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RNA and Protein Synthesis

RNA and Protein Synthesis. 12-3. Protein Synthesis. Ribonucleic acid, RNA, plays a role in protein synthesis. Central Concept DNA RNA protein. A. RNA Structure & Function. Differences in RNA than in DNA Sugar ribose instead of deoxyribose

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RNA and Protein Synthesis

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  1. RNA and Protein Synthesis 12-3

  2. Protein Synthesis • Ribonucleic acid, RNA, plays a role in protein synthesis. • Central Concept DNA RNA protein

  3. A. RNA Structure & Function • Differences in RNA than in DNA • Sugar ribose instead of deoxyribose • Nitrogenous base uracil instead thymine • Single stranded instead of double stranded • Shorter than DNA

  4. Messenger RNA (mRNA) – carries instructions from a gene to make a protein Ribosomal RNA (rRNA) – part of the structure of ribosomes Transfer RNA (tRNA) – transfer amino acids to the ribosomes to make a protein Types of RNA

  5. B. Transcription • The process by which the genetic instructions in a specific gene are transcribed into an RNA molecule. • Takes place in the nucleus of eukaryotic cells and in the DNA-containing region in the cytoplasm of prokaryotic cells. • Figure 12-14 of Prentice Hall Biology

  6. RNA Editing • After the RNA is produced, it must be edited before it can be used. • Introns are removed and exons are spliced together before the RNA leaves the nucleus.

  7. C. The Genetic Code • The term for the rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid. • Three adjacent nucleotides (“letters”) in mRNA specify an amino acid (“word”) • Three adjacent nucleotides are called a codon and encodes for an amino acid or signifies a start or stop signal.

  8. No codon encodes more than one amino acid. There are 64 possible codons and amino acids are can be specified by more than one codon. • A start codon is a specific sequence of nucleotides in mRNA that indicates where translation should begin. AUG. • Three stop codons are specific sequences of nucleotides in mRNA that indicates where translation should end.

  9. Figure 12-17

  10. D. Translation • Decoding of the genetic instructions to form a polypeptide • Takes place on the surface of the ribosome • Protein structure • Made of one or more polypeptides • Polypeptides are chains of amino acids linked by peptide bonds. • Only 20 different amino acids • The amino acids sequence determines how the polypeptides will twist and fold into the protein. The shape of the protein is critical to its function.

  11. Translation • Figure 12-18 • Beginning at the start codon, tRNA carrying an amino acid pairs its anticodons pair up with the complementary codon on the mRNA. • This continues as an assembly line linking the amino acids and breaking bonds between the tRNA and the amino acids. • The linked amino acids form a polypeptide until a stop codon is reached.

  12. E. The Human Genome • A genome is the complete genetic content. • Biologists have now decoded the order of the 3.2 billion base pairs in the 23 human chromosomes. • Bioinformatics compares different DNA sequences to try to determine what information the DNA codon encodes.

  13. Nitrogen Base – the “rung on the ladder” Gene – Short Segment of double helix Deoxyribose – “sugar side of the ladder” Nucleotide – composed of 3 parts floating free in the cytoplasm DNA – the double helix DNA

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