CHAPTER 10 Molecular Biology of the Gene Modules 10.1 – 10.5

Saboteurs Inside Our Cells The invasion and damage of cells by the herpesvirus can be compared to the actions of a saboteur intent on taking over a factory The herpesvirus hijacks the host cell’s molecules and organelles to produce new copies of the virus

Viruses provided some of the earliest evidence that genes are made of DNA Molecular biology studies how DNA serves as the molecular basis of heredity

In 1928, Frederick Griffith, an English army doctor, wanted to make a vaccine against a bacteria named Streptococcus pneumoniae, which caused a type of pneumonia. Since the time of Pasteur, about 50 years before, vaccines had been made using killed microorganisms which could be injected into patients to elicit the immune response of live cells without risk of disease. Though he failed in making the vaccine he stumbled on a demonstration of the transmission of genetic instructions by a process we now call the "transformation principle".

Experiments showed that DNA is the genetic material

What was the transforming principal??????

Experiments showed that DNA is the genetic material

DNA was the genetic, transforming principal…. Oswald Avery: the professor, DNA, and the Nobel Prize that eluded him. Professor Emeritus of Pathology, Dalhousie University. In 1944, two Canadians, Oswald Avery and Colin MacLeod, and an American, McCarty, published a paper in The Journal of Experimental Medicine that demonstrated genes to be the chemical, deoxyribonucleic acid (DNA). Even though this paper is now regarded as the single most important publication in biology of the 20th century, Avery was not awarded the Nobel Prize. This raises the question as to why his work did not earn him the Prize. These are several possible reasons: the discovery may have been ahead of tis time; all three authors were physician-scientists and not recognized chemists or geneticists; and Avery, the principal author, had reached an advanced age and characteristically took an extremely cautious and low-key approach to his work. Discussion of these reasons in turn raises other issues surrounding the recognition of the work of celebrated scientist, from Galileo and Copernicus onwards.

Experiments showed that DNA is the genetic material The Hershey-Chase experiment showed that certain viruses reprogram host cells to produce more viruses by injecting their DNA Head DNA Tail Tail fiber Figure 10.1A

Phage reproductive cycle Phage attaches to bacterial cell. Phage injects DNA. Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble. Cell lyses and releases new phages. Figure 10.1C

The Hershey-Chase Experiment 1 Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. 2 Agitate in a blender to separate phages outside the bacteria from the cells and their contents. 3 Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. 4 Measure the radioactivity in the pellet and liquid. Radioactive protein Empty protein shell Radioactivity in liquid Phage Bacterium Phage DNA DNA Batch 1 Radioactive protein Centrifuge Pellet Radioactive DNA Batch 2 Radioactive DNA Centrifuge Radioactivity in pellet Figure 10.1B Pellet

For his fundamental contributions to molecular biology, Hershey received the 1958 Albert Lasker Award and the 1965 Kimber Genetics Award. However, it was not until 1969 that Hershey, together with Delbrück and Luria, was awarded the Nobel Prize for physiology or medicine. Martha Chase was a lab assistant in the 1950’s and did not receive the Nobel Prize for her work.

DNA and RNA are polymers of nucleotides DNA is a nucleic acid, made of long chains of nucleotides Phosphate group Nitrogenous base Nitrogenous base (A, G, C, or T) Sugar Phosphate group Nucleotide Thymine (T) Sugar (deoxyribose) DNA nucleotide Polynucleotide Sugar-phosphate backbone Figure 10.2A

DNA has four kinds of bases, A, T, C, and G Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines Purines Figure 10.2B

Note the designation of the Carbons as 1-5.

10.3 DNA is a double-stranded helix James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B

The structure of DNA consists of two polynucleotide strands wrapped around each other in a double helix 1 chocolate coat, Blind (PRA) Figure 10.3C Twist

Z-form right-handed A-form B-form right-handed left-handed

10.4 DNA replication depends on specific base pairing In DNA replication, the strands separate Enzymes use each strand as a template to assemble the new strands A A Nucleotides Parental molecule of DNA Both parental strands serve as templates Two identical daughter molecules of DNA Figure 10.4A

Untwisting and replication of DNA Figure 10.4B

Overall direction of replication 3 DNA polymerase molecule How DNA daughter strands are synthesized 5’ – 3’ direction 5 end 5 Daughter strand synthesized continuously Parental DNA 5 3 Daughter strand synthesized in pieces 3 P 5 The daughter strands are identical to the parent molecule 5 P 3 DNA ligase Overall direction of replication Figure 10.5C

10.5 DNA replication: A closer look DNA replication begins at specific sites Parental strand Origin of replication Daughter strand Bubble Two daughter DNA molecules Figure 10.5A

Tid Bits 1. If multiple sites were not being replicated simultaneously: Fruit fly DNA would take 16 days to replicate only 8 chromosomes In bacteria, 500 nucleotides are being added per second/ eukaryotes are adding 50 nucleotides per second. 2. Replication must take place in a 5’ to 3’ direction and the DNA strand is antiparallel 3. Eukaryotes have directional issues and telomere issues!!! (To be discussed soon, stay tuned)

Each strand of the double helix is oriented in the opposite direction Nucleotides can only be added to the free 3’ end of the DNA strand. There is only 1 error per billion base pairs!! 5 end 3 end P P P P P P P P 3 end 5 end Figure 10.5B

The Enzymes of DNA Synthesis

DNA polymerase I fills in the spaces between the Okasaki Fragments. DNA polymerase III adds nucleotides to the “free 3.” Gyrase unwinds the DNA by catalyzing the formation of negative supercoils. Helicase separates the strands. DNA polymerase II is a prokaryotic DNA polymerase most likely involved in DNA repair

The initial requirement for a free 3' hydroxyl group is fulfilled by the RNA primers that are synthesized at the initiation sites by primase enzymes.

Nitrogenous base (A, G, C, or U) RNA is also a nucleic acid RNA has a slightly different sugar RNA has U instead of T Nitrogenous base (A, G, C, or U) Phosphate group Uracil (U) Sugar (ribose) Figure 10.2C, D