DNA And Protein Synthesis (8.1-8.4)

8.1 - The Discovery of DNA’s Function

Objectives: Identify the 4 properties required of every genetic material, Summarize the classic experiments determining that DNA is genetic material

Classic Experiments Determining that DNA Is Genetic Material

• DNA was first described by Mischer, who determined the following:

  • DNA is not a protein
  • DNA is rich in nitrogen and phosphorus
  • Never learned DNA function

• Griffin got a hint of DNA’s function (hereditary information)

  • Studied 2 bacteria, one harmless and one harmful, and found that heat destroyed the harmful bacteria’s ability to cause disease but not its hereditary material

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Oswald, Avery, MacLeod, and McCarty identified that the principle must be a nucleic acid. It used enzymes that destroyed DNA and RNA to decide which one it was, and came to the conclusion it was DNA.

• Prior to this, scientists believed that proteins controlled heredity, not nucleic acids

  • DNA was assumed to be too simple

• They published their findings and concluded that DNA must be genetic material

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Four Properties Required Of Genetic Material

Their discovery prompted new scientists to do further research:

• Confirmed DNA’s ability to carry genetic information

  • Realized that any molecule had to have a certain set of properties to store hereditary information. These are the following:

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1. Hereditary information must be passed on from one generation to the next

2. Cells of a certain species should contain the same amount of it

3. Not susceptible to major change

4. Must be able to encode a huge amount of information to build life

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How does DNA fulfill these requirements?

• Transmits full hereditary information

• Body cells of certain species had all the same amounts of DNA

• DNA is not involved in metabolism, therefore, its content does not change over time

• DNA’s structure allows it to encode large amounts of genetic information

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8.2 - Discovery of DNA’s Structure

Objectives: Summarize the events that led to the discovery of DNA’s structure, identify the subunits of DNA and how they combine into a DNA molecule, explain how DNA holds information, describe base pairing

Subunits Of DNA and How They Combine into a DNA Molecule

DNA is a polymer of 4 different nucleotides:

1. Adenine
2. Guanine
3. Thymine
4. Cytosine

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Each has 3 phosphate groups, deoxyribose sugar, and a nitrogenous base.

\n Events that led to the Discovery of DNA’s Structure

Chargaff made 2 important discoveries about DNA’s structure:

• Amounts of thymine and adenine are identical in any DNA molecule, and Amounts of cytosine and guanine are identical in any DNA molecule

  • Chargaff’s First RUle

• DNA of different species differs in proportion of adenine and guanine

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Watson and Crickhat been theorizing about DNA’s structure.

• Used an X-ray to decipher shape, size, spacing between elements

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• Since DNA was large, it was hard to crystallize w/ techniques of the time

  • Identified a repeating pattern and length

Base Pairing

• Thus, DNA is characterized by the following:

  • 2 chains/strands of nucleotides in opposite directions, in a double helix
  • Covalent bonds link deoxyribose to phosphate groups, leading to sugar-phosphate backbone
  • Hydrogen bonds hold the pair of strands together
  • Only Adenine to Thymine and Cytosine to Guanine

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How DNA Holds Information

DNA sequence is the order of nucleotides bases, greatly differ from organism to organism. DNA molecules can hold hundreds of millions of nucleotides, thus, a sequence of nucleotides can hold a lot of information.

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