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BIOL 3200 Study Guide - Final Guide: Microtubule, Cyanobacteria, Tetrahymena


Department
Biology
Course Code
BIOL 3200
Professor
Jan Sapp
Study Guide
Final

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Central Dogma and The origins of life : DNA RNA Protein Cell
Organism!
DISCOVERY OF DNA
Friedrich Meischer, 1871
-Washed pus cells (later salmon sperm) in very dilute hydrochloric acid
to remove the cytoplasm.
-He then filtered out the nuclei without cytoplasm.
-Called the stuff “nuclein” because it was in the nucleus, --still in the
world nucleic acid today.
The molecular approach to the gene involved a merger of several techniques
-chromatography used to analyse the composition of DNA and
proteins
-x-ray crystallography – reveal the 3 dimensional structure of proteins
and DNA
-Radioisotopes –helped identify DNA as the basis of the gene
Cell functions could be understood in terms of the structure of
macromolecules
DNA wasn’t thought to be the basis of a gene
-Gene would have to be a complex molecule. DNA seemed to be too
simple
-DNA was thought to be a monotonous polymer like starch with
repeat sets of four nucleotides followed in a fixed ordered: AGCT AGT
AGCT-
-It seemed as if there were equal amounts of AGCT present in the
DNA of all organisms
Protein was considered to be a good candidate for the gene
-Complex, diverse- the most important molecules in the cell
-By 1940s, proteins shown to be made up of about 20 amino-acids in
chains from 100s to 1000s.
-Known to differ in the amount of amino acids.
The first evidence that DNA was basis of the gene
-Bacterial transformations by Frederick Griffith in London in the 1928-
-Pneumococcus
-Two kinds smooth: virulent
-Rough strain: non virulent
-Griffiths concluded that R form had been transformed to virulent S form
-Dead S + live R live S
What was the transforming principle?

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-Exposed the R strain to purified
protein, RNA sugar, and DNA
extracted from the dead killer S strain
of pneumococcus.
-Only the bacteria exposed to DNA
was transformed.
-That paper was published in 1944
Both Beadle and Dobzhansky thought this was a case of environmentally
directed specific change - because they still thought protein was the basis of
the gene.
Also not shown yet that bacteria possessed genes like other organisms-
Lederberg and Tatum in 1946.
DNA THE BASIS OF THE GENE: RADIOACTIVE BACTERIOPHAGE
Martha Chase and Alfred Hershey,
1952
Labelled DNA found inside
infected E. coli, not labelled protein

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Late 1940s Erwin Chargaff applied chromatography to nucleic acid
composition of several organisms
Nucleotide base AGCT composition differed between organisms.
-Amount of A=T
-Amount of G=C
3D structure of of proteins was determined by X-ray crystallography (William
Bragg (Leeds) and Lawrence Bragg at Cambridge (father and son won the
Nobel prize in 1915)
Three groups were interested in X-ray crystallography of DNA (Linus Pauling
and Paul Corey at Cal Tech.)
Alpha helix is a common secondary structure of proteins, 1951
X-ray crystallography of DNA (Maurice Wilkins and Rosalind Franklin at Kings
College, London)
James Watson and Francis Crick at Cambridge took credit for her work
DNA replication; Transcription and translation
CODE CRACKING : I THE THEORETICAL PHASE
How can a four letter alphabet AGCT encode 20 amino acids?
If code was 2 nucleotides 4 X 4= 16
If the code was triplet it would be 4 X 4 X 4= 64. More than enough
combinations- code has redundancy.
In 1957 Sydney Brenner coined the word “codon” for each triplet.
THEORETICAL PHASE ENDS IN 1961 AND EXPERIMENTAL PHASE BEGINS
Marshall Nirenberg and Heinrich Matthaei
At the National Institutes of Health
Prepare cell-free extract of E. coli that could synthesis protein/peptides when
they added an external source of RNA
At first they used viral RNA to stimulate their system
Then used synthetic RNA UUU
Tested individually labeled amino acids one by one.. When they added UUU
RNA to radioactive phenylalanine, the resulting protein was composed solely
of phenylalanine
Then other synthetic inputs UUC,UUG,UUA
Cryptographic problem of the code solved by 1965:
All 64 triplets codons had been assigned
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