Dna

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Dna

  1. 1. DNA Structure & Function
  2. 2. Key terms  Genome = complete set of sequences in the genetic material of an org.  Nucleic acids = Macromolecules (large RMM).  Chromosomes = Discrete unit of the genome carrying many genes. NA and protein.  Gene = Segment of DNA specifying production of a polypeptide chain. It codes for a RNA protein.
  3. 3. • Genotypic = Replication. Store &transmit info. • Phenotypic = Gene expression. Control devlp of phenotype. • Evolutionary = Mutation. Changes produce variations. Fx…..preserving, copying and transmitting information.
  4. 4.  Chromosomes composed of 2 macmol.  i. Protein.  ii. Nucleic acids DNA(d) and RNA(s)
  5. 5. Structure of nucleotides..  A ) 5 carbon pentose sugar ; RNA = Ribose, DNA = Deoxyribose. b) A nitrogen containing base; 2 Purines (A,G) 2 Pyrimidines (C,T/U) RNA = CGAU, DNA = CGAT c) A phosphate group
  6. 6. Pentose sugars
  7. 7. Structure of nucleotides
  8. 8. Watson and Crick’s model  double helix  sugar-phosphate backbone = sugar is deoxyribose  4 types of nucleotide base : A, C, G, T  : 2 complementary strands where A = T, C = G in anti parallel fashion – "complementary“ = fitting together of 2 molecules with hydrogen bonds
  9. 9. Phosphodiester bonds..  A dinucleotide is formed when a condensation reaction occurs between the phosphate group of one nucleotide and pentose of another forming a phosphodiester bridge linking the 2 nucleotides together.
  10. 10. More nucleotides can be added, building up a long polynucleotide chain.
  11. 11.  The stability of the double helix is due to the large number of covalent, H+ and hydrophobic bonds.
  12. 12. Double Helix.. Uprights = Sugar phosphate bond, Rungs = Bases (A+T/G+C) 2 strands running in opposite direction (5’ – 3’) <>
  13. 13. Genetic code  These bases always pair up in the same way.  A single strand of DNA is made of letters: ATGCTCGAATAAATG  The letters make words: ATG CTC GAA TAA ATG TGA ATT TGA  The words make sentences: <ATG CTC GAA TAA> <ATG TGA ATT TGA>  These "sentences" are called genes
  14. 14. Genetic code  The instructions in a gene that tell the cell how to make a specific protein. A, T, G, and C.  3 letter word = codon = Triplet code.  Fx of codon = tell the cell how to make proteins  Start and stop codon.
  15. 15. Genetic code contd..  Inside the nucleus, the DNA message is copied onto RNA. to transmit the message or genetic code.  It has 4 subunits A, T, G, C and are arranged in triplet codes. Eg ATTGCCTAG read from left to right ATT/GCC/TAG. Each triplet code specifies different amino acids. Eg. ATT = amino acid “X” GCC = amino acid “Y” TAG = amino acid “Z”  This piece of genetic code will instruct the cell to make a protein in which X,Y and Z are joined together in that order.

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