1. DNA
Ch 8
Standard 4

2. History of DNA 1. Hershey & Chase  proved DNA is the
genetic material found in cells

3. Erwin Chargaff DNA composition all 4 bases not in equal quantity
bases present in characteristic ratio
A = T ~ 40%
G = C ~ 60%
varies from species to species

4. Rosalind Franklin  took x-ray photos of DNA that showed it’s 3-D structure

5. Watson & Crick made the first 3-D model of DNA in 1953
Won the Nobel Prize in 1962

6. Why is DNA important?
It stores genetic information in cells & this information is used to make proteins

7. DNA is a double helix (twisted ladder)
DNA Structure
DNA is a double helix (twisted ladder)

8. DNA is made of nucleotides
3 nucleotide parts
Deoxyribose sugar
Phosphate
Nitrogen base
- adenine (A)
- thymine (T)
- guanine (G)
- cytosine (C)

9. Adenine binds only with Thymine Cytosine binds only with Guanine
----Straight letters together
Curvy letters together

10. Sugars & phosphates make up the sides of the ladder,
the nitrogen bases are the steps (rungs)
Phosphodiester bonds

11. Difference in their shapes causes the DNA to twist
Base Pair Shape
Pyrimadine
Single ring bases
(Thymine or Cytosine)
Purine
Double ring bases
(Adenine or Guanine)
Difference in their shapes causes the DNA to twist

12. Hydrogen Bonds Adenine Thymine Thymine Adenine Guanine Cytosine

13. A T G G A C T A C T A C C T G A T G Practice
If one side of DNA has this base sequence, what does the other side have?
A T G G A C T A C
T A C C T G A T G

14. DNA Replication

15. How Does DNA Replicate Process discovered by Meselson & Stahl
Semi-conservative replication
Half old strand, Half new strand
Anti-parallel
New strands are made in opposite directions

16. When does DNA replicate?
During the cell cycle before mitosis & meiosis

17. Why does DNA replicate?
So new cells
will have their
own copy of DNA

18. Six Steps of DNA Replication
DNA is unzipped by the Helicase enzyme (breaks hydrogen bond)
DNA polymerase enzyme binds DNA begins attaching complimentary nucleotides
Same thing happens on the other side, but in opposite direction

19. 4) Bonds Reform
Helicase reforms Hydrogen bonds (between bases)
Ligase reforms Phosphodiester bonds (sugar & phosphate)
5) DNA polymerase “proofreads” checking each strand for errors.
6) DNA rewinds itself into two identical double helix strands
Let’s watch

20. Protein Synthesis
DNA RNA Proteins

21. DNA
sugar = deoxyribose
bases = A, C, G, T
double strand
stays in nucleus
RNA
sugar = ribose
bases = A, C, G, U
single strand
leaves nucleus

22. 3 Types of RNA mRNA  made from DNA in nucleus
“messenger”
tRNA  brings amino acids to the ribosomes; found in cytoplasm
“transfer”
3. rRNA  part of the ribosome; this is where proteins are made
“ribosomal”

23. DNA vs. RNA

24. TRANSCRIPTION How RNA is made from DNA

25. Transcription Steps DNA is unzipped by Helicase
all genes start with the code “TAC”
RNA polymerase adds RNA nucleotides to the DNA strand
mRNA is complete when it reaches a stop code on DNA
mRNA then leaves nucleus & carries code into the cytoplasm
DNA never leaves the nucleus

26. Don’t Confuse Replication with Transcription!
DNA Replication
A – T
C – G
G – C
T - A
Transcription
A – U
C – G
G – C
T - A

27. Transcribe this……
TACGTATTCCGG
| | | | | | | | | | I
AUGCAUAAGGCC

29. Translation Decoding the Message
Steps
mRNA leave nucleus and enters ribosome
mRNA codons read & tRNA brings matching amino acid to the ribosome
Amino acids are strung together like beads on a necklace
Amino Acids are held together by peptide bonds
1000 or more Amino Acids = protein

30. WHEN WE DECODE DNA Example: AUG= Methylamine (Start)
Use the “Genetic Code” 
Convert mRNA 3 letter groupings called codons
Example:
AUG= Methylamine (Start)
The mRNA Code tells us what amino acid each codon codes for.

31. Transcribe and Translate this DNA Strand without looking at your notes
TACAGTACCATAATC
NOW, Label the DNA, mRNA, tRNA, rRNA
Which part is transcription
Which is translation ?

33. rRNA MET-SER-TRP-TYR-STOP
DNA TACAGTACCATAATC
mRNA AUGUCAUGGUAUUAG
tRNA UACAGUACCAUAAUC
rRNA MET-SER-TRP-TYR-STOP

34. DNA RNA Protein Transcription Translation
A, T, C, G A, U, C, G Amino Acids
Double Strand
Single Strand
Codons & Anti-codons
In Cytoplasm
In The Nucleus

35. Is it all DNA? There are different parts of the chromosome
Entire chromosome is made of DNA
Humans~ 3 billion base pairs
Only part of the DNA codes for Genes
Gene: The DNA that codes for a Protein.
There are different parts of the chromosome
Exons and Introns
Introns are cut out before translation
Exons are left, and get Translated to make Proteins

37. GENETIC VARIATION There are some variations in genes Effects
~every 1350th bp (average)
Known as polymorphisms “different forms”
Different gene forms are called alleles
Effects
How well the protein works. EX: Melanin
How the protein interacts with another protein or substrate. EX: Enzymes
Click and type your text here 3 2

38. Proteins do the work of the cell
Proteins are chains of amino acids.
The amino acids are coded by the bases that make up that gene
Each gene codes for a different protein.

39. Gene Expression
All cells within an organism have the same DNA and genes.
What makes cells different from each other is that different genes are turned on and turned off in different cells.
Pigment in Eyes or Skin
Keratin in Nails or Hair

40. How can organisms be different from each other if their DNA is made of the same nucleotides?
Two individuals DNA are different because of the order of nitrogen bases
The more closely related two organisms are, the more alike the order of nucleotides in their DNA will be.