acid of any protein? 11. Which 3 codons cue the ribosome to stop adding more amino acids (stop codons)? 5