Ch 9 DNA Structure And Replication Flashcards
History of DNA
Archibald Garrod
Linked inheritance to “inborn errors of metabolism” with lack of particular enzymes
Ex. PKU
First described the disease alkaptonuria (black urine) caused by enzyme error
History of DNA
Friedrich Miescher
Physician
Isolated white blood cell nuclei from pus (WBC, DNA)
Found an acid substance with nitrogen and phosphorus(negatively charged, in the nucleus)
Called it nuclein
Later it was called nucleic acid (by his student)
History of DNA
Frederick Griffith
Worked with diplodocus (2 bacteria mixed together) pneumonia (streptococcus pneumoniae) , which exists in two types
Type S (smooth) = produces capsule Type R (Rough) = no capsule
Capsule associated with virulence
Transformation
Grew Bacteria in petri dish exposes to heat and killed the bacteria injected it into the mouse and the mouse lived
Bacterial ability to take up DNA from its environment and incorporate it into its ow genome
History of DNA
Avery MacLeod and McCarty
Treated lysed S bacteria with protease (DNA) and DNase (enzyme)
Only DNase prevented transformation
Thus DNA is transforming principle c
- can convert type R bacteria into S
This allow them to figure out what the Bacteria was picking up that was causing the transformation
Transforming Principle
They took type R and Type S mixture and added protease (which breaks down protein) to one and DNase (DNA fragments) to the other
Transformation could not occur without DNA
History of DNA
Alfred Hershey and Martha Chase
Viruses can infect E. coli bacteria
Used radioactive 35S and 32P to label protein
The blender experiments showed that the virus transfer DNA not protein into bacterial cell
thus DNA is genetic material
Discover Structure of DNA
Phoebus Levine
Identified the 5-carbon sugars ribose and deoxyribose
Discovered that the three parts of a milestone are found in equal proportions
- sugar
- phosphate
- Base
DNA Structure
A single building block is a nucleotide
Each nucleotide is composed of
- a deoxyribose sugar H
- a phosphate group PO4-
- a nitrogenous base one of fours types
- Adenine (A), Guanine (G) are purines
- Thymine (T), Cytosine (C) are pyrimidines
Two polynucleotide chains align forming a Double Helix
Discovering DNA Structure
Erwin Chargaff
Analyzed base composition of DNA from Various species and observed regular relationships:
A=T and C=G
If A is used 20% T=20% then C is used 30% G= 30%
Discovered that DNA was made up of all 4 bases, but not equally used
Discovering the structure of DNA
Rosalind Franklin and Maurice Wilkins
Distinguished two forms of DNA
“A” form, which is dry and crystalline (compact no water)
“B” form, which is wet and cellular (lots of water)
Used a X-Ray diffraction technique
It took Franklin 100hrs to obtain photo 51 of B-form of DNA
Franklin Reasoned that the DNA is a helix with symmetrically organized
Crystallized the molecule then bombard with X-Ray how the light bounces out then you can see the shape
Molecular Definition of a Gene
A gene is a segment of DNA
It directs the formation of RNA to produce protein
The protein(or functional RNA) creates the phenotype
Information is conveyed by the sequence of the nucleotide
DNA Replication Early Beliefs
At first research suggested DNA might replicate in any 3 possible ways
Conservative: old/old + new/new
Semiconservative: old/ new + new/old
Dispersive : mixed old & new
DNA Replication
Mathew Meselson and Franklin Stahl
Grew E. Coli on media containing 15N for several generations
- thus making all DNA heavy
Shifted bacteria to media containing 14N
Then traced replicating DNA
Determined that DNA replications is semi conservative
Discovering the structure of DNA
James Watson and Francis Crick
Did not preform experiments
Rather they used the earlier research and inferences from model building with cardboard cutouts to solve the structure of DNA
They built a model based on published and unpublished findings
Antiparallelism
The opposing direction head to toe is called antiparallelism
Note that one strand of the double-helix runs in a 5’ to 3’ direction and other strand runs in a 3’ to 5’ direction
DNA Complementary Base Pairs
Adenine pairs with thymine
Cytosine pairs with Guanine
The key to the constant width of the double helix is specific pairing of purines and pyrimidines via hydrogen bonds
