DNA Structure and Replication.

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  • 1. DNA Structure and Replication Submitted by: Esguerra, Joanna Marie Evaristo, Roselle AAPD2G 1
  • 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.  In the 1940s, various researchers showed that DNA was the genetic material In the 1950s, the structure of DNA was determined. 3
  • 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.  The sugar in DNA is deoxyribose The four different bases in DNA are: adenine (A), thymine (T), guanine (G), and cytosine (C). 5
  • 6. A nucleotide 6
  • 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
  • 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. DNAdoublehelix 10
  • 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.  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. DNA replication 13
  • 14. Ladder configuration and DNA replication 14
  • 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. 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.  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. Structure of RNA 18
  • 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. 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.  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
  • 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. Overviewof geneexpression 24
  • 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. Transcription and mRNA synthesis 26
  • 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. 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.  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