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DNA and Genes Chapter 11
(Proteins or Nucleic Acids) Nucleic Acids Proteins Scientists spent many years trying to determine which macromolecule was the source of genetic information for all cells.
Hershey and Chase Bacteriophage: a type of virus that attacks bacteria Viruses can not replicate themselves, they must inject their genetic material into a living cell in order to reproduce Viruses are only made of DNA and Protein Performed experiments infecting bacteria with radioactively labeled bacteriophages.
Hershey and Chase • The goal was to track what part the bacteriophage was injecting into the bacteria (the DNA or the Protein) Conclusion: Genetic material injected into the bacteria was in the form of DNA, not proteins.
What is DNA? • The genetic information determines an organism’s 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 thinking • Within the structure of DNA is the information for life—the complete instructions for manufacturing all the proteins for an organism.
The structure of nucleotides • DNA can hold all of its information because it is a very long molecule. (Polymer) • The repeating subunits are known as nucleotides • Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base.
Section 11.1 Summary – pages 281 - 287 The structure of nucleotides • The simple sugar in DNA, called deoxyribose(deeahksih RI bos), gives DNA its name—deoxyribonucleic acid. • The phosphate groupis composed of one atom of phosphorus surrounded by four oxygen atoms.
The structure of nucleotides A 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.
Erwin Chargaff • Used 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 - 287 The structure of nucleotides Result: Chargaff’s Rule Cytosine only matches to Guanine (C=G) and Adenine only matches to Thymine (A=T)
Complementary Base Pairs • 1 Purine (double ringed) + 1 Pyrimidine (single ringed) • Adenine + Thymine • Guanine + Cytosine
Section 11.1 Summary – pages 281 - 287 Watson and Crick • Published a 1 page letter • They 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.
The importance of nucleotide sequences Section 11.1 Summary – pages 281 - 287 The 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. Chromosome
The importance of nucleotide sequences Section 11.1 Summary – pages 281 - 287 Scientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims.