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RNA and Protein Synthesis Chapter 12, section 3 The Structure of RNA “Central Dogma” of Biology: DNA is “read” by RNA which then travels to the ribosomes to make proteins. DNA RNA Proteins The Structure of RNA RNA, like DNA, is made up of nucleotides However, there are 4 major differences between DNA and RNA: RNA has ribose instead of deoxyribose RNA has uracil instead of thymine RNA is single-stranded instead of doublestranded RNA is able to leave the nucleus. 3 Types of RNA Messenger RNA (mRNA) – carries the message from the DNA to the ribosomes Ribosomal RNA (rRNA) – make up part of the structure of a ribosome Transfer RNA (tRNA) – transfers amino acids to the ribosomes Transcription DNA mRNA Making RNA from DNA (in the nucleus) RNA polymerase binds to DNA and begins building a complementary strand of mRNA A will now pair with U, T still pairs with A C and G still pair with each other Why mRNA? mRNA can leave the nucleus! Transcription The Genetic Code DNA and RNA are “read” 3 bases at a time A codon is a 3 base sequence that codes (“signals”) for a specific amino acid There are 64 possible codons (3 letter combinations) Proteins are made of amino acids There are 20 different amino acids Practice Transcription… DNA – AGC TCC GAT GCA TAC TTG CCA mRNA– UCG AGG CUA CGU AUG AAC GGU DNA – GCC AGT GCT TAC GAA CTG AGT mRNA– CGG UCA CGA AUG CUU GAC UCA The Genetic Code RNA sequence: UCGAGGCUA Separate into codons: UCG-AGG-CUA Identify the “signaled” amino acids: Serine-Arginine-Leucine The Genetic Code Translation mRNA Proteins Making of proteins using the instructions from the mRNA message (“translating the code”) Occurs at the ribosomes Translation 1. 2. 3. Following transcription, mRNA leaves the nucleus and enters the cytoplasm. The mRNA attaches to the ribosome The tRNA brings the proper amino acid to the ribosome Anticodon – sequence of bases on the tRNA that pair with the mRNA Translation 4. 5. 6. The amino acids form a peptide bond to hold them together. The next amino acid is brought in and is attached This continues until the ribosome reaches a stop codon The completed protein (polypeptide chain) is then released Translation Mutations Changes in the DNA sequence that affect genetic information Gene mutations – result from changes in a single gene. A gene carries the “recipe” for a single protein. Chromosomal mutations – involve changes in whole chromosomes Mutations Body-cell v. Sex-cell Mutation Somatic cell mutations are not passed on to the next generation. Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring. Gene Mutations Point mutations – a mutation that occurs at a single point (only 1 nitrogen base) Substitution – a single nucleotide is substituted for another one (A instead of G) Frameshift mutations– a mutation that occurs when a nucleotide is inserted or deleted Insertion – a nucleotide is added Deletion – a nucleotide is removed Gene Mutations Insertions and deletions cause frameshift mutations because they shift the “reading frame” of the genetic message. Gene Mutations