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Transcript
DNA and Replication 1 Rosalind Franklin 2 Chargaff’s Rule • Adenine must pair with Thymine • Guanine must pair with Cytosine • The bases form weak hydrogen bonds T A G C 3 DNA • Two strands coiled called a double helix • Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO4) groups • Center made of nitrogen bases bonded together by weak hydrogen bonds 4 Three Parts of the DNA Nucleotide Phosphate Group O O=P-O O CH2 O N C C Sugar (deoxyribose) C C Nitrogenous base (A, G, C, or T) 5 DNA O O P P O O P C G O T P A O P P6 Question • If there is 30% Adenine, how much Cytosine is present? 7 Answer • There would be 20% Cytosine • Adenine (30%) = Thymine (30%) • Guanine (20%) = Cytosine (20%) • Therefore, 60% A-T and 40% C-G 8 DNA Replication 9 Replication Facts • DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission. 10 DNA Replication • Begins at Origins of Replication • Two strands open forming Replication Forks (Y-shaped region) • New strands grow at the forks 5’ Parental DNA Molecule 3’ 3’ Replication Fork 11 5’ DNA as a Zipper 12 DNA Replication • Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds 13 Question • How does the structure of DNA make it easy to copy? 14 DNA Replication • DNA polymerase (enzyme) adds the new nucleotides • Covalent bonds form between deoxyribose sugar and phosphate group. • Hydrogen bonds between nitrogenous bases. 15 Zipper Movement 16 Question • Are the nucleotides of the new sequences of the new strand identical to the original? 17 Synthesis of the New DNA Strands • The Leading Strand is synthesized as a single strand from the point of origin toward the opening replication fork 5’ 3’ Nucleotides DNA Polymerase 5’ RNA Primer 18 Synthesis of the New DNA Strands • The Lagging Strand is made in MANY short segments It is replicated from the replication fork toward the origin • Leaves gaps in new strand. Gaps filled in by DNA ligase Leading Strand 5 ’ 3’ DNA Polymerase 5’ 3’ Lagging Strand RNA Primer 3’ 5’ 3’ 5’ 19 Replication of Strands Replication Fork Point of Origin 20 Semiconservative Model of Replication • New DNA consists of 1 PARENTAL (template) and 1 NEW (complementary) strand of DNA DNA Template Parental DNA New DNA 21 Question • Why is the new strand complementary to the original strand? 22 Question • After a cell’s DNA is replicated, the cell may divide in two. Each new cell receives one copy of the original cell’s DNA. How are the new strands and the original strands divided between the two new cells? 23 • Explain the statement, “DNA replication depends on specific base pairs”. 24 Activity: • Is photography a document similar to DNA replication? Think of the original materials, the copying process, and the final products. Explain how the two processes are alike. Identify major differences. 25