1. Lesson starter Name the four bases found in DNA
Which DNA bases pair together in complementary base pairing?
What determines the order of amino acids found in protein?
Name is the name of the three adjacent bases in an mRNA molecule called?
Where in the cell is mRNA made?

2. Translation Learning objectives:
Describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acid sequence in a polypeptide, including the role of messenger RNA, transfer RNA and ribosomes.
State that cyclic AMP activates proteins by altering their three-dimensional structure

3. Summary So Far…
Use the pictures to help you describe what you have learned so far.

4. Summary So Far… What is happening here?
What stage of protein synthesis is taking place?
What molecule is being formed?

5. The Nucleolus Nucleoli are found with in the nucleus
dense with no membrane
made of DNA, RNA and protein
control RNA synthesis and other parts that make ribosomes
ribosome parts are sent out of the nucleus to be assembled into ribosomes

6. Ribosomes
Ribosomes
Small, almost spherical. Manufactured in nucleolus in eukaryotic cells
Found free in cytoplasm or attached to endoplasmic reticulum
Site of translation of mRNA into protein
Contains enzymes essential for translation to occur

7. Ribosomes Made of two subunits.
What is significant about the groove in the middle of the ribosome?
Groove in the middle is where mRNA code is fed through and read
Assembly of amino acids in the correct sequence occurs here to make a functioning protein.

8. Making the correct proteins
Amino acids joined by peptide bonds make the primary structure of protein
Explain how the primary structure of a protein determines the tertiary structure
The primary structure determines the tertiary structure
How protein folds to made 3D structure
3D structure is held in place by hydrogen/ionic bonds and hydrophobic interactions between R groups of amino acids
Tertiary structure is the functional protein. Therefore if the genetic sequence to make the primary structure is incorrect, the final protein will not function correctly.

10. Translation
The completed strand of mRNA is made of many repeating nucleotides which contain 4 different bases (A, U, C, G)
A group of three bases (a triplet) is called a codon

11. Translation
A second type of RNA is called transfer RNA (tRNA) which is also made in the nucleus but transferred into the cytoplasm
Molecules of tRNA have a set of triplet bases – these are known as anticodons
Anticodons have base sequences that are complementary to mRNA codons
At the top of tRNA molecule, there are 3 unpaired bases where a particular amino acid will join on to.

14. Translation
The mRNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosome.
The first amino acid in any polypeptide is usually methionine. The codon for this is AUG, which has come to be known as the initiation codon as a result.
The tRNA anticodon is therefore UAC. These attach together by complementary base pairing
The second tRNA molecule attaches itself to the next codon on the mRNA in the same way.
The two amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA moves away, leaving the amino acid behind.
A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away.
This process continues, producing a chain of linked amino acids (a polypeptide chain) until there is a stop codon on the mRNA molecule.
The polypeptide chain moves away from the ribosome and translation is complete.

16. U G C A
U U A G C A U C G U A C G U A
Shows the exit of the mRNA from the nucleus

17. U G C A
U U A G C A U C G U A C G U A

18. U G C A
U U A G C A U C G U A C G U A

19. the mRNA leaves the nucleus via a pore in the nuclear membraneG C A
U U A G C A U C G U A C G U A

20. U G C A
U U A G C A U C G U A C G U A

21. U G C A
U U A G C A U C G U A C G U A

22. U G C A
U U A G C A U C G U A C G U A

23. U G C A
U U A G C A U C G U A C G U A

24. U U U C G A U G C A U C G C A A C U C G C
Shows how a ribosome binds to the mRNA

25. U U U C G A U G C A U C G C A A C U C G C

26. U U U C G A U G C A U C G C A A C U C G C

27. U U U C G A U G C A U C G C A A C U C G C

28. U U U C G A U G C A U C G C A A C U C G C
a ribosome binds to the mRNA
Introduces the concept of the triplet code

29. codon
U U U C G A U G C A U C G C A A C U C G C
the genetic code is read in groups of 3 letters called codons

30. U U U C G A U G C A U C G C A A C U C G C
codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
Shows the structure of tRNA including the anticodon

31. codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1

32. U U U C G A U G C A U C G C A A C U C G C
codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
tRNA molecules have specific anticodons for each of the 20 amino acids
anticodon

33. U U U C G A U G C A U C G C A A C U C G C
codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
anticodon
Shows how the tRNA molecules read the triplet code of the mRNA

34. codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1

35. codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1

36. codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
the complementary anticodon is attracted to the first codon on the mRNA

37. U U U C G A U G C A U C G C A A C U C G C A A A
codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
G C U
aa2
And how the polypeptide chain builds up

38. codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
G C U
aa2

39. codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
G C U
aa2

40. codon
codon
codon
codon
codon
codon
codon
U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
G C U
aa2

41. U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
G C U
aa2
the second codon also attracts its complementary anticodon

42. U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
G C U
aa2

43. U U U C G A U G C A U C G C A A C U C G C
A A A
G C U
aa2
A C G
aa2
aa1
a peptide bond is formed

44. U U U C G A U G C A U C G C A A C U C G C
G C U
aa2
A A A
A C G
aa3
aa1

45. U U U C G A U G C A U C G C A A C U C G C
G C U
aa2
A C G
aa3
A A A
aa1

46. U U U C G A U G C A U C G C A A C U C G C
A C G
aa3
G C U
aa1
aa2

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

48. U U U C G A U G C A U C G C A A C U C G C
A C G
aa3
U A G
aa4
the ribosome moves along the mRNA forming a polypeptide
aa1
aa2

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

50. U U U C G A U G C A U C G C A A C U C G C
C G U
aa5
U G A
aa6
aa1
aa2
aa3
aa4

51. U U U C G A U G C A U C G C A A C U C G C
U G A
aa6
aa1
aa2
aa3
aa4
aa5

52. U U U C G A U G C A U C G C A A C U C G C
U G A
once a stop sequence is reached the polypeptide is cast off
aa1
aa2
aa3
aa4
aa5
aa6

53. U U U C G A U G C A U C G C A A C U C G C
U G A
aa1
aa2
aa3
aa4
aa5
aa6

54. U U U C G A U G C A U C G C A A C U C G C A A A
G C U
aa2
aa1
aa2
aa3
aa4
aa5
aa6
Shows how several ribosomes may read a piece of mRNA at once

55. U U U C G A U G C A U C G C A A C U C G C
A A A
aa1
G C U
aa2
several ribosomes may pass along the mRNA behind the first - each producing an identical polypeptide
aa1
aa2
aa3
aa4
aa5
aa6

56. A A A +
aa1
Shows how tRNA is reactivated

57. A A A +
aa1

58. A A A
ATP AMP +
aa1

59. A A A
aa1
A A A
ATP AMP +
aa1

60. A A A
aa1
A A A
ATP AMP +
aa1
the tRNA molecules are activated after use by recombining with their specific amino acid

61. Plenary __________is the second stage of protein synthesis
________ _________ assemble to make a protein
This happens in a sequence dictated by the sequence of __________(triplet of bases of mRNA)
The genetic code for this is copied from ______in the nucleus on to mRNA and now translated into a sequence of amino acids, attached to moleucles of _________
____________are the site of protein synthesis. They can be found free in the cytoplasm or attached to endoplasmic reticulum (rough ER)

62. Plenary Translation is the second stage of protein synthesis
Amino acids assemble to make a protein
This happens in a sequence dictated by the sequence of codons (triplet of bases of mRNA)
The genetic code for this is copied from DNA in the nucleus on to mRNA and now translated into a sequence of amino acids, attached to moleucles of tRNA
Ribosomes are the site of protein synthesis. They can be found free in the cytoplasm or attached to endoplasmic reticulum (rough ER)

63. Cyclic AMP– protein activation
Some proteins need to be activated before they will work
Protein activation is also controlled by molecules e.g. hormones and sugars
Some of these molecules work by binding to cell membranes and triggering the production of cAMP inside the cell
cAMP activates proteins – alters 3D structure
Enzymes can be made active by cAMP binding to protein and moving the active site so that it is open

64. Cyclic AMP – protein activation
Example – protein kinase A (PKA)
PKA has 4 subunits
When cAMP is not bound, the four subunits are bound together and are therefore inactive
When cAMP binds at receptor sites, it causes a change in the enzyme’s 3D structure, releasing the active subunits.
Now PKA is active
Your task: Read the stretch and challenge section on page 107.
Draw out a series of diagrams to go with the above description of cAMP activity in protein activation.
Answer questions A and B to consolidate this note.

65. Quiz Questions What are the two stages of protein synthesis called?
Where does the first stage of protein synthesis take place?
When does RNA polymerase stop making mRNA?
Where does the second stage of protein synthesis take place?

66. Exam questions
A drug that inhibits cell growth is found to be able to bind to DNA, preventing RNA polymerase from binding. Explain how this drug will affect protein synthesis (2)
A polypeptide chain (protein) from a eukaryotic cell is 10 amino acids long.
Predict how ling the mRNA for this protein would be in nucleotides (without the start and stop codons). Explain your answer.(2)
Describe how mRNA is translated into the polypeptide chain (6)

67. Exam answers
The drug binds to DNA, preventing RNA polymerase from binding, so transcription cannot take place and no mRNA can be made (1 mark)
This means that there is no mRNA for translation and so protein synthesis is inhibited (1 mark)
2. (a) 10 x 3 = 30 nucleotides long (1 mark)
each amino acid is coded for by three nucleotides (a codon), so the mRNA length is nucleotides is the number of amino acids multiplied by three (1 mark)

68. Exam answers
2(b)
The mRNA molecule attaches itself to a ribosome and transfer RNA (tRNA) molecule carry amino acids to the ribosome
A tRNA molecule, with an anticodon that is complementary to the first codon on the mRNA (the start codon), attaches itself to the mRNA by complementary base paring.
A second tRNA molecule attaches itself to the codon on the mRNA in the same way
The two amino acids attached to the tRNA molecules are joined by a peptide bond and the first tRNA molecule moves away, leaving its amino acid behind
A third tRNA molecule binds to the next codon on the mRNA and its amino acid binds to the first two and the second tRNA molecule moves away
This process continues, producing a chain of linked amino acids (a polypeptide chain), until there is a stop codon on the mRNA molecule