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Section 11.2 Summary – pages 288 - 295

Section 11.2 Summary – pages 288 - 295. The Genetic Code. The nucleotide sequence transcribed from DNA to a strand of messenger RNA acts as a genetic message, the complete information for the building of a protein.

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Section 11.2 Summary – pages 288 - 295

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  1. Section 11.2 Summary – pages 288 - 295 The Genetic Code • The nucleotide sequence transcribed from DNA to a strand of messenger RNA acts as a genetic message, the complete information for the building of a protein. • As you know, proteins contain chains of amino acids. You could say that the language of proteins uses an alphabet of amino acids.

  2. The Genetic Code • A code is needed to convert the language of mRNA into the language of proteins. • What is the language of a protein?

  3. -There are 20 different amino acids used to make a protein. -So there must be at least 20 different codes on the mRNA to select for the amino acids use to make a protein. -Scientists arranged the nitrogen bases of mRNA into different mathematical groups

  4. -the 4 bases as single codes = How many? Is this enough? -bases arranged as pairs = How many? Is this enough? -bases arranged as triplets = How many? is this enough?

  5. Biochemists did show that the genetic code on mRNA was formed by groups of three bases that code for one unit of info. Each group of three bases on mRNA is known as a codon. 64 different mRNA codons are in the genetic code.

  6. Section 11.2 Summary – pages 288 - 295 The Messenger RNA Genetic Code First Letter Third Letter Second Letter U A G C U U Phenylalanine (UUU) Serine (UCU) Tyrosine (UAU) Cysteine (UGU) C Cysteine (UGC) Phenylalanine (UUC) Serine (UCC) Tyrosine (UAC) A Stop (UGA) Serine (UCA) Stop (UAA) Leucine (UUA) G Leucine (UUG) Serine (UCG) Stop (UAG) Tryptophan (UGG) C U Arginine (CGU) Leucine (CUU) Proline (CCU) Histadine (CAU) Arginine (CGC) Proline (CCC) C Leucine (CUC) Histadine (CAC) A Proline (CCA) Arginine (CGA) Leucine (CUA) Glutamine (CAA) Arginine (CGG) G Glutamine (CAG) Proline (CCG) Leucine (CUG) A U Isoleucine (AUU) Threonine (ACU) Asparagine (AAU) Serine (AGU) C Serine (AGC) Asparagine (AAC) Isoleucine (AUC) Threonine (ACC) A Arginine (AGA) Isoleucine (AUA) Threonine (ACA) Lysine (AAA) G Arginine (AGG) Methionine;Start (AUG) Threonine (ACG) Lysine (AAG) G Glycine (GGU) U Valine (GUU) Alanine (GCU) Aspartate (GAU) Valine (GUC) Aspartate (GAC) Glycine (GGC) Glycine (GGC) C Alanine (GCC) A Glycine (GGA) Alanine (GCA) Glutamate (GAA) Valine (GUA) Glutamate (GAG) Glycine (GGG) Alanine (GCG) G Valine (GUG)

  7. Section 11.2 Summary – pages 288 - 295 -60 codons code for general amino acids. -4 codons code for starting or stopping translation AUG = Start UAA =Stop UAG = Stop know these four!! UGA = Stop -More than one codon can code for the same amino acid (redundancy). -However, for any one codon, there can be only one amino acid.

  8. Section 11.2 Summary – pages 288 - 295 • All organisms use the same genetic code. • This evidence supports the theory that all life on Earth evolved from a common origin.

  9. Section 11.2 Summary – pages 288 - 295 Translation: From mRNA to Protein • The process of converting the info in codons in mRNA into a sequence of amino acids in a protein is known as translation. • Translation takes place at the ribosomes in the cytoplasm.

  10. Section 11.2 Summary – pages 288 - 295 • In eukaryotic cells, mRNA is made in the nucleus and travels to the cytoplasm. • In the cytoplasm, a ribosome attaches to the strand of mRNA like a clothespin clamped onto a clothesline.

  11. Section 11.2 Summary – pages 288 - 295 transfer RNA (tRNA) --For proteins to be built, the 20 different amino acids dissolved in the cytoplasm must be supplied to the ribosomes. --tRNA supplies the 20 different amino acids to the ribosomes.

  12. Section 11.2 Summary – pages 288 - 295 transfer RNA Amino acid -Each tRNA attaches to only one type of amino acid. -Each tRNA has an anticodon that is complementary to a codon on the mRNA. Chain of RNA nucleotides Transfer RNA molecule Anticondon

  13. Section 11.2 Summary – pages 288 - 295 -The ribosome will read or translate the mRNA codons into amino acids and link them together to form a long chain. Ribosome mRNA codon

  14. Section 11.2 Summary – pages 288 - 295 Translation

  15. Section 11.2 Summary – pages 288 - 295 -The first codon on mRNA is AUG, which codes for the amino acid methionine. -AUG signals the start of protein synthesis or translation.

  16. Section 11.2 Summary – pages 288 - 295 Methionine tRNA anticodon

  17. Section 11.2 Summary – pages 288 - 295 -The ribosome then slides along the mRNA to the next codon. -A new tRNA molecule carrying another amino acid pairs with the second mRNA codon. Alanine

  18. Section 11.2 Summary – pages 288- 295 -The first two amino acids are joined when a peptide bond is formed between them. Methionine Alanine Peptide bond

  19. Section 11.2 Summary – pages 288 - 295 -Each mRNA codon is translated forming a chain of amino acids. -The process continues until a stop codon is reached on the mRNA strand. Stop codon

  20. -The stop codon does not code for an amino acid but for a release factor. -The release factor caused the ribosome, mRNA, and new protein to come apart. -The mRNA and ribosome can be used over and over again to make multiple copies of the same protein or any other protein.

  21. DNA mRNA tRNA Amino Acid codon anticodon AAT UCA CCG Try

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