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38 Cards in this Set

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Frederick Griffith
1928- tried to learn how bacteria made people sick, specifically how certain types of bacteria produce pneumonia by injecting mice with two strains of bacteria - the S strain and the R strain.
S strain
Disease causing bacteria that grew in smooth colonies
R strain
Harmless bacteria that grew in rough colonies
Griffith's experiments
To find out why the S strain killed the mice, Griffith took a culture of the s strain and heated the cells to kill them and injected the mice. The mice survived, therefore the cause of pneumonia was not a toxin from the disease causing bacteria.
Griffith next mixed the heat killed, s strain bacteria with live, harmless bacteria from the R strain and injected the mice. The mice died, and when he examined their lungs, he found them to be filled with the disease causing bacteria.
Results of Griffith's experiments
He found that the heat-killed bacteria had passed their disease-causing ability to the harmless bacteria. He called this transformation.
He also concluded that the transforming factor had to be a gene.
The process in which one type of bacteria changes permanently into another.
Oswald Avery
1944 - led a group of scientists in repeating Griffith's work to find the specific molecule in the heat-killed bacteria that was responsible for transformation.
Oswald Avery's results
By the process of elimination, Avery and his team discovered that the nucleic acid DNA stores transmits genetic information from one generation of bacteria to the next.
Alfred Hershey and Martha Chase
1952 - collaborated in studying viruses
A kind of virus that infects bacteria by attaching to the surface of the cell and injecting its genetic information
Hershey and Chase's experiments
They studied a bacteriophage that was composed of a DNA core and a protein coat to determine what part of the virus entered the bacterial cell. They grew viruses in cultures containing radioactive isotopes of phosphorus -32 and sulphur -35. They mixed the marked viruses with bacterial cells. Then they separated the viruses from the bacteria and tested the bacteria for radioactivity.
Results of Hershey and Chase
Nearly all the radioactivity in the bacteria was from phosphorus, the marker found in DNA.
Their experiment also confirmed Avery's results - DNA was the genetic material found in genes - not just in viruses and bacteria, but in all living cells.
The DNA that makes up the genes must be capable of storing, copying, and transmitting the genetic information in a cell.
DNA is a _______ ______ made up of nucleotides joined into long strands of chains made by _____ ______.
Nucleic acid, covalant bonds
The building blocks of nucleic acids
Nitrogenous bases
Bases that contain nitrogen
Name the four nitrogenous bases.
Adenine, guanine, cytosine, and thymine.
What are the four nitrogenous bases joined together by?
The covalant bonds between the sugar of one nucleotide and the phosphate group of the next
Chargoff's Rule
[A]=[T] and [G]=[C]
Rosalind Franklin
Early 1950's - Studied DNA using a technique using X-ray diffraction
Process of X-ray diffraction
1. A large amount of DNA was purified
2. The DNA fibers were stretched in a thin glass tube so that most of the strands were parallel
3. A powerful x-ray beam was aimed at the concentrated DNA samples and the scattering the x-rays were recorded on film
Results of x-ray diffraction
The X shaped pattern revealed the strands of DNA were twisted in a helix and that the angle of the X suggests there are two strands in the structure.
James Watson and Francis Cruck
Built 3D models of the molecule
In early 1953, Watson was shown Franklin's x-ray pattern. The clues in Franklin's x-ray pattern enabled Watson and Crick to build a model that explained the specific structure and properties of DNA, which led to the double helix.
What did the double helix model explain?
Chargoff's rule of base pairing and how the two strains of DNA are held together.
Significance of the strands of DNA being "antiparallel"
Enables the nitrogenous bases on both strands to come into contact at the center of the molecule and also allows each strand of the double helix to carry a sequence of nucleotides, arranged almost like letters.
What did Watson and Crick discover about the bonds between nitrogenous bases?
Hydrogen bonds could form between certain nitrogenous bases, providing just enough force to hold the two strands together.
Base pairing
A-T and G-C
A copying process which occurs during late interphase (S phase) which ensures that each resulting cell had the same complete set of DNA molecules
Process of replication
The DNA molecule separated into two strands and then produces two new complementary strands following the rules of base pairing. The enzymes "unzip" a molecule by braking the hydrogen bonds between base pairs and unwinding the two strands of the molecule. Each strand then serves as a template for the attachment of complementary bases.
Proteins with highly specific functions
DNA polymerase
The principal enzyme involved in DNA replication; an enzyme that joins individual nucleotides to produce a new strand of DNA.
It also proof reads each new DNA strand so that each molecule is a near-perfect copy of the original.
DNA at the tips of chromosomes which is particularly difficult to replicate
A special enzyme used by cells to replicate telomeres by adding short, repeated DNA sequences to the telomeres.
DNA replication in prokaryotic cells
Starts from a single point and proceeds in two directions until the entire chromosome is copied
DNA replication in eukaryotic cells
Can begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied
List the three components of a nuclleotide
A 5-carbon sugar, a phosphate group, and a nitrogenous base
Where is DNA located in a cell?
What transports the genetic information from the nucleus to the cytoplasm?
________ is primarily a single stranded molecule.