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12.3 RNA and Protein Synthesis

12.3 RNA and Protein Synthesis. 12.3 RNA and Protein Synthesis. Genes are coded instructions that control the production of proteins within the cell. The Structure of RNA.

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12.3 RNA and Protein Synthesis

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  1. 12.3 RNA and Protein Synthesis

  2. 12.3 RNA and Protein Synthesis • Genes are coded instructions that control the production of proteins within the cell

  3. The Structure of RNA • There are 3 main differences between RNA and DNA: The sugar in RNA is ribose instead of deoxyribose, RNA is generally single-stranded, and RNA contains uracil in place of thymine.

  4. Types of RNA • There are three main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA. • Messenger RNA (mRNA) carries copies of messages encoded on DNA to the rest of the cell. • Ribosomal RNA (rRNA) makes up part of the ribosome

  5. Transfer RNA (tRNA) carries amino acids to ribosomes

  6. Transcription • During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA. • RNA polymerase will only bind to regions of DNA known as promoters.

  7. RNA Editing • The DNA of eukaryotic genes contains sequences of nucleotides, called introns, that are not involved in coding for proteins. • The DNA sequences that code for proteins are called exons because they are expressed in protein synthesis.

  8. The Genetic Code • Proteins are made by joining amino acids into long chains called polypeptides. • A codon consists of three consecutive nucleotides that specify a single amino acid to be added to the polypeptide. • There are 64 possible 3 base codons.

  9. Translation • The decoding of an mRNA message into a polypeptide chain (protein) is known as translation. • Translation takes place on ribosomes. • During translation, the cell uses information from mRNA to produce proteins.

  10. A) mRNA is transcribed from DNA. • B) Translation starts when an mRNA molecule attaches to a ribosome. As each codon moves through the ribosome, the proper amino acid is brought to the ribosome by tRNA. • Each tRNA has 3 unpaired bases, the anticodon, which is complementary to one mRNA codon.

  11. C) The ribosome forms a bond between the first 2 amino acids, and breaks the bond that held the first tRNA to its amino acid. • D) The polypeptide chain continues to grow until the ribosome reaches a stop codon on the mRNA molecule.

  12. The Roles of RNA and DNA • The master plan is stored safely in an office, and the blueprints are taken to the job site. Similarly, the cell uses the DNA “master plan” to prepare RNA “blueprints.”

  13. Genes and Proteins • A gene that codes for an enzyme to produce pigment can control the color of a flower. • Another gene controls the production of an enzyme that determines blood type.

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