Nucleic acids 1
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  • The nucleus contains the cell’s DNA, which makes up the genome. The nucleus is surrounded by a nuclear envelope, two membrane bilayers Molecules come into and out of the nucleus through nuclear pores The inside of the nucleus is called the nucleoplasm. Chromatin is the name given to DNA complexed with proteins (histones) The nucleolus is a region where the DNA is concentrated for replication
  • The nucleus contains the cell’s DNA, which makes up the genome. The nucleus is surrounded by a nuclear envelope, two membrane bilayers Molecules come into and out of the nucleus through nuclear pores The inside of the nucleus is called the nucleoplasm. Chromatin is the name given to DNA complexed with proteins (histones) The nucleolus is a region where the DNA is concentrated for replication

Nucleic acids 1 Nucleic acids 1 Presentation Transcript

  • NUCLEIC ACIDS
  • 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.
  • The Tetranucleotidehypothesisadenine phosphate uracil pentose pentose phosphate phosphate pentose pentosecytosine phosphate guanine
  • 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.
  • RNA structures have manyhairpins and loops
  • Structure of RNA Hairpin