DNA replication Chapter 16 Summary of history n

DNA replication Chapter 16

Summary of history n Griffith n Mice & Strep n Transformation n External DNA taken in by cell

Summary of history n Hershey-Chase n Bacteriophages n Supported DNA heredity information was

Bacteriophages

n D: Chapter_16A_Power. Point_Lectures 16_Lecture_Presentation1604 Hershey Chase. Exp. A. html

Summary of history n Franklin n X-ray diffraction n Double helix n Watson-Crick n Double helix model

Nucleic acid structure n DNA deoxyribonucleic acid n RNA ribonucleic acid n Nucleotides

Nucleotide structure n 1. 5 carbon sugar (ribose) n 2. Phosphate n 3. Nitrogenous base

Nucleotide structure

Nitrogenous base n Purines (2 rings) n Adenine(A) & Guanine(G) n Pyrimidines (1 ring) n Cytosine (C), Thymine (T) DNA only n Uracil (U) RNA only

Phosphodiester bond Links 2 sugars (nucleotides)

Nucleic acids n 5’ Phosphate group (5’C) at one end n 3’ Hydroxyl group (3’C) at the other end n Sequence of bases is expressed in the 5’ to 3’ direction n GTCCAT 5’p. Gp. Tp. Cp. Ap. T---OH 3’

Double helix n Complementary n Sequence on one chain of DNA n Determines sequence of other chain n 5’-ATTGCAT-3’ n 3’-TAACGTA-5’

Double Helix n Complementary n Purines pair with pyrimidines n Diameter of base pairs are the same n Adenine (A) forms 2 hydrogen bonds with Thymine (T) n Guanine (G) forms 3 hydrogen bonds with cytosine (C)

Double Helix n Sugar-phosphates are the backbone n Complementary n Phosphodiester bonds n Strands are antiparrellel n Bases extend into interior of helix n Base-pairs form to join the two strands

Fig. 16 -7 5 end Hydrogen bond 3 end 1 nm 3. 4 nm 3 end 0. 34 nm (a) Key features of DNA structure (b) Partial chemical structure 5 end

Duplication n DNA unzips-breaks hydrogen bonds n New strand forms based on existing strand n Old strand is saved n Compliment of new strand n New DNA-one old strand & one new strand n Semiconservative replication

Fig. 16 -9 -3 A T A T C G C G T A T A T G C G C (a) Parent molecule (b) Separation of strands (c) “Daughter” DNA molecules, each consisting of one parental strand one new strand

Duplication study n Meselson and Stahl n Bacteria and 15 N n Semiconservative method. n 14 N

Fig. 16 -10 Parent cell (a) Conservative model (b) Semiconservative model (c) Dispersive model First replication Second replication

Summary G: Chapter_16A_Power. Point_Lectures16_Lec ture_Presentation1605 DNAand. RNAStructure. A. html

Duplication Enzymes n DNA helicase: n Enzyme opens helix starts duplication n Separates parental strands n Single-strand binding protein: n Binds to unpaired DNA n After separation n Stabilizes DNA

Duplication Enzymes n DNA polymerases: n Help lengthen new strand of DNA n Adds new nucleotides strand n Synthesis occurs only one direction n 5’ to 3’ n Adding new nucleotides to the 3’OH

Duplication Enzymes n Primer: n Section of RNA n Complementary to the parental DNA n Synthesis occurs only one direction n 5’ to 3’ n DNA primase: n Enzyme creates the primer

Duplication Enzymes n n n n Topoisomerase: Relieves strain of unwinding DNA pol 1: Removes primers Replaces with DNA nucleotides DNA ligase: Creates phosphodiester bonds between Okazaki fragments

Duplication n n n Ori. C Origins of replication Starting point in DNA synthesis Replication is bidirectional Proceeds in both directions from origin 5’to 3’direction

Duplication n. E coli (bacteria) n Circular DNA n One origin n Eurkaryotes n Multiple origins

Duplication n Replication bubble: n Separation of strands of DNA n Replication fork: n Y-shaped region n End of replication bubble n Site of active replication

Duplication

Duplication

Duplication n n n Leading strand: DNA continuous 5’ to 3’ replication (towards fork) Template is 3’ to 5’ Lagging strand: DNA duplicated in short segments (away from fork) Okazaki fragments: Short stretches of new DNA-lagging side

Duplication D: Chapter_16A_Power. Point_Lectures16_ Lecture_Presentation1609 DNAReplicat. Ov erview. A. html

Duplication n Unzips (helicase, single-strand binding protein, topoisomerase) n Primer n DNA polymerase (5’to 3’) n DNA ligase

Duplication

Fig. 16 -14 New strand 5 end Sugar 5 end 3 end T A T C G G C T A A Base Phosphate Template strand 3 end DNA polymerase 3 end A T Pyrophosphate 3 end C Nucleoside triphosphate 5 end C 5 end

D: Chapter_16A_Power. Point_Lectures16_Lecture_ Presentation1615 Leading. Strand. A. html

Fig. 16 -13 Primase Single-strand binding proteins 3 Topoisomerase 5 3 5 Helicase 5 RNA primer 3

Fig. 16 -15 b Origin of replication 3 5 RNA primer 5 “Sliding clamp” 3 5 Parental DNA pol III 3 5 5 3 5

Fig. 16 -16 a Overview Origin of replication Leading strand Lagging strand 2 1 Leading strand Overall directions of replication

n D: Chapter_16A_Power. Point_Lectures 16_Lecture_Presentation1616 Lagging Strand. A. html

Fig. 16 -17 Overview Origin of replication Lagging strand Leading strand Lagging strand Overall directions of replication Single-strand binding protein Helicase 5 3 Parental DNA Leading strand 3 DNA pol III Primer 5 Primase 3 5 DNA pol III 4 3 5 Lagging strand DNA pol I 3 2 DNA ligase 1 3 5

Fig. 16 -16 Overview Origin of replication Lagging strand Leading strand Lagging strand 2 1 Leading strand Overall directions of replication 3 5 5 Template strand 3 RNA primer 3 5 3 1 5 3 5 Okazaki fragment 3 1 5 3 5 2 3 3 5 1 5 2 1 3 5 Overall direction of replication

Duplication

Duplication

Duplication n n n n Telomers: Sequences at ends of chromosomes Short nucleotide sequences Repeated 100 -1000 times Prevents 5’ end erosion Telomerase: Enzyme that lengthens telomers Usually in germ cells

Repairs n n n n Mismatched pair: Duplication error Enzymes remove error Nucleotide excision repair: Damaged section removed Nuclease New nucleotides fill gap Complement DNA section not damaged

Chromosome packaging n n n n Chromatin: Complex composed of DNA and proteins 40% DNA 60% protein Heterochromatin: More compacted chromatin Euchromatin: Loosely packed chromatin

Chromosome packaging n Double helix n Histones: proteins n Nucleosome: DNA coiled around 8 histones (10 nm) n Nucleosomes then coil (30 nm) n Looped domains attach to chromosome scaffold (300 nm) n Domains coil form chromosome

D: Chapter_16A_Power. Point_Lectures16_Lecture_Pres entation1621 DNAPacking_A. html