Bellringer Chemical structures that are involved in physiological processes, such as hemoglobin in blood, insulin that regulates blood glucose levels, and enzymes that regulate body functions, are all made of proteins. Name some parts of the human body that contain proteins. Construct a DNA model Using Base-pairing Rules. Homework: 25 Pts. Due tomorrow to gain access to DNA Extraction Lab. Template Strand 2 rings G A T T A C A C T G T C A G A A A C C T A A T G T G A C A G T C T T T G 3 bonds 1 ring Directions: Template Strand: _G_ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ 1) Answer Review Questions on back: 1. What is the basic subunit for DNA? Complementary Strand:___ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ 2. What are the three parts? 3. Which parts are the backbone? 4. Which nucleotides are purines? Nucleotide Bank 5. Which nucleotides are pyrimidines? 6. How do you tell the difference between the two? 7. What type of bond holds together DNA strands? 2) Cut out the nucleotides from the Nucleotide Bank (right). 3) Match them up with the template strand above based upon base-pairing rules then tape/glue beneath. 4) Determine the sequence (order of the string of nucleotides read left to right) for both the template strand and the new complimentary strand. Label the sequence of the template and complimentary strand on the lines with the nucleotide abbreviation. Key Ideas What is the process of gene expression? What role does RNA play in gene expression? What happens during transcription? How do codons determine the sequence of amino acids that results after translation? What are the major steps of translation? Do traits result from the expression of a single gene? Objectives: Transcription & Translation Today: Transcription Describe gene expression Explain the role of RNA in gene expression Summarize transcription Practice transcribing a gene. Tomorrow: Translation Explain how codons determine the amino acid sequence of a protein Describe the steps of translation Identify the complexity of gene expression Practice translating a gene. Gene Expression How we get from DNA to traits. Vocabulary Gene expression Transcription Translation RNA mRNA tRNA rRNA RNA polymerase Codon An Overview of Gene Expression So far, we’ve discussed the structure of DNA… being made of nucleotides that contain 1 of 4 different nitrogenous bases. You should know that DNA’s job is to store genetic information. You’ve also learned the cell cycle. We’ll be spending the next few days on G1 of the cell cycle. This is the phase where most of “living” takes place. It’s the phase that proteins and traits are made. The Purpose of DNA… The purpose of DNA itself is to house the information necessary for heritable traits…meaning that it holds the information from which proteins are made. This is what living is all about. The DNA in our chromosomes is like books on the shelf of a library… just waiting to be read. DNA provides the original information from which proteins are made in a cell, but DNA does not directly make proteins. The Purpose of Life An Overview of Gene Expression, Gene expression is the manifestation of genes (contained in DNA) into specific traits. What does manifestation mean? THE CENTRAL DOGMA OF BIOLOGY = DNA mRNA Protein Trait This process takes place in two main stages, Transcription: the process of copying the directions for traits out of DNA by making mRNA 2. Translation: reading the directions copied in RNA and turning them into the amino acid sequences for the gene. 1. THE CENTRAL DOGMA OF BIOLOGY Directions to make HAIR COLOR ACTGAACTGCACTG… Genes: The basic units of heredity. They are located on specific regions of chromosomes, contained in DNA. There are thousands of genes “written” into each of the 23 chromosomes in our cells. They come from the original genes given to us from mom & dad. So What Does a Real Gene Look Like? Pro-melanin-concentrating hormone tacagcgtgt ggcattctcc ccacattctc cttcggcttt acggagcagc aaacaggatg gcgaagatga gcctctcttc ctacatgtta atgctggcct tttctttgtt ttctcacggc attttacttt cggcctccaa gtccatcagg aacgtagaag cgacatagt atttaataca ttcaggatgg ggaaagcctt tcagaaggaa ataccgcagaagatcggt tgttgctcct tctctggaag gatacaaaaa tgatgagagc ggcttcatga aggatgaaga tgacaagacc acaaaggtac gtgtatgcag tctgcctttt attgcactag agatgaaaac gatgtttaca attataagcc acccagaagt aaattttgta ttttaatttt ataaataggc tacatacag tcattgtgtg tattaagata actaggaaaa cgtcatacaa accaggcatt tccccattct atccagaatc ttgtatcttg tctcgcatat ggaggtaaag acagtataca gcatcttaga actgatcagc aagaatgttg tacaactgta ttctagctct actctgaaga agacagctgg gatacaaacc aatcttctct tcacagaaca caggctccaa gcagaatctc gtaactcacg gtctgcccct cagtctggct gtaaaacctt acctcgctct gaaaggacca gcagtcttcc cagctgagaa tggagttcag aatactgagt ccacacagga aaagagggaa attggggatg aagaaaactc agctaaattt cccataggaa ggagagattt tgacagtgag tagccttcta aacatgcaat tcctacatat taattttata aaagagctct gagcttcact gagttggatc tgaccataac aaaatcaaga ccatagttca gttctatcaa atagtaggca gcccacgtca aaatggggaa tttttcaaaa tcagtaatag tggtttgttt tattctggat tcattataag tccacagatt ctcttaattc tgtgtggtaa ttatagtcat tgtttgttcc ttttcagtgc tcaggtgtat gctgggacga gtctaccgac cctgttggca agtctgatac ctgctggtcc acaacatcct ttcagaagaa aacgattcat tgcaagtgga gagaaaagcc cttaatgttg atgtaacttg tgtatcatcc taaatgtctg ttttaaaaga aactggttac aatatgtaaa tgctatgtaa atgatatgct ttgacttgtg cattaaactt cacaaaaatt ctgcata -http://www.ncbi.nlm.nih.gov/gene/24659#reference-sequences Hemoglobin Gene taccacgacagaggacggctgttctggttgcagttccggcgga ccccgttccaaccgcgcgtgcgaccgctcataccacgcctcc gggacctctcctacaaggacaggaaggggtggtggttctggat gaagggcgtgaagctggactcggtgccgagacgggtccaatt cccggtccgttcttccaccggctgcgcgactggttgcggcacc gcgtgcacctgctgtacgggttgcgcgacaggcgggactcgc tggacgtgcgcgtgttcgaagcccacctgggccagttgaagtt cgaggattcggtgacggacgaccactgggaccggcgggtgg aggggcggctcaagtggggacgccacgtgcggagggacct gttcaaggaccgaagacactcgtggcacgactggaggtttatg gcaattcgacctcggagccatcgtcaaggaggacggtctacc cggagggttgcccgggaggaggggaggaacgtggccggga aggaccagaaacttatttcagactcacccgccg http://www.bio.davidson.edu/courses/Bio111/Hemo mut.html Gene Transcription and Translation Where Does it Occur? RNA: A Major Player All of the steps in gene expression involve RNA. What exactly is RNA, & how does is compare to DNA? First, like DNA, RNA is a nucleic acid made of nucleotide subunits linked together. RNA vs. DNA RNA is a nucleic acid like DNA But RNA differs from DNA in 3 ways. 1. First, RNA usually is composed of one strand of nucleotides rather than two strands. a. The exception occurs in viruses 2. Second, RNA nucleotides contain the fivecarbon sugar ribose rather than the sugar deoxyribose. 3. Third, RNA nucleotides have a nitrogenous base called uracil (U) instead of the base thymine (T). a. Uracil (U) is complementary to adenine (A) whenever RNA pairs with another nucleic acid. DNA vs RNA Structure Deoxyribose Nucleic Acid = DNA ◦ Is missing one oxygen in the ribose sugar. Ribose Nucleic Acid = RNA ◦ Has all oxygens Visual Concept: Ribonucleic Acid (RNA) RNA: A Major Player In cells, three types of RNA complement DNA and translate the genetic code into proteins. 1. Messenger RNA (mRNA) is produced when DNA is transcribed into RNA. The mRNA carries instructions for making a protein from a gene and delivers the instructions to the site of translation. RNA: A Major Player 2. Transfer RNA (tRNA) “reads” the instructions carried by the mRNA at the site of translation, then translates the mRNA sequence into protein subunits called amino acids. 3. Ribosomal RNA (rRNA) is an RNA molecule that is part of the structure of ribosomes. Recall from CH7, ribosomes are the cellular structure where protein production occurs. Objectives Define Transcription Summarize the steps of transcription Step 1 2 3 In order to help keep this straight, make a chart like the one below. Major events Transcription: Reading the Gene Transcription is the process of creating a copy of a gene in DNA as an mRNA molecule. Transcription Steps 1. INITIATION: Transcription begins when the enzyme RNA polymerase binds to the specific DNA sequence in the gene that is called the promoter. - The promoter’s role is to signal the RNA polymerase where to start transcription. The DNA always contains the sequence TAC for the “start” signal. Transcription: Reading the Gene Step 1 Transcription: Reading the Gene 2. ELONGATION: RNA polymerase then unwinds and separates the two strands of the DNA double helix to expose the DNA bases on each strand. RNA polymerase adds RNA nucleotides. Transcription: Reading the Gene Step 1 Transcription: Reading the Gene, 3. TERMINATION: RNA polymerase moves along the bases on the DNA strand and adds complementary RNA nucleotides to a growing mRNA as it “reads” the DNA of the gene until it reaches the “stop” signal. Remember that in transcription “U” matches with “A”, not “T” like in replication. - - - The “A” still matched to “T” though. As RNA polymerase moves down the DNA strand, a single strand of mRNA grows. Just as there is a “start” signal on the DNA, signaling the start of the gene, there is a “stop” signal as well. This region is specially designed to let the RNA polymerase know when the gene ends & therefore when to stop transcription. This stop signal is one of 3 DNA sequences: ATT, ATC, or ACT. What would the RNA sequences be? UAA, UAG, or UGA Transcription: Reading the Gene Step 1 Visual Concept: Transcription Transcription Concept Check What is the point of transcription? What enzyme is used in transcription? What are the signals for starting and stopping a gene? Why is mRNA necessary? Review A gene is similar to a recipe. Gene expression is like the process of baking a secret cake recipe, complicated because the recipe is written in a language the chefs don’t understand. It is written as one long sentence composed of just one word. The word is written in the language of the nitrogenous bases, A, T, G, & C A gene is written in a unique language that must be transcribed by a messenger that speaks the language of the chefs. The way the recipe is delivered to the chefs (the ribosomes) in the cytoplasm (the bakery) is by the messenger “mRNA”. mRNA copies the recipe during transcription and delivers it to the bakery in the cytoplasm for translation to occur (decoding the recipe in a different language to allow for baking the recipe). In the cytoplasm the recipe is translated into the language of proteins (amino acids) and finally made into proteins. Finally, the secret cake is made. Now it’s your turn to read the recipe. Practice Transcription…making an mRNA complement to the gene in DNA. DNA= TCTACAGGAGCGCTGGCAAGACTGCCG RNA= You make it. Examine the DNA sequence above. Look through and identify the promoter region containing the “start signal” of DNA. Underline it. Do the same for the “stop signal”. Write an RNA sequence of bases using the complement to the entire DNA sequence using the RNA bases (A-U-C-G), starting with the sequence of the “start” site all the way until you reach one of the 3 “stop” sequences. Only write the RNA sequence that complements the DNA sequence from the “start” to “stop” signals. You have 5 minutes. Ask questions if you need to. DNA: Practice… TCTACAGGTGCAAGACTGCCG mRNA: o Find the start sequence…underline it. o Find the stop sequence…underline it. o Starting with the start sequence, transcribe the gene using the RNA bases. o What you end up with is an mRNA transcript of the gene contained in the DNA. In-class Exercise/HW Practice Transcribing: You’re going to play the role of the messenger now. You need to be able to take a DNA sequence and identify the mRNA that will “copy” the recipe, the gene for a protein, so the recipe can be made by the ribosomes. Gene Xlr23: CGAACCTACAGTTCCGCGTCGGGCTAGACTGGCAATG Copy this sequence down on a sheet of paper. 2. Identify the “start” sequence within the DNA above (underline it). 3. From the start sequence, count in groups of three until you reach one of the three “stop” signals. 4. What is the “stop” sequence (underline it). 5. Just below the DNA sequence you copied, transcribe the DNA into a sequence of mRNA for the gene Xlr23. Tomorrow we will use this sequence to practice translation. 1. Reflections What did you learn today? Design an acronym of pneumonic device to remember the types of RNA and steps in transcription. In-class Exercise/HW Practice Transcribing: You’re going to play the role of the messenger now. You need to be able to take a DNA sequence and identify the mRNA that will “copy” the recipe, the gene for a protein, so the recipe can be made by the ribosomes. Gene Xlr23: CGAACCTACAGTTCCGCGTCGGGCTAGACTGGCAATG Copy this sequence down on a sheet of paper. 2. Identify the “start” sequence within the DNA above (underline it). 3. From the start sequence, count in groups of three until you reach one of the three “stop” signals. 4. What is the “stop” sequence (underline it). 5. Just below the DNA sequence you copied, transcribe the DNA into a sequence of mRNA for the gene Xlr23. Tomorrow we will use this sequence to practice translation. 1. Objectives Day 2 Explain how codons determine the amino acid sequence of a protein Describe the steps of translation Identify a complexity of gene expression This is a short lecture so stay focused. The Genetic Code: ThreeLetter “Words” What is the mRNA you decoded for gene Xlr23? DNA C G A A C C T A C A G T T C C G C G T C G G G C T A G A C T G G AUGUCAAGGCGCAGCCCGAUCUGA mRNA ◦ What do you notice that is similar about the start and stop sequences? There is significance in the number 3 in RNA. ◦ Save this and we’ll move on… It corresponds to what’s called a codon. A codon is a three-nucleotide sequence in mRNA. The Genetic Code: ThreeLetter “Words” A codon is a key that corresponds to 1 of 20 amino acids. An amino acid is the building block of a protein. Codons also act as the start or stop signal for translation. These “signals” are referred to as “start” and “stop” codons on mRNA in genetics. So the start codon is…AUG (signals the start of the gene) The stop codons are… UAA, UGA, UAG (signals the end) The Genetic Code: ThreeLetter “Words” Refer to you handout. There are 64 mRNA codons. The mRNA that is created in transcription is actually a collection of a series of 3nucleotide sequences called codons. So each gene will contain nucleotides in multiples of 3 The Genetic Code: ThreeLetter “Words” Your practice from last night… AUGUCAAGGCGCAGCCCGAUCUGA AUG-UCA-AGG-CGC-AGC-CCG-AUC-UGA Notice that the length of the gene is a multiple of 3… This is the way all genes are…in multiples of 3. This is why I asked you to count by threes until you reached the “stop” codon. The Genetic Code: Three-Letter “Words” Each codon specifies for only one amino acid, but several amino acids have more than one codon. See leucine This system of matching codons and amino acids is called the genetic code. The genetic code is based on codons that each represent a specific amino acid. This is the translation tool that helps to translate the mRNA from the nucleotide language into the language of amino acids. Figure 13. The amino acid coded be a specific mRNA codon can be determined by following the three steps below. What amino acid does the codon GAA code for? Codons in mRNA Translation: RNA to Proteins Translation is the process that changes the mRNA molecule into the complementary amino acid sequence. Takes place in the cytoplasm occurs in a sequence of 5 steps Involves all three kinds of RNA and results in a complete polypeptide. Translation: RNA to Proteins Translation relies upon the tRNA molecule to act as the gobetween for mRNA codon & the amino acid that corresponds to it. There is only one specific amino acid for each codon. The mRNA gets matched up with the right tRNA molecule because of the anti-codon region An anticodon is a threenucleotide sequence on tRNA that is complementary to an mRNA codon. There are two important regions of a tRNA. The area where the amino acid attaches & The anticodon region, which is complementary to the codon of mRNA The anticodon always decides which amino acid is carried. AMINO ACID GOES HERE ANTICODON tRNA matches mRNA here The Steps to Translation Translation: RNA to Proteins, Step 1 A ribosome attaches to the mRNA The UAC (methionine) tRNA attaches to the start codon on mRNA within the ribosome. Step 2 The tRNA molecule that has the correct anticodon and amino acid binds to the second codon on the mRNA. A peptide bond then forms between the two amino acids, and the first tRNA is released from the ribosome. Translation: RNA to Proteins, Step 3 The ribosome then moves one codon down the mRNA, kicking the 1st tRNA out. The amino acid chain continues to grow as each new amino acid binds to the chain and the previous tRNA is released. Step 4 This process is repeated until one of three stop codons is reached. A stop codon does not have an anticodon, so protein production stops. Translation: RNA to Proteins, Step 5 The newly made polypeptide falls of the ribosome, the tRNA leaves the ribosome, & the ribosome falls apart. Translation is complete & the polypeptide is free to go get processed into a protein in either the ER or the Golgi. This is where translation ends but it doesn’t have to be the only protein made. Repeating Translation Many copies of the same protein can be made rapidly from a single mRNA molecule because several ribosomes can translate the same mRNA at the same time. Translation: RNA to Proteins PEPTIDE BOND FORMS: Then the ribosome moves forward Methionine RIBOSOME Anticodon UAC mRNA AUG UCA AGG CGC AGC CCG AUC UGA Start Codon Other amino codons Stop Codon Methionine Serine Anticodon UAC AGU mRNA AUG UCA AGG CGC AGC CCG AUC UGA PEPTIDE BOND FORMS: Then the ribosome moves forward Methionine Serine The growing chain of amino acids is a polypeptide, or in other words…a protein Anticodon mRNA AGU AUG UCA AGG CGC AGC CCG AUC UGA PEPTIDE BOND FORMS: Then the ribosome moves forward Methionine Serine Anticodon mRNA ? UCC AUG UCA AGG CGC AGC CCG AUC UGA PEPTIDE BOND FORMS: Then the ribosome moves forward Methionine Serine Anticodon mRNA ? ? GCG AUG UCA AGG CGC AGC CCG AUC UGA PEPTIDE BOND FORMS: Then the ribosome moves forward Methionine Serine Anticodon mRNA ? ? ? UCG AUG UCA AGG CGC AGC CCG AUC UGA PEPTIDE BOND FORMS: Then the ribosome moves forward Methionine Serine Anticodon mRNA ? ? ? ? GGC AUG UCA AGG CGC AGC CCG AUC UGA Methionine Serine Anticodon mRNA ? ? ? ? ? UAG AUG UCA AGG CGC AGC CCG AUC UGA Once the stop codon is reached translation terminates. There is no tRNA for the stop codon so the ribosome know to detach. The newly formed polypeptide then leaves to get processed. Complexities of Gene Expression The relationship between genes and their effects is complex. Not 1 simple outcome… 1 gene = multiple traits Multiple genes required for 1 trait 1 gene = 1 trait Some genes are expressed only at certain times or under specific conditions. Variations and mistakes can occur at each of the steps in replication and expression. The final outcome of gene expression is affected by the environment of the cells, the presence of other cells, and the timing of gene expression. The environment can also affect gene expression. In summary, one gene can be used for many trait outcomes. 7 different trait possibilities for the same gene. Summary Gene expression produces proteins by transcription and translation. This process takes place in two stages, both of which involve RNA. In cells, three types of RNA complement DNA and translate the genetic code into proteins. During transcription, the information in a specific region of DNA (a gene) is transcribed, or copied, into mRNA. Summary, continued The genetic code is based on codons that each represent a specific amino acid. Translation occurs in a sequence of steps, involves three kinds of RNA, and results in a complete polypeptide. The relationship between genes and their effects is complex. Despite the neatness of the genetic code, every gene cannot be simply linked to a single outcome. In Class Exercise CGAACCTACAGTTCCGCGTCGGGCTAGACTGGCAATG AUGUCAAGGCGCAGCCCGAUCUGA Complete the Gene. Translation is the last step of gene expression as it forms the final polypeptide. Your exercise today is to take the gene we transcribed into mRNA yesterday and translate it into a polypeptide. Write your polypeptide as a series of circles with the name of the corresponding amino acid within. This is the protein for the gene you transcribed. Methionine ? ? ? ? ? Check these off with me to make sure you got it… Tomorrow ? you’ll have to transcribe & translate a much bigger gene. AUG UCA AGG CGC AGC CCG AUC UGA Codons in mRNA mRNA How are you progressing? Answers to IC/HW Exercise = AUGUCAAGGCGCAGCCCGAUCUGA Poly peptide chain = Isoleucine Practice the Process: Find, transcribe and translate the gene into a polypeptide sequence. DNA: mRNA: GCAATACGTAAATAGATCTATCGC AUG Polypeptide: CAU UUA UCU AGA UAG Met-His-Leu-Ser-Arg-(stop) “Rosetta Stone” of Genetics Complement Gene (DNA) mRNA (codon) Anticodon T A U A A T A U G C G C C G C G Fill in the lines for the following sequences. ATGACTAGCTGGGGGTATTACTTTTAG Complement:___________________________________________________________________ Gene: TACTGATCGACCCCCATAATGAAAATC ____________________________________________________________________ mRNA: AUG - ACU - AGC - UGG - GGG - UAU - UAC - UUU - UAG tRNA: UACUGAUCGACCCCCAUAAUGAAAAUC ___________________________________________________________________ AA: MET-THR-SER-TYR-GLY-TYR-TYR-PHE-STOP ___________________________________________________________________ Fill in the lines for the following sequences. Complement ATG Gene TAC ATG mRNA tRNA Amino Acid UGU GAU CUC UUG ala AUU pro Fill in the lines for the following sequences. Complement ATG GAG TGT GAT GCC TAC AAC CCT Gene TAC CTC CTA CGG ATG TTG GGA ATT mRNA AUG GAG UGU GAU GCU UAC AAC CCU tRNA UAC CUC ACA CUA CG AUG UUG GGA AUU Amino Acid MET GLU CYS AST ala TYR ASP pro XXX ACA asparta te GCC GCA GCG TGTGAT(GCC…)TACAAC(AAC…)TAA XXXCTCACACTA(CGG…)XXXTTG(GGA…)ATT AUGGAGXXXXXX(GCC…)UACAAC(CCU…)UAA UACXXXACACUA(CGG…)AUGXXX(GGA…)XXX MET-GLU-CYS-VAL-XXX-TYR-THR-XXX-STOP asparagi ne CCC CCA CCG TAA UAA TRX/TRL: CW/HW: Using the Genetic Code HW Genetic Code of Keratin Keratin is one of the proteins in hair. The gene for keratin is transcribed and translated by certain skin cells just underneath the growing hair. The sequence below is part of the mRNA molecule that is transcribed from the gene for keratin. Analysis 1. Determine the sequence of amino acids that will result from the translation of the segment of mRNA above. Use the genetic code in Figure 13. _____Methionine – Serine – Arginine – Glutamic Acid – Phenylalanine – Serine - __________ 2. Determine the anticodon of each tRNA molecule that will bind to this mRNA segment. _____UAC – AGA – GCA – CUU – AAA – AGG ______________________________________________________________________ 3. Critical Thinking Recognizing Patterns: Determine the sequence of nucleotides in the segment of template DNA from which this mRNA strand was transcribed. ____TAC – AGA – GCA – CTT – AAA – AGG ______________________________________________________________________________ 4. Critical Thinking Recognizing Patterns: Determine the sequence of nucleotides in the segment of DNA that is complementary to the DNA segment that is described in item 3. ____ATG – TCT – CGT – GAA – TTT – TCC ______________________________________________________________________________ Transcription/Translation Lab Working with a partner, analyze the gene Xlr24 to determine the DNA sequence of the gene, the sequence of the mRNA, and the sequence of the amino acids that will form the polypeptide. Answer the associated questions. This is a 100pt lab due next Monday.