1. DNA, RNA, & Protein Synthesis
The foundation of the study of Genetics

2. Discovery of DNA & its structure
DNA structure was not discovered until the 1950’s
After looking at an X-ray diffraction photo stolen from Rosalind Franklin by her co- worker (Wilkins), James Watson and Francis Crick were able to create a model of DNA
The model depicted a double helix of even width
In 1953, James Watson, Francis Crick, and Maurice Wilkins received the Nobel Prize (no mention of Rosalind Franklin)

3. Rosalind Franklin
Franklin’s x-ray images suggested that DNA was a double helix of even width.

4. James Watson & Francis Crick

5. Other Evidence Erwin Chargaff, in his biochemical studies, discovered:
The amount of Adenine in a DNA sample always equaled the amount of Thymine
The amount of Cytosine, likewise, was equal to the amount of Guanine
This became known as Chargaff’s rule
This information further served to confirm the model created by James Watson and Francis Crick
Adenine pairs with Thymine
Cytosine pairs with Guanine

6. Structure of DNA
DNA (deoxyribonucleic acid) is made up of long chains of nucleotides
Nucleotide structure
Phosphate Group
5 carbon sugar (deoxyribose)
Nitrogen Base (4 different bases)
Adenine
Thymine
Guanine
Cytosine

7. Nucleotide phosphate group nitrogen-containing base
deoxyribose (sugar)
nitrogen-containing
base

8. DNA structure Continued
DNA is double stranded
The two strands are equally spaced & twist
This is why the structure of DNA is referred to as a double helix

9. Bonding in DNA
The backbone of each side of DNA is held together by covalent bonds and is made up of the phosphate groups and deoxyribose sugars

10. Bonding in DNA
The two complementary strands (the rungs of the DNA ladder) of DNA are held together by weak hydrogen bonds between the complementary nitrogen base pairs
These attractions are easily broken and reformed
Important for DNA replication and transcription

11. Bonding in DNA
hydrogen bond
covalent bond

12. DNA Replication
Making copies of DNA

13. DNA Replication Occurs during Interphase (S phase) of the cell cycle
DNA replication is required such that the two new daughter cells created will have a complete set of DNA
Enzymes break the hydrogen bonds, separating the two strands
Other enzymes bring free nucleotides in the nucleus to build the new strands of DNA

14. Semiconservative
DNA replication is called a semiconservative process as the two double helices created consists of:
One old strand of DNA
One new strand of DNA
The “old” sides of the DNA strands are used as the template (building instructions) for building the “new” strands of DNA
Two double helices are created in the end

15. The DNA molecule unzips in both directions.
DNA Replication
nucleotide
The DNA molecule unzips in both directions.

16. End Result DNA Replication
original strand
new strand
Two molecules of DNA

17. The basis of gene expression
Protein Synthesis
The basis of gene expression

18. Central Dogma
States that information stored in DNA flows in one direction from DNA, to RNA, to proteins

19. Protein Synthesis Phases
Transcription
The 1st phase of protein synthesis
DNA can’t leave the nucleus, so a smaller molecule that can leave has to be made
Occurs in the nucleus
Translation
The 2nd and final phase of protein synthesis
The molecule made in transcription is used to build a protein
Occurs at the site of a ribosome

20. Organelles Review
Nucleus- where DNA is located; where transcription occurs
Ribosome- where proteins are built (site of protein synthesis); where translation occurs
Rough ER- Newly made proteins enter this transport organelle
Golgi Apparatus/Body-The protein is checked, modified, and re-packaged for transport to its final destination
Vesicles-Transport vehicles for the protein around the cell

21. Transcription
A segment of DNA called a gene with the information for building a protein is used as a template (building instructions) to build a messenger RNA (mRNA) molecule
Enzymes open the double helix
Other enzymes build the mRNA molecule from the gene of DNA
Messenger RNA is a copy of the DNA instructions
Like a secretary or a transcriptionist that records information

22. Transcription
DNA

23. DNA vs RNA Double helix Nucleotide sugar: deoxyribose Nitrogen bases
Adenine
Thymine
Cytosine
Guanine
Base Pair Rule
A-T
C-G
Single stranded
Nucleotide sugar: ribose
Nitrogen bases
Adenine
Uracil
Cytosine
Guanine
Base Pair Rule
A-U
C-G
DNA
RNA

25. Translation

26. RNA molecules involved in Transcription & Translation
DNA
Messenger RNA (mRNA)
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
Transcription
Translation

27. Ribosome Structure

28. Translation
The mRNA molecule leaves the nucleus and moves to a ribosome
The mRNA “sticks” to the small subunit of the ribosome, which is made up of a ribosomal RNA (rRNA) molecule
The mRNA is fed between the small subunit of the ribosome and the large subunit
The mRNA message is “read” by the ribosome 3 nucleotides at a time
Each set of 3 nucleotides on mRNA is called a codon

29. Messenger RNA & codons
codon for
methionine (Met)
leucine (Leu)

30. Translation Continued
For each codon of mRNA, there is a transfer RNA (tRNA) molecule that has the anticodon
An anticodon is a set of three nucleotides that is complementary to the mRNA codon
Needed for bonding to the mRNA to make a “drop off”
The transfer RNA also carries ONE amino acid
The transfer RNA bonds temporarily to its mRNA complement codon
A chemical reaction occurs that causes the tRNA to let go of its amino acid

31. Transfer RNA

32. Translation Continued
The amino acids that are dropped off by the tRNA are linked together by a peptide bond
This continues until a polypeptide chain or a protein is made based on the instructions originally provided by the DNA.

33. Transfer RNA at Work

34. A closer Look at Translation

35. How protein synthesis is altered when there is a change in the DNA
DNA Mutations
How protein synthesis is altered when there is a change in the DNA

36. Mutations Any change in the DNA nucleotide sequence
The DNA is checked twice for this during Interphase of the cell cycle
After G1: The existing DNA is checked
After G2: The replicated DNA is checked to make sure no mutations occurred in the replication of DNA
Causes of mutations
DNA Replication errors
Caused by mutagens: UV light, chemicals, pollutants, changes in the environment etc.

37. Protein Synthesis & Mutations
How mutations can effect protein synthesis
No effect: The same amino acid sequence is created regardless
Good result: A new adaptive trait comes about as a result (evolution)
Bad result: Controls over the cell cycle are lost and rapid cell division (cancer) results.

38. Two Types of Mutations The overall length of the DNA does NOT change
Substitution: Another nucleotide replaces an existing one
Inversion: Two, or more, nucleotides switch locations
The overall length of the DNA is changed
Deletion: One or more nucleotides are removed
Insertion: One or more extra nucleotides are added
Translocation: A part of one DNA moves to another strand of DNA
Point Mutations
Frameshift Mutations

39. Point Mutations
mutated
base

40. Frameshift Mutations

41. Translocation

42. Can mutations be passed on?
Yes
If the mutation occurs in the germ cells that divide through meiosis to create a sperm or an egg
These remain “hidden” until an offspring is created using either the sperm or the egg with the mutation No
If the mutation occurs in the somatic cells that divide through mitosis
These will only affect the individual, not their offspring