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DNA, RNA, and Protein Synthesis Notes 2006 I. DNA A. The Genetic Code 1. Most of the cells in living things contain DNA. 2. DNA stores the information of life. It contributes to making you the person that you are. 3. DNA codes for proteins which contribute to determining the physical characteristics of an organism. 4. Genetic code-how the information of life is stored in a cell’s DNA. B. DNA structure 1. DNA is a polymer that is formed by units of nucleotides. All nucleotides in DNA have 3 parts: a 5 carbon sugar (deoxyribose), a phosphate group, and a nitrogen containing base. 2.Nitrogen containing bases (nitrogenous bases) a. purines 1. adenine 2. guanine b. pyrimidines 1. cytosine 2. thymine 3. Individual nucleotides join together to form a molecule of DNA. 4. Nitrogenous bases do what is called base pairing. 5. Base pairing-attraction between complementary nitrogenous bases that produces a force that holds the two strands of DNA together 6. In DNA, adenine and thymine are complementary to each other, so are cytosine and guanine. 7. DNA molecules are in the shape of a double helix. a. resembles a twisted ladder b. sugar-phosphate backbone is on outside c. nitrogenous bases are on the inside C. DNA Replication 1.The two strands that make up the double helix of DNA are complementary to each other. This means that you can tell what the one strand will look like by looking at the other strand. 2. Each strand of DNA serves as a pattern for a new strand to be made. 3. Replication-the copying of DNA, occurs prior to cell division and is facilitated by DNA polymerases (special enzymes). 4. During replication a. the two strands of the double helix get unzipped b. matching bases are inserted c. sugar phosphate links are created 5. The scientists James Watson and Francis Crick were the first to describe the structure of DNA and how it replicates. II. RNA A. RNA Structure 1. composed of a 5 carbon sugar (ribose), a phosphate group, and a nitrogenous base 2. differences with DNA a. 5 carbon sugar is ribose not deoxyribose b. nitrogenous bases are adenine, cytosine, guanine, and uracil c. single stranded molecule as opposed to double stranded B. Types of RNA 1. messenger RNA (mRNA) – carries information from the DNA to the ribosomes. 2. ribosomal RNA (rRNA) - type of RNA that makes up the major part of the ribosome. 3. transfer RNA (tRNA) – type of RNA that carries amino acids to the ribosomes where the amino acids join to form proteins. III. Protein synthesis – the process by which proteins are formed A. Transcription 1. definition– the process by which a molecule of DNA is copied into a complementary strand of mRNA. 2. mRNA carries the genetic code from DNA in the nucleus to the rribosomes in the cytoplasm. 3. RNA polymerase connects the RNA nucleotides to each other. 4. The synthesized strand of RNA is complementary to one of the DNA strands. B. The triplet code 1. proteins are formed from chains of amino acids 2. there are 20 different amino acids. 3. groups of 3 consecutive nucleotides (triplets) in mRNA strands code for different amino acids 4. codon- a group of three nucleotides on an mRNA strand that codes for an amino acid. 5. some codons are refered to as “stop codons” because they end an amino acid chain. C. Editing the RNA Message 1. In prokaryotic cells, the mRNA molecule that is transcribed from the gene directly serves as the code to make proteins. 2. In eukaryotic cells, the RNA is modified or processed before it is used to make proteins. 3. Introns-noncoding regions in mRNA (found in most plant and animal cells) 4. Exons-the parts of mRNA that are used to form proteins 5. RNA splicing-the process that occurs before the mRNA leaves the nucleus for translation. RNA splicing removes the introns and joins the exons together. D. Translation 1. definition-the process in which mRNA messages get decoded into proteins. 2. The process a. tRNA molecules have 3 bases on them that are complementary to the codons in mRNA. These base sequences are called anticodons b. attached to each tRNA molecule is an amino acid specified to the codon to which it base pairs c. by matching the anticodons of tRNA to the codons of mRNA, the correct amino acids are put into place d. the amino acids are then assembled by the ribosomes e. the chain of amino acids continues until a stop codon on the mRNA ends it.