1. Protein Synthesis: Making Those Proteins!

2. Review: DNA
Hershey and Chase’s experiment showed that DNA was the genetic material

3. So What are Proteins?
Proteins are the “work-horses” of the cell…they do a lot of different jobs!
A) Antibodies – immune system (defense)
B) Structure – hair and nails
C) Speeding Up Reactions – enzymes
D) Transport – hemoglobin (in blood)
E) Movement – muscle
And the list goes on!

4. Question: Why do these proteins all have different shapes?

5. How do our cells make proteins?
DNA contains genes, sections of nucleotide chains
Genes code for polypeptides (proteins)
Polypeptides are amino acid chains

6. DNA is found inside the nucleus, but proteins are made in ribosomes
Predictions: So how do we get the message from DNA in the nucleus to the ribosomes?

7. The Solution?
A molecule called RNA carries the message from the nucleus to the cytoplasm!
Unlike DNA, RNA is small enough to fit through the pores in the nuclear membrane

8. Roles of DNA and RNA DNA is the master plan
RNA is the copy of the master plan!

9. Differences between RNA and DNA
#1: Number of Strands
-DNA  Double
-RNA  Single
Question:
Why might RNA mutate
(shuffle its bases) more
easily than DNA?
2) Do you think the HIV virus is
an RNA or DNA virus?

10. #2: Nitrogen bases
-DNA  Thymine (T)
-RNA  Uracil (U)
#3: Sugars
-DNA  deoxyribose
-RNA  ribose

11. Question: What base does Uracil pair with?

12. 3 Types of RNA
Messenger RNA (mRNA) copies DNA’s code & carries it to the ribosome
Transfer RNA (tRNA) takes amino acids to the ribosomes, where they can be joined into a chain
Ribosomal RNA (rRNA) makes up the ribosomes

13. Messenger RNA (mRNA) Long Straight chain of Nucleotides
Made in the Nucleus
Copies DNA & leaves through nuclear pores
Contains the Nitrogen Bases A, G, C, U ( no T )

14. Transfer RNA (tRNA) Clover-leaf shape
Has an attachment site at one end for an amino acid…each tRNA carries a specific amino acid

15. Ribosomal RNA (rRNA) Globular in shape
Together with proteins, makes up ribosomes

16. Protein Synthesis ? Process of making proteins…. 2 parts
1) Transcription
2) Translation ?

17. Part 1: Transcription
mRNA picks up the code from the DNA template strand and takes it from the nucleus to ribosomes in the cytoplasm
Main goal: make a copy of the code and get it out of the nucleus!
Question: Why can’t DNA leave the nucleus?

18. Steps of Transcription
1) DNA unzips
2) RNA polymerase (an enzyme) matches RNA bases with DNA template to make a strand
3) mRNA is released and leaves through the nuclear pore
Question: How is this similar to replication?

19. RNA
Free Nucleotides
RNA Polymerase
DNA

20. Let’s Transcribe!
Let’s transcribe an mRNA molecule from a DNA template strand…
DNA  A C T G G C A A T C G C
mRNA 

21. Part 2: Translation
The instructions (mRNA) are read by tRNA, and tRNA joins amino acids in the right order in the ribosome
Main Goal: make a polypeptide!

22. Steps of Translation mRNA goes to the ribosome
tRNA brings amino acids to the ribosome
tRNA “reads” the mRNA instructions and puts the amino acids in the right order
Amino acids link together by peptide bonds to make a polypeptide (protein)
How does tRNA “read” the mRNA instructions?

23. tRNA…”The Reader” 3 bases on mRNA strand = codon
3 bases at bottom of each tRNA = anticodon

24. More complementary base pairing…HOW THRILLING!

25. Labeling an image of translation
Ribosome
mRNA

26. Let’s See Translation in Action!G
aa2 A U U A C
aa1 A U G C U A C U U C G A 26

27. G A
aa3
peptide bond
aa1
aa2 U A C G A U A U G C U A C U U C G A 27

28. aa3
aa1
aa2 G A A
(leaves) G A U A U G C U A C U U C G A 28

29. aa1
aa4
aa2
aa3 G C U G A U G A A A U G C U A C U U C G A A C U 29

30. aa1
aa4
aa2
aa3
(leaves) G C U G A A A U G C U A C U U C G A A C U 30

31. aa5
aa1
aa2
aa4
aa3 U G A G A A G C U G C U A C U U C G A A C U 31

32. aa5
aa1
aa2
aa3
aa4 U G A
(leaves) G C U G C U A C U U C G A A C U 32

33. Stop Codon says STOP TRANSLATING!
aa5
aa4
Stop Codon says STOP TRANSLATING!
aa199
aa3
aa200
aa2
aa1 A C U C A U G U U U A G 33

34. Transcription and Translation Video

35. Flowchart
DNA
mRNA
tRNA (ribosomes)
Protein
Transcription
Translation

36. Drawing a Diagram of Protein Synthesis

37. An Analogy to Help You Remember- Baking a Cake 
DNA = Recipe book at the library
Nucleus = Library
mRNA = Handwritten copy of recipe
tRNA = You (read recipe and put ingredients together)
Ribosome = Kitchen
Amino Acids = Ingredients
Polypeptide = CAKE!!!!

38. Stop Codons: UAA, UAG, UGA
Scientists can “read” the mRNA by using a “codon” table that matches codons with their amino acids
Start Codon: AUG
Stop Codons: UAA, UAG, UGA

39. Codon charts can look different from one
another but be used for the same thing!
Use the mRNA strand and codon chart in your notes to make an amino acid chain!

40. End Result of Transcription and Translation
A beautiful polypeptide that can fold into a protein and do an important job in the cell!

41. Mutations

42. What is a mutation?
A change in the sequence of nitrogen bases (A,T,C, and G’s) in the DNA code.

43. The sequence of bases in DNA  sequence of amino acids in a polypeptide
So… changes in the DNA sequence may affect the resulting polypeptide

44. Example: Sickle Cell Disease
A mutation in the gene coding for the hemoglobin protein causes an abnormally shaped protein that causes red blood cells to form a crescent moon shape. These abnormally shaped red blood cells can clog arteries.

46. Example: Tay-Sacchs Disease
A mutation in the gene coding for an enzyme normally found in lysosomes causes the enzyme to change shape and become dysfunctional.
The enzyme can no longer break down a fat called GM2 in the brain and spinal tissue. This build-up impairs nerve function and causes death by approximately age 4

47. Types of Mutations – Gene Mutations
Two types of gene mutations – point mutations and frameshift mutations
Point mutations are caused by a substitution of one base for another in the DNA sequence
Frameshift mutations are caused by insertions or deletions of bases in the DNA sequence

48. Point Mutations
Silent Mutation – DNA change results in an mRNA codon that codes for the same amino acid
Missense Mutation – DNA change results in an mRNA codon that codes for a different amino acid
Nonsense Mutation – DNA change results in an mRNA “stop” codon (polypeptide ends early)

49. Example Point Mutation

50. Frameshift Mutations
Mutations caused by an insertion or deletion of bases in the DNA sequence  different DNA triplets for the rest of the sequence  different mRNA codons  rest of the polypeptide is different!

51. Example Frameshift Mutation

52. Types of Mutations – Large Chromosomal Mutations
Mutations that affect large chunks of a chromosome
Duplication – Large section of the chromosome is copied
Inversion – Large section of the chromosome is flipped around

53. C. Insertion – A large section from one chromosome is “stuck” into another D. Translocation – Large sections from two chromosomes are switched

54. Causes of Mutations
DNA fails to copy accurately: If DNA polymerase makes an error during DNA replication
External influences: Mutagens (chemicals or radiation damage the DNA
-Carcinogens: cancer-causing mutagens

55. Can mutations be passed down to offspring?
Somatic mutations occur in normal body cells and cannot be passed down to offspring (ex: somatic mutation in Red Delicious apple)
Germ-line mutations occur in gametes so they will be passed down to offspring

56. Are all mutations “bad”?
No!
Neutral Mutations: Silent mutations do not change the amino acid sequence at all!
Positive Mutations: Mutations could result in a trait that is beneficial to an organism (ex: some bacteria have a mutation that allows them to produce a protein to break down antibiotics)