1. Chapter 10 Molecular Biology of the Gene

2. Section 10.1 – Experiments
1928 – English bacteriologist, Frederick Griffith

3. Section 10.1 – Conclusion from Griffith’s experiment
The heat-killed S strain (mixed with the live R strain) was able to give its “deadly” properties to the R strain
This is because the DNA from the S was taken in by the R.
Result: R strain becomes deadly

4. Section 10.1 - Bacteriophages
A virus that infects bacteria and turns it into a “phage-making factory”. Contains DNA inside of its head The head is made of protein

5. Section 10.1 – Experiments
1952 – American biologists, Hershey and Chase

6. Section 10.1 – Conclusion from Phage Experiment
Phages leave their “head” or “shell” outside of a cell
Phages insert their DNA into the cell
The inserted “phage DNA” is what turns the cell into a phage-making factory

7. Section 10.2 – DNA

8. Section DNA
The sides of a DNA molecule are composed of alternating deoxyribose sugars and phosphate groups

10. Section 10.2 – DNA
Purines – Nitrogenous bases in DNA with a double ring structure

11. Section 10.2 – DNA
Pyrimidines – Nitrogenous bases in DNA with a single ring structure

12. Section 10.2 – DNA
Purines match up with pyrimidines

13. Section 10.2 – DNA vs. RNA DNA RNA Sugar = Deoxyribose
Twisted into a double helix
Double stranded
A,T,C,G
Found mainly in nucleus
1 Type
RNA
Sugar = Ribose
Not shaped into a double helix
Single Stranded
A,U,C,G (has uracil instead of thymine)
Found mainly in nucleolus
3 Types: mRNA, tRNA, and rRNA

15. Section 10.3 - Scientists Erwin Chargaff – 1949 – American
Noticed that there were equal amount of adenine and thymine in DNA; also there are equal amounts of cytosine and guanine in DNA
For example: if a DNA molecule is 30% adenine, it is also 30% thymine. Therefore it must be 20% cytosine and 20% guanine.
(all percentages total 100%)

16. Section 10.3 - Scientists 2. Maurice Wilkins & Rosalind Franklin
- 1952, England
Took X- ray pictures of DNA to try to solve its structure

17. The actual DNA X-ray photo that Wilkins and Franklin took
Section 10.3 Scientists
The actual DNA X-ray photo that Wilkins and Franklin took

18. Section 10.3 - Scientists James Watson and Francis Crick
1953, England (Watson was American)
Using the X-ray picture that Wilkins and Franklin took, Watson and Crick determined that DNA is a double helix structure
They then built a model of DNA

19. Section Scientists
Francis Crick
James Watson

20. Section 10.4 – DNA Replication
To “replicate” means to “copy”
DNA has a special ability: with the help of enzymes, it can make an exact copy of itself.
1 DNA strand will make 2 “daughter” DNA strands

21. Section 10.5 – DNA Orientation
DNA has two “sides” to it, like a ladder.
One end of a side of the ladder is called the 5’ (prime) end. The other end of that same side is called the 3’ end.
Please see the next picture to understand this concept.

22. Section 10.5 – DNA Orientation

23. Section 10.5 – DNA Orientation
If the 5’ end is up, then the DNA molecule is oriented so that the deoxyribose looks like a pentagon with the point at the top
If the 3’ end is up, then the DNA molecule is oriented so that the deoxyribose looks like an upside down pentagon

24. Section 10.5 – DNA Replication

25. Section 10.6 - Transcription
To “transcribe” means to write something down
In Biology, transcription means that DNA language is rewritten as mRNA language
This occurs in the cell’s nucleus

26. Section Translation
To “translate” means to take something that is in one language and convert it to another language
In Biology, translation is taking the code that is in mRNA and converting it into a polypeptide/ protein
Occurs in the cytoplasm

27. Section Codons
A triplet code is what DNA and RNA have. The bases of each are “read” in threes.
For example: ATT CCC GTG GAG TTA
A codon is what the three letters are called collectively.
For example: ATA is a codon.
TTT is a codon.
CG is not a codon.

28. Section 10.7 – Turning mRNA into a polypeptide/protein
First, a “start codon” is found in the mRNA. The start codon for mRNA is always AUG.
Take the amino acid chart, find “AUG” in the chart, and see what amino acid it corresponds to.
If done correctly, AUG should correspond to methionine (met).
Keep translating mRNA into amino acids until you reach a stop codon
Can you find the 3 stop codons from the amino acid chart on the next slide?

29. Section 10.7 – The Amino Acid Chart

30. Section 10.9 - Transcription
Name of enzyme that start transcription = RNA polymerase
How RNA polymerase knows where to “start” transcribing DNA into mRNA
RNA polymerase finds the “start codon” in DNA, which is TAC.
TAC in DNA will make AUG in mRNA.

31. Section 10.9 – 3 Stages of Transcription
Initiation – RNA polymerase finds the “start codon” in DNA (which is TAC)
Elongation – RNA polymerase then continues along the DNA strand to make mRNA from the DNA code.
Termination – RNA polymerase stops because it reaches a stop codon in the DNA.

33. Three types of RNA that are used in translation
Sections 10.10, 10.11, and 10.12
Three types of RNA that are used in translation
mRNA = messenger RNA. It is made directly from DNA
tRNA = transfer RNA. It is attached to an amino acid and has an anticodon that matches up to mRNA’s codon.
rRNA = ribosomal RNA. It is part of a ribosome (which is where translation occurs)

34. Pictures of the 3 RNAs

35. Section Translation
Codon recognition = tRNA’s anticodon pairs up with mRNA’s codon
Peptide bond formation = The polypeptide separates from the tRNA to which it was bound and forms a peptide bond with the amino acid on the new tRNA coming to the ribosome.

36. Section Translation
3. Translocation = The tRNA that is in the A-site of the ribosome moves to the P-site
- The tRNA carries the growing polypeptide with it to the P-site

37. tRNAs move from the A-site to the P-site.
Then the tRNA exits the ribosome from the E-site.

38. Picture of Translation

39. Section 10.16 Mutation – Any change in the nucleotide sequence in DNA
For example: If an A gets replaced with a G or if a letter gets deleted altogether
Reading Frame – A triplet grouping of the genetic message (a.k.a a codon)
Mutagen – A physical or chemical agent that can cause a DNA mutation
Radiation such as X-rays or UV light
Chemicals such as cancer- causing agents

40. The Whole Picture