Topic Outline: History of Nucleic Acids Structure and Function Types of Nucleic Acids 1. DNA 2. RNA Central Dogma of Life
Friedrich Miescher in 1869 isolated what he called nuclein from the nuclei of pus cells
Richard Altmann in 1889 Nuclein was shown to have acidic properties, hence it became called nucleic acid
1920s the tetranucleotide hypothesis was introduced
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.
Astbury and Bell in 1938 First X-ray diffraction pattern of DNA is published. The pattern indicates a helical structure, indicated periodicity.
X-ray diffraction of DNA
Wilkins & Franklin (1952): X-raycrystallography
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.
The Avery, MacLeod, andMcCarty Experiment Mice injected with virulent bacteria die
The Avery, MacLeod, and McCarty ExperimentMice injected with nonvirulent bacteria live
The Avery, MacLeod, and McCarty Experiment Mice injected with heat-killed virulent bacteria live
The Avery, MacLeod, and McCartyExperiment Mice injected with a mixture of nonvirulent bacteria and heat-killed virulent bacteria die
The Avery, MacLeod, and McCartyExperiment Mice injected with a mixture of nonvirulent bacteria and DNA from heat-killed virulent bacteria die
Erwin Chargaff in late 1940s used paper chromatography for separation of DNA hydrolysates. Amount of adenine is equal to amount of thymine and amount of guanine is equal to amount of cytosine.
Hershey and Chase in 1952 confirm DNA is a molecule of heredity.
The Hershey-Chase Experiment
The Hershey-Chase Experiment
Watson and Crick in 1953 determine the structure of DNA
Watson & Crick Base pairing
Francis Crick in 1958 proposes the “central dogma of molecular biology” . Kornberg purifies DNA polymerase I
1969 Entire genetic code determined
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
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 bacterium Haemophilus influenzae at TIGR 2001 – Human genome sequenced by NIH and Celera Genomics
Nucleic Acids• Nucleic Acids are very long, thread-likepolymers, made up of a linear array of monomerscalled nucleotides.• Nucleic acids vary in size in nature• tRNA molecules contain as few as 80 nucleotides• Eukaryotic chromosomes contain as many as100,000,000 nucleotides.
Two types of nucleic acidare found Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA)
DNA and RNADNAdeoxyribonucleic 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
The distribution of nucleicacids in the eukaryoticcell is found in the nucleus DNA with small amounts in mitochondria and chloroplasts RNA is found throughout the cell
The nucleus contains the cell’s DNA(genome) Nucleus
RNA is synthesized in the nucleusandexported to the cytoplasm NucleusCytoplasm
Deoxyribonucleotides foundin DNA dA dG dT dC
Ribonucleotides found inRNA A G U C
DNA as genetic material:The circumstantial evidence1. Present in all cells and virtually restricted to the nucleus2. 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 factor4. The mutagenic effect of UV light peaks at 253.7nm. The peak for the absorption of UV light by DNA
NUCLEIC ACID STRUCTURE Nucleic acids are polynucleotides Their building blocks are nucleotides
NUCLEOTIDE STRUCTUREPHOSPATE SUGAR BASE Ribose or PURINES PYRIMIDINES Deoxyribose Adenine (A) Cytocine (C) Guanine(G) Thymine (T) Uracil (U) NUCLEOTIDE
Nucleotide StructureAll nucleotides contain three components:1. A nitrogen heterocyclic base2. A pentose sugar3. A phosphate residue
Ribose is a pentose C5 O C4 C1 C3 C2
Spot the difference RIBOSE DEOXYRIBOSECH2OH CH2OH O OH O OHC C C CH H H H H H H H C C C C OH OH OH H
Chemical Structure of DNA vs RNA Ribonucleotides have a 2’-OH Deoxyribonucleotides have a 2’-H
PTHE SUGAR-PHOSPHATEBACKBONE P The nucleotides are all orientated in the same P direction The phosphate group joins the P 3rd Carbon of one sugar to the 5th Carbon of the next in line. P P
P GADDING IN THE BASES P C The bases are P attached to the 1 st C Carbon Their order is P important A It determines the P genetic information of T the molecule P T
Hydrogen bondsDNA IS MADE OF P GTWO STRANDS OF C PPOLYNUCLEOTIDE P C G P P C G P P A T P P T A P P T A P
DNA IS MADE OF TWO STRANDS OFPOLYNUCLEOTIDE 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
Purines & PyrimidinesStructure of NucleotideBases
5’ End Nucleotides are linked by phosphodies ter bonds 3’ End
Three-dimensional structure of BDNA 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 al Journal of the American Chemical Society (2000) 122, 6190
Cellular Processes replication DNA transcription RNA (mRNA) translation Proteins
RNA and TranscriptionDNA is in the nucleusProteins are synthesized on ribosomes in thecytoplasmRNA carries the genetic information from thenucleus to the cytoplasmThis RNA is called messenger RNA (mRNA)
RNA StructureTranscription of a DNA molecule results in a mRNA molecule 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 DNA or RNA sequences.G pairs with C, A pairs with U, and G pairs with U.