Topic 3: The Chemistry of Life

Topic 3: The Chemistry of Life

3.5 Transcription and Translation

3.5.1 Compare the structure of RNA and DNA

3.5.1 Compare the structure of RNA and DNA

3.5.2 Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase

DNA messenger RNA (mRNA)transcription

3.5.3 Describe the genetic code in terms of codons composed of triplets of basesEach triplet or codon in the mRNA codes for 1 of the 20 amino acids

3.5.4 Explain the process of translation, leading to polypeptide formation

mRNA polypeptidetranslation

3.5.4 Explain the process of translation, leading to polypeptide formation

mRNA polypeptidetranslation

3.5.5 Discuss the relationship between one gene and one polypeptide

• Modification of mRNA after transcription has led to the revision of the ‘One gene, one hypothesis’ concept

• The bond between the first tRNA and its amino acid is broken as the third tRNA-amino acid complex binds to the third codon. The now empty tRNA goes into the cytoplasm and finds another amino acid to bond with.

• RNA polymerase binds to the beginning of a gene• mRNA strand will leave nucleus via nuclear pores and enter the

cytoplasm• The polypeptide disassociates from the ribosome and tRNA and

floats freely into the cytoplasm• This process continues until the STOP codon• Helicase unzips dsDNA by breaking the hydrogen bonds• Ribosome attaches to mRNA in cytoplasm• RNA polymerase synthesises a new strand of mRNA

complementary to a DNA template strand. Adenine is complementary to uracil and guanine is complementary to cytosine

• An enzyme catalyses a condensation reaction between the amino acids to create a peptide bond.

• A second tRNA complimentary to the second codon on the mRNA binds and brings along the second amino acid in the polypeptide.

• A tRNA molecule with an anticodon that is complementary to the mRNAcodon binds to the complex of ribosome and mRNA. This tRNA holds the first amino acid in the polypeptide

1. Helicase unzips dsDNA by breaking the hydrogen bonds2. RNA polymerase binds to the beginning of a gene3. RNA polymerase synthesises a new strand of mRNA

complementary to a DNA template strand. Adenine is complementary to uracil and guanine is complementary to cytosine

4. mRNA strand will leave nucleus via nuclear pores and enter the cytoplasm

5. Ribosome attaches to mRNA in cytoplasm6. A tRNA molecule with an anticodon that is complementary to the

mRNAcodon binds to the complex of ribosome and mRNA. This tRNA holds the first amino acid in the polypeptide

7. A second tRNA complimentary to the second codon on the mRNA binds and brings along the second amino acid in the polypeptide.

8. An enzyme catalyses a condensation reaction between the amino acids to create a peptide bond.

9. The bond between the first tRNA and its amino acid is broken as the third tRNA-amino acid complex binds to the third codon. The now empty tRNA goes into the cytoplasm and finds another amino acid to bond with.

10. This process continues until the STOP codon11. The polypeptide disassociates from the ribosome and tRNA and

floats freely into the cytoplasm