1. Biology
DNA Unit

2. PDE Big Idea 8A
The basic molecular and the associated genetic code structure of DNA are universal, revolutionizing our understanding of disease, heredity, and evolution.

3. Griffith’s Experiments
Frederick Griffith did a series of experiments with Streptococcus pneumoniae (pneumonia) in 1928.
He noticed that one strain (the S strain) of the bacteria caused disease, the other (the R strain) didn’t.

4. Griffith’s Experiments
Griffith did four experiments using mice and various mixtures of the disease causing and non disease causing bacteria.

5. Experiment 1 He injected a mouse with live S strain bacteria.
As a result, the mouse died.

6. Experiment 2 He injected a mouse with live R strain bacteria.
As a result, the mouse lived.

7. Experiment 3 Mouse was injected with heat killed S strain cells
The mouse lived

8. Experiment 4
Mouse was injected with heat killed S strain cells and live R strain cells
The mouse died

9. Griffith’s Conclusion
Griffith concluded that there was some hereditary factor released by the dead S cells and absorbed by the live R cells
Today we call this transfer of genetic material from one organism to another transformation

10. Avery’s Experiment
Oswald Avery later did three experiments in which he used enzymes to deactivate protein, RNA and DNA and injected them into mice
He found that DNA was the hereditary factor from Griffith’s conclusion

11. Watson and Crick
James Watson and Francis Crick discovered the double helix shape of DNA in 1953

12. DNA Anatomy Further studies of DNA showed that it contains three parts
Deoxyribose (sugar)
Phosphate
A nitrogenous base
- Put all three parts together and you have a nucleotide, the building blocks of DNA

13. Nucleotides
The four nucleotides of DNA are known as Adenine (A), Guanine (G), Cytosine (C) and Thymine (T)
RNA also has nucleotides, but Thymine is replaced with Uracil (U)

14. Purines and Pyrimidines
Purines have 2 rings and Pyrimidines have 1.
Purines and Pyrimidines Hydrogen bond to one another

15. Base Pairing
Because of the bonding pattern of the purines and pyrimidines, how the bases pair up can easily be predicted
C and G always pair up
In DNA, A and T pair up
In RNA, A and U pair up
G – C A – T C – G T – A A – U U – A

16. DNA and RNA Functions
DNA contains the directions for making all of the proteins in the body, but it can not leave the nucleus
RNA is made from DNA and contains selected information from the DNA
RNA leaves the nucleus and is used to make protein in the cytoplasm

17. Replication The process in which copies of DNA are made
The enzyme helicase unzips the DNA into two separate strands.
New strands are then built onto the old strands
Each new double helix has half of the old one
Because of this, we say that the process is conservative

19. Replication Example
Old Strand G A T T A C A T C C G T A New Strand C T A A T G T A G G C A T

20. Transcription
This is when DNA is used to make RNA, which will be used to make protein
The base thymine (T) is replaced with uracil (U)

21. Transcription Example
DNA Strand G T A C G C T A T T C G RNA Strand C A U G C G A U A A G C

22. Transcription Makes Three Main Types of RNA
mRNA – the blueprint for making protein (messenger)
tRNA – (transfer)carries amino acids to ribosomes (transfer)
rRNA – becomes part of the ribosome (ribosomal)

23. Translation Making protein from RNA
mRNA is read by the ribosome (part rRNA) in order to construct a new protein made from amino acids which are supplied by the tRNA

24. mRNA
In order to determine the order of the amino acid sequence, scientists had to crack the genetic code
Within the mRNA there is a code that specifies what amino acid goes where in the protein

25. Codons Examples: AGA = arginine GGA = glycine UGC = cysteine
* See page 207 in your textbook
Scientists found that the mRNA was organized into segments 3 bases long, that they called codons
Each codon specifies an amino acid
The genetic code has a lot of repetition

26. Start Codon
Transcription often makes long strands of mRNA that may have directions for many proteins
The cell needs to know where to begin translating
The “on switch” is known as the start codon
Start Codon = AUG AUG = methionine

27. Stop Codons The cell also needs to know where to stop translating
Because of this there are 3 “off switches” or stop codons
They are UAA, UAG and UGA

28. Anticodons
The tRNA knows where to attach to the mRNA because it contains the complimentary bases to the codon
These bases are called an anticodon
Codon Anticodon AUG UAC GAC CUG UCA AGU

29. Translation
mRNA slides between the large and small subunit of a ribosome until AUG is found

30. Translation
A tRNA brings in the necessary amino acid and its anticodon binds to the codon

31. Translation
The next codon slides through the ribosome

32. Translation
The next tRNA brings its amino acid. Its anticodon binds to the codon and a peptide bond forms between the amino acids.

33. Translation
The next codon slides through the ribosome and the first tRNA is released.

34. Translation
The process continues over and over again until a stop codon is reached. Then the polypeptide is released and the ribosome can start over.

35. Transcription/Translation Practice
DNA A G T A C G C T T C G A C T G T mRNA U C A U G C G A A G C U G A C A

36. Protein Structure
After proteins are made, they often bend, twist, fold and interact with other proteins to make a useable product for an organism

37. Primary Protein Structure
This refers to the order of the amino acids in the polypeptide (protein) chain

38. Secondary Protein Structure
Certain amino acids have charged regions and will form hydrogen bonds
This causes the protein chain to fold, twist or change shape in some way

39. Tertiary Protein Structure
Most protein chains include many different features (twists, sheets, and folds)
The final 3-dimensional shape of the entire protein is the tertiary structure

40. Quaternary Protein Structure
In many cases, different proteins will bind together to make a final product
Quaternary structure is the interaction between two or more protein chains

41. Enzymes
Enzymes are special proteins that catalyze (speed up) chemical reactions
The beginning substances they work on are called substrates
The substrates are changed into different molecules

42. Enzymes Enzymes catalyze more than 4,000 biochemical reactions
Enzymes are essential to the survival of many organisms
For example, without them we could not digest our food, get rid of carbon dioxide or send messages through our nerves

43. How Enzymes Work