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RNA and Protein Synthesis

RNA and Protein Synthesis. The Function of DNA. The DNA molecule contains all of your hereditary information in the form of genes. Genes are portions of the DNA molecule that code for the production of specific types of proteins.

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RNA and Protein Synthesis

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  1. RNA and Protein Synthesis

  2. The Function of DNA • The DNA molecule contains all of your hereditary information in the form of genes. • Genes are portions of the DNA molecule that code for the production of specific types of proteins. • However, DNA is confined to the nucleus, while proteins are made by ribosomes in the cytoplasm. • Thus, a messenger molecule is needed. http://www.accessexcellence.org/RC/VL/GG/images/genes.gif

  3. Comparing DNA and RNA • RNA is the nucleic acid that acts as a messenger between DNA and the ribosomes. • The RNA produced during transcription is structurally different from DNA in 3 basic ways: • 1. The sugar in RNA is ribose whereas the sugar in DNA is deoxyribose. • 2. RNA is single stranded while DNA is double stranded. • 3. RNA contains a base called uracil instead of thymine. http://www.dkimages.com/discover/previews/769/85011519.JPG

  4. Protein Synthesis • During protein synthesis, genes copied onto RNA are expressed by the production of specific types of proteins. • Protein synthesis involves two processes: • 1. Transcription – the process where a portion of the DNA sequence is copied into a complementary RNA sequence. • 2. Translation – the decoding of an mRNA message into a polypeptide chain (protein).

  5. Transcription • Transcription occurs on the DNA in the nucleus. • Transcription Demo

  6. Types of RNA • The RNA produced during transcription is modified into 3 basic types: • 1. messenger RNA (mRNA) is responsible for copying one strand of DNA in the nucleus and carrying that information to the ribosomes in the cytoplasm. • 2. ribosomal RNA (rRNA) makes up a large part of the ribosome and is responsible for reading and decoding mRNA. • 3. transfer RNA (tRNA) carries amino acids to the ribosome where they are joined to form proteins. http://images.encarta.msn.com/xrefmedia/zencmed/targets/illus/ilt/T068340A.gif

  7. Translation • Translation is completed by the ribosomes located in the cell’s cytoplasm. • All three types of RNA work together during translation to produce polypeptides (proteins). • Translation Demo

  8. Decoding mRNA • The sequence of bases in an mRNA molecule serves as instructions for the order in which amino acids are joined to produce a polypeptide. • Ribosomes decode these instructions by using codons, sets of 3 bases that each code for 1 amino acid. • Each codon is matched to an anticodon, or coplementary sequence on the tRNA to determine the order of the amino acids. http://www.gwu.edu/~darwin/BiSc150/One/codon.gif

  9. Using a Codon Chart • When given a sequence of mRNA bases, a codon chart can be used to determine the sequence of the amino acids in the polypeptide. http://www.safarikscience.org/biologyhome/7_dna/codon_question.png

  10. Decoding Practice • For the following examples, give the appropriate mRNA sequence and amino acid sequence. (Remember: U replaces T in mRNA.) Example 1: DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA Amino Acids: Met Arg Thr Leu Example 2: DNA: CGT GGA GAT ATT mRNA: GCA CCU CUA UAA tRNA: CGU GGA GAU AUU Amino Acids: Ala Pro Leu stop

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