Welcome to the world of DNA DNA Replication Welcome to the world of DNA Packet #17

DNA Replication (S Synthesis Phase) DNA Deoxyribonucleic Acid Double stranded Three major parts Phosphate Group Sugar--deoxyribose Nitrogenous base (Look at pictures of Bases for rings) Adenine (two rings--Purine) Cytosine (one ring--pyrimidine) Guanine (two rings--Purine) Thymine (one ring--pyrimidine)

DNA Continued Nucleotide Nucleotide Pair A molecule composed of a nitrogen base, a sugar and a phosphate group The basic building block of nucleic acids Nucleotide Pair A pair of bases (one in each strand of DNA) that are joined by hydrogen bonds

DNA Continued Antiparallel In double stranded DNA molecule, the backbones are in opposite, or antiparallel, orientation One strand runs from 5’ to 3’ The other strand runs 3’ to 5’ 5’ end contains phosphate group 3’ end contains hydroxyl group (OH)

DNA Functions Replication of the genetic code in order to maintain genetic continuity from generation to generation Control of the production of cellular enzymes, in order to control the chemical activities of the cell and thereby the phenotypical characteristics of the organism

RNA and Properties RNA Properties Ribonucleic Acid A single stranded nucleic acid similar to DNA Three major parts Phosphate group Sugar--Ribose (change here from DNA) Nitrogenous bases Adenine Cytosine Guanine Uracil--replaces thymine found in DNA Sugar is Ribose--not Deoxyribose that is found in DNA Uracil replaces thymine as the nitrogen base

Watson & Crick I Semi Conservative Replication Known as the Watson and Crick experiment The mechanism for DNA replication in eukaryotes Remember: -The double helix is like a zipper that unzips, starting at one end.

Watson & Crick II In the end, the double helix will contain one parental and one newly synthesized strand Once DNA replication is completed, each DNA strand contains one “old strand/mom/original template strand” and one “new/daughter strand/complementary strand” After DNA replication, we end up with two DNA molecules identical to the one molecule with which we started--if there are no mutations (or no new recombination of genes)**

Semi-Conservative Continued Watson & Crick III Template Strand Aka parental strand Alignment guide Used to reform a double helix identical with the original

Playas of DNA Replication DNA Strands Template Strands {The Parental Strands} Are the strands being copied The original DNA strands During DNA replication, both strands are copied This means that there are TWO template strands Complementary Strands {The Daughter Strands} The NEW DNA strands produced from the Template Strands During DNA replication, there are TWO complementary strands Always remember that the process started with TWO template strands

DNA Strands II Template {Parent} Strand #1 Template {Parent}Strand #2 Produces Complementary (Daughter) Strand Type #1 Template {Parent}Strand #2 Produces Complementary (Daughter) Strand Type #2

Closer Look at the Complementary Strands Complementary (Daughter) Strand Type I “Normal daughter” Known as the LEADING STRAND Complementary (Daughter) Strand Type II “The Crazy-One” Called the”Crazy-One” because the strand is made as a result of combining “Mini-me strands” known as Okazaki Fragments Known as the LAGGING STRAND

Playas of DNA Replication Enzymes Helicase Unzips DNA double-helix RNA primase Initiates the formation of “daughter” strands Forms a segment known as the RNA primer The RNA primer contains the nitrogenous base Uracil DNA Polymerase Enzyme that catalyzes the polymerization (making) of nucleotides Adds Deoxyribonucleotides (nucleotides only found in DNA, as opposed to RNA) to the 3’ end of a growing nucleotide chain Acts at the replication fork A type of DNA polymerase will change the RNA primers into DNA Changing the base Uracil into Thymine

Playas of DNA Replication Enzymes II DNA Ligase Enzyme responsible for joining Okazaki fragments (mini-me daughters) **Gyrase Returns the DNA strands into a Double Helix Zips the DNA back together

The Making of the Complementary Strands Important Note New DNA strands can ONLY be made 5’ to 3’ Nucleotides can ONLY be added at the 3’ END What is a nucleotide?

The Making of the Leading Strand This DNA strand is produced in a “Normal” way The template strand, that is used to produce the Complementary Strand, will run 3’ to 5’ This allows the complementary strand to copied 5’ to 3’ Why? Remember, DNA strands run anti-parallel Nucleotides are only added at the 3’ end Remember the Replication Fork

Order of Enzymes Used in the Production of the Leading Strand Helicase RNA Primase DNA Polymerase Gyrase

The Making of the Lagging Strand This DNA strand is produced in a “crazy” way The template strand, that is used to produce the Lagging Strand, runs 5’ to 3’ This means that the complementary strand should be copied 3’ to 5’ But we know that the DNA strands CANNOT be made in this direction. Why? Because nucleotides can only be added onto the 3’end How is this problem fixed?

Okazaki Fragments These are known as the “Mini-me’s” The problem is solved by making short segments in the correct direction of 5’ to 3’ Examination Question Why are Okazaki fragments produced while making the lagging strand? Because nucleotides can only be added onto the 3’end of a synthesizing DNA strand

Enzymes Used in the Production of the Lagging Strand Helicase RNA Primase DNA Polymerase DNA Ligase Remember, this enzyme is used to join the Okazaki fragments Gyrase

DNA Replication Step by Step Scene I The enzyme, helicase, binds to DNA double helix Unzips DNA at the “Origin of Replication” AKA The entrance ramp to I95

Scene II Elongation RNA Primase makes the RNA primers DNA polymerase adds nucleotides to the 3’ end DNA polymerase changes the RNA primers into DNA DNA Ligase (Only on the Lagging Strand) Joins together the Okazaki fragments

Scene III Reformation of the Double Helix Gyrase zips up the strands together in the form of a Double Helix In the end, there are two double helix DNA molecules similar to the original

Mutations New alleles originate only by mutation or change in nucleotide sequence of DNA Remember that genes are composed of DNA More to come later in Transcription {Packet #18} & Translation {Packet #19}

DNA Technology I

DNA Technology II

DNA Technology III