Chapter 10 DNA: The Chemical Nature of the Gene

Johann Friedrich Miescher

1868; studied white blood cells in pus; he did establish that the nuclear material contained a novel substance that was slightly acidic and high in phosphorus. This material, which consisted of DNA and protein, called nuclein. The substance was later renamed nucleic acid by one of his students.

phosphate group

A phosphorus atom attached to four oxygen atoms; one of the three components of a nucleotide. Carry a negative charge; bound to the 5' carbon

phosphodiester linkage

Phosphodiester bond connecting two nucleotides in a polynucleotide strand.

Chargaff's Rules

Rules developed by Erwin Chargaff and his colleagues concerning the ratios of bases in DNA. A= T and G=C

polynucleotide strand

Series of nucleotides linked together by phosphodiester bonds.The backbone of the polynucleotide strand is composed of alternating sugars and phosphates; the bases project away from the long axis of the strand. The negative charges of the phosphate groups are frequently neutralized by the association of positive charges on proteins, metals, or other molecules.

Fraenkel-Conrat & Singer (1956)

The tobacco mosaic virus possesses a single molecule of RNA surrounded by a helically arranged cylinder of protein molecules. Fraenkel-Conrat found that, after separating the RNA and protein of TMV, he could remix the RNA and protein of different strains of TMV and obtain intact, infectious viral particles. They then created hybrid viruses by mixing RNA and protein from different strains of TMV. When these hybrid viruses infected tobacco leaves, new viral particles were produced. The new viral progeny were identical with the strain from which the RNA had been isolated and did not exhibit the characteristics of the strain that donated the protein. These results showed that RNA carries the genetic information in TMV.

Albrecht Kossel

determined that DNA contained nitrogenous bases: adenine, cytosine, guanine, and thymine (abbreviated A, C, G, and T).

Watson and Crick

discovered helical organization of DNA; 3D structure

ribose

has a hydroxyl group (—OH) attached to the 2′-carbon atom

transforming Principle

is capable of genetically altering bacteria

Erwin Chargaff

measured the amounts of the four bases in DNA from a variety of organisms and found that DNA from different organisms varies greatly in base composition. This finding disproved the tetranucleotide hypothesis. They discovered that, within each species, there is some regularity in the ratios of the bases: the amount of adenine is always equal to the amount of thymine (A = T), and the amount of guanine is always equal to the amount of cytosine

DNA nucleoside

sugar and base

nucleotide

sugar, phosphate, and a nitrogen-containing base

tetranucleotide theory

theory which states that DNA contained 4-nucleotide units, each containing all 4 nucleotides

Rosalind Franklin

x-ray diffraction--Method for analyzing the three-dimensional shape and structure of chemical substances. Crystals of a substance are bombarded with X-rays, which hit the crystals, bounce off, and produce a diffraction pattern on a detector. The pattern of the spots produced on the detector provides information about the molecular structure.

deoxyribose

Five-carbon sugar in DNA; lacks a hydroxyl group on the 2′-carbon atom.

Phoebus Aaron Levene

He discovered that DNA consists of a large number of linked, repeating units, called nucleotides; each nucleotide contains a sugar, a phosphate, and a base.incorrectly proposed that DNA consists of a series of four-nucleotide units, each unit containing all four bases—adenine, guanine, cytosine, and thymine—in a fixed sequence.

Avery, MacLeod, McCarty (1943)

Identified the transforming substance: DNA; Used heat to kill virulent bacteria, homogenize, and filter. Treat samples with enzymes (RNase, protease, DNase) that destroy protein, DNA, and RNA. Add the treated samples to cultures of IIR (nonvirulent) bacteria. Cultures treated with RNase and protease contained transformed IIS (virulent) bacteria, but the cultures treated with DNase did not. This demonstrated the DNA is the transforming substance.

nitrogenous base

Nitrogen-containing base that is one of the three parts of a nucleotide.a purine or a pyrimidine

Bonding

A=T Two hydrogen bonds G\\\C Three hydrogen bonds

deoxyribonucleotide

Basic building block of DNA, consisting of deoxyribose, a phosphate, and a nitrogenous base. deoxyribonucleoside 5′-monophosphates.

3' end

End of a polynucleotide chain where an OH group is attached to the 3′-carbon atom of the nucleotide.

5' end

End of the polynucleotide chain where a phosphate is attached to the 5′-carbon atom of the nucleotide.

ribonucleotide

Nucleotide containing ribose; present in RNA. ribonucleoside 5′-monophosphates

antiparallel

Refers to a characteristic of the DNA double helix in which the two polynucleotide strands run in opposite directions.

B-DNA

Right-handed helical structure of DNA that exists when water is abundant; the secondary structure described by Watson and Crick and probably the most common DNA structure in cells.

Fred Griffith

The Transforming Principle; Injected virulent and nonvirulent bacteria into mice and recorded the mice's reaction to the virulent or nonvirulent bacteria. Those injected with virulent bacteria died. Those injected with nonvirulent bacteria lived. When heat killed virulent bacteria was injected into mice, the mice lived. Mice injected with a mixture of heat killed virulent and nonvirulent bacteria died.

Key Characteristics of Genetic Material

The genetic material must be capable of carrying large amounts of information, replicating faithfully, expressing its coding instructions as phenotypes, and having the capacity to vary.

complementary DNA strands

The relation between the two nucleotide strands of DNA in which each purine on one strand pairs with a specific pyrimidine on the opposite strand (A pairs with T, and G pairs with C).

purine

Type of nitrogenous base in DNA and RNA. Adenine and guanine are purines. Two-ring structure

pyrimidine

Type of nitrogenous base in DNA and RNA. Cytosine, thymine, and uracil are pyrimidines.

Primary Structure of DNA

consists of a string of nucleotides joined together by phosphodiester linkages. it is a polymer—that is, a chain made up of many repeating units linked together. The repeating units of DNA are nucleotides, each comprised of three parts: (1) a sugar, (2) a phosphate, and (3) a nitrogen-containing base.

The Hershey-Chase Experiment

designed a series of experiments to determine whether the phage protein or the phage DNA is transmitted in phage reproduction. To follow the fate of protein and DNA, they used radioactive forms, or isotopes, of phosphorus and sulfur. A radioactive isotope can be used as a tracer to identify the location of a specific molecule because any molecule containing the isotope will be radioactive and therefore easily detected. DNA contains phosphorus but not sulfur, so Hershey and Chase used 32P to follow phage DNA during reproduction. Protein contains sulfur but not phosphorus, so they used 35S to follow the protein. After centrifugation, infected bacteria form a pellet containing 32P in the bottom of the tube.

Secondary Structure of DNA

refers to its three-dimensional configuration—its fundamental helical structure.