nucleic acids 1
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NUCLEIC ACIDS
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Topic Outline:
History of Nucleic Acids Structure and Function Types of Nucleic Acids
1. DNA2. RNA
Central Dogma of Life
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Friedrich Miescher in 1869
isolated what he called nuclein from the nuclei of pus cells
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Richard Altmann in 1889
Nuclein was shown to have acidic properties, hence it became called nucleic acid
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1920s
the tetranucleotide hypothesis was introduced
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The Tetranucleotide hypothesis
Up to 1940 researchers were convinced that hydrolysis of nucleic acids yielded the four bases in equal amounts.
Nucleic acid was postulated to contain one of each of the four nucleotides, the tetranucleotide hypothesis.
Takahashi (1932) proposed a structure of nucleotide bases connected by phosphodiester linkages.
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The Tetranucleotide hypothesis
adenine uracil
cytosine guaninephosphate
phosphate phosphate
phosphate
pentose
pentosepentose
pentose
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Astbury and Bell in 1938
First X-ray diffraction pattern of DNA is published.
The pattern indicates a helical structure, indicated periodicity.
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X-ray diffraction of DNA
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Wilkins & Franklin (1952): X-ray crystallography
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Avery, MacLeod, and Mc Carty in 1944
demonstrate DNA could “transform” cells.
Supporters of the tetranucleotide hypothesis did not believe nucleic acid was variable enough to be a molecule of heredity and store genetic information.
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Mice injected with virulent bacteria die
The Avery, MacLeod, and McCarty Experiment
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Mice injected with nonvirulent bacteria live
The Avery, MacLeod, and McCarty Experiment
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Mice injected with heat-killed virulent bacteria live
The Avery, MacLeod, and McCarty Experiment
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Mice injected with a mixture of nonvirulent bacteria and heat-killed virulent bacteria die
The Avery, MacLeod, and McCarty Experiment
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Mice injected with a mixture of nonvirulent bacteria and DNA from heat-killed virulent
bacteria die
The Avery, MacLeod, and McCarty Experiment
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Erwin Chargaff in late 1940s
used paper chromatography forseparation of DNA
hydrolysates. Amount of adenine is equal to
amount of thymine and amount of guanine is equal to amount of cytosine.
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Hershey and Chase in 1952
confirm DNA is a molecule of heredity.
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The Hershey-Chase Experiment
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The Hershey-Chase Experiment
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Watson and Crick in 1953
determine the structure of DNA
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Watson & Crick Base pairing
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Francis Crick in 1958
proposes the “central dogma of molecular biology” .
Kornberg purifies DNA polymerase I
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1969
Entire genetic code determined
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Important Developments 1972 – First recombinant DNA molecule
constructed Lambda phage DNA inserted into SV40 virus
- Restriction enzyme EcoRI used to
create a recombinant plasmid containing penicillin and tetracycline resistance
1982 – Tetrahymena ribosomal RNA splicing shown to be self- splicing
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Important Developments
1986 – RNA is shown to act as an enzyme
- The polymerase chain reaction
(PCR) was developed by Kari Mullis at Cetus
Corporation. 1995 – First complete genome
sequenced of the bacteriumHaemophilus influenzae at TIGR
2001 – Human genome sequenced by
NIH and Celera Genomics
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Nucleic Acids
• Nucleic Acids are very long, thread-like polymers, made up of a linear array of monomers called nucleotides.
• Nucleic acids vary in size in nature
• tRNA molecules contain as few as 80 nucleotides
• Eukaryotic chromosomes contain as many as 100,000,000 nucleotides.
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Two types of nucleic acid are found
Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA)
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DNA and RNA
DNAdeoxyribonucleic acidnucleic acid that stores genetic informationfound in the nucleus of a mammalian cell.
RNAribonucleic acid3 types of RNA in a cellRibosomal RNAs (rRNA) are components of ribosomesMessenger RNAs (mRNA) carry genetic informationTransfer RNAs (tRNA) are adapter molecules in translation
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The distribution of nucleic acids in the eukaryotic cell DNA is found in the nucleus
with small amounts in mitochondria and chloroplasts
RNA is found throughout the cell
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The nucleus contains the cell’s DNA (genome)
Nucleus
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RNA is synthesized in the nucleus andexported to the cytoplasm
Nucleus
Cytoplasm
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dA dG dT dC
Deoxyribonucleotides found in DNA
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A G U C
Ribonucleotides found in RNA
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DNA as genetic material: The circumstantial evidence1. Present in all cells and virtually restricted to the
nucleus
2. The amount of DNA in somatic cells (body cells) of any given species is constant (like the number of chromosomes)
3. The DNA content of gametes (sex cells) is half that of somatic cells. In cases of polyploidy (multiple sets of chromosomes) the DNA content increases by a proportional factor
4. The mutagenic effect of UV light peaks at 253.7nm. The peak for the absorption of UV light by DNA
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NUCLEIC ACID STRUCTURE
Nucleic acids are polynucleotides
Their building blocks are nucleotides
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NUCLEOTIDE STRUCTURE
PHOSPATE SUGAR
Ribose or Deoxyribose
NUCLEOTIDE
BASEPURINES PYRIMIDINES
Adenine (A)Guanine(G)
Cytocine (C)Thymine (T)Uracil (U)
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All nucleotides contain three components:1. A nitrogen heterocyclic base2. A pentose sugar3. A phosphate residue
Nucleotide Structure
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Ribose is a pentose
C1
C5
C4
C3 C2
O
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RIBOSE DEOXYRIBOSE
CH2OH
H
OH
C
C
OH OH
C
O
H HH
C
CH2OH
H
OH
C
C
OH H
C
O
H HH
C
Spot the difference
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Ribonucleotides have a 2’-OHDeoxyribonucleotides have a 2’-H
Chemical Structure of DNA vs RNA
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THE SUGAR-PHOSPHATE BACKBONE
The nucleotides are all orientated in the same direction
The phosphate group joins the 3rd Carbon of one sugar to the 5th Carbon of the next in line.
P
P
P
P
P
P
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ADDING IN THE BASES
The bases are attached to the 1st Carbon
Their order is important It determines the genetic information of the molecule
P
P
P
P
P
P
G
C
C
A
T
T
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DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE
P
P
P
P
P
P
C
G
G
T
A
A
P
P
P
P
P
P
G
C
C
A
T
T
Hydrogen bonds
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DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE
The sister strands of the DNA molecule run in opposite directions (antiparallel)
They are joined by the bases Each base is paired with a specific partner:
A is always paired with T G is always paired with C“Purine with Pyrimidine”
The sister strands are complementary but not identical
The bases are joined by hydrogen bonds, individually weak but collectively strong
There are 10 base pairs per turn
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Structure of Nucleotide Bases
Purines & Pyrimidines
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5’ End
3’ End
Nucleotides arelinked byphosphodiesterbonds
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Three-dimensional structure of B DNA
NMR solution structure of a 12 nucleotide fragment of DNA
5’- C G C G A A T T C G C G –3’
3’- G C G C T T A A G C G C –5’
Total of 32 hydrogen bonds.
Reading Assignment: Tjandra et alJournal of the American Chemical Society (2000) 122, 6190
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Cellular Processes
DNA
RNA (mRNA)
Proteins
replication
transcription
translation
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RNA and Transcription
DNA is in the nucleus
Proteins are synthesized on ribosomes in the cytoplasm
RNA carries the genetic information from the nucleus to the cytoplasm
This RNA is called messenger RNA (mRNA)
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Transcription of a DNA molecule results in a mRNAmolecule that is single-stranded.
RNA molecules do not have a regular structure like DNA.
The structures of RNA molecules are complex and unique.
RNA molecules can base pair with complementary DNAor RNA sequences.
G pairs with C, A pairs with U, and G pairs with U.
RNA Structure
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RNA structures have many hairpins and loops
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Structure of RNA Hairpin