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Topic 3.4 Review Book Transcription & Translation Name: ___________________ Topic 3 The Chemistry of Life Topic 3.4: Transcription and Translation (Textbook Pages 66-74) Key facts 1. To replicate a molecule of DNA must unwind to expose the nitrogenous bases. 2. Helicase is the enzyme that breaks the hydrogen bonds to allow the unwinding. 3. The exposed bases of each strand are then paired with an available nucleotide by complementary base pairing. The result is two strands where only one was first present. 4. DNA polymerase is an enzyme that allows the connection between nucleotides lined up by basepairing. 5. This replication is called semi-conservative replication because each of the two formed molecules of DNA contains one of the original strands and one new strand. 6. The daughter DNA strands are identical to one another thus preserving the genetic code. 7. RNA contains the 5C sugar ribose, is single stranded and contains the bases adenine, uracil, cytosine, and guanine. Notice thymine is missing in RNA. RNA is a chain of RNA nucleotides connected by a covalent bond between the phosphate of one nucleotide and the 3C of the next nucleotide. 8. DNA transcription involves the copying of the genetic code from DNA onto a strand of RNA. 9. This RNA strand is complementary to the DNA template strand. 10. The genetic code is actually composed of triplets of bases called codons. The codons are present on the RNA formed during translation. Therefore, codons do not contain thymine. 11. The RNA formed during transcription is called messenger or mRNA. This mRNA carries the genetic code out of the nucleus to the ribosomes in the cytoplasm. 12. It is at the ribosomes where the process of translation occurs. Translation is the process that leads to the formation of polypeptides, proteins. 13. In the cytoplasm tRNA molecules contain anticodons. The tRNA anticodons pair with the mRNA codons through base pairing. Because each tRNA with a particular anticodon carries a specific amino acid, the codon – anticodon match allows a very specific protein or polypeptide to be produced. 14. A particular sequence on a DNA molecule that codes for a specific protein is called a gene. This gene will always code for the formation of the same protein during the process of its transcription and translation. 15. There is a third type of RNA called ribosomal RNA (rRNA). This rRNA composes a significant part of the ribosome which is the structure at which protein synthesis occurs via the process of translation. 16. The term translation is appropriate as during the process there is a change from the language of DNA (nitrogenous base sequence) to the language of proteins (amino acid sequence). Additional notes Name ______________________________ Section _____________ Complete the following. 1. Why is DNA replication said to be semi-conservative? 2. What enzyme breaks the hydrogen bonds of DNA to produce separation of the two strands so that replication may occur? 3. What enzyme is directly involved in the linking of nucleotides to produce the new strand of DNA in replication? 4. List three differences between RNA and DNA. RNA DNA 1________________________________ 1______________________________ 2________________________________ 2______________________________ 3________________________________ 3______________________________ 5. In general, what happens in DNA transcription? 6. What type of RNA is produced by transcription? 7. Why must helicase be involved in transcription? 8. In general, how are replication and transcription similar? 2 of 14 Name ______________________________ Section _____________ 9. In general, how are replication and transcription different? 10. On what molecule would one find a codon?__________________ 11. What is a codon? 12. What is the function of RNA polymerase? 13. What organelle does mRNA deliver the genetic code to?__________________ 14. Name the process that results in protein synthesis.____________________ 15. What is the function of tRNA in protein synthesis? 16. What part of the tRNA binds with the codon of the mRNA at the ribosome? 17. What does tRNA transport to the ribosomal-mRNA complex?___________________ 18. The genetic code is said to be universal. What does this mean? 19. The genetic code is said to be degenerate. What does this mean? 20. How many different amino acids are there that make up proteins (polypeptides)?____ 3 of 14 Name ______________________________ Section _____________ 21. What type of bond allows the connection between the anti-codon of the tRNA and the codon of the mRNA at the ribosome?_____________________ 22. How many subunits does a ribosome have?____________ 23. Are there differences between prokaryotic and eukaryotic cell ribosomes?_______ Explain. 24. What is a third type of RNA involved in translation?________ What does it do? 25. What does the one gene/one polypeptide hypothesis state? 26. Follow the genetic code through protein synthesis. a. DNA TTACGGCTA b. mRNA- _____________ c. tRNA anticodons- _____________ 4 of 14