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38 Cards in this Set
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Frederick Griffith
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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.
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S strain
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Disease causing bacteria that grew in smooth colonies
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R strain
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Harmless bacteria that grew in rough colonies
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Griffith's experiments
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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. |
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Results of Griffith's experiments
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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. |
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Transformation
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The process in which one type of bacteria changes permanently into another.
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Oswald Avery
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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.
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Oswald Avery's results
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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.
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Alfred Hershey and Martha Chase
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1952 - collaborated in studying viruses
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Bacteriophage
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A kind of virus that infects bacteria by attaching to the surface of the cell and injecting its genetic information
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Hershey and Chase's experiments
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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.
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Results of Hershey and Chase
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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. |
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DNA is a _______ ______ made up of nucleotides joined into long strands of chains made by _____ ______.
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Nucleic acid, covalant bonds
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Nucleotides
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The building blocks of nucleic acids
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Nitrogenous bases
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Bases that contain nitrogen
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Name the four nitrogenous bases.
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Adenine, guanine, cytosine, and thymine.
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What are the four nitrogenous bases joined together by?
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The covalant bonds between the sugar of one nucleotide and the phosphate group of the next
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Chargoff's Rule
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[A]=[T] and [G]=[C]
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Rosalind Franklin
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Early 1950's - Studied DNA using a technique using X-ray diffraction
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Process of X-ray diffraction
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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 |
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Results of x-ray diffraction
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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.
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James Watson and Francis Cruck
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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. |
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What did the double helix model explain?
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Chargoff's rule of base pairing and how the two strains of DNA are held together.
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Significance of the strands of DNA being "antiparallel"
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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.
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What did Watson and Crick discover about the bonds between nitrogenous bases?
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Hydrogen bonds could form between certain nitrogenous bases, providing just enough force to hold the two strands together.
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Base pairing
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A-T and G-C
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Replication
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A copying process which occurs during late interphase (S phase) which ensures that each resulting cell had the same complete set of DNA molecules
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Process of replication
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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.
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Enzymes
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Proteins with highly specific functions
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DNA polymerase
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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. |
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Telomeres
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DNA at the tips of chromosomes which is particularly difficult to replicate
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Telomerase
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A special enzyme used by cells to replicate telomeres by adding short, repeated DNA sequences to the telomeres.
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DNA replication in prokaryotic cells
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Starts from a single point and proceeds in two directions until the entire chromosome is copied
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DNA replication in eukaryotic cells
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Can begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied
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List the three components of a nuclleotide
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A 5-carbon sugar, a phosphate group, and a nitrogenous base
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Where is DNA located in a cell?
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Ribosomes
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What transports the genetic information from the nucleus to the cytoplasm?
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tRna
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________ is primarily a single stranded molecule.
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mRNA
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