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Nucleic Acids, DNA Replication and Transcription

Nucleic Acids, DNA Replication and Transcription. BY: JAVIERA CORTES, MARINA GUANGORENA AND LILY HARRIS. Nucleic Acids. Nucleic Acids. Essential for all life Two categories of nucleic acids: D exoyribo N ucleic A cid (DNA) and R ibo N ucleic Acid (RNA) Both RNA and DNA are polymers.

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Nucleic Acids, DNA Replication and Transcription

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  1. Nucleic Acids, DNA Replication and Transcription BY: JAVIERA CORTES, MARINA GUANGORENA AND LILY HARRIS

  2. Nucleic Acids

  3. Nucleic Acids • Essential for all life • Two categories of nucleic acids: DexoyriboNucleic Acid (DNA) and RiboNucleic Acid (RNA) • Both RNA and DNA are polymers

  4. Nucleic Acid Structure Monomers that make up nucleic acids are known as nucleotides Nucleotides in turn have 3 components: A phosphate group A heterocyclic base A sugar

  5. The Basics of Bases • Heterocyclic bases come in two general flavors: • Pyrimidinesand purines • 3 pyrimidines: • Uracil (U), thymine (T) and cytosine (C) • 2 purines: • Adenine (A) and guanine (G)

  6. Ribose Sugars Both sugars are made up of a ribose base Both are in the β configuration Only difference is the absence of an –OH group

  7. DNA Structure A DNA molecule can contain between 1 and 1 million nucleotides! Phosphate groups connect the 5’ carbon of one nucleotide to the 3’ carbon of the next nucleotide Chain goes phosphate-sugar-phosphate (repeating) with different bases attached to the sugars

  8. The Double Helix • Two polynucleotide chains intertwine around each other forming a double helix structure • The two phosphate sugar backbones are pulled together by complementary bases attracted via IMFs • Hydrogen bonds form between A-T bases and C-G bases • For RNA it is A-U instead of A-T

  9. DNA Replication

  10. The process in which an identical strand of DNA is produced • One strand creates two new strands (semiconservative replication) • Process occurs in 3 steps DNA Replication

  11. Enzymes of Replication Helicase DNA Polymerase Primase DNA Ligase DNA Gyrase (bacteria)

  12. Steps of Replication • Step 1: Unwinding the Double Helix • Helicase separates the strands • Unwinding occurs at replication fork • Step 2: DNA Synthesis • DNA polymerase • Leading strand and lagging strand

  13. Lagging Strand • DNA strands run antiparallel • Must be made 5′ to 3′ • Lagging strand in wrong direction • DNA Primase • Okazaki Fragments 3’ to 5’

  14. Lagging Strand

  15. Final Step • Synthesized strands must be rewound • DNA ligase binds segments of the lagging strand • Daughter strands are born

  16. DNA Transcription

  17. DNA is found in the nucleus of a eukaryotic cell and contains the information needed to synthesize proteins • Proteins are made by ribosome in the cytoplasm of the cell • A messenger, mRNA, is responsible for getting the message there! DNA Transcription

  18. mRNA RNA that carries genetic information from the nucleus to the cytoplasm The bases of RNA complement one strand of the DNA sequence Has a short lifespan

  19. Key Players in Transcription • RNA Polymerase • Transcription factor • Ribonucleotides • Spliceosomes

  20. Step 1: Initiation • A gene activating chemical “transcription factor” stimulates loosening of histones and the double helix unwinds • The transcription factor allows RNA Polymerase to bind to the promoter • The promoter is a sequence that specifies where mRNA synthesis should start

  21. Step 2: Elongation RNA polymerase begins to catalyze mRNA in the 5’ to 3’ direction in the template strand (travels 3' to 5' along the DNA strand) It unwinds the DNA strand 16-18 base pairs at a time It aligns complementary ribonucleotides with the DNA strand

  22. Example • A DNA base sequence5’ G-C-A-A-C-T-T-G 3’would have a matching RNA sequence that looks like this 3’ C-G-U-U-G-A-A-C 5’

  23. Some Important Facts • The RNA sequence will contain the nucleutide U (uracil) instead of T (thymine) • The strand of DNA that the RNA polymarase attaches to is called the “template strand” • The other strand is called “coding strand” because mRNA produced will look just like it

  24. Step 3: Termination DNA will contain a special three-base sequence (a codon) that indicates the end of the sequence RNA sequence then detaches from DNA and can then be “edited” in the final step

  25. Final Step • Some genes found in DNA do not code for amino acids and are called introns • Spliceosomes remove introns and splice extrons (which code for amino acids) • mRNA can now move on to the ribosome of the cell where it will be translated

  26. Citations • Image 1: www.britannica.com/EBchecked/media/110068/In-semiconservative-DNA-replication-an-existing-DNA-molecule-is-separated • Image 2: www.cbu.edu/~seisen/DNAStructure. • Image 3: www.dna-sequencing-service.com/dna-sequencing/dna-replication-process/ • Image 4: www.en.wikibooks.org/semiconservative_replication*.png • Chemistry for Today. Spencer L. Seager, Michael R. Slabaugh. Brooks/Cole, Cengage Learning 2011, 2008. Pg. 644-645 • Microbiology (A Human Prospective). Eugene Nester, Denise Anderson, Jr., C. Evans Roberts, Martha Nester. McGraw-Hill Higher Education 2009. Pg. 165-167

  27. Citations Continued • Image 1: dna-rna.net/wp-content/uploads/2011/08/rna-transcription2.jpg • Image 2: leavingbio.net/HEREDITY-HIGHER LEVEL_files/image048.gif • Chemistry for Today. Spencer L. Seager, Michael R. Slabaugh. Brooks/Cole, Cengage Learning 2011, 2008. Pg. 649-654 • Human Anatomy and Physiology 6th ed. Marieb E.  San Francisco CA: Pearson Education, Inc; 2004. p 490-497. • Campbell, N. A., & Reece, J. B. (2005). Biology. (7th ed.). Pearson.

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