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Transcription and Translation 9/12

Transcription and Translation 9/12. Why does DNA take a double helical orientation? How is an mRNA sequence translated to produce a specific sequence of specific amino acids? What happens if mutations occur during semiconservative DNA replication? Why are ribosomes important for translation?

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Transcription and Translation 9/12

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  1. Transcription and Translation 9/12 • Why does DNA take a double helical orientation? • How is an mRNA sequence translated to produce a specific sequence of specific amino acids? • What happens if mutations occur during semiconservative DNA replication? • Why are ribosomes important for translation? • Could you describe all steps and organelles that permit the gene on DNA for insulin to become a protein called insulin that leaves a cell.

  2. Don’t Forget: DNA forms a double helix because the two base types on the two sides can hydrogen bond to each other! The helix forms in “antiparallel” orientation. The presence of uracil in RNA prevents a helix from forming in RNA.

  3. Semiconservative replication means that each strand of the original pair is used to make a new strand. “Semi” means the new cell has half the original strands and half “new” strands.

  4. Semiconservative replication also means that a mistake (mutation) in the original is passed on to all further replications of the original DNA sequence. • Consider This: It is possible that one or two of the original stands of DNA from your mom or dad could still exist in your body! (semiconservative DNA replication) • Math: mom23chromosomes (23dsDNA)46ssDNA • Dad23 chromosomes (23ds DNA)—46ssDNA • You: sum of several trillion cells with 92 original strands still possible floating around unchanged since inception!  • Fatal mutations can kill a cell immediately and end the cell genetic contribution of the cell to the body. • Deleterious mutations to DNA can change the proteins produced by a cell and cause cellular dysfunction….i.e. Cancer • Why are they passed to cell in same body but not next generation? • Why can mutations to your DNA can be passed on to future generations if they occur in the cells that become an Egg or Sperm

  5. Key Codons on mRNA: #1: AUG “start codon” This is where protein is started! #2: a.a. to protein chain #3: Stop signal is created by UAG, UAA and UGA DNA makes mRNA and mRNA bases (codons) code for/are translated into amino acids in the growing protein chain (peptide bonds link aa). tRNA (with an anticodon tRNA) carries each new amino acid to the new (nascent) growing chain of amino acids.

  6. The DNA sequence that codes for a protein is called a “GENE”.

  7. A series of special transfer RNA molecules (tRNAs) carry the amino acids to the new protein chain being created. Anti-codons of tRNAs (i.e. UUA below) bind the codons of the mRNA (would be AAU on mRNA), when tRNA-aa bind to mRNA, amino acids are linked together by peptide bonds.

  8. How do we convert regular old cholesterol into testosterone? To do this we need to make enzymes from DNA/mRNA that make the chemical reactions possible. How do we make these enzymes?

  9. There are 20 different amino acids (see below) to choose from. Each A.A. has at least one 3-base codon, some amino acids have several different codons. A total of 64 different mRNA codons exist.

  10. Don’t Memorize this list! Just realize there are 64 different possible combinations for a 3-base codon given four different kinds of base. (Do remember AUG is the start codon and that UAA, UAG and UGA are stop codons).

  11. What happens to mRNA with respect to making codons and a protein from the codons? How do I translate mRNA into a specific amino acid sequence? Great Test Question Remember these codons: • AUG= starts a protein with the amino acid methionine • UAG, UAA and UGA stop protein synthesis from mRNA • All other base triplets (codons) make a specific amino acid • Identify where the protein starts (AUG)? • Every three bases on mRNA after this makes an amino acid in the protein chain being produced. • Any time a triplet of bases (codon) is UAG, UAA and UGA protein synthesis stops • All proteins are made from 20 different amino acids • Each amino acid has a specific mRNA codon of three bases on the mRNA that signal that it should be placed at the growing end of the protein chain. • Each codon on the mRNA is read by an anti-codon on tRNA. Each special tRNA carries its unique amino acid to the new protein. • A protein that contains 10 amino acids had to be made from 10 codons, each codon is from 3 bases in the mRNA. The stop codon does not make an amino acid, it simply says “stop”. • A 10 amino acid protein would need how many bases? [10 codons X 3 bases/codon] + 3 bases for the stop codon= 33 bases 30 bases for codons for the 10 amino acids plus 3 bases from the stop codon

  12. Lets look at how the base sequence of mRNA is translated into an amino acid sequence before (original) and after we change the mRNA base sequence.Ultimately mutations to DNA are what change the mRNA sequence! 1) How many amino acids long is this protein? UUCGAUG-GCC-UCU-UGC-AUG-GCG-UAG-UUU-AG 1 5go 10 stop 30 2) If Base #5 is removed does the base sequence down stream change? Where does synthesis start after the change? A-removed UUCGUGGCCUCUUGC-AUG-GCG-UAG-UUU-AG 1 5 10 go stop 29 3) If an extra base (G) is ADDED immediately after #7 the total mRNA becomes 31 bases, how many amino acids are produced? UUCGAUG-GGC-CUC-UUG-CAU-GGC-GUA-GUU-UGC... • 5go 10 31 “Additional” nucleotide added to mRNA sequence Is a stop codon present? Will protein production stop? For more help go to Supplemental Instruction!

  13. Ribosomes are large protein-RNA structures that hold the mRNA during translation so tRNA can add new amino acids to the nascent end of the peptide chain! Facts: -Ribosomes are large particles made of many proteins and pieces of rRNA -Many ribosomes can translate a single mRNA at the same time to make several proteins at the same time -Ribosomes can be free floating in the cytosol -Ribosomes can attach to the endoplasmic reticulum giving it a studded appearance (Rough ER)

  14. How do we get insulin into the blood after a meal? -mRNA associates with a ribosome and the rough side of the endoplasmic reticulum -The protein (insulin) is pushed into the E.R. -Insulin can then be modified in the E.R. -After modification in the ER they are sent to the Golgi Apparatus for additional modification -The Golgi Apparatus loads proteins into vesicles for secretion -The vesicle fuses with the plasma membrane (exocytosis) and the insulin can now pass on to the blood and the body. -Insulin is secreted into the blood when second messengers tell the pancreatic beta-cells you have just eaten your meal and need to focus on anabolic reactions!

  15. Proteins are sent into vesicles that are created at the Golgi apparatus. Secretory vesicles release their contents when they fuse with the plasma membrane. Protein is packaged into vesicles and secreted out of the cell after your meal. mRNA Insulin can now diffuse into blood stream! Protein is created and modified

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