Chpt 12 Flashcards
First to build a three-dimensional model of the DNA molecule.
DNA has two strands (double helix)
- The two strands twist around a central axis to form a
spiral structure called a double helix.
James Watson and Francis Crick
[A]=[T] and [C]=[G]
Chargaff’s Rule
enzyme that begins the replication process by attaching to a DNA molecule and breaking the hydrogen bonds between the nitrogen bases. moves along the molecule and “unzips” the two strands of DNA.
DNA Helicase
enzyme that catalyzes the formation of the sugar-to-phosphate bonds that connect one nucleotide to the next one. only work in the 5-3 direction
DNA Polymerase
covalently joins the Okazaki fragments on the lagging strand.
DNA Ligase
is the enzyme that adds a short stretch of RNA (about 5 nucleotides long) that acts as an RNA primer. An RNA primer is used to initiate the synthesis of each Okazaki fragment.
Primase
help keep the DNA strands separated.
Single-Stranded binding proteins
(5—->3) replication is continuous.
Leading Strand
(3—->5) replication is discontinuous (Okazaki fragments)
Lagging Strand
the process in which DNA copies itself (duplicates).
- Replication of DNA is semiconservative
This results in two new DNA molecules; each consisting of an “old” strand and a “new” strand of DNA.
DNA Replication
Injected S strain: mice died
Injected R Strain: mice survived.
Mixture of both: he heat killed the S strain and mixed it with the R strain- Mice died.
Griffith
wanted to determine which molecule in the heat-killed bacteria was most important for transformation. his team extracted a mixture of various molecules from the heat-killed bacteria and treated this mixture with enzymes that destroyed proteins, lipids, carbohydrates, and some other molecules, including the nucleic acid RNA.- transformation still occurred. repeated the experiment using enzymes that would break down DNA. When they destroyed the DNA in the mixture, transformation did not occur. Therefore, DNA was the transforming factor.
Oswald Avery
studied a bacteriophage that was composed of a DNA core and a protein coat.They wanted to determine which part of the virus—the protein coat or the DNA core—entered the bacterial cell. Their results would either support or disprove Avery’s finding that genes were made of DNA. Nearly all the radioactivity in the bacteria was from phosphorus P-32 , the marker found in DNA. concluded that the genetic material of the bacteriophage was DNA, not protein.
Alfred Hershey and Martha Chase
used a technique called X-ray diffraction to get information about
the structure of the DNA molecule. The X-shaped pattern in the center indicates that the structure of DNA is helical.
Rosalind Franklin
