1. Protein Synthesis
The process where genetic information coded on DNA will be used by RNA to form proteins
Intro movie: DNA & Prot Syn

2. What is RNA? Ribonucleic Acid
The nucleic acid responsible for moving the genetic information from DNA in the nucleus to the site of protein synthesis in the cytoplasm.
Similar to DNA, but . . .

3. 1. 5-carbon sugar RIBOSE

4. URACIL replaces thymine as a nitrogen base

5. 3. ONE strand, not 2

6. The Complete RNA Nucleotide

7. Comparing DNA with RNA

8. Three Kinds of RNA
mRNA (messenger)
And . . .

9. tRNA (transfer)
And . . .

10. rRNA (ribosomal)
Makes up ribosomes – in two pieces

11. Two Stages of Protein Synthesis

12. 1. TRANSCRIPTION
The process of copying genetic information from DNA to a complementary strand of RNA
Necessary b/c DNA never leaves the nucleus, yet must direct protein synthesis in the cytoplasm
Carried out by mRNA (messenger) in the nucleus

13. Steps in Transcription
1. RNA polymerase (enzyme) binds to “start” sites on DNA and separates DNA strand
2. RNA polymerase adds complementary RNA nucleotides to new mRNA molecule as it moves along DNA template
3. Transcription continues until the polymerase reaches a “stop” site.

14. Transcription Animation:Transcription (simple)
Animation: Transcription (moderate)

15. DNA transfers information to RNA in the form of a code
Try this:
DNA: C - G - A - T - G - A - T
mRNA: G C U A C U A
(Complementary nucleotides !)
Remember: Uracil replaces Thymine in RNA !

16. Why Must Protein Be Synthesized?
Protein forms most cell structures, directs cell activities, and is responsible for making carbo’s and lipids
Protein is formed from amino acids
1. There are 20 amino acids but only 4 nitrogen bases to make them!
2. Must have more than 1 nitrogen base as the “code” for amino acids
3. Three DNA nitrogen bases form the “code” for amino acids.

17. What is a CODON?
Three DNA nitrogen bases will “code” for a particular amino acid.
Thus, DNA transfers information to mRNA in the form of a “codon”
Let’s look at the “Genetic Code” table . . .

18. Genetic Code Table
1. If the mRNA codon is GCC, what is the amino acid it codes for?
Ans: Alanine
2. If the mRNA is AUG . . .?
Ans: Methionine
3. If the mRNA is CAC . . .?
Ans: Histidine
4. If the mRNA is UAA . . .?
Ans: Stop transcription !

19. Special Codons:
AUG is a “start” codon but also forms the amino acid, methionine
There are 3 “stop” codons but these don’t form amino acids

20. Before translation . . .
In eukaryotic cells (cells with nuclei), DNA has areas that do not code for a protein
These areas must be “cut out” of the new mRNA before it leaves the nucleus
The areas cut out are INTRONS
The areas left, that do make the protein, are EXONS

21. Introns and Exons

22. 2. TRANSLATION
The process of forming an amino acid chain (protein) from information encoded in mRNA
Begins when mRNA leaves nucleus and enters the cytoplasm
Involves mRNA, tRNA, and rRNA

23. Steps in Translation
A ribosome (made of protein and rRNA) attaches to start codon (AUG) on the mRNA
Ribosome moves along mRNA pairing each mRNA codon with a tRNA anticodon
Amino acids join with peptide bonds to form a polypeptide (protein) chain
Translation stops when ribosome reaches a stop codon

24. Translation Animation: Translation (good)
Animation:Translation (simple)
Animation:Translation (moderate)

25. Try this . . . DNA: AAC - TAG - GGT - CTC - AGC - ACG mRNA: tRNA:
Amino
Acid:
UUG
AUC
CCA
GAG
UCG
UGC
AAC
UAG
GGU
CUC
AGC
ACG
Leucine
Proline
Serine
Isoleucine
Cystine
Glutamic
acid
NOTE: You must use the mRNA strand code to determine the amino acid from the genetic code table because it is a table of mRNA.
Do NOT use the tRNA strand!)

26. Putting it all together . . .
Transcription
Translation

27. Try labeling these . . .  1 - The place Ans: Cytoplasm 2 – The strand
Ans: mRNA A
3 – The structure
Ans: Ribosome
4 – The strand
Ans: Polypeptide
5 – The structure
Ans: tRNA B
A – The process
Ans: Transcription
B – The process
Ans: Translation

28. Label these . . .  1 3?  2 1 – The 3 bases are called an _____
Ans: Anticodon
2 – The 3 bases are
called a _____
Ans: Codon  2
3 - The tRNA is bringing the amino acid Proline.
Use the Genetic Code table to determine the next a.a. to be added.
Ans: Glycine

29. Finishing Touches . . .
The polypeptide chain must take on the characteristic shape and function of the final protein molecule
It folds several times and in several ways
Primary, secondary, tertiary structures are formed
Other molecules can be incorporated into the final protein molecule

30. Primary Protein Structure
A chain of amino acids – the polypeptide

31. Secondary Protein Structure
The polypeptide will fold into alpha helices and beta pleated sheets

32. Tertiary Protein Structure
Secondary structure will fold on itself several times making a “globular” structure
Other molecules, such as iron (heme), can be incorporated into the final structure
Proteins are the most complicated of all biomolecules

33. Gene Structure
Eukaryotic genes contain non-coding regions called INTRONS and coding regions called EXONS
Introns must be removed (called splicing) and the remaining exons ligated (joined) together. This is a complicated process involving numerous enzymes and other proteins
The mature mRNA transcript then can leave the nucleus and translation can begin

34. Gene Structure (Advanced)
Transcription involves many transcription factors (proteins) and various gene regions upstream of the actual site to be transcribed
The actual site of transcription is an “Open Reading Frame” (ORF)
Promoter regions include a TATA box, enhancer genes, repressor and activator genes
Numerous enzymes are involved: RNA polymerases, ribozymes, endonucleases, etc.
After transcription, a Poly A “tail” will be added at the end of the primary mRNA transcript

35. Basic Gene Structure

36. Open Reading Frame

37. TATA Box

38. Poly A Tail

39. Advanced Protein Synthesis
Transcription
Translation
Animation:Virtual cell: Transcription, (advanced with sound, 3-D)
Animation:Translation (advanced)
Animation:Virtual cell: Translation, (advanced with sound, 3-D)

40. Eukaryotic gene regulation
Eukaryotic genes are “turned on or off” by repressor or activator proteins (called transcription factors) upstream of the ORF
This is a form of “feedback” control that regulates if and when DNA will be transcribed into mRNA

41. Prokaryotic Gene Regulation
Prokaryotic genes with regulators are called “Operons” ( set of 3 genes that turn on/off transcription) and the best example is the “Lac Operon” that controls the production of ß-Galactosidase (an enzyme that will break down lactose into two monosaccharides)
Many prokaryotic genes have operons to control their activity

42. Lac Operon
Animation:Virtual cell: lac operon (advanced with sound, 3-D)