1. C-Notes: DNA Replication
Stnd: BI.5.b
C-Notes: DNA Replication
9/23/13
SWBAT describe the base-pairing rules to explain precise copying of DNA during Semi-Conservative Replication.
Objective:

2. The DNA backbone Putting the DNA backbone together5
PO4
Putting the DNA backbone together
refer to the 3 and 5 ends of the DNA
the last trailing carbon
base
CH2 5 O 4 1 C 3 2 O –O P O
Sounds trivial, but… this will be IMPORTANT!! O
base
CH2 5 O 4 1 3 2 OH 3

3. Anti-parallel strands
Nucleotides in DNA backbone are bonded from phosphate to sugar between 3 & 5 carbons
DNA molecule has “direction”
complementary strand runs in opposite direction 5 3 3 5

4. Where does DNA get replicated at?
Your DNA is divided into 46 chromosomes that are replicated during the S phase of the Cell Cycle
Your DNA is copied once in each round of the Cell Cycle.
Occurs within the Nucleus

5. Important Enzymes for DNA Replication
1. Helicase: catalyze by unwinding and separation (breaking H-Bonds) of the parental double helix.
2. Single-Strand Binding Proteins: help keep the separated strands apart.
3. Topoisomerase: allowing free rotation around a single strand by removing any twisted knots when unwinding.
4. DNA Polymerase: proofreads & repairs mismatched bases and removes incorrect bases
5. DNA Replicase: brings in complementary Nitrogenous bases
6. DNA Ligase: seals up the fragments into one long continuous strand

6. DNA Replication Strand Separation:
3. Topoisomerase: enzyme which relieves stress on the DNA molecule by allowing free rotation around a single strand.
Enzyme
DNA
Enzyme

7. 06_04_replic.rounds.jpg
06_04_replic.rounds.jpg

8. How does DNA replication begin making copies of itself?
Step 1: “UNZIP” or “UNTWISTING” of the parent (original) DNA Molecule.
Step 2: Form hydrogen bonds with a Complementary nucleotide on each TEMPLATE strand (old parent strand)
**Because base pairing is SPECIFIC, the sequence of one strand dictates what the sequence of the other strand has to be. **
Step 3: Backbone formation in daughter strands
**Each new DNA molecule contains one strand from the parent DNA that acted as a template and a second strand that is newly formed making the copies semi-conservative.**

9. What are the steps for DNA Replication?
Step1: DNA unwinds into 2 strands with the help of the enzyme “Helicase” . (This breaks the hydrogen bonds that are between the nitrogenous bases.)
As “Helicase” unwinds the top, “Topoisomerase” Enzyme will bind to the opposite end to remove any twisting and knots that has formed at the bottom as
Step 2: “Single-Strand binding” (SSB) proteins binds to the single strand to stabilize the separated strands from joining back together
About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.

10. Replication: 1st step Unwind DNA helicase enzyme
unwinds part of DNA helix
stabilized by single-stranded binding proteins
Replication
Fork
Parental DNA Molecule 3’ 5’
helicase
single-stranded binding proteins
replication fork

11. Replication fork lagging strand leading strand 3’ 5’ 5’ 3’ 5’ 3’ 5’ 3’
DNA polymerase III
lagging strand
DNA polymerase I 3’
primase
Okazaki fragments 5’ 5’
ligase
SSB 3’ 5’ 3’
helicase
DNA polymerase III 5’
leading strand 3’
direction of replication
SSB = single-stranded binding proteins

12. What are the steps for DNA Replication?
At the Replication Fork, new complementary N-Bases are added to the 3’-5’ template strand according to the base pairing rules by “DNA Polymerase” enzyme.Making the NEW strand, a “Leading Strand”.
Elongating only in the 5’-3’ direction by enzyme “DNA Replicase” bringing in
About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.
RNA
Primer
DNA Polymerase
Nucleotides 3’ 5’

13. C - G A - T Enzyme “DNA Replicase” brings in complementary N-bases

14. What are the steps for DNA Replication?
To make the 2nd new strand, the other 5’-3’ template strand is made in the same way EXCEPT in “Small Discontinuous Segments” called “Okazaki Fragments” which are later joined by “DNA Ligase” enzyme
Which is elongating in the 3’-5’ direction, making it the “Lagging Strand”
About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.
Lagging Strand
Okazaki Fragment 2
DNA ligase
Okazaki Fragment 1 5’ 3’

15. What are the steps for DNA Replication?
7. Once the 2 strands completely break off, you have 2 identical Double Stranded DNA molecules as a results.
8. Each new molecule has 1 original (template) and 1 “new” strand.
9. This is known as “Semi-Conservative” Replication, because each replicated molecule has one old strand conserved which is used as a template, and one complementary NEW strand is made.
About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.

16. 06_11_oppositepolarity.jpg

18. Semi-Conservative Replication
DNA Replication Tutorial
(Go here for on-your-own learning/review)
Semi-Conservative Replication
Each new DNA molecule
contains
one old strand
&
one new strand

19. How do cells help ensure that DNA replication is accurate ?
Has the enzyme “DNA Polymerase” to proof read and make sure that each newly added nucleotide is accurately paired with the nucleotide on the template (old) strand. If not, it is removed and replaced with a correct one.
**Any mistake in copying  MUTATION**
DNA Mutation Chromosomal Mutation

20. Editing & proofreading DNA
1000 bases/second = lots of typos!
DNA polymerase I
proofreads & corrects typos
repairs mismatched bases
removes abnormal bases
repairs damage throughout life
reduces error rate from 1 in 10,000 to 1 in 100 million bases

21. Summary DNA replication 5’->3’ DNA proof reading
Lagging strand, back-stitching, Okazaki fragment
Proteins involved:
DNA polymerase, primase
DNA helicase and single-strand DNA-binding protein (SSB)
DNA ligase, and enzyme to degrade RNA
DNA topoisomerases
DNA Ligase

22. Summary

23. Why does the function of DNA replication need to take place in living cells?
To assure that every cell has a complete set of identical genetic information (make a copy of itself), so that it can be passed on to a new cell.

24. How does DNA replication ensure that cells have complete sets of DNA?
It doubles the amount of DNA so that both of the daughter cells resulting from Mitosis have their own complete set of DNA.

25. Any Questions??

26. DNA vs. RNA DNA RNA Sugar = deoxyribose Sugar = ribose
Double-stranded molecule
Single-stranded molecule
Thymine bonds with adenine
Uracil instead of thymine

27. DNA vs. RNA DNA RNA Nuclear DNA Mitochondrial DNA Chloroplast DNA
mRNA = messenger
tRNA = transfer
rRNA = ribosomal
Nuclear DNA never leaves the nucleus
Assembled in nucleus, moves to cytoplasm
(leaves the nucleus)