DNA Replication

POINT > Explain how the structure of DNA makes replication possible POINT > Show how synthesis of new DNA strands is directional POINT > Describe the formation of Okazaki fragments POINT > Identify some of the key enzymes in the replication process

POINT > Explain how the structure of DNA makes replication possible Recall that nucleotide base pairing is very specific between two complementary DNA strands: A – T and G - C

POINT > Explain how the structure of DNA makes replication possible Adenine always hydrogen bonds with thymine (A-T) Guanine always hydrogen bonds with cytosine (G-C)

POINT > Explain how the structure of DNA makes replication possible During DNA replication the two strands are separated. Then other nucleotides fill in, A with T G with C This creates two new DNA strands

POINT > Explain how the structure of DNA makes replication possible

WB CHECK: What kind of bonds have to be broken to separate the two strands of a DNA molecule? How many sugar-phosphate backbones does a double-stranded DNA molecule have?

POINT > Explain how the structure of DNA makes replication possible 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ Complementary strands in a DNA molecule 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ The two DNA strands are separated 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ Complementary nucleotides are incorporated into new DNA strands

POINT > Explain how the structure of DNA makes replication possible 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ 3’ATCGGACTAGCATAG5 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ The two original DNA molecule strands are not conserved intact together However, the two original strands are intact as part of new DNA molecules We call this semi-conservative replication

POINT > Explain how the structure of DNA makes replication possible Replication Fork

WB CHECK: “Semi-conservative” replication means that a) both new DNA molecules have one strand from the original molecule b) both new DNA molecules have two strands from the original molecule c) both new DNA molecules are made from scratch with new nucleotides

POINT > Show how synthesis of a new DNA strand is directional New strands of DNA (or RNA) are only synthesized in the 5’ >> 3’ direction

POINT > Show how synthesis of a new DNA strand is directional The 5’ >> 3’ direction of synthesis means that 1 strand is “leading” and 1 strand is “lagging”

POINT > Describe the formation of Okazaki fragments The 5’ >> 3’ direction of synthesis results in the formation of Okazaki fragments: short DNA pieces

POINT > Describe the formation of Okazaki fragments The 5’ >> 3’ direction of synthesis results in the formation of Okazaki fragments: short DNA pieces

POINT > Show how synthesis of a new DNA strand is directional Because DNA molecules are so long (millions of base pairs) replication starts at lots of different sites along the length of the DNA molecule This causes replication bubbles

WB CHECK: Okazaki fragments appear a) on both new DNA strands b) only on the leading strand c) only on the lagging strand

WB CHECK: Okazaki fragments appear because a) the new nucleotides get added on too fast b) the replication fork opens too slowly c) DNA can only be made in a 5` >> 3` direction d) DNA can only be made in a 3` >> 5` direction

WB CHECK: DNA molecules are very long. It would be impossible to get replication done if you just started at one end of the DNA. So, DNA replication starts at many different points along the DNA molecule. This results in a) Okazaki fragments b) replication bubbles c) mutations d) semi-conservative replication

POINT > Identify some of the key enzymes in the replication process

POINT > Identify some of the key enzymes in the replication process Helicase – responsible for unwinding the DNA ahead of the replication fork DNA Polymerase – responsible for adding the new and correct nucleotides to the growing strands DNA Ligase – responsible for patching the Okazaki fragments together (the gaps in the sugar-phosphate backbone)

WB CHECK: The enzyme responsible for “patching” the sugar-phosphate backbone between Okazaki fragments is a) helicase b) DNA ligase c) DNA polymerase d) RNA polymerase

WB CHECK: The enzyme responsible separating the two original DNA strands and creating the replication fork is a) helicase b) DNA ligase c) DNA polymerase d) RNA polymerase

WB CHECK: DNA polymerase a) adds new nucleotides in a 5` >> 3` direction b) unwinds the DNA at the replication fork c) builds the new DNA strands d) patches together Okazaki fragments e) a and b f) a and c g) b and c

Homework: 1. Read Pages 350-353 2. Assess page 353 #1-2 3. Workbook pages 209-211 4. Choose one DNA researcher, and write a short Bio 150-200 words typed. In your own words: **birth and death **education **contribution to science ** Due Wednesday