DNA and Genes

DNA and GenesChapter 11 Scientists spent many years trying to determine which macromolecule was the source of genetic information for all cells.

(Proteins or Nucleic Acids)ProteinsNucleic AcidsHershey and ChaseViruses can not replicate themselves, they must inject their genetic material into a living cell in order to reproduceViruses are only made of DNA and Protein Performed experiments infecting bacteria with radioactively labeled bacteriophages.

Bacteriophage: a type of virus that attacks bacteriaHershey and Chase Conclusion: Genetic material injected into the bacteria was in the form of DNA, not proteins.

The goal was to track what part the bacteriophage was injecting into the bacteria (the DNA or the Protein)The genetic information determines an organisms traits.DNA achieves its control by determining the structure of proteins.Enzymes (a type of protein) control the chemical reactions needed for life.Eating, running, even thinkingWithin the structure of DNA is the information for lifethe complete instructions for manufacturing all the proteins for an organism.

What is DNA?DNA can hold all of its information because it is a very long molecule. (Polymer)The repeating subunits are known as nucleotidesNucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base.The structure of nucleotides

Section 11.1 Summary pages 281 - 287The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms.The simple sugar in DNA, called deoxyribose (dee ahk sih RI bos), gives DNA its namedeoxyribonucleic acid.The structure of nucleotidesA nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen.There are Single-Ringed bases (Pyrimidines) and Double-Ringed bases (Purines). The structure of nucleotides

Nucleotides join together to form long chains.Phosphate group of one nucleotide bonds to the deoxyribose sugar of an adjacent nucleotide.The phosphate groups and deoxyribose (sugar) molecules form the backbone of the chain, and the nitrogenous bases stick out like the teeth of a zipper.

The structure of nucleotides

Erwin ChargaffUsed chemical analysis to provided evidence of a relationship among the nitrogen bases of DNA.Found that the amounts of guanine nearly equals the amount of cytosine and the amounts of adenine nearly equals the amount of thymine within a species.

Section 11.1 Summary pages 281 - 287The structure of nucleotidesResult: Chargaffs Rule Cytosine only matches to Guanine (C=G) and Adenine only matches to Thymine (A=T)Complementary Base Pairs1 Purine (double ringed) + 1 Pyrimidine (single ringed)Adenine + ThymineGuanine + Cytosine

Section 11.1 Summary pages 281 - 287Published a 1 page letterThey proposed that DNA is made of two chains of nucleotides held together at the nitrogenous bases by hydrogen bonds.Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring.Because DNA is composed of two strands twisted together, its shape is called double helix.

Watson and CrickStructure of DNA

Section 11.1 Summary pages 281 - 287The importance of nucleotide sequencesChromosomeThe sequence of nucleotides forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.

Section 11.1 Summary pages 281 - 287The importance of nucleotide sequencesScientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims.