 Living bacteria and dead bacteria killed mouse  Harmless bacteria picked up DNA from harmful bacteria – changed into harmful bacteria

 Chargaff’s Rule – Percentages of adenine = thymine, percentages of guanine = cytosine.  Rosalind Franklin – used X-ray diffraction › X-shaped pattern showed shape › 1952  Watson and Crick › James Watson – American biologist › Francis Crick – British physicist › The clues in Franklin’s X-ray pattern enabled Watson and Crick to build a model that explained the specific structures and properties of DNA – 1953 ›

 DNA = Deoxyribonucleic acid – a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds.  Nucleotides – three basic components: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base. › Nitrogenous bases – Adenine, Guanine, Cytosine, Thymine

 Features: 1. Two main sides – ladder 2. Double-helix structure 3. Four nitrogen bases – A,T,C,G  A always pairs with T  C always pairs with G 4. DNA polymerase – an enzyme that joins individual nucleotides to produce a new strand of DNA.

 The order of nitrogen bases, A, T, C, and G, is the coded message › A – T › C - G › The order of the bases can be slightly different and cause traits to be very different  Sickle cell anemia › Nitrogen bases make new messages – similar to the alphabet  Letters w, o, and l form the word owl. They also form the word low.

1. DNA ready to make a copy of itself 2. Molecule opens up in middle 3. DNA polymerase molecule runs along original DNA strand. Loose nitrogen bases are present in nucleus. DNA polymerase joins bases on the open rungs. A pairs with T and C pairs with G. 4. Two DNA molecules form. They are exactly alike. feature=related eature=related

 Three important differences: 1. The sugar in RNA is ribose instead of deoxyribose. 2. RNA is single-stranded. 3. RNA contains uracil in place of thymine.

 Messenger RNA (mRNA) – carry information from DNA to other parts of the cell.  Ribosomal RNA (rRNA) – Make up ribosomes, where proteins are made.  Transfer RNA (tRNA) – transfers each amino acid to the ribosome as it is specified by the coded messages in mRNA.

 Where are proteins made? › Ribosomes  How can DNA in the nucleus control what happens at the ribosomes? › RNA – ribonucleic acid – a chemical that acts as a messenger for DNA  Carries coded DNA message from nucleus to ribosomes › Transcription – the process of making RNA from a DNA template

 RNA arrives at ribosomes, and must be decoded. › Translation – the synthesis of a protein from an mRNA template  Once message is translated, protein is made.  Kinds of proteins determine traits you have.

 Polypeptides – proteins are made by joining amino acids together into long chains.  The genetic code is read three “letters” at a time, so that each “word” is three bases long and corresponds to a single amino acid. › Codon – each three-letter “word” in mRNA. › Anticodon – each tRNA molecule has three unpaired bases. Complementary to one mRNA codon.

 Any change in copying the DNA message › Bases A, T, C, and G may join incorrectly  Point mutations – occur at a single point in the DNA sequence. › Substitutions – one base changed to a different base. › Insertions and Deletions – one base inserted or removed.  Also called frameshift mutations – shift the “reading frame” of the genetic message. Change every amino acid that follows the point of the mutation.

 Mutagens – chemical and physical agents in the environment. › Pesticides, tobacco smoke, X-rays, UV light  Harmful and Helpful Mutations – › Sickle cell disease – disorder associated with changes in the shape of red blood cells. › Beneficial – mosquitoes becoming pesticide resistant.