1. PAP Biology DNA What are nucleic acids? Why is DNA important?
Structure of DNA
Scientists

2. Review
What are the two types of nucleic acids? _________________ & _______________
Is a nucleic acid a monomer or polymer? __________________________
What is the monomer of DNA and RNA? _________________________
DNA
RNA
POLYMER
nucleotide

3. Understanding DNA video (6 min)

4. Summary of Scientists Griffith—
Avery—
Hershey & Chase—
Chargaff—
Wilkins & Franklin—
Watson & Crick—
discovered genetic transformation of bacteria
discovered DNA is genetic material
confirmed DNA is genetic material
discovered nitrogen base pairing rules
developed X-ray pictures of DNA
discovered shape/structure of DNA

5. DNA The Master Molecule video (stop at 5:50)

6. DNA Location DNA stands for deoxyribonucleic acid Location:
DNA is found in the nucleus of eukaryotic organisms
like plants, animals, protists and fungi
In prokaryotic organisms (like bacteria) that do not have a nucleus, DNA can be found in a single circular chromosome within the cell

8. DNA Function
Function: DNA stores and carries the information that is passed from one organism to its offspring (from parent to child)

9. What is DNA?
The information is coded in the order of the nucleotide bases (the monomers)
The monomer of DNA is made of:
Phosphate group
5 carbon sugar (deoxyribose)
Nitrogen containing base
These three components make up the monomer called a nucleotide

10. Nucleotide

11. Why is DNA Important? DNA is in all living things
DNA is the informational code that makes each organism unique.

12. The Structure of DNA
double helix- two strands of nucleotides twisted around each other, like a winding staircase
there is a “right side up” strand and an “upside down” strand.
this arrangement of 2 strands running side by side but in opposite directions is described as antiparallel

14. The Structure of DNA
Nucleotides- subunits (monomers) that make up DNA composed of:
Phosphate group
5- carbon sugar (deoxyribose in DNA)
Nitrogen containing base:
The bases pair in the same way in every DNA molecule, we call this complementary base pairing
Adenine Thymine (A – T)
Guanine Cytosine (G – C)
* Weak hydrogen bonds hold bases together

15. Base Pairs
We refer to adenine, thymine, cytosine and guanine as the nitrogen bases or just “bases”
So, when you say “a sugar, a phosphate and a base” you are implying that the base is either adenine, thymine, guanine or cytosine

17. Base Pairs
The order of the base pairs provides that “unique code” that makes us all different.
GTAACTTAG does not contain the same information as GGACAATTT even though both sequences contain the same nucleotides
However, if the nucleotide sequences of nitrogenous bases (adenine, guanine, cytosine, thymine) are in a similar order, the two organisms are closely related
This concept is used in forensic science and is called DNA fingerprinting

18. Label complementary bases and draw the appropriate number of hydrogen bonds 

19. The Structure of DNA *Note about bases:
Pyrimidines- single ring of carbon
Thymine and Cytosine
Purine- two rings of carbon
Adenine and Guanine
A purine must always hydrogen bond with a pyrimidine!

21. Label all hydrogen bonds with an H3’ P T H A S
Label:
Phosphate (P)
5 carbon sugar (S)
- Correct base pairs
(A, T, C, G)
Label all hydrogen bonds with an H
-Label the 5’ and 3’ ends
Circle a nucleotide T A C G T A G C T A 5’

23. DNA Review What does DNA store that is important?
If a DNA strand read 3’ AGT-CCG-GTA 5’ what would the complementary strand read?
What holds the nitrogen bases together?
What are the 3 components of a nucleotide?
Genetic information in its sequence of nitrogen bases
5’ TCA-GGC-CAT 3’
Hydrogen bonds
Sugar, phosphate group, and nitrogen base

24. 1 DNA molecule  2 identical DNA molecules
DNA Replication
DNA replication- the process of making a copy of DNA
1 DNA molecule  2 identical DNA molecules
Why is this important?
cells need to copy their DNA before the cells divide in mitosis (growth, repair, and maintenance)
Where does DNA replication occur?
in the nucleus (because DNA is found in the nucleus in eukaryotic cells)

25. DNA Replication Summary of what we will learn
There are three steps to DNA replication:
1) helicase unwinds the double helix opens the strand by breaking the hydrogen bonds between the bases
2) DNA polymerases add nucleotides in a 5’ to 3’ direction, moving TOWARD the replication fork; The leading strand is built quickly and the lagging strand is built more slowly in short 5’ to 3’ segments.
3) DNA polymerases detach once replication is complete and you end with 2 identical molecules of DNA, each made of one old strand and one new strand

26. DNA Replication
Step 1:
the double helix must unwind before replication can begin.
then the DNA “unzips”
DNA helicase is an enzyme that opens the double helix by breaking the hydrogen bonds that hold the complementary bases together (think of a zipper)
enzymes end in (-ase)

27. DNA Replication Step 1 con’t:
once separated, additional proteins hold the strands apart
the place where the double helix splits is called the replication fork (it’s Y-shaped)

28. DNA Replication
Step 2:
at the replication fork, enzymes called DNA polymerases move along each of the DNA strands
DNA polymerases add nucleotides to the 3’ end exposed bases according to the base pairing rules

29. DNA Replication
The overall direction of adding nucleotides is toward the replication fork
goes from 5’ to 3’

30. One strand, called the leading strand, grows quickly in the 5’ – 3’ direction toward the replication fork.
The other strand, called the lagging strandis created next to the 3’5’ strand.
It must add nucleotides in short 5’3’ segments (called Okasaki fragments), but goes slowly since it has to wait for it to unzip then fill in backwards a little section at a time making it “grow” in the wrong direction (away from the replication fork).
These fragments are joined by ligase.
Ultimately the overall direction of “growth” is toward the replication fork, but must be done in small segments filling in away from the fork.

32. DNA Replication
Step 3:
step 2 continues until all DNA has been copied and the polymerases detach
produces 2 DNA molecules that are identical to each other

34. DNA Replication
is semiconservative
semi – half
conserve – to save

35. DNA Replication Semiconservative:
This means that every double stranded molecule of DNA has one strand that is from the “old” DNA and one strand is “new”

38. Summary DNA unwinds & unzips using helicase
DNA polymerases add nucleotides to the 3’ end of the strands, moving toward the replication fork (5’  3’)
2 new strands of DNA are made that are identical to the original strands and to each other
The process is semiconservative