1. (Deoxyribonucleic Acid)
The Structure of DNA
(Deoxyribonucleic Acid)
DNA Video

2. Bell Ringer What biomolecule holds genetic information?
Where do organisms get genetic information from?
Why is it important to pass on genetic information?
What four characteristics do all cells have in common?

3. BELL RINGER What are the four nucleotides in DNA?
How are the traits of an organism determined?
What is the difference between the DNA
of yeast and the DNA of humans?

4. ALL living organisms have DNA!
Remember…all living organisms are made up
cells.
ALL cells have 4 characteristics in common:
Cell membrane
Genetic material (DNA)
Ribosomes
Cytoplasm

5. Discovery of DNA Griffiths and Avery Experiments
Show that genetic information can be transferred from one bacteria to another.
Oswald Avery repeated the experiment and concluded that the nucleic acid DNA stores and transmits the genetic information.
Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease causing bacteria nor live, harmless bacteria killed the mice. The two types injected together however caused the mice to die of fatal pneumonia. From this experiment it was proven that genetic information could be transferred from one bacteria to another. This provided further study that genes are passed down to offspring and can be transferred from one organism to another.

6. Hershey and Chase
In the early 1950’s scientists were trying to determine what structure was carrying genetic information
Two Scientists, Hershey and Chase, experimented by infecting bacteria with radioactively labeled viruses
When the radioactive markers showed up in the bacteria, they realized it was DNA that was carrying the genetic code.

7. DNA (deoxyribonucleic acid)
DNA is often referred to as the “instructions” for ALL life
In simple terms, DNA
contains the instructions to synthesize proteins within
the cell

8. DNA and Proteins DNA holds instructions for proteins.
Protein found in hair, skin, bones, and muscles
Proteins called enzymes control the chemical reactions needed for life.

9. Where is DNA found in the following cells?
Eukaryote Nucleus
Nuclear Membrane
Prokaryote Cytoplasm
Where is DNA found in an Eukaryote Cell?

10. DNA is a Nucleic Acid The monomer of nucleic acids are nucleotides.
A nucleotides have 3 parts:
Deoxyribose (sugar CHO)
Phosphate group (P)
Nitrogen Base (N) (4 possibilities)
Adenine
Thymine
Cytosine
Guanine

11. Nucleotide Structure O O -P O O Phosphate C C Nitrogenous base C C
{Ask students where they have seen a similar molecule before in this class.
Answer: ATP Emphasize that nucleotides are the basic building blocks or units of a DNA molecule and that a single molecule has many millions of nucleotides.} C C
Deoxyribose O

12. 2 Different kinds of bases in DNA
Purines
Pyrimidines
Single-ring nitrogen bases
Double-ring nitrogen bases C N O
thymine C N O
Guanine C N O
cytosine C N
Adenine

13. Watson & Crick- 1953
Proposed that DNA is made of 2 strands of nucleotides held together by nitrogen bases
The complementary nitrogen base pairs were held together by hydrogen bonds
The idea of the double helix shape was aided through the work of Rosalind Franklin
Franklin was taking X-rays of DNA, and one picture showed an “X” shape, a characteristic of a helix
Watson and Crick “borrowed” from Franklin, got their worked published, and went on to earn the Nobel Prize for their work. Franklin received no recognition

14. The Double Helix Model
The structure of the DNA molecule is helical with nucleotide stacked on top of each other.
DNA is a very long polymer
The basic shape is like a twisted ladder or zipper
This is called the DOUBLE HELIX

15. DNA: The Molecule
The backbone of DNA is made up of alternating phosphate (P) molecules and sugar (S) molecules held together by STRONG bonds
The nitrogen bases are held together by WEAK hydrogen bonds

16. Chargraff’s Rule:
The 4 nitrogen bases are arranged in complementary base pairs.
….this means that….
Adenine (A) will always pair with Thymine (T)
A – T
T – A Apples go in Trees
Cytosine (C) will always pair with Guanine (G)
C – G
G – C Cars go in Garages

17. Chargaff’s Rule The amount of: A = T The amount of: C = G
If a molecule of DNA contains
24% adenine how much of the
following will there be?
Thymine (T) =
Cytosine (C) =
Guanine (G) =

18. DNA, DAN, AND What makes the 3 words above different from each other?
All living organisms from bacteria to you have the same DNA alphabet (A,T,C,G)
The only difference is the SEQUENCE (order) of the nucleotides (nitrogen bases)
It is the SEQUENCE of nitrogen bases that will determine what proteins are built.

19. Importance of nucleotide sequence
Differences in sequences = differences in organisms
More similar sequences mean closer relationship between organisms
Nucleotide sequences are used to:
Determine evolutionary relationships
Determine familial relationships
Identify the bodies of crime victims

20. Summary: DNA Structure
DNA is a nucleic acid
The monomer of DNA is a nucleotide
Nucleotides have 3 parts (phosphate, sugar, nitrogen base)
There are 4 nitrogen bases (A,T,C,G)
A pairs with T; C pairs with G
The shape of DNA is described as a double helix
DNA is found in all living organisms
The sequence of nucleotides determines the type of organism

21. Let’s practice make the COMPLEMENTARY strand of DNA…
ACC GGGCTA TAC TGG ACC GTC CCC ACC GGGCTA TAC TGA CCC CGA AAC ACC GGA CCT TGA CTT TTT ACC GGA

22. Bell Ringer How are DNA bases complimentary?
What are the DNA base paring rules?
What is the structure below?
What is the shape of DNA called?

23. DNA Replication

25. Replication Facts
DNA has to be copied before a cell divides in a process call DNA replication
New cells will need identical DNA strands
DNA is copied during the S or synthesis phase of interphase then it proceeds to M phase

26. Semi-conservative Replication
Idea presented by Watson & Crick
The two strands of the parental molecule separate, and each acts as a template for a new complementary strand
Semi-conservative replication: new DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA
DNA Template
New DNA
Parental DNA

27. Parent Strand
DNA Unzips
Each original strand is completed by have new complementary base pairs replaced

28. Steps of DNA Replication
Begins at Origins of Replication
Two strands open forming Replication Forks (Y-shaped region)
New strands grow at the forks
Replication
Fork
Parental DNA Molecule 3’ 5’

29. DNA Replication
Enzyme helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds
This process is called unzipping
Single-strand binding proteins attach and keep the 2 DNA strands separated and untwisted

30. DNA Replication DNA separates and unwinds
Enzyme topoisomerase attaches to the 2 forks of the bubble to relieve stress on the DNA molecule as it separates
Enzyme
DNA
Enzyme

31. DNA Replication
Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides
Primase is the enzyme that synthesizes the RNA Primer
DNA polymerase can then acts as a catalyst to add the new nucleotides

32. Hydrogen bonds form to create new strands of DNA
The 2 new DNA strands are identical to each other and identical to the parent strand

33. DNA Strands are Anti-parallelO 1 2 3 4 5 P O 1 2 3 4 5
5’ pairs with 3’ G C T A

34. Label 5’ and 3’ label parent and daughter strands.

35. Proofreading New DNA
DNA polymerase initially makes about 1 in 10,000 base pairing errors
Enzymes proofread and correct these mistakes
The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

36. Question DNA 5’-CGCTATG-3’ DNA 3’-GCGATAC-5’
What would be the complementary DNA strand for the following DNA sequence?
DNA 5’-CGCTATG-3’
DNA 3’-GCGATAC-5’

37. DNA Damage & Repair
Chemicals & ultraviolet radiation damage the DNA in our body cells
Cells must continuously repair DAMAGED DNA
Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA
DNA polymerase and DNA ligase replace and bond the new nucleotides together

38. Replication Steps…quick version
DNA is double stranded
The base order on one strand predicts the base order on the other strand (They are complementary)
Enzymes break hydrogen bonds between the two strands of DNA
Complementary bases then pair up (base pairing) and two identical molecules of DNA are made

39. IN A EUKARYOTE WHERE DOES REPLICATION TAKE PLACE!!
(WHAT ORGANELLE)
NUCLEUS!!

40. More Practice! DNA 5’-TATCTAGCTAGGTCCATT-3’
DNA 5’-ATAGACCGTAAGTACCTG-3’
DNA 5’-CGCGCAATTTCGCCGAAT-3’

41. BELL RINGER What would happen!!
If mitosis occurred before replication of the DNA?
The new cells wouldn’t have DNA!
When does replication of DNA take place?
S phase!
What enzyme adds back the new complimentary nucleotides?
DNA Polymerase