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

2. 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)

5. 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

7. 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)

9. 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

10. 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

12. 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.

15. 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)**

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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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?

24. 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

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

27. 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?

28. 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

29. 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

31. 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

34. 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

35. 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

36. 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}

37. DNA Technology I

38. DNA Technology II

39. DNA Technology III