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DNA Transcription and Translation Sections 12.3 and 12.4 DNA vs. RNA! DNA RNA T A C G A T A C G A Structure: Sugar: Bases: DNA example strand: Complimentary: Gene Segment of DNA that codes for a protein The Central Dogma of Biology: DNA codes for RNA and RNA makes protein (the synthesis of) One Gene – One Enzyme Beadle and Tatum’s experiment showed that one gene codes for one polypeptide polypeptide - a chain of covalently bonded amino acids. (proteins are made of one or more polypeptides) Do Now!! What is the central dogma? Create a Venn Diagram for RNA and DNA. Objectives To compare and contrast the three different kinds of RNA To define transcription To identify the steps involved in transcription RNA RNA Ribonucleic acid RNA stands for: is found: Nucleus and/or Cytoplasm RNA Structure Like DNA, RNA is made up of subunits called _____________, which are made of three parts: Sugar (ribose) Phosphate Nitrogen Base DNA RNA RNA’s Nitrogen Bases Adenine (A) Cytosine (C) Guanine (G) Uracil (U) There are 3 types of RNA: Messenger RNA (mRNA) – linear, brings genetic code from DNA to ribosome to make protein Transfer RNA (tRNA) – clover-like segments of RNA nucleotides that transport amino acids to the ribosomes Ribosomal RNA (rRNA) – helps give ribosome its structure Transcription First step in making proteins Process of taking one gene and copying it into mRNA: Only individual genes are transcribed, NOT a whole DNA molecule! DNA -> RNA Location: Nucleus of the cell Steps to Transcription 1. RNA polymerase attaches to the promoter (start signal region) of a gene and unwinds the DNA “Initiation” stage Steps to Transcription (cont.) 2. Only one strand acts as a template: Other strand known as coding (non-template) strand Steps to Transcription (Cont.) 3. A mRNA copy is made from the DNA template strand by RNA polymerase: (RNA polymerase makes… RNA!) Elongation stage Steps to Transcription (cont.) 4. A mRNA copy is made until it reaches the termination (stop signal) sequence 5. Termination stage The two strands of DNA rejoin. Template vs. Non Template Strand Transcription animation https://www.youtube.com/watch?v=ztPkv7w c3yU https://www.youtube.com/watch?v=5MfSYnI tYvg Do Now!! 1. What is a protein made of? 2. What are the three types of RNA? Where do you think they’re all found? 3. What is the central dogma? Objectives To identify the steps of transcription To define the enzymes involved To identify the product of translation Do Now!! Label the transcription diagram! Transcribe this DNA to mRNA 3’ T A C G C A A C G A C G T T A 5’ 5’ A T G C G T T G C T G C A A T 3’ * Which strand is the template strand? How do you know?? Objectives To review the steps of transcription To define mRNA processing and identify its importance To define poly-A tail and cap mRNA Processing Scientists found mRNA in cytoplasm was shorter than DNA sequence mRNA processing: pre-mRNA to mRNA Pre-mRNA – the original sequence of RNA created during transcription mRNA- result of processing (reaches the ribosomes) RNA Processing Cap What is RNA Processing? After transcription, the premRNA molecule undergoes processing: 5’ methyl cap is added Splicing (introns removed) Poly A tail is added to the 3’ end Poly A Tail RNA Processing In Eukaryotes only: Introns- non-coded sections Exons- codes for a protein Before RNA leaves the nucleus, introns are removed and exons are spliced together A cap and poly A tail are added to ends of the sequence mRNA leaves the nucleus through the nuclear pores Why is it necessary to add the poly A tail and 5’ cap? Let’s try an example… Original o DNA Sequence (DNA): 3’ TACGTATCGTACATCATG 5’ Transcribe it (pre mRNA): 5’ AUGCAUAGCAUGUAGUAC 3’ Add cap the 5’ cap: 5’ AUGCAUAGCAUGUAGUAC 3’ Remove the introns “UGUA” and “AUAG”: cap 5’ AUGCAUAGCAUGUAGUAC 3’ cap 5’ AUGCCAGUAC 3’ Add a poly A tail onto the 3’ end cap 5’ AUGCCAGUAC 3’ Poly A tail Do Now!! Perform transcription on this DNA segment: 3’ GCTTCATACGA 5’ Do RNA processing and remove the introns: GAA and UGC Add the cap and tail How does this mRNA sequence leave the nucleus? Where does it go? PROTEINS! Proteins are made up of amino acids!!! Proteins are polymers of amino acids Only 20 different amino acids BUT there are hundreds of thousands of different proteins How is this possible? Proteins -made of 20 different Amino Acids - Amino Acids bond to form polypeptide chains How do amino acids form these peptide chains? o Peptide Bonds – Link each amino acids together to form proteins o Dehydration synthesis! (lose a water molecule) How many amino acids are in a dipeptide chain? How about a tripeptide chain? How many water molecules are formed from 2 amino acids? How many water molecules are formed from 100 amino acids? Translation! https://www.youtube.com/watch?v=h5mJbP23Buo Translation Production of proteins from mRNA mRNA goes to the ribosomes in the cytoplasm or the RER and produces proteins Main stages: 1. Initiation 2. Elongation 3. Termination Ribosome Two subunits to the ribosome (large and small) 3 grooves on the ribosome (A, P, E) A: tRNA binding site P: polypeptite bonding site E: exit site Steps to Translation Initiation: 1. mRNA leaves the nucleus and binds to a ribosome 2. The two ribosomal subunits come together at the 5’ end of the mRNA Steps to Translation (cont.) Initiation (cont.): 3. Ribosome will find the start Codon (AUG) and the first tRNA molecule will attach This is the only tRNA that will attach to the P site (and skip the A site) The first amino acid is always methionine. **Codon: group of 3 nucleotides on the messenger RNA that specifies one amino acid (64 different codons) Steps to Translation (Cont.) Elongation: 4. Amino acids attached to a tRNA molecule are brought over to the mRNA (A site of ribosome) This tRNA has an anticodon that matches the codon on the mRNA strand Anticodon: Group of 3 unpaired nucleotides on a tRNA strand. (binds to mRNA codon) tRNA Think-Pair-Share The tRNA sequence reads the following anti-codons: What amino acids do they stand for? UAC CCU CUC GUU Steps to Translation (cont.) Elongation (cont.): 5. Peptide bond formed between amino acids in P and A sites 6. Ribosome shifts over Translocation “A” site now open for new tRNA! 7. tRNA leaves E site and amino acids behind Steps to Translation (Cont.) Termination: 8. The mRNA sequence continues to be read until a stop codon is reached What are the stop codons? 9. The amino acids disconnect from the mRNA sequence and a protein is formed. Video!! https://www.youtube.com/watch?v=5bLEDd- PSTQ Think – Pair - Share Find the amino acid sequence mRNA sequence (translation) AUGCGACGAAUUUAA for the following Do Now!! (P. 1) What are the three phases of translation? List the 3 grooves in a ribosome. How many water molecules are lost when 20 amino acids are joined together? 2,000? Do Now!! (P. 6) What are the 3 phases of translation? Label the diagram: 1. 2. 3. 1 What happens at each site? 2 3 Do Now!! (P. 6) What are the 3 parts of mRNA processing? Perform transcription then mRNA processing of this DNA sequence: 3’ T A C T T A A C G A T C C G T C 5’ *introns: AUU, GGC Objectives To identify the steps of translation To define codon and practice using a codon chart Do Now!! (P. 6) Find the amino acid sequence for the following mRNA sequence (translation) AUGGGACGAUUUUUCCGGUUAUAG Which amino acid do these anti-codons *UAC, GCU, AAA, AUC code for? Do Now!! Transcribe the following DNA sequence and process the pre- mRNA: 3’ CCTTACCCAGATCCGTAAATC 5’ ** introns: GGU AUU Determine protein sequence Do Now!! Transcribe the following DNA sequence and process the pre- mRNA: 3’ CAGGTATACGATCCTCCGTTAATC 5’ ** introns: CUA GGA Determine protein sequence Mutations! https://www.youtube.com/watch?v=GieZ3pk9YVo Mistakes in DNA Cells can make mistakes in replication and transcription Most often these mistakes are fixed by enzymes Causes of Mutations Can happen spontaneously or by mutagens: Mutagens: Certain chemicals or radiation that can cause DNA damage Causes bases to pair incorrectly: Proteins fold incorrectly, become unstable, or are not made High-energy forms of radiation, such as X rays and gamma rays, are highly mutagenic. Mutations A permanent change that occurs in a cell’s DNA Three types of mutations: 1. Point mutation 2. Insertion 3. Deletion Color-blindness Progeria Lewandowsky-Lutz dysplasia Hypertrichosis Point Mutation Substitution: A change in just one base pair Missense Mutation: amino acid is changed Nonsense Mutation: amino acid is changed to a stop codon Silent Mutation: no change is made in amino acid sequence Normal RBC Sickled RBC Insertion Addition of one or more nucleotides Deletion Removal of nucleotides Ex: cri du chat syndrome- part of chromosome 5 is broken off (a chromosomal mutation) Frameshift Mutations Causes the reading frame to shift to the left or the right Caused by insertion and deletion mutations Normal: THE FAT CAT ATE THE WET RAT Mutated: HEF ATC ATA TET HEW ETR AT ACGAAATACAGACAT Decide what type of mutation occurred: ACGAAATAGAGACAT ACAAATACAGACAT ACGAAATACAGGACAT Which resulted in a frameshift? Sex Cell vs. Somatic Cell Mutations Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring Somatic cell (non-sex cell) mutations are not passed on to the next generation Chromosomal Mutations Deletion Duplication Inversion Translocation Protein Structure http://www3.interscience.wiley.com:8100/legacy/college/boyer/0471661791/structure/HbMb/hbmb.htm Do Now!! ATGGAGCCATGAAGGTC Determine the kind of mutations: ATGGACCCATGAAGGTC oATGGAGCCATGAATC oATGGAGCGCATGAAGGTC o o Which mutations resulted in a frameshift?