Section 1 Workbook (unit 2) ANSWERS Complete the following table: nucleotide DNA RN Name: B5. Describe DNA replication 1) Label each base given in the diagram below and describe the 4 primary characteristics of DNA. - Deoxyribose sugar, phosphate group and one of nitrogen bases making up a nucleotide. - Double helix shape - Two strands held together by hydrogen bonds between the nitrogen bases Sugar phosphate backbone A G T C 2) Identify the site of DNA replication within the cell. Nucleus 3) Explain the three major steps, and all of the enzymes involved, in semi-conservative replication of DNA. What is meant by semi-conservative replication? 1. Helicase unzips DNA strand 2. DNA polymerase joins DNA bases that are complementary to the template strand. One strand is the original / old one while the other strand is new. = semiconservative replication. Covalent bonds between the backbone and H-bonds between strands are added 3. Proof reading enzyme checks for mistakes semiconservative replication means that there is one new and one original strand of DNA 4) Describe the purpose of DNA replication. To make a copy of the DNA for the new cell during cell division Page 1 of 10
5) If a cell is exposed to acidic conditions during cell division, how would this affect the cell s ability to divide? Why? Enzymes are proteins so a specific shape is needed in order to function. The change in ph would cause the enzymes, such as helicase and polymerase to denature. When these enzymes denature, they change shape and therefore, will not function anymore so cell division cannot occur. 6) How does the amount of: a. Adenine compare to the amount of thymine in DNA? Same amount, A pairs with T b. Guanine compare to the amount of cytosine in DNA? Same amount, G pairs with C c. Purines compared to the number of pyrimidines? Same amount 7) How are DNA and RNA chemically similar? Different? Similar: polymers of nucleotides, phosphate groups, nitrogen bases AGC, & pentose sugar Different: DNA has thymine while RNA has uracil. RNA single stranded while DNA double stranded with hydrogen bonds, DNA deoxyribose sugar, RNA ribose sugar. B6. Describe recombinant DNA (rdna) 8) Describe recombinant DNA. Include the enzymes required for the formation of rdna. Use a diagram to help your explanation. 1. DNA from human gene of interest is isolated and removed with restriction enzyme (cuts DNA) 2. Plasmid from bacteria removed and cut with same restriction enzyme 3. Gene put into plasmid = recombined into a single DNA strand = rdna 4. Put into bacteria bacteria divide & give off product such as insulin. 9) Describe at least three uses for recombinant DNA. Make insulin, human growth hormone, TPA Create disease resistant plants Add nutrient to food crop (Golden rice) Page 2 of 10
B7. Demonstrate an understanding of the process of protein synthesis 10) Complete the following table: Describe both processes. Use diagrams to help in your explanation Transcription 1. Helicase opens DNA where gene located 2. RNA polymerase adds complementary RNA bases to create mrna molecule from initiation site to termination site. (DNA serves as template for mrna) 3. mrna molecule leaves through nuclear pores to cytoplasm linear so it fits through the nuclear pores. Translation 1. Initiation 2 halves of ribosome (large & small subunits) come around the mrna molecule and the start codon (AUG) turns on translation 2. Elongation trna brings AA to ribosome. Codon on mrna matches with anticodon on trna (A with U & G with C) and AA left to be added to the polypeptide chain with peptide bonds. 3. Termination - elongation continues until a stop codon is reached (3 of these) which turns off translation. Ribosome separates releasing mrna & primary protein structure to be bent and folded into its functional shape 11) Which process, transcription or translation, is depicted here? Label the molecules. ribosome Translation is shown here Amino acids mrna trna 12) Complete the following table: Describe each molecules role in Protein Synthesis DNA Has instructions on how to make a protein = code mrna Copies instructions and takes them to ribosome trna Brings AA to ribosome to be added to polypeptide chain ribosomes Builds polypeptide chain site for codons & anticodons to meet Page 3 of 10
13) Of the 5 nitrogen bases, which one is X in the below diagram? How do you know (support your answer)? Adenine has 2 hydrogen bonds and is a purine (double ring) Since molecule X is on an mrna molecule, and RNA does not have thymine, the pyrimidine molecule is uracil. Adenine 14) Label the following in the diagram below: mrna (3 times), ribosome, anticodon, trna, DNA, amino acid, codon, primary protein, nucleus, cytoplasm. cytoplasm DNA Nucleus mrna Amino acid Primary protein trna anticodon codon ribosome Page 4 of 10
15) Use the aa codon chart to determine the amino acid sequence produced by the section of an mrna molecule below and determine the DNA strand that provided the instructions. mrna= CGC UAU - UGG DNA= GCG ATA - ACC Amino Acids: 16) = Arg Tyr - Try Use the aa codon chart to predict the amino acid sequence produced by this sequence of bases on a DNA molecule and label transcription and translation DNA= mrna= TAC-GAA-CTT-GGG-TCC AUG -CUU-GAA-CCC-AGG Amino Acids = Met Leu Glu Pro - Arg 17) What anti-codon would be present on the trna that is complementary to the mrna codons given? Anti-codon on trna always complements mrna codon AUG _UAC_ UAA _AUU AGA UCU CGU GCA Page 5 of 10
18) Explain what would occur during translation of the following DNA sequence if ACG underwent a mutation and was converted to ACT. Unmutated DNA: GCA CCT ACG GGA ACC DNA mutation: GCA CCT ACT GGA ACC mrna: CGU GGA UGA CCU UGG AA sequence: Arg Gly - stop Explanation: The mutation causes a stop codon to occur early in the synthesis of the protein. Therefore, the protein will be incomplete and not be able to function. 19) Production of mrna is called transcription 20) Production of a protein is called translation 21) Given the following trna sequence, find the DNA strand and polypeptide chain created: trna: UAC ACC GCC CUA CCC AAA mrna: AUG UGG CGG GAU GGG UUU DNA: TAC ACC GCC CTA CCC AAA AA: Met trp arg asp gly phe 22) In an experiment conducted to study proteins synthesis, radioactive thymine and radioactive uracil were added to a culture of human cells. A few hours later, the culture was analyzed and radioactive mrna was found. a. Explain how an mrna molecule is produced: TRANSCRIPTION Helicase opens DNA where gene located RNA polymerase adds complementary RNA bases to create mrna molecule from initiation site to termination site. (DNA serves as template for mrna) mrna molecule leaves through nuclear pores to cytoplasm linear so it fits through the nuclear pores. b. Explain why the mrna produced is radioactive Because uracil was incorporated into the mrna molecule causing it to be radioactive. c. In a different experiment, radioactive uracil was added to a culture of human cells undergoing DNA replication. What will be the characteristic of the resulting DNA in terms of radioactivity? Explain. DNA does not have uracil therefore it would not be incorporated into the DNA molecule. So the DNA would NOT be radioactive Page 6 of 10
B8. Explain how mutations in DNA affect protein synthesis 23) Give examples of two environmental mutagens that can cause mutations in humans. How do they cause a mutation? Biological: viruses and bacteria that increase the chance of a mutation Chemical: food additives, hallucinogenic drugs, asbestos, DDT, pesticides, manufactured chemicals. affect enzymes of DNA replication, increasing the chance of mutation Radiation: UV & cosmic rays - increasing the chance of mutation 24) Define transgenic organisms. Give an example. An organism that has the DNA of another organism inserted into it is called a transgenic organism. Example: bacteria with the human insulin gene 25) Use the examples to explain how mutations in DNA change the sequence of amino acids in a polypeptide chain, and as a result, may lead to genetic disorders. a. point mutations, sickle cell anemia Changes the amino acid glutamate into valine. This results in abnormal hemoglobin molecule that causes the red blood cell to have a sickle shape that can clog blood vessels and lead to pain. b. gene mutation, hemophilia / cystic fibrosis A gene mutation that causes a lack of or minimal amount of clotting factors to be produced resulting in excessive bleeding. c. chromosomal mutation, Trisomy 21 An extra chromosome #21 results in Down s syndrome. This causes high levels of purines in the blood which leads to mental deficiencies. 26) Define gene therapy. What is its purpose? = alteration of afflicted individuals genes (of the same species) could help with genetic diseases like cystic fibrosis, Alzheimer s, some cancers, AIDS Page 7 of 10
Types of gene mutations Here is a section of DNA before a mutation. DNA: TAC GGG CTC TAG CGA GAT ATT mrna: AUG CCC GAG AUC GCU CUA UAA AA s: Met Pro Glu Ile Ala Leu stop 27) Insertion mutation - What would happen to the AA sequence above if one extra base (a G at the start of the 3 rd codon) were added to the original DNA sequence? Inserted DNA TAC GGG GCT CTA GCG AGA TAT T Resultant mrna AUG CCC CGA GAU CGC UCU AUA Mutated AA Met Pro Arg Asp Arg Ser Ile a. What conclusions can you draw regarding the effect of insertion mutations on the polypeptide chain that would be produced? They cause an incomplete protein to be made there is an extra base that does not make up a codon. Frameshift mutation compared to the original strand, every aa after the insertion changes. b. Do you think that insertion mutations would likely improve or negatively impact the intended function of the protein produced? Negative impact 28) Deletion mutation - What would happen to the AA sequence if one base (the 1 st G in the 2 nd codon) were deleted from the original DNA sequence? DNA TAC GGC TCT AGC GAG ATA TT mrna AUG CCG AGA UCG CUC UAU AA AA Met Pro Arg Ser Leu Tyr a. What conclusions can you draw regarding the effect of deletion mutations on the polypeptide chain that would be produced? There is an incomplete codon because only 2 bases at the end. Frameshift mutation compared to the original strand, every aa after the deletion changes. b. Do you think that deletion would likely improve or negatively impact the intended function of the protein produced? Negative impact 29) Substitution mutation - What would happen to the AA produced if a base were substituted for another base in the original DNA strand? (The substituted bases are highlighted below) DNA TAC CGG CTC TAG CGG GAT ATT mrna AUG GCC GAG AUC GCC CUA UAA AA Met Ala Glu Ile Ala Leu Stop Page 8 of 10
a. What can you conclude about the effect of substitution mutations on the polypeptide produced from a strand of DNA? You can get a complete protein made unlike the other types of point mutations. The amino acid may not even change so the same protein could still be made having no affect on the organism. b. Would substitutions improve or negatively impact the intended function of the protein produced? Why? They could negatively impact the function of the protein by changing the amino acid, thereby changing the protein. They could have no impact because the amino acid does not change resulting in the same protein Page 9 of 10
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