DNA REPLICATION REVIEW

Transcription

1 Biology Ms. Ye DNA REPLICATION REVIEW 1. Number the steps of DNA replication the correct order (1, 2, 3): Name Date Block Daughter strands are formed using complementary base pairing DNA unwinds The DNA of the daughter strands winds together with its parent strand 2. Why is DNA replication called semi-conservative? Why is this important? 3. What enzyme unwinds or unzips the parent strands of DNA? 4. What enzyme connects the new nucleotide bases to the old bases in the DNA template? 5. What enzyme connects the new nucleotides together? 6. Show the complementary base pairing that would occur in the replication of the short DNA molecule below. Use two different colors (pencils, pen, etc) to show which strands are the original and which are newly synthesized.

2 PROTEIN SYNTHESIS REVIEW: TRANSCRIPTION AND TRANSLATION Transcription In transcription, RNA polymerase splits the two halves of a strand of DNA. RNA then uses one half as a template to make a copy of the other half. RNA contains the nucleotide uracil instead of the nucleotide thymine. Comparing DNA Replication and Transcription DNA replication is the process by which a cell copies its DNA. During replication, both strands of the double helix are used as templates to make complementary, or matching, strands of DNA. DNA transcription is the process by which a single strand of DNA is used as a template to generate a strand of mrna. Fill in the missing information. One row has been completed for you.

3 Translation During translation, transfer RNA (trna) anticodons match to messenger RNA (mrna) codons. Each trna molecule can carry one particular amino acid. The amino acids are joined to form a polypeptide. 1. Number the four trna anticodons in the order in which they should appear to match the codons in the mrna strand. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

4 Practice Example: DNA : G T A C G C G T A T A C C G A C A T T C mrna: C A U G C G C A U A U G G C U G U A A G Codons: AUG-CGC-AUA-UGG-CUG-UAA Anticodons: UAC-GCG-UAU-ACC-GAC-AUU Amino Acids: METHIONINE-ARGININE-ISOLEUCINE-TRYPTOPHAN-LEUCINE Using the example above, transcribe the following DNA strand into mrna and translate that strand into a polypeptide chain, identifying the codons, anticodons, and amino acid sequence. *To identify your first codon on the mrna, remember that the start codon is AUG * 1. DNA: A T A C G A A A T C G C G A T C G C G G C G A T T C G G mrna: Codon: Anticodon: Amino Acids: 2. DNA: T T T A C G G C C A T C A G G C A A T A C T G G mrna: Codon: Anitcodon: Amino Acids: 3. DNA: T A C G G G C C T A T A C G C T A C T A C T CA T G G A T C G G mrna: Codon: Anitcodon: Amino Acids: 4. DNA: G T A C G C G T A T A C C G A C A T T C mrna: Codon: Anitcodon: Amino Acids:

5 Questions: 1. How many nucleotides are present in the normal DNA sequence in Model 1? 2. How many codons (3 nucleotide sequences) are contained in the mrna that is produced by the normal DNA in Model 1? 3. How many amino acids will be in the polypeptide produced by the normal DNA/mRNA sequence?

6 4. What is the amino acid sequence of the polypeptide produced by the normal DNA sequence in Model 1? 5. Consider DNA sequence 2 in Model 1. The mutation in that sequence is a substitution mutation. a. Compare sequence 2 with sequence 1 and describe the mutation that has occurred. b. What is the effect of this substitution mutation on the amino acid sequence? 6. Consider DNA sequence 3 in Model 1. The mutation in that sequence is an insertion mutation. a. Compare sequence 3 with sequence 1 and describe the mutation that has occurred. b. What is the effect of the insertion mutation on the amino acid sequence as compared to the normal amino acid sequence in Model 1? 7. Consider DNA sequence 4 in Model 1. The mutation in that sequence is a deletion mutation. a. Compare sequence 4 with sequence 1 and describe the mutation that has occurred. b. What is the effect of the deletion mutation on the amino acid sequence as it is compared to the normal amino acid sequence in Model 1? 8. Based on Model 1 and your answers to the questions above, come up with a definition for each of the following mutations. a. Substitution mutation b. Insertion mutation c. Deletion mutation

7 9. Considering your knowledge of codons and how they code for an amino acid, would all substitution mutations lead to a change in the amino acid sequence? Explain your reasoning. 10. Would all insertion or deletion mutations lead to a change in the amino acid sequence? Explain your reasoning. 11. What could potentially cause more damage (or a greater benefit) to an organism, a substitution mutation or an insertion mutation? Explain your reasoning. 12. What could potentially cause more damage (or a greater benefit) to an organism, a deletion mutation at the beginning of a DNA sequence or at the end of a DNA sequence? 13. Which types of mutations, positive, negative or neutral, are most likely to be seen in offspring several generations after the mutation occurred? Explain your reasoning. 14. Consider the following scenarios. State whether the mutation is likely to be passed on to the offspring of the organism. Explain your reasoning. a. A single bacteria cell contains a positive mutation in its DNA. b. A skin cell on a cat contains a positive mutation in its DNA. c. A sperm cell in a whale contains a positive mutation in its DNA.

8 15. All cells have DNA errors due to the mistakes that occur each time DNA is replicated prior to cell division. There are proofreading enzymes in cells that correct many of these mistakes, but on average, 3 5 errors are found in DNA after each replication. a. If each cell has multiple mutations, why do most of us have normally-functioning tissues and organs? b. Why is only a tiny subset of these mutations passed on to our children?