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NUCLEIC ACIDS

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For human beings there are 22 pair of chromosomes which ... Two type of nucleic acids in the cell. DNA - deoxyribose nucleic acid. RNA ... property of ... – PowerPoint PPT presentation

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Title: NUCLEIC ACIDS


1
NUCLEIC ACIDS
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Course outline
  • 1 DNA and RNA
  • 2 Structure
  • 3 Elucidation of DNA as genetic material

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1 DNA and RNA ---a comparison
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Where is DNA found
Chromosome
Cells
  • For human beings there are 22 pair of chromosomes
    which determines traits with 23rd pair
    determining sex. XX - female and XY - males.

Genes
DNA
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5
3
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Components of Nucleic Acid
  • Two type of nucleic acids in the cell
  • DNA - deoxyribose nucleic acid
  • RNA - ribose nucleic acid
  • DNA is found in the chromosomes whereas RNA is
    found elsewhere in the nucleus.
  • Building Blocks of DNA and RNA are Nucleotides
    Nucleotide are made of base, sugar (ribose or
    deoxyribose) and a phosphate.

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  • Nucleoside - Base sugar

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Nucleotides
  • Nucleotides can form DNA or RNA
  • Nucleoside triphosphates can store energy such as
    ATP
  • Nucleoside triphosphates are involved in cell
    signaling such as GTP

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Deoxyribonucleic Acid (DNA)
  • Structural Components
  • Sugar (deoxyribose) and phosphate
  • Genetic material
  • Bases
  • Purines (Adenine and Guanine)
  • Pyrimidines (Thymine and Cytosine)

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Deoxyribonucleotides
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Ribonucleosides
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What is the chemical difference between RNA and
DNA?
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Nucleotide Bases
  • DNA is a polynucleotide containing A, T, G, and C
  • RNA is a polynucleotide containing A, U, G, and C

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What are the different types of RNA and what is
their function?
  • mRNAs
  • codes for proteins
  • rRNAs
  • part of the ribosome, site of protein synthesis
  • tRNAs
  • carries amino acids to the ribosome

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Differences between procaryotic mRNA and
eucaryotic mRNA
  • Polycistronic versus moncistronic
  • 5 cap
  • 3 tail
  • Introns and Exons
  • Compartmentalization

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Eucaryotic mRNAs have a 5 cap
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Eucaryotic mRNAs have a 3 poly(A) tail
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Eucaryotic mRNAs have introns
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2 DNA Structure
  • Sugar-Phosphate backbone is invariable
  • Sugar bound to phosphate in a phosphodiester bond
    between 5C and 3C
  • Base region of DNA variable
  • DNA is directional
  • Always write sequence 5 to 3

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Backbone
  • Nucleotides joined into chain by covalent bonds
    between phosphate and sugar units
  • Bases extend to side joined to sugar
  • Chemical Direction to chain
  • Phosphate at one end, Hydroxyl in sugar at other
  • 5 to 3 (Carbons) by convention

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3 Elucidation of DNA as Genetic Material
  • 1928 - Griffith Experiment- bacteria
  • 1944- Avery, Macleod and McCarty- isolated DNA
  • 1952 - Hershey and Chase
  • 1953- Watson and Crick

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Avery, Macleod, McCarty
  • Determine the identity of the transforming agent
  • Chemical analysis, electrophoresis and
    ultracentrifugation- consistent with DNA
  • No loss of transforming activity when lipid or
    protein removed
  • No loss of activity with proteases, lipases or
    ribonucleases
  • Loss of activity with deoxyribonucleases

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DNA Double Helix ----secondary
structure
  • 1953
  • Rosalind Franklin Maurice Wilkins (X-ray
    studies)
  • Watson and Crick elucidated the structure
  • Antiparallel chains
  • 5 to 3
  • 3 to 5
  • Right handed helix coiled about central axis

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Structure of B DNA
  • Purines and pyrimidines on inside of helix
  • Sugar-phosphate backbone on outside
  • Sugars are perpendicular to bases
  • Chains held together by hydrogen bonding
  • A hydrogen bonds to T
  • G hydrogen bonds to C

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Base Pairing
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Base Pairing
  • Watson-Crick Complements (Pyrimidine to Purine)
  • T-A
  • C-G
  • W-C Complements pair by hydrogen bonds
  • Nucleotide Bases Hydrophobic

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Major groove and minor groove
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Unusual DNA Structures
  • Palindromes
  • Inverted repeat
  • Mirror repeats
  • Triple helix pairing

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Hoogsteen Pairing
  • Unusual pairing formation
  • Triple helix pairing at low pH

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Remember DNA Structure
  • What are the chemical components of DNA?
  • What chemical bond links the sugar-phosphate
    backbone?
  • What is the difference between a 3 end and a 5
    end?
  • What chemical bond links the sugar to the base?
  • Describe the structure of DNA

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RNA
  • RNA are single strand nucleic acid with Uracil as
    a base instead of Thymine. Sugar is ribose
    instead of deoxyribose.
  • m-RNA (messenger RNA) transcribe info. from DNA
    a-helices.
  • r-RNA (ribosome RNA) this is where protein
    synthesis occurs also known as the protein
    factory.
  • t-RNA (transfer RNA) smallest of RNA, this
    chemical is responsible for carrying amino acids
    to the protein factory (r-RNA) and coordinating
    the amino acid monomeric unit to make a protein..

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Example of folded structures assumed by tRNA
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Denaturation Renaturation
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Denaturation Renaturation
The double helix of DNA can be reversibly melted
by heating the DNA solution This process is
called melting because it occurs abruptly at a
certain temperature. Tm (melting temperature)
half of the helical structure is lost. It
isdepends markedly on base composition(GC 20 to
78----77ºCto 100ºC). The AT rich regions are the
first to melt
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Denaturation Renaturation
Annealing separated complementary strands of DNA
reassociate to form a double helix when
temperature is lowered below Tm Hybridization
annealing of DNA strands from different origins
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Some property of DNA
  • MW 106-109
  • E.coli chromsome four million base pairs,
    2.6109D, 1.4mm (2nm in diameter) the largest
    chromsome of Drosophila melanogaster is 2.1cm in
    length.
  • Absorbance 260nm
  • Hyperchromism the unstacking of the base pairs
    results in the increased absorbance.
  • Electrophoresis PAGE, Agrose gel
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