NUCLEIC ACIDS Chapter 12 DNA and RNA

Where did we find Genes and who discovered them?  In 1928 Frederick Griffith tried to figure out how bacteria made people sick.  What caused pneumonia?  His experiments lead to the discovery of genes.

Frederick Griffith  Two different strains (types) of same bacteria, one strain caused pneumonia  Strain S – smooth colonies (cause disease)  Strain R – rough colonies (harmless)

 Griffith injected mice with disease-causing bacteria (Smooth strain), the mice developed pneumonia and died  He injected mice with harmless bacteria (Rough Strain), the mice stayed healthy.

 Griffith took a culture of the Smooth strain, heated the cells to kill them, and then injected the heat- killed bacteria into mice.  Mice survived.

 He mixed the heat-killed, S-strain bacteria with live, harmless bacteria R strain and injected it into laboratory mice  Injected mice developed pneumonia, and died.

 The heat-killed cells of the S strain (disease- causing) transferred its information into the live cells of the R strain (harmless) making it change from harmless to disease causing.  This is known as Transformation.

Transformation  Process where one strain of bacteria is changed by a gene from another strain of bacteria.

Avery  1944 Oswald Avery took Griffith’s work farther.  Extracted a mixture of various molecules from the heat-killed bacteria  Added enzymes one at a time that broke down proteins, lipids, carbohydrates, and RNA  Transformation still occurred.

 Avery’s team repeated the experiment using enzymes that would break down DNA  Transformation did not occur  DNA is the transforming factor.

Hershey and Chase  Experiment with bacteriophages  Confirmed Avery’s results.

Bacteriophages  Virus that infects bacteria  Attaches to the surface of the bacterial cell  Injects its genetic information so new bacteriophages are produced.

Hershey-Chase Experiment  What part of the virus - the protein coat or the DNA core - entered the bacterial cell?

Hershey-Chase Experiment  Grew viruses in cultures containing radioactive isotopes of phosphorus-32 (P-32) sulfur-35 (S-35)  Proteins contain almost no phosphorus and DNA contains no sulfur.

 If they found S-35 in the bacteria then the virus’s protein coat had been injected into the bacteria  If they found P-32 then the DNA core had been injected  They mixed the marked viruses with bacterial cells.

 In the bacteria they found phosphorus P-32, the marker found in DNA  DNA was the genetic material not the protein coat.

DNA  DNA is capable of storing, copying, and transmitting genetic information in a cell.  DNA  DNA is a long molecule made up of nucleotides.  Nucleotide: 5 carbon sugar (Deoxyribose) Nitrogen base Phosphate group  DNA  DNA is made up of 4 kinds of nitrogen bases……

Kinds of Nitrogen Bases  Adenine and Guanine: Purines  Purine bases have 2 ring structures  Cystosine and Thymine: Pyrimidines  Pyrimidine bases only have 1 ring structures

Components and Structure of Components and Structure of DNA DNA  The backbone of a DNA chain is made up of the sugar and phosphate groups of each nucleotide. Sugar and Phosphate Back Bone

Watson and Crick  Watson and Crick developed the DNA double helix model. Looks like a spiral staircase.  They discovered hydrogen bonds hold DNA together.  Confirmed base pairing.

Chromosomes and DNA  Where do we find DNA?  Eukaryotes – DNA is inside the nucleus. In the nucleus are chromosomes which store the DNA.  Prokaryotes – DNA is in cytoplasm

Chromosomes Structure  Each chromosome has DNA and proteins in it.  Chromatin: DNA coiled or wrapped around a histone (protein). Many histones packed together are called a nucleosome.  Basically a chromosome is made up of DNA wrapped around proteins, coiled together to form nucleosomes that coil up into supercoils called a CHROMOSOME.

The structure of a Chromosome DNA Double Helix Histones Nucleosomes Supercoils Chromosome