Lesson 1: The History Flashcards
Phoebus Levene (1910) p1
An american biochemist, isolated two diffferent types of nucleic acids that could be distinguished by the sugars involved in their composition.
-One contained the sugar ribose whch he termed ribonucleic acid
-the other contained an unknown sugar that was similar to ribose but was missing an oxygen atom, therefore he called it deoxyribose and termed the nucleic acid as deoxyribonucleic acid
showed the DNA and RNA were composed of long chains of nucleotides
Phoebus Levene p2
Levene also discovered the structure of a nucleotide:
a phosphate group, a pentose sugar and one of five nitrogenous bases
—nucleotides make up DNA
—Levene concluded equal amounts of e/ base must be present in a chain of nucleic acid.
Phoebuus Levene p2 - nitrogenous bases in DNA
Adenine, Thymine, Guanine and Cytosine
—Thymine is replaced by Uracil in RNA
DNA structure: The sugar
In DNA the sugar is called deoxyribose, this is a pentose sugar because it contains 5 carbon atoms
DNA structure: Phosphate Group
The acidic part of the nucleotide, connects the 5’ carbon of one nucleotide to the hydroxid (-OH) group on the 3’ carbon of the neighbouring nucleotide
DNA structure: Nitrogenous Bases
The nucleotide is named for the nitrogenous base attached.
There are 4 bases found in DNA:
1. Purine : Adenine and Guanine
2. Pyrimidines: Thymine and Cytosine
Purines
The nitrogenous bases that have a double-ringed structure
Pyrimidines
The nitrogenous bases that have a single-ringed structure
Fred Griffith (1928), Oswald Avery (1944)
Experiments suggest that DNA is the “genetic” material.Due to Griffith’s investigation thatinvolved transforming factors in pneumococcus bacteria in mice.
- Griffith was killed during World War II before confirming the transforming factorsand publishing his findings.
-Avery proposed DNA as the transformative component, building on Griffith’s findings.
Alfred Hershey and Martha Chase (1953)
The “Blender Experiment” included tagging bacteriophages with radioactive isotopes and blending them with non-radioactive E. Coli bacteria. Only radioactively tagged viral DNA was transmitted to E. Coli, indicating that DNA serves as the cell’s transforming factor/genetic material.
Erwin Chargaff - Chargaff Ratio’s (1952)
Chargaffbelieved DNA was more than just the repeated tetranucleotide blocks outlined by Levine. It was observed that the number of adenine bases was always equal to the number of thymine bases, whereas the number of cytosines was always equal to the number of guanines. However, the quantity of adenines and thymines did not always match the amount of cytosines and guanines.
Rosalind Franklin and Maurice Wilkins
(1952 – 1953)
Franklin was an expert in X-ray crystallography.
The researcher used X-ray crystallography to create two sets of X-ray photographs of DNA, indicating a helical shape. However, they were unable to determine how the nucleotides fit into this stable configuration.
-Wilkins shared one batch of X-ray photos with another group of scientists.
-Franklin died from cancer in 1953.
James Watson and Francis Crick (1953)
Identified the structure of DNA using Franklin and Wilkins’ X-ray pictures and Pauling’s method.The proposed DNA structure was a double helix.
A base pairing approach using hydrogen and covalent bonds;confirmingChargaff’s ratios.The DNA strands of the double helix were found to be “anti-parallel” (meaning they ran in opposing directions).
DNA p1
DNA is a threaad-like molecule made up of 2 long strands of nucleotides bound together in the shape of a double helix
If the helix was unwound it would look like a “ladder”
DNA p2: The Sugar—Phosphate Backbone
would be the “rails” and are held together by covalent bonds
DNA p3: Nitrogenous Base Pairs
Would be the “rungs” and are held together by weaker h-bonds
DNA p4: Dimension
-the distance between nucleotides is constant (0.34 nm or 3.4 angstroms)
-the diameter of the molecule is 2nm or 20 angstroms
-e/ turn contains 10 nucleotides
DNA p5: Complementary Base Pairing
-A purine is always bonded to a pyrimidine
-in order to fit the double helix structure:
A forms a stable bond with T
C forms a stable bond with G
DNA p6: nucleotide strands are anti-parallel
-the 2 nucleotide strands that make up the DNA molecule run in opposite directions
-at the end of e/ DNA molecule will be the 5’ end of one strand and the 3’ end of the other
Naming —> DNA Sequence
By rule, we read DNA from the 5’ end to the 3’ end; we name the strand by listing the bases in series of said rule.
genes p1
the functional subunits of DNA
-certain sequences of DNA that have the potential to be “expressed” in order to guide an organisms development
-also called the code as it provides instructions for the assembly of proteins, enzymes and polypeptides
genes p2 : Exons
One of two of the gene regions:
-these are coding regions and are active
genes p2: introns
one of two of the gene regions
-unused portion of DNA; may have had a purpose in an earlier form of the organism but isn’t required anymore
genome
the sum of all DNA carried in an organism’s cells
-human genome contains 6 billion base pairs
-if we could arrange DNA end to end, the length would 2 x 10^10 km which is about 100x the distance between the Earth & Sun
