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Chapter 13 From DNA to Proteins

Chapter 13 From DNA to Proteins. RNA: Background There are 3 Types of RNA. transfer RNA tRNA -used in translation -brings the amino acids to the ribosome. ribosomal RNA rRNA -used in translation -a component of ribosomes. messenger RNA mRNA -used in transcription

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Chapter 13 From DNA to Proteins

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  1. Chapter 13 From DNA to Proteins

  2. RNA: BackgroundThere are 3 Types of RNA transfer RNA tRNA -used in translation -brings the amino acids to the ribosome ribosomal RNA rRNA -used in translation -a component of ribosomes messenger RNA mRNA -used in transcription -contains uracil instead of thymine

  3. RNA- Comparing it to DNA RNADNA • the sugar in RNA is ribose - the sugar is deoxyribose. • is single-stranded - is double-stranded. • contains uracil (U) - containsthymine(T) A + U A + T

  4. Protein Synthesis in Eukaryotic Cells • The goal of this chapter is to learn how proteins are made. • Proteins carry out all the functions in the body. • The instructions for making proteins in contained in the DNA. So, we will start in the nucleus of the eukaryotic cell at the DNA………….. http://www.youtube.com/watch?v=NJxobgkPEAo&feature=related

  5. The Steps of Protein Synthesis • DNA codes are first copied by “transcription” into messenger RNA. This happens in the nucleus. • messenger RNA is edited and then it leaves the nucleus. It attaches to a ribosome in the cytoplasm. • The information carried by the messenger RNA is used to make amino acids by “translation”. This happens in the cytoplasm and involves ribosomes, transfer RNA and ribosomal RNA. • The amino acids combine to form the final product, a protein.

  6. http://www.youtube.com/watch?v=ztPkv7wc3yU&feature=related http://www.youtube.com/watch?v=bpMhgAGybe4&feature=related Transcription – Step 1 • During transcription, segments of DNA serve as templates to produce complementary RNA molecules. • Transcription requires an enzyme, known as RNA polymerase, RNA polymerase binds to DNA during transcription and separates the DNA strands.

  7. Messenger RNA is transcribed in the nucleus and then enters the cytoplasm for translation. • But first, it must be edited………

  8. RNA Editing - Step 2 RNA molecules sometimes require bits and pieces to be cut out of them before they can go into action. The portions that are cut out and discarded are called introns. In eukaryotes, introns are taken out of pre-mRNA molecules while they are still in the nucleus. The remaining pieces, known as exons, are then spliced back together to form the final mRNA.

  9. Translation: Step 3 (reading codons on mRNA to make amino acids) • Each three-letter “word” in mRNA is known as a codon. • A codon consists of three consecutive bases that specify a single amino acid to be added to the polypeptide chain.

  10. Did you know………. • Because there are four different bases in RNA, there are 64 possible three-base codons (4 × 4 × 4 = 64) in the genetic code. • This circular table shows the amino acid to which each of the 64 codons corresponds.

  11. Translation- Step 3 • Translation begins when a ribosome attaches to an mRNA molecule in the cytoplasm. • As the ribosome reads each codon of mRNA, it directs tRNA to bring the specified amino acid into the ribosome. • One at a time, the ribosome then attaches each amino acid to the growing chain. http://www.youtube.com/watch?v=B6O6uRb1D38&feature=related http://www.youtube.com/watch?v=BYPLz543Xgg&feature=related

  12. Steps in Translation • Each tRNA molecule carries just one kind of amino acid. • In addition, each tRNA molecule has three unpaired bases, collectively called the anticodon—which is complementary to one mRNA codon. • The tRNA molecule for methionine has the anticodon UAC, which pairs with the methionine codon, AUG.

  13. Steps in Translation • The ribosome has a second binding site for a tRNA molecule for the next codon. • If that next codon is UUC, a tRNA molecule with an AAG anticodon brings the amino acid phenylalanine into the ribosome.

  14. Steps in Translation • The ribosome helps form a peptide bond between the first and second amino acids—methionine and phenylalanine. • At the same time, the bond holding the first tRNA molecule to its amino acid is broken. http://www.youtube.com/watch?v=KvYEqGb7XN8&feature=related http://www.youtube.com/watch?v=NJxobgkPEAo&feature=related

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