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MR. SURRETTE VAN NUYS HIGH SCHOOL CHAPTER 18: NUCLEIC ACIDS CLASS NOTES NUCLEIC ACIDS Nucleic acids consist of DNA and RNA. They make up the genetic code and control the cell. Chromosomes are long strands of nucleic acids wrapped and folded around proteins called histones. DNA The chromosomal DNA, deoxyribonucleic acid, consists of four nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C). DNA NUCLEOTIDES Adenine, thymine, guanine, and cytosine are composed of a deoxyribose sugar, a phosphate group, and a single or double- ringed base. DNA STRUCTURE The double helix structure of DNA was discovered by James Watson and Francis Crick in 1953. The sugar and phosphate components join together by dehydration synthesis to form a strand of nucleotides. The two strands line up looking like a two-dimensional ladder. THE DNA DOUBLE-HELIX 1|Page INTEGRATED SCIENCE MR. SURRETTE VAN NUYS HIGH SCHOOL DNA STRUCTURE Adenine on one strand always matches a thymine on the other. Guanine is always matched with cytosine. RNA Another form of nucleic acid, ribonucleic acid (RNA) transcribes the code from sections of the chromosomes, carries this copy to the cytoplasm of the cell, and constructs proteins. This allows the nucleus to control the activities of the cell. RNA RNA is found in the nucleus and in the cytoplasm of cells. It conducts the synthesis of proteins. RNA VERSUS DNA The structure of RNA is similar to DNA, but there are three major differences: 1. RNA is single stranded. 2. The base sugar for RNA is ribose (not deoxyribose) 3. RNA has a uracil (U) nucleotide instead of thymine (T). The uracil pairs with adenine on the DNA strand. REPLICATION During replication (the copying of the double helix) the two strands separate so that the matched bases are unmatched. New complementary strands are made on each of the original strands, resulting in two double strands. DNA REPLICATION 2|Page INTEGRATED SCIENCE MR. SURRETTE VAN NUYS HIGH SCHOOL REPLICATION The duplication of DNA is called semiconservative replication, because one new half is joined to each old half to create two new DNA strands. DNA CODE The DNA code is a sequence of three nucleotides: ATA (adenine, thymine, adenine), CCG, TCA, and so forth. This sequence of triplets in the DNA determines the sequence of amino acids in the protein that is produced. THE CENTRAL DOGMA “DNA replicates itself and is able to transcribe and translate itself into proteins.” CENTRAL DOGMA DIAGRAM 3|Page INTEGRATED SCIENCE MR. SURRETTE VAN NUYS HIGH SCHOOL TRANSCRIPTION Transcription is similar to replication except that only one strand of DNA is copied. This single strand of DNA is copied onto RNA nucleotides. This process begins with initiation as RNA polymerase attaches to a section of DNA. TRANSCRIPTION RNA nucleotides find their complementary DNA bases and are joined in a long strand. The nucleotides of the growing RNA strand peel away as messenger RNA (mRNA). TRANSLATION Translation is the process where a cell reads the mRNA and makes amino acid chains (proteins). TRANSLATION Genes (sequences of nucleotides on DNA molecules) express themselves by controlling the sequence of amino acids in proteins that are manufactured in the cell. For example, the DNA sequence AGT will be copied as UCA by the messenger RNA. This produces the amino acid serine. Nucleotide triplets are called codons. TRANSLATION Transfer RNA (tRNA) are small and roughly “L” shaped. They do their work in the cytoplasm. The most important feature of tRNA is a group of three nucleotides called the anticodon, at the bottom of the “L.” Every anticodon is complementary to a particular mRNA codon. 4|Page INTEGRATED SCIENCE