Lies, Thieves and DNA
120.9 هزار بار بازدید -
12 سال پیش
-
Science isn't pretty - there's
Science isn't pretty - there's a lot at stake and things can get ugly. So it was with the discovery of DNA, for which only Watson and Crick get credit. But not on my watch.
CORRECTION: Francis Crick was NOT an American as shown in the caption beneath his photo. He was born in Northamptonshire, England. I made the correction using the YouTube annotations feature, but not all devices show annotations.
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VIDEO DETAILS:
DNA: The Backstory
What gets passed down from generation to generation?
What does the molecule look like?
How does it work?
How does it replicate itself?
Discovery of Nucleic Acids
Friedrich Miescher (1869)
Isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein
Discovery of DNA Components
Phoebus Levene
Determined the components of DNA:
adenine, guanine, thymine, cytosine, deoxyribose phosphate
defined phosphate-sugar-base units called nucleotides
Levene's Tetranucleotide (1910)
Levene proposed that there were four nucleotides per molecule
Said DNA could not store the genetic code because it was chemically far too simple
Frederick Griffith and his Transformation Experiment
Studied the epidemiology and pathology of 2 strains of Streptococcus pneumoniae
In January 1928 reported the first widely accepted demonstrations of bacterial transformation
Griffith used two strains of Streptococcus:
Type S: virulent (deadly)
Type R: non-virulent (harmless)
Observed bacterial transformation but did not understand the mechanism
Avery, MacLeod and McCarty 1944
Determined the cause of the transformation in Griffith's Experiment
They took live R and heat-treated S and mixed it with one of two enzymes:
a protease (destroys protein)
a DNAse (destroys DNA)
Published in the Journal of Experimental Medicine
February, 1944
Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Deoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III
DNA not protein was responsible for the bacterial transformation Griffith observed!
DNA Discovery Timeline
Erwin Chargoff was Counting Nucleobasesm in 1952
Used paper chromatography and UV spectroscopy to examine the abundance of the nucleobases and he started to notice something VERY odd...
Came to be known as "Chargoff's Rules"
Amounts of Adenine = Amounts of Thymine
Amounts of Cytosine = Amounts of Guanine
ALWAYS in EVERY SPECIES!!!
Hershey-Chase Experiments
(1952)
Used phages and radiolabeled phosphorus and sulfur
Hershey and Chase concluded that DNA, not protein, was the genetic material.
A protective protein coat was formed around the bacteriophage, but the internal DNA is what conferred its ability to produce progeny inside bacteria
So, it's the DNA
The race was on to determine the structure of DNA in cells and to determine how it codes for proteins and how it replicates
The problem: DNA exists in two forms
A form (dry form)
B form (wet form, as DNA exists in cells)
In 1951, Watson and Crick wrote a paper in which they described DNA as a double helix with sugars and phosphates at the center and the nucleobases facing the outside
This model was quickly shown to be incorrect and in fact it made no chemical sense
Triple Helix?
Linus Pauling and Robert Corey proposed a triple helix structure for DNA
Eureka
James Watson and Francis Crick 1953
BUT now the story of thieves and lies...
Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin
Papers in sequence in Nature April 25, 1953 (THREE papers, not 1)
DNA Discovery Timeline
So now we have it.
DNA is a Double-Stranded Helix
The backbone is made of sugar (deoxyribose) and phosphate groups
Hydrogen bonds between the nucleobases: A-T and G-C
The sequence of nucleobases codifies the amino acid sequence of a protein.
Strings of base pairs that code for a product are called genes
CORRECTION: Francis Crick was NOT an American as shown in the caption beneath his photo. He was born in Northamptonshire, England. I made the correction using the YouTube annotations feature, but not all devices show annotations.
Want more?
Subscribe: thepenguinprof
FB Page: Facebook: ThePenguinProf
Twitter: Twitter: penguinprof
Web: http://www.penguinprof.com/
VIDEO DETAILS:
DNA: The Backstory
What gets passed down from generation to generation?
What does the molecule look like?
How does it work?
How does it replicate itself?
Discovery of Nucleic Acids
Friedrich Miescher (1869)
Isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein
Discovery of DNA Components
Phoebus Levene
Determined the components of DNA:
adenine, guanine, thymine, cytosine, deoxyribose phosphate
defined phosphate-sugar-base units called nucleotides
Levene's Tetranucleotide (1910)
Levene proposed that there were four nucleotides per molecule
Said DNA could not store the genetic code because it was chemically far too simple
Frederick Griffith and his Transformation Experiment
Studied the epidemiology and pathology of 2 strains of Streptococcus pneumoniae
In January 1928 reported the first widely accepted demonstrations of bacterial transformation
Griffith used two strains of Streptococcus:
Type S: virulent (deadly)
Type R: non-virulent (harmless)
Observed bacterial transformation but did not understand the mechanism
Avery, MacLeod and McCarty 1944
Determined the cause of the transformation in Griffith's Experiment
They took live R and heat-treated S and mixed it with one of two enzymes:
a protease (destroys protein)
a DNAse (destroys DNA)
Published in the Journal of Experimental Medicine
February, 1944
Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Deoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III
DNA not protein was responsible for the bacterial transformation Griffith observed!
DNA Discovery Timeline
Erwin Chargoff was Counting Nucleobasesm in 1952
Used paper chromatography and UV spectroscopy to examine the abundance of the nucleobases and he started to notice something VERY odd...
Came to be known as "Chargoff's Rules"
Amounts of Adenine = Amounts of Thymine
Amounts of Cytosine = Amounts of Guanine
ALWAYS in EVERY SPECIES!!!
Hershey-Chase Experiments
(1952)
Used phages and radiolabeled phosphorus and sulfur
Hershey and Chase concluded that DNA, not protein, was the genetic material.
A protective protein coat was formed around the bacteriophage, but the internal DNA is what conferred its ability to produce progeny inside bacteria
So, it's the DNA
The race was on to determine the structure of DNA in cells and to determine how it codes for proteins and how it replicates
The problem: DNA exists in two forms
A form (dry form)
B form (wet form, as DNA exists in cells)
In 1951, Watson and Crick wrote a paper in which they described DNA as a double helix with sugars and phosphates at the center and the nucleobases facing the outside
This model was quickly shown to be incorrect and in fact it made no chemical sense
Triple Helix?
Linus Pauling and Robert Corey proposed a triple helix structure for DNA
Eureka
James Watson and Francis Crick 1953
BUT now the story of thieves and lies...
Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin
Papers in sequence in Nature April 25, 1953 (THREE papers, not 1)
DNA Discovery Timeline
So now we have it.
DNA is a Double-Stranded Helix
The backbone is made of sugar (deoxyribose) and phosphate groups
Hydrogen bonds between the nucleobases: A-T and G-C
The sequence of nucleobases codifies the amino acid sequence of a protein.
Strings of base pairs that code for a product are called genes
12 سال پیش
در تاریخ 1391/09/09 منتشر شده
است.
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