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Protein Synthesis and Mutations Review 1. 2. Explain the differences and similarities between DNA and RNA. Nucleic Acid Sugar Bases Strands DNA Deoxyribose ATGC 2-double helix RNA Ribose AUGC 1-single strand Given a sequence of DNA, be able to write the DNA copy, the RNA transcript, the codons, the anticodons and use a table to determine the amino acids. a. Transcribe the following DNA sequence into mRNA (codons): A – G –– A – T – A – C – G– C – G –C – C –T –A U – C -- U – A – U – G – C – G – C – G –G –A –U b. Below is a list of the mRNA codons for each amino acid. Alanine: GCU Arginine: CGU Asparagine: AAU Aspartic Acid: GAU Cysteine: UGU Glutamic Acid: GAA Glycine: GGU Histidine: CAU Isoleucine: AUU Leucine: UUA Lysine: AAA Methionine: AUG Phenylalanine: UUU Proline: CCC Serine: UCU Threonine: ACU Tryptophan: UGG Tyrosine: UAU Valine: GUU Terminator: UAA If the sequence on the DNA molecule calls for a protein with the following DNA codons, (1) what would be the sequence on the mRNA and (2) what would be the amino acid sequence of the protein being made? DNA TAC TTA mRNA AUG UUA GUU UGG UAU UAA Amino Acids: Met Leu 3. CAA ACC ATA ATT Val Trp Tyr Terminator (Stop) In the DNA sequence : TACTTACAAACCATAATT a. What would be the effect if one of the bases were deleted in the very first mRNA codon? Frameshift Mutation, which would cause a change in 1 or more amino acids, altering the protein possibly causing a faulty or nonfunctional protein. b. What would happen if there was a substitution of one base for another in one of the mRNA codons? Point mutation, which could cause a change in 1 amino acid, cause a premature stop codon causing a faulty protein to be made, or no change at all could occur. 4. 5. 6. 7. 8. Mutations that occur at one single nitrogen base are referred to as __point__ mutations. A mutation involving the insertion or deletion of a nucleotide is called a ___frameshift_____ mutation. In DNA what are the complementary nucleotide pairs? In RNA what are the complementary nucleotide pairs? A-T & G-C; A-U & G-C What are the three types of RNA? Include the functions and shapes of each. rRNA-along with protein, makes up the ribosomes tRNA-transfers amino acids to the ribosomes where proteins are synthesized mRNA-copies DNA’s code & carries the genetic information to the ribosomes Draw or explain the structure of the ribosome? What is the purpose of the ribosome? Protein Synthesis Explain the process for protein synthesis to occur, in detail. Where does each stage occur and what are the steps at each stage? In the Nucleus: First the DNA must be unpackaged (unwrapped) from the proteins so that the gene becomes exposed. Then Transcription factors must help bind the RNA polymerase to the promoter region on the DNA. RNA polymerase will then unwind the DNA chain while walking down using the template strand to transcribe the DNA sequence into a mRNA 9. 10. 11. strand. Once finished the mRNA strand may be further processed by alternative splicing (if needed) to create the final mRNA strand that is then taken out of the nucleus into the cytoplasm where the small ribosomal subunit will bind with it. The small ribosomal subunit (with the mRNA strand) will then bind with the large ribosomal subunit. The ribosome will then scan the mRNA strand looking for the “Start” codon (AUG). tRNA will bring in the amino acids by matching the codons on the mRNA with their anticodons. This process begins at a site called the P site in the ribsosome (where the polypeptide (protein) strand will grow). Next another tRNA will come in with the correct anticodon to the next codon in the A site and a peptide bond will form between the two amino acids. The ribosome will then move down the mRNA sequence so the next codon is in the A site, and then next tRNA can come in bringing in the next amino acid. This will continue until the ribosome comes upon to a terminator codon, thus causing the ribosome to release both the protein (amino acid strand) and the mRNA. In the diagram below, label which process is Transcription and which is Translation. a. For Transcription label the template strand, the mRNA, and draw in where the RNA polymerase would be b. For Translation label the start codon, the tRNAs, the amino acids, the mRNA and the ribosome c. Below each diagram write Define Transcription. Define Translation. What is a codon? How many nucleotides make up a codon? What is an anticodon? Where are codons and anticodons found? A codon is sequence of 3 nucleotides that together form a genetic code in DNA & RNA. 3 nucleotides make up one codon. An anticodon is the complementary sequence on the tRNA that matches the codon on the mRNA. Codons are found in DNA and mRNA, anticodons are found on tRNA. Briefly describe how eukaryotes and prokaryotes control their gene expression. Eukaryotes regulate their gene expression through 1)DNA/Gene packaging where the DNA is wound around proteins limiting access to the RNA polymerase for transcription. 2) Transcription Factors are proteins that bind to the DNA and help RNA polymerase bind to the promoter region in order to transcribe the gene into mRNA. 3) RNA Alternative Splicing is where after DNA is transcribed, intron (noncoding sequences) are cut out of the gene and removed while the exons (coding sequences) are pieced back together to make the protein. Some genes have the ability to have 2-3 different proteins pieced back together from their exons. Prokaryotes have their genes under the control of an operon (which is a sequence of DNA that contains an operator sequence, promoter sequence, and the gene). Repressors bind to the operator sequence preventing RNA polymerase from being able to bind to the promoter sequence and transcribe the DNA. There are two types of operons, 1) Repressible operons which are normally transcribing the DNA into mRNA to create protein and when we need to turn off the gene a repressor is activated and binds to the operator region preventing further transcription. 2) Inducible operon where the gene is normally turned off because the repressor is bound and when the gene needs to be turned on to make the protein, a inducer 12. 13. 14. 15. binds to the repressor removing it from the operator sequence and therefore allows RNA polymerase to bind and make the mRNA transcript. Describe what an operator is and its function. What does a repressor protein do? An operator is sequence of DNA that transcription factors/repressors bind to in order to regulate the gene expression (turn the genes on or off). A repressor protein binds to the operator sequence and blocks RNA polymerase from being able to bind and transcribe the DNA. Describe exons and introns. What are the functions of each? Exons are the part of a gene that code for protein. Introns are nucleotide sequences that are removed during RNA splicing. Describe Alternative RNA splicing. Why do we need alternative splicing? RNA Alternative Splicing is where after DNA is transcribed, intron (noncoding sequences) are cut out of the gene and removed while the exons (coding sequences) are pieced back together to make the protein. Some genes have the ability to have 2-3 different proteins pieced back together from their exons. What are the two types of mutations and their subtypes? Point Mutation Substitution (where a nucleotide is swapped for a different nucleotide); Frameshift Insertion(the addition of 1 or more extra nucleotides) or Deletion (the removal of 1 or more nucleotides from the DNA sequence). a. Which type of mutation is most likely to have the least effect on protein synthesis? Point mutation b. Which type of mutation is most likely to have the most harmful effect on protein synthesis? Frameshift mutation Amino acids Template Strand Ribosome tRNAs RNA polymerase Transcription Start codon Ribosome Translation