DNA structure, Functions and properties
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DNA structure, Functions and properties

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Structure of DNA , Functions and Properties

Structure of DNA , Functions and Properties

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DNA structure, Functions and properties DNA structure, Functions and properties Presentation Transcript

  • DNA Structure,Functions and Properties Biochemistry for Medics dr-namrata.blogspot.com Biochemistry for Medics
  • DNA
    • DNA - a polymer of deoxyribo nucleotides
    • found in chromosomes, mitochondria and chloroplasts
    • carries the genetic information
    Biochemistry for Medics
  • Components of a nucleotide Base Sugar Phosphate Biochemistry for Medics
  • Base Phosphate Biochemistry for Medics Nucleotide Nucleoside Sugar X=H: DNA X=OH: RNA
  • Basic structure of pyrimidine and purine Biochemistry for Medics
  • Pyrimidines Biochemistry for Medics
  • Purines Biochemistry for Medics
  • Nomenclature of Nucleic Acid Components Base Nucleoside Nucleotide Nucleic acid Purines Adenine Adenosine Adenylate RNA Deoxyadenosine Deoxyadenylate DNA Guanine Guanosine Guanylate RNA Deoxy guanosine Deoxyguanylate DNA Pyrimidine s Cytosine Cytidine Cytidylate RNA Deoxycytidine Deoxycytidylate DNA Thymine Thymidine Thymidylate DNA (deoxythymidine) (deoxythymidylate) Uracil Uridine Uridylate RNA Biochemistry for Medics
  • 5-Fluorouracil 6-Mercaptopurine Anticancer agents Azidothymidine Dideoxyinosine Antiretroviral agents Nucleoside and base analogs can be used as anti-cancer and anti-virus drugs Biochemistry for Medics
  • DNA structure
    • Primary structure
    • Secondary structure
    • Tertiary structure
    Biochemistry for Medics
  • The primary structure of DNA is the sequence 5’ end 3’ end 5’ 3’ Phosphodiester linkage Biochemistry for Medics
  • Traditionally, a DNA sequence is drawn from 5’ to 3’ end. A shorthand notation for this sequence is ACGTA Biochemistry for Medics
  • The secondary structure of DNA is the double helix Biochemistry for Medics
  • The secondary structure of DNA Two anti-parallel polynucleotide chains wound around the same axis. Sugar-phosphate chains wrap around the periphery. Bases (A, T, C and G) occupy the core, forming complementary A · T and G · C Watson-Crick base pairs. Biochemistry for Medics
    • hydrogen bonding;
    • base stacking
    The DNA double helix is held together mainly by- Hydrogen bonds Biochemistry for Medics
  • Hydrogen bond a chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom, especially a nitrogen, oxygen, or fluorine atom, usually of another molecule. Biochemistry for Medics
  • Two hydrogen bonds between A:T pairs Three hydrogen bonds between C: G paire Biochemistry for Medics
    • Base Stacking
    • The bases in DNA are planar and have a tendency to "stack".
    • Major stacking forces:
    • hydrophobic interaction
    • van der Waals forces.
    Biochemistry for Medics
  • Structural forms of DNA Biochemistry for Medics Property A-DNA B-DNA Z-DNA Helix Handedness Right Right Left Base Pairs per turn 11 10.4 12 Rise per base pair along axis 0.23nm 0.34nm 0.38nm Pitch 2.46nm 3.40nm 4.56nm Diameter 2.55nm 2.37nm 1.84nm Conformation of Glycosidic bond anti anti Alternating anti and syn Major Groove Present Present Absent Minor Groove Present Present Deep cleft
  • Helical sense: right handed Base pairs: almost perpendicular to the helix axis; 3.4 Å apart One turn of the helix: 36 Å; ~10.4 base pairs Minor groove: 12 Å across Major groove: 22 Å across Normally hydrated DNA: B-form DNA Biochemistry for Medics
  • In eukaryotic cells, DNA is folded into chromatin Biochemistry for Medics
  • DNA Tertiary Structure
    • DNA DOUBLE HELICAL STRUCTURE COILS ROUND HISTONES.
    • DNA BOUND TO HISTONES FORM S
    • NUCLEOSOMES (10nm FIBRES)
    • NUCLEOSOMES CONTAIN 146 NUCLEOTIDES
    Biochemistry for Medics
  • Nucleosomes any of the repeating globular subunits of chromatin that consist of a complex of DNA and histone Biochemistry for Medics
  • Structure of nucleosome core Biochemistry for Medics
  • Compaction of DNA in a eukaryotic chromosome Biochemistry for Medics
  • Supercoil = coil over coil Biochemistry for Medics
  • DNA melting and annealing Biochemistry for Medics
  • Reversible denaturation and annealing of DNA Biochemistry for Medics
  • Melting point ( t m ) of DNA The temperature at the mid-point of the transition Biochemistry for Medics
  • The t m of DNA depends on:
    • size of DNA
    • pH
    • ionic strength
    • Content of G·C base pairs
    Biochemistry for Medics
  • Biochemistry for Medics Functions of DNA and summary of structure DNA consists of four bases—A, G, C, and T—that are held in linear array by phosphodiester bonds through the 3' and 5' positions of adjacent deoxyribose moieties. DNA is organized into two strands by the pairing of bases A to T and G to C on complementary strands. These strands form a double helix around a central axis. The 3 x 10 9 base pairs of DNA in humans are organized into the haploid complement of 23 chromosomes. DNA provides a template for its own replication and thus maintenance of the genotype and for the transcription of the roughly 30,000 human genes into a variety of RNA molecules.