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!!!

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 =41aqxcxsX2w&feature=related =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)

DNA Scientists Erwin Chargaff’s Rule – Base pairing – A-T and C-G Rosalind Franklin – Used x-ray diffraction to study DNA and gain information about it’s structure James Watson & Francis Crick (1953): – Double Helix model from evidence from Franklins x- ray 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

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