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UNIT 6 – DNA Chapters 12 & 13 12.1: The Role of DNA The Role of DNA • Storing information—genes found within DNA control cell functions • Copying information—all genetic information copied before cell division • Transmitting information—new cells get copies of DNA 12.2: The Structure of DNA The Components of DNA • DNA • is composed of chains of nucleotides Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base • DNA • has 4 kinds of nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T) • Nucleotides bond between sugar of one nucleotide and phosphate of another • Nitrogenous bases stick out sideways Solving the Structure of DNA • Rosalind Franklin used X-rays to show DNA was twisted into a helix shape • James Watson & Francis Crick used Franklin’s work to show DNA as a double helix The Double-Helix Model • DNA consists of 2 strands twisted around each other • Nitrogenous bases joined by hydrogen bonds in the center of the double helix • Base pairing—nitrogenous bases only pair with certain bases • • Adenine (A) with Thymine (T) Guanine (G) with Cytosine (C) 12.3: DNA Replication Copying the Code • Each strand of DNA has the information to make copies of the other strand • Replication—the process that duplicates DNA • • DNA separates into 2 strands Each strand acts as a model for a new strand • Process 1. 2. of replication Two strands of DNA “unzip” in nucleus New strand forms by adding base pairs to “parent strand” of DNA • If A is on parent strand, a new T pairs with strand; C with G; etc. • Replication produces 2 DNA molecules identical to each other • Half of DNA is old strand, half is new strand • Enzymes • • are used to help replication Enzymes “unzip” DNA to begin replication DNA polymerase joins individual nucleotides to produce a new DNA strand and proofreads DNA strand 13.1: RNA The Role of RNA • RNA (ribonucleic acid)—nucleic acid that produces proteins from DNA’s genetic code • Differences • • • between RNA & DNA: RNA has ribose (not deoxyribose) RNA is single-stranded (not double-stranded) RNA contains Uracil (U) (instead of thymine) • Functions • • • of RNA: Messenger RNA (mRNA)—carry information from DNA to other parts of the cell Ribosomal RNA (rRNA)—compose ribosomes Transfer RNA (tRNA)—transfers amino acids to ribosome to build proteins RNA Synthesis • Transcription—production of RNA molecules using segments of DNA • Uses the enzyme RNA polymerase • Process 1. 2. 3. 4. of transcription DNA strands separated in nucleus One strand of DNA used as a template for RNA strand Uracil (U) pairs with A instead of T • G and C pair normally Messenger RNA (mRNA) strand leaves nucleus Transcription Animation 13.2: Ribosomes & Protein Synthesis The Genetic Code • RNA contains code from DNA for making proteins • Genetic code—series of three letters (A, C, G, or U) that forms an amino acid • Codon—three-letter series in mRNA • Codons form a code for different amino acids • AUG = start codon (starts protein synthesis) Translation • Translation—decodes an mRNA message into a protein • Uses ribosomes & tRNA molecules • tRNA • • molecules join with mRNA molecules Carries one amino acid tRNA has an anticodon—three letters complementary to codon • Process 1. 2. 3. 4. 5. of translation mRNA strand attaches to ribosome tRNA anticodon binds to “start” codon (AUG) on mRNA Another tRNA binds to mRNA strand Amino acid on first tRNA transferred to second tRNA, forming a protein chain Process continues until “stop” codon is reached Translation Animation 13.3: Mutations Types of Mutations • Mutations—changes in genetic information • Result from changes in single gene or changes in whole chromosomes • Point mutations—changes in one or a few nucleotides • • • Substitutions—one base changed to another (may have no effect) Insertions—one base added (major effect) Deletions—one base deleted (major effect) • Insertions & deletions also called frameshift mutations—change the entire genetic message after the mutation Effects of Mutations • Mutagens—chemical or physical agents that cause mutations • Ex: pesticides, tobacco smoke, radiation • Harmful effects of mutations: genetic disorders, cancers, lack of cell function • Helpful effects of mutations: resistance to chemicals, larger & stronger crops