Chapter 12: DNA Lab Biology CP Chapter 12: DNA • 12.1 Identifying the Substance of Genes • 12.2 The Structure of DNA • 12.3 DNA Replication 12.1 Identifying the Substance in Genes Genes – A section of DNA on a chromosome in a nucleus – Each chromosome contains hundreds of genes – contains most of your characteristics: hair color, skin color, how things taste to you, etc. – Contains the instructions for making a specific protein – Determines the order of amino acids in making proteins Bacterial Transformation Frederick Griffith’s Experiment • Injected mice with 4 different samples of bacteria • Heat-killed diseasing causing bacteria injected mice LIVED • Live, harmless bacteria injected mice LIVED • The 2 strains together caused fatal pneumonia • Concluded: genetic info could be transferred from one bacterial strain to another • Transformation: when one type of bacteria (harmless) changed permanently into another (disease causing form) • The transforming factor must be a GENE!!! http://www.youtube.com/watch?v=eovTbQgan5M Griffith’s Experiment Oswald Avery’s Experiment • By observing bacterial transformation, he discovered that DNA stores and transmits genetic information from one generation to the next. • DNA is responsible for transformation Avery’s Experiment Bacterial Viruses • Bacteriophage: a virus that infects bacteria • http://www.youtube.com/watch?v =41aqxcxsX2w&feature=related The Hershey-Chase Experiment • Studied a bacteriophage composed of a DNA core and a protein coat • They wanted to determine what part entered the bacterial cell (the DNA or protein coat) • Used radioactive markers to label the DNA and proteins • Results: The bacteriophages only injected DNA, not proteins, into the bacterial cells The Role of DNA • The DNA that makes up genes must be capable of: – 1.) storing, – 2.) copying, – 3.) transmitting, and the genetic information in a cell 12.2 The Structure of DNA DNA • Deoxyribonucleic Acid Structure of DNA • Double-stranded • Double-helix • Side ladders: – Sugar (deoxyribose) and phosphate group – Held together by hydrogen bonds • Steps of ladder: – 4 nitrogen bases (nucleotides) • A-T (adenine and thymine) • C-G (cytosine and guanine) http://www.youtube.com/watch?v=qy8dk5iS1f0 DNA Scientists • Erwin Chargaff’s Rule – Base pairing – A-T and C-G • http://www.youtube.com/watch?v=VIlF6fovLZE&feature=related • Rosalind Franklin – Used x-ray diffraction to study DNA and gain information about it’s structure • http://www.youtube.com/watch?v=VIlF6fovLZE&feature=related • James Watson & Francis Crick (1953): – Double Helix model from evidence from Franklins xray pattern 12.3 DNA Replication • DNA unzips and new base pairs are formed 2 new strands of DNA DNA Replication • • • • • DNA must get copied BEFORE a cell can divide Occurs during late interphase (S phase) DNA “unzips” into 2 strands 2 new complementary strands are produced Each new copy has one original strand and one new strand • DNA polymerase: An enzyme that joins individual nucleotides to produce a new strand of DNA http://www.youtube.com/watch?v=teV62zrm2P0&feature=related Telomeres • Telomeres: – DNA at the tips of chromosomes – Very difficult to replicate • Telomerase: a special enzyme to solve this problem by adding short, repeated DNA sequences to the telomeres – Often switched off in adult cells – In cancer, telomerase may be activated to enable cancer cells to grow rapidly DNA Replication in Prokaryotes and Eukaryotes • Prokaryotes: – have a singular, circular DNA – in the cytoplasm – Begins at a single point • Eukaryotes: – – – – – have 1000x more DNA than prokaryotes Found in the nucleus Packed into chromosomes DNA and proteins packed together: chromatin Can begin at hundreds of places
