DNA Structure and Replication.


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DNA Structure and Replication.

  1. 1. DNA Structure and Replication Submitted by: Esguerra, Joanna Marie Evaristo, Roselle AAPD2G 1
  2. 2.  In the early 1900s, scientists knew that chromosomes are made up of DNA (deoxyribonucleic acid) and proteins, contained genetic information. However, they did not know whether the DNA or the proteins was the actual genetic material. 2
  3. 3.  In the 1940s, various researchers showed that DNA was the genetic material In the 1950s, the structure of DNA was determined. 3
  4. 4. Structure of DNAThe structure of DNA was determined byJames Watson and Francis Crick inthe early 1950s.DNA is a polynucleotide; nucleotides arecomposed of a phosphate, a sugar, and anitrogen-containing base. 4
  5. 5.  The sugar in DNA is deoxyribose The four different bases in DNA are: adenine (A), thymine (T), guanine (G), and cytosine (C). 5
  6. 6. A nucleotide 6
  7. 7. Watson and Crick showed that DNA is a doublehelix in which A is paired with T G is paired with CThis is called complementary base pairingbecause a purine is always paired with apyrimidine. 7
  8. 8. 8
  9. 9. When the DNA double helix unwinds, it resembles aladder.The sides of the ladder are the sugar-phosphatebackbones, and the rungs of the ladder are thecomplementary paired bases.The two DNA strands are anti-parallel – they runin opposite directions. 9
  10. 10. DNAdoublehelix 10
  11. 11. Replication of DNADNA replication occurs during chromosomeduplication.An exact copy of the DNA is produced with the aid ofDNA polymerase.Hydrogen bonds between bases break and enzymes“unzip” the molecule. 11
  12. 12.  Each old strand of nucleotides serves as a template for each new strand. New nucleotides move into complementary positions are joined by DNA polymerase. 12
  13. 13. DNA replication 13
  14. 14. Ladder configuration and DNA replication 14
  15. 15. Gene ExpressionA gene is a segment of DNA that specifies the aminoacid sequence of a protein.Gene expression occurs when gene activity leads toa protein product in the cell.A gene does not directly control protein synthesis;instead, it passes its genetic information on to RNA,which is more directly involved in protein synthesis. 15
  16. 16. RNA (ribonucleic acid ) is a single-stranded nucleic acid in which (adenine) A pairs with U (uracil ) (guanine) G pairs with C. (cytosine) 16
  17. 17.  messenger RNA (mRNA) carries genetic information to the ribosomes, ribosomal RNA (rRNA) is found in the ribosomes, transferRNA (tRNA) transfers amino acids to the ribosomes, where the protein product is synthesized. 17
  18. 18. Structure of RNA 18
  19. 19. Two processes are involved in the synthesis ofproteins in the cell: Transcription makes an RNA molecule complementary to a portion of DNA. Translation occurs when the sequence of bases of mRNA directs the sequence ofamino acids in a polypeptide. 19
  20. 20. The Genetic CodeDNA specifies the synthesis of proteinsbecause it contains a triplet code: everythree bases stand for one amino acid.Each three-letter unit of an mRNAmolecule is called a codon. 20
  21. 21.  Most amino acids have more than one codon; there are 20 amino acids with a possible 64 different triplets. The code is nearly universal among living organisms. 21
  22. 22. 22
  23. 23. Central Concept or " The Central Dogma"The central concept of genetics involves the DNA-to-protein sequence involving transcription andtranslation.DNA has a sequence of bases that is transcribed intoa sequence of bases in mRNA.Every three bases is a codon that stands for aparticular amino acid. 23
  24. 24. Overviewof geneexpression 24
  25. 25.  During transcription in the nucleus, a segment of DNA unwinds and unzips, and the DNA serves as a template for mRNA formation. RNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to the triplet code in DNA. 25
  26. 26. Transcription and mRNA synthesis 26
  27. 27. TranslationTranslation is the second step by which geneexpression leads to protein synthesis.During translation, the sequence of codons in mRNAspecifies the order of amino acids in a protein.Translation requires several enzymes and two othertypes of RNA: transfer RNA and ribosomal RNA. 27
  28. 28. Review of Gene ExpressionDNA in the nucleus contains a tripletcode; each group of three bases standsfor one amino acid.During transcription, an mRNA copy ofthe DNA template is made. 28
  29. 29.  The mRNA is processed before leaving the nucleus. The mRNA joins with a ribosome, where tRNA carries the amino acids into position during translation. 29