What is the chemical structure of Deoxyribonucleic Acid

What is the chemical structure of Deoxyribonucleic Acid (DNA) and how does that structure relate to is functions?

• What is the purpose of DNA? • Where is DNA located? • What types of cells contain DNA, prokaryotic or eukaryotic? • Which of your cells do not contain DNA?

• What is the purpose of DNA? Storage of instructions for all cellular processes • Where is DNA located? The Nucleus (Euk) or Nucleiod (Prok) • What types of cells contain DNA, prokaryotic or eukaryotic? Prok & Euk • Which of your cells do not contain DNA? Red blood cells

• https: //www. dnalc. org/resources/3 d/07 -howdna-is-packaged-basic. html

HL Only : Histones & Nucleosomes

Prokaryotic vs. Eukaryotic Chromosomes • Prokaryotes (Bacteria & Archaea) have one single, circular chromosome • Humans have 46 total chromosomes that are linear ; 23 from mom, and 23 from dad

Extra Extension: Why is DNA split into different chromosomes, versus just being one large chromosome? • http: //genetics. thetech. org/ask 184

DNA : deoxyribonucleic acid The double helix

Maurice Wilkins • Developed a way to isolate single fibers of DNA • Would later partner with Rosalind Franklin so that it could be used in a light diffraction imaging method.

Rosalind Franklin • Developed a method to produce clear images of diffraction patterns from DNA

• Source: http: //images. slideplayer. com/13/3866721/slides/slide_18. jpg

The Structure of DNA • Structurally, DNA is made up of nucleotides. • A nucleotide is made up of sugar, a phosphate, and a nitrogenous base. • Nucleotides bond together to make the sugar-phosphate backbone of every strand of DNA. • The sugar-phosphate backbone is held together by strong covalent bonds (phosphodiester bonds). • Organic bases pair up with complimentary bases on the opposite strand of DNA. • There are four kinds of organic bases: adenine (A), thymine (T), guanine (G), and cytosine (C). • Adenine always pairs with thymine, and guanine with cytosine (base pairs) • The two strands of DNA are held together by weak hydrogen bonds.

Specific Base Pairing Due to Number of Hydrogen Bonds Required • Adenine and Thymine – How many hydrogen bonds can they each form? • Cytosine and Guanine – How many hydrogen bonds can they each form?

Significance of DNA Structure & Complimentary Base Pairing • Allows for accurate replication, transcription, and translation of DNA. • Allows for DNA molecules to be identical to one another. • Allows for conservation of original base sequence of DNA.

DNA Strands are “Anti-Parallel” to each other (HL Only)

DNA Structure • DNA is organized comprised of long chains of nucleotides twisted into a double helix. • DNA is a polymer of DNA nucleotide monomers

THINK BACK: Mitosis • How did you start as one cell and end up as trillions of cells? • What is mitosis?

THINK BACK: Mitosis • How did you start as one cell and end up as trillions of cells? • What is mitosis? Process of making an IDENTICAL copy of 1 cell – daughter cells are genetically identical to parent cell

DNA REPLICATION: Making exact copies of DNA • WHEN does DNA replication occur in the cell? • WHERE must DNA replication occur in the cell? • WHY does DNA replication occur there?

DNA REPLICATION • Replication is a process in which two exact copies of DNA are made from ONE DNA molecule • WHEN does DNA replication occur in the cell? At the end of interphase, before mitosis. • WHERE must DNA replication occur in the cell? In the nucleus. • WHY does DNA replication occur in the cell? DNA must be copied before the cell divides so that each daughter cell contains identical DNA.

DNA Replication Occurs During the S- Phase of the Cell Cycle

DNA Replication: • Video to Review Mitosis + DNA Replication: https: //www. youtube. com/watch? v=5 q. Srmei. Wsuc

• Helicase: separates and unwinds double helix • DNA Polymerase III: brings and adds new nucleotides to growing daughter strand • Ligase: chemically bonds new nucleotides together (glue for new DNA strand)

Key Players Continued (HL Only) • Primase: “flags” site of replication by adding a small molecule called RNA primer that DNA Polymerase III to bind and begin replication • DNA Polymerase I: removes RNA primers • Gyrase: relieves strain in the uncoiled helix so that helicase can attach and act • Single-stranded binding proteins (SSBs): keep DNA strands apart long enough to allow the template (parent) strand to be copied • Ligase: chemically bonds Okazaki fragments together

DNA Replication is “Semi-conservative” as a result of “Complimentary base pairing” When a new double-stranded DNA molecule is formed: § One strand will be from the original template molecule § One strand will be newly synthesized

DNA Replication can only occur in a 5’ → 3’ direction • Nucleotides are covalently bonded together in a 5’ → 3’ direction

DNA Replication Animation • Animation Link: http: //highered. mheducation. com/sites/0072943696/studen t_view 0/chapter 3/animation__dna_replication__quiz_1_. ht

Steps of DNA Replication (SL Version) 1. Helicase enzyme (unzip yo’ genes) opens the DNA helix by breaking the hydrogen bonds between the nitrogenous base pairs. The helicase separate the base pairs and expose the bases to the nucleoplasm (liquid in the nucleus). 2. DNA polymerase III enzyme bring the complementary (matching) nitrogenous bases to the open helix. 3. Added nucleotides are covalently bonded together by the enzyme ligase, forming the sugar-phosphate backbone. 4. Enzymes will continue doing their work until the parent strand is completely copied, resulting in two semiconservative strands of DNA that are identical to one another. Each daughter strand compliments the bases from the original parent strand.

HL: Replication including DNA Polymerase III, DNA Polymerase I, Primase, RNA Primer, & Okazaki Fragments

HL Version 1) Gyrase attaches to, and stabilizes the double helix so that helicase 2) 3) 4) 5) 6) 7) 8) 9) can attach and unwind. Helicase unwinds the parental double helix by breaking the hydrogen bonds between the base pairs. Single strand binding proteins (SSBs) stabilize the unwound helix. DNA can only be synthesized in the 5’ → 3’ direction, so there is a leading strand a lagging strand. The leading strand is synthesized continuously in the 5’ → 3’ direction by DNA Polymerase III. The lagging strand is synthesized discontinuously, starting with primase. Primase synthesizes a small RNA primer molecule as a starting point for DNA Polymerase III to add new nucleotides. Nucleotides are added to the RNA primer, forming short Okazaki fragments. Once the fragment is synthesized, DNA Polymerase I removes the RNA primer molecule. Ligase fills in the gaps from the RNA primer, and covalently bonds Okazaki fragments together.

DNA Replication Diagram (HL)