DNA Replication Biology Mrs. Harper 2/13/18

February 13, 2018 Download notes Begin working on Do Now

Do Now 12/1/15 Who was the first person to get a photograph of DNA? Which scientist(s) discovered the double helix structure? Besides DNA, what did some scientists believe to be the heredity molecule? What did Gregor Mendel discover? Which three scientists made their discovery in 1944? What are the three parts of a nucleotide? What does DNA stand for?

DNA Replication

DNA Replication What is the purpose of DNA replication? To copy genetic material Occurs during S phase of interphase

Complementary Base Pairing (makes replication possible) Adenine pairs with Thymine Guanine pairs with Cytosine Bases form weak hydrogen bonds T A G C copyright cmassengale

Semi-Conservative Replication One side of DNA is the template (old strand) and one side is the complementary (new strand), this is called semi-conservative replication

Antiparallel Strands Strands move in opposite directions (5’ to 3’ or 3’ to 5’) Sugars are connected to phosphates through COVALENT BONDS. copyright cmassengale

Single ring PYRIMIDINES 1.Thymine (T) 2.Cytosine (C) Nitrogenous Bases (Purines only pair with pyrimidines because otherwise the helix would be too wide) Double ring PURINES 1.Adenine (A) 2.Guanine (G) Single ring PYRIMIDINES 1.Thymine (T) 2.Cytosine (C) A or G T or C copyright cmassengale

DNA P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A copyright cmassengale

DNA Replication Origins of replication 1. Replication Forks: site where new DNA strands start growing Replication Fork Parental DNA Molecule 3’ 5’

DNA Replication Strand Separation: 1. Helicase: enzyme which catalyzes the unwinding and separation (breaking the hydrogen bonds) of the parental double helix. 2. Single-Strand Binding Proteins: proteins that help keep the separated strands apart.

DNA Replication Synthesis of the new DNA Strands: 1. DNA Polymerase: with a RNA primer in place, DNA Polymerase (enzyme) catalyze the synthesis of a new DNA strand in the 5’ to 3’ direction. RNA Primer DNA Polymerase Nucleotide 5’ 3’

DNA Replication 2. Leading Strand: synthesized as a single polymer in the 5’ to 3’ direction. RNA Primer DNA Polymerase Nucleotides 3’ 5’

DNA Replication 3. Lagging Strand: also synthesized in the 5’ to 3’ direction, but discontinuously against overall direction of replication. RNA Primer Leading Strand DNA Polymerase 5’ 3’ Lagging Strand 5’ 3’

DNA Replication 4. Okazaki Fragments: series of short segments on the lagging strand. Lagging Strand RNA Primer DNA Polymerase 3’ 5’ Okazaki Fragment

DNA Replication 5. DNA ligase: a linking enzyme that catalyzes the formation of a covalent bond from the 3’ to 5’ end of joining stands. Example: joining two Okazaki fragments together. Lagging Strand Okazaki Fragment 2 DNA ligase Okazaki Fragment 1 5’ 3’

Question: DNA 5’-GCGTATG-3’ What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’

Answer: DNA 5’-GCGTATG-3’ (Old) 3’-CGCATAC-5’ (New)

Correct Answer Problem #1 5’ ACTGA 3’ Old Strand 3’ TGACT 5’ New Strand Problem #2 5’ CTAAG 3’ Find its complementary new strand

Correct Answer Problem #2 5’ CTAAG 3’ Old Strand 3’ GATTC 3’ New Strand Problem # 3: 5’ GCATA 3’ Find its complementary strand

Correct Answer Problem #3 5’ GCATA 3’ Old Strand 3’ CGTAT 5’ New Strand

Nucleotide

Assignment Complete the worksheet independently on CODE RED. Unfinished classwork is homework In a couple minutes, we will begin our activity creating a DNA model.

Creating DNA Models We will create DNA models using the supplies provided in the bag. The twizzlers will represents our sugar-phosphate backbone. The toothpicks will be the hydrogen bonds holding the bases together. Red/orange gummies = Adenine (A) Blue gummies = Thymine (T) Green gummies = Guanine (G) Yellow gummies = Cytosine (C) Build your model. Once finished, raise your hand so I can check to make sure you have the correct sequence to receive credit. You may then eat your model or throw it away at the END of class.

DNA Model Hydrogen bonds (toothpicks) Sugar-Phosphate Backbone (twizzlers) **Make sure you pair each base with its proper pair! Remember the pairing rules! Nitrogen bases (gummy bears)