WH term 2 Final Flashcards
Griffith
Mouse experiment - transformation
Bacterial transformation experiments
Griffith - worked with phnemonia. He used live bacteria in a mouse and it died, then gave another non pathogenic phnemonia and it lived. He then heat killed the pathogenic bacteria, and the mouse lived. When he mixed heat killed bacteria with non pathogenic live bacteria, the bacteria transformed and the mouse died
Hershey and chase
Bacteriophages-
They injected virus with radioactive sulfur protein coat and it was NOT infected
Injected a different virus with radioactive DNA so it could be followed- it DID infect
proved that DNA carried hereditary information
Meselson and Stahl
The Meselson–Stahl experiment was an experiment by Matthew Meselson and Franklin Stahl in 1958 which supported the hypothesis that DNA replication was semiconservative.
E. coli were grown for in a medium with 15N. DNA was centrifuged on a salt density gradient, the DNA separated out at the point at which its density equaled the salt solution. The DNA of the cells grown in 15N medium had a higher density than cells grown in normal 14N medium.
After that, E. coli cells with only 15N in their DNA were transferred to a 14N medium and were allowed to divide.
DNA was compared to pure 14N DNA and 15N DNA. After one replication, the DNA was found to have intermediate density. Since conservative replication would result in equal amounts of DNA of the higher and lower densities (but no DNA of an intermediate density), conservative replication was excluded. this result was consistent with semiconservative and dispersive replication. Semiconservative replication would result in double-stranded DNA with one strand of 15N DNA, and one of 14N DNA, while dispersive replication would result in double-stranded DNA with both strands having mixtures of 15N and 14N DNA, either of which would have appeared as DNA of an intermediate density.
Avery, McCarty, MacLeod experiment
experimental demonstration that DNA is the substance that causes bacterial transformation.
purify and characterize the “transforming principle” responsible for the transformation phenomenon first described in Griffith’s experiment with killed pneumoniae.
Avery and his colleagues suggest that DNA was the the hereditary material of bacteria, and could be analogous to genes and/or viruses in higher organisms.
DNA structure
Double helix (Watson & crick) Anti-parallel (the ends go in opposite directions of each other) A-T C-G DEOXYRIBOSE nucleic acid 5'->3' : replication begins at 5'
Watson and crick
Discovered the DNA Double helix structure with the help of scientists like Franklin, chargaff etc
Rosalind Franklin
X-Ray crystallographer who took the famous photo that helped Watson and crick to discover the structure of DNA
Primase
Creates RNA primer at the 5’ end- allows other proteins and things to connect to DNA
Helicase
Unwinds DNA at the replication fork
DNA Polymerase
enzymes in DNA replication that assemble nucleotides. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from a single original DNA molecule.
Work in opposite directions
DNA REPLICATION
- helicase binds and unzips DNA at the replication fork
- leading strand(top strand) lagging strand (bottom strand)
- RNA Primase creates a primer that allows DNA polymerase to attach
- DNA polymerase adds matching nucleotides along the leading strand - CAN ONLY COPY IN 5’-3’
- RNA Primase lays down short primers for DNA polymerase to work down the segment backwards on the lagging strand. Fragments called Okazaki fragments
- ligase joins okazaki fragments
Ligase
Joins together all of the Okazaki fragments on the lagging strand
Telomeres
Prevent DNA from degrading - they are strands of continuous repeating base pairs that do NOT have genes. When DNA is shortened after each replication, telomeres are the parts that come off so genes don’t degrade
Poly ribosome
Multiple ribosomes that attach to DNA molecules and make proteins
