Chapter 12 – DNA Chapter 13 – RNA and Protein Synthesis

Proof that DNA Controls Traits Living bacteria and dead bacteria killed mouse Harmless bacteria picked up DNA from harmful bacteria – changed into harmful bacteria

Solving the Structure of DNA 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 http://www.youtube.com/watch?v=JiME-W58KpU

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

DNA and Chromosomes

How DNA Works 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.

How DNA Copies Itself DNA ready to make a copy of itself Molecule opens up in middle 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. Two DNA molecules form. They are exactly alike. http://www.youtube.com/watch?v=z685FFqmrpo&feature=related http://www.youtube.com/watch?v=hfZ8o9D1tus&feature=related

Comparing RNA and DNA Three important differences: The sugar in RNA is ribose instead of deoxyribose. RNA is single-stranded. RNA contains uracil in place of thymine.

Functions of RNA 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.

Making Proteins 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

Making Proteins 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.

Protein Examples Protein Function Examples Effect if Protein is Missing Enzyme Enzyme for synthesizing melanin (pigment that gives our skin and hair color) Albinism (very pale skin and hair) Lactase (breaks down lactose) Lactose intolerance (difficulty digesting milk) Acetaldehyde dehydrogenase (breaks down acetaldehyde, a harmful product of alcohol metabolism) Alcohol sensitivity (skin flushing and unpleasant symptoms after drinking alcohol) Transport Hemoglobin (protein in red blood cells which transports oxygen in the blood) Sickle cell anemia Clotting Hemophilia (excessive bleeding)

The Genetic Code 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.

Mutations 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.

Effects of Mutations 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.

Who was Rosalind Franklin? What does DNA stand for? What are the four nitrogen bases? What pairs together? In what three differences between DNA and RNA? What are the three types are RNA and what are their functions? Where are proteins made? What is transcription? What is translation? What are polypeptides? What is a codon? What is a substitution mutation? What is an insertion or deletion mutation? What are they also known as? What is a mutagen?