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Chapter 12: DNA, RNA and Protein Synthesis Name __________________ Section 12-1 I. Important DNA experiments A. Griffith (1928) discovered transformation – genetic information can be transferred from one living thing to another (fig. 12-2) B. Avery (1944) discovered that DNA stores and transmits genetic information C. Hershey and Chase (1952) discovered that the genetic information in a virus is DNA, not protein. (fig. 12-3 and 12-4) II. Structure of DNA A. DNA is made of nucleotides. (fig 12-5) a. Nucleotides are made of a: 1. phosphate group 2. sugar 3. base (A = adenine; T = thymine; C = cytosine; G = guanine) B. Chargoff’s base-pairing rules: (fig 12-6) a. Showed that the percentages of the bases A and T are approximately equal and C and T are approximately equal b. Therefore, in DNA, A pairs with T; C pairs with G C. Rosalind Franklin (1952) used X-ray diffraction to study the structure of DNA D. Watson and Crick (1953) made a model of DNA (fig 12-7) a. Showed that DNA was a double stranded molecule, called a double helix b. DNA is 2 strands of nucleotides wrapped around each other, and connected by base pairs in the middle, forming a twisted ladder shape Section 12-2: DNA Replication I. Chromosomes are made of DNA. Chromosomes must copy before a cell can divide Chromosome differences between prokaryotes and eukaryotes: Prokaryotes Eukaryotes Chromosomes in cytoplasm (no nucleus) Chromosomes in nucleus Contain 1 chromosome that is circular Contain many chromosomes See figure 12-8 See figure 12-10 Chromosomes contain DNA wrapped around proteins. II. Chromatin – substance made of DNA wrapped around proteins. The proteins are called histones. III. Genes – sections of DNA that control protein production IV. DNA replication – how DNA is copied A. Steps of DNA replication: 1. DNA strands separate “unzip” 2. Two new strands form, called complementary strands 3. DNA polymerase forms the new strands DNA replication follows the base pairing rules. Example: old strand: A T T A C G G G A A G C new strand: T A A T G C C C T TCG Section 12-3: Protein Synthesis – how proteins are made I. RNA reads the message in DNA and helps to make proteins II. Differences between DNA and RNA: DNA RNA Double stranded Single stranded Contains deoxyribose sugar Contains Thymine (T) Contains ribose sugar Contains Uracil (U) instead of thymine III. Proteins are made of many amino acids linked together. IV. Proteins are made in ribosomes. Types of RNA Function Messenger RNA (mRNA) Makes a copy of a section of DNA and brings it to ribosome Transfer RNA (tRNA) Brings amino acids to the ribosome to form protein Ribosomal RNA (rRNA) Makes of part of the ribosome V. Steps of protein synthesis: (*fig 12-18) A. Transcription – RNA makes a complementary copy of a section of DNA and takes to ribosome ex: DNA strand: A A T T G G C C C RNA copy: U U A A C C G G G a. DNA contains coding regions called exons and noncoding regions called introns (RNA only takes copy of exons to ribosome) B. Translation – tRNA read bases in mRNA and bring amino acids to ribosome in correct sequence using the genetic code Genetic Code: (fig 12-17) -mRNA is read by tRNA 3 bases at a time. -Each 3 base sequence is called a codon -Each codon codes for a certain amino acid (there are 20 different amino acids) C. Protein assembly – the ribosome moves along the mRNA, connecting new tRNA molecules and amino acids Example of protein synthesis: Strand of DNA: TAC GCA mRNA codon: AUG CGU tRNA anticodon: UAC GCA amino acids: Met - Arg - TGG ACC UGG Thr - AAT UUA A AU Leu- Section 12-4: Mutations I. Mutation – A change in a gene. Mutations are a source of genetic variation. Not all mutations are harmful! A. Two types of mutations: a. Point mutations – change in a single base (see fig 12-20) 1. Substitution – one base is substituted for another Original Sequence: DNA: GCA TAT ATG mRNA: CGU AUA UAC amino acid: Arg- Iso- TyrAfter Substitution: DNA: GTA TAT ATG mRNA: CAU AUA UAC amino acid: Hist- Iso- Tyr2. Frameshift mutations: *harmful point mutations because they change the “reading frame” i. insertion – an extra base in inserted ii. Substitution deletion – a base is left out Insertion Deletion b. Chromosomal mutations – change in a structure of chromosome (see fig 12-21)