1. Key area 3 – Control of gene expression
CfE Higher Biology
Key area 3 – Control of gene expression

2. How are proteins synthesised?
Learning Intention
How are proteins synthesised?

3. Success Criteria All pupils will…..
State the building blocks of proteins
Most pupils will…..
Describe the 2 possible structures of proteins with examples
Some pupils will……
Explain the function of a specific protein found in the body.

4. This topic covers: Structure and function of proteins
Structure and function of RNA
Transcription
Translation
One gene…many proteins

5. Proteins

6. What are proteins made of?
Think back to National 5… What elements are in proteins? Nitrogen, Hydrogen, Carbon, Oxygen What are the sub-units in proteins called? Amino Acids

7. What are proteins made of?
Proteins are made of long chains of amino acids.
There are 20 different amino acids.
They are joined together by peptide bonds.
The proteins fold into different shapes.
The shape of the protein dictates the role it will have in the cell.

8. Protein structure Proteins fall into two distinct groups:
Fibrous proteins
Globular proteins

9. EXAMPLES Fibrous Globular Keratin Enzymes – Elastin Messengers –
Collagen
Transporters
Regulatory roles

10. Protein function
You will have come across many proteins before and covered some of the many roles they undertake in living organisms.
Choose one of the proteins listed below to research and complete its identity card, which will be used to create a classroom display.
kinase
helicase
oxytocin
elastin
catalase
actin
polymerase
integrins
keratin
insulin
myosin
pepsin
collagen
antibody
haemoglobin
phosphorylase
tubulin
amylase
porin
cytochromes 10

11. Structure: _____________________________
Location: _____________________________
Function: _____________________________
_____________________________________ 11

12. Protein folding
Once the polypeptide has formed, hydrogen bonds can form between amino acids – creating secondary structures.
These can fold again to form – tertiary structures
Several different polypeptides can then join together forming the final protein.

13. Starter Questions
How many different types of amino acids are known to occur in proteins? 20
What name is given to the chain formed when several amino acids become linked together?
polypeptide
What determines the order in which amino acids are joined together?
The sequence of bases in DNA
Describe 2 ways in which chains of amino acids can become arranged to form a protein?
Fibrous or globular

14. Structure and function of RNA

15. Learning Intention
What is RNA?
And
What does it do?

16. Success Criteria All pupils will….. State the base pairs found in RNA
Most pupils will…..
Describe the difference between DNA and RNA
Some pupils will……
Explain why tRNA has a 3D structure

17. RNA There is a second type of nucleic acid in the cell, called RNA.
RNA plays a vital role in the production of protein from the code in the DNA.

18. Differences between DNA and RNA
Phosphate
Ribose Sugar
… and Uracil replaces thymine
5’ end
3’ end
5’ pronounced “5 prime”
RNA nucleotides are similar in structure to DNA, except Ribose sugar replaces Deoxyribose sugar…

19. Differences between DNA and RNA

20. *Uracil replaces thymine
Differences between DNA and RNA
DNA
RNA
Double stranded
Single stranded
Deoxyribose sugar
Ribose sugar
Bases: A, T, C and G
Bases: A, U*, C and G
*Uracil replaces thymine

21. Making proteins protein molecule amino acid
Proteins are long molecules made up of amino acids.
Different combinations of amino acids make different proteins.
Genes contain the instructions for making proteins.
The sequence of bases in a gene determines the amino acid sequence in a protein.
amino acid
protein
molecule

22. How do Genes make proteins?
Each amino acid is coded for by its own special sequence of three bases called a triplet (codon).
triplet
amino acid

23. The order of triplets in a gene determines the sequence of amino acids.
The amino acids join together to form a protein molecule.

24. DNA, RNA and protein
The instructions to make protein are copied from part of the DNA strand onto a molecule called messenger RNA (mRNA).
The mRNA carries these instructions out of the cell nucleus, to ribosomes.
Proteins are assembled from amino acids on ribosomes.
crick and watson
show model of DNA

26. Types of RNA There are three types of RNA: Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)

27. mRNA
mRNA is formed in the nucleus from free nucleotides and carries a copy of the DNA code from the nucleus to the ribosomes (where protein synthesis occurs).
A sequence of 3 bases along a strand of mRNA is called a codon.

28. tRNA
tRNA molecules collect amino acids and bring them to the ribosome to build proteins and is found in the cytoplasm.
They are composed of a single strand of nucleotides.
However due to hydrogen bonds that form between the bases is has a 3D structure.
Each molecule has
An attachment site for a specific amino acid
An exposed triplet of bases called an anti-codon

30. rRNA
rRNA molecules combine with proteins to create the ribosome – the organelle responsible for assembling proteins following the DNA code.

31. Success Criteria All pupils will….. State the base pairs found in RNA
Most pupils will…..
Describe the difference between DNA and RNA
Some pupils will……
Explain why tRNA has a 3D structure

32. Transcription

33. Starter questions State 3 ways in which RNA is different to DNA.
DNA is double stranded, has deoxyribose sugar, has thymine instead of uracil.
How many bases in the genetic code correspond to make one amino acid? 3
What name is given to the groups of bases that make up the genetic code?
triplets
Draw a diagram of the mRNA strand with the code ----ATGGCATAC------
UACCGUAUG

34. What are the stages of protein synthesis?
Learning Intention
What are the stages of protein synthesis?

35. Success Criteria All pupils will…..
State the two main stages of protein synthesis.
Most pupils will…..
Describe the stages of transcription.
Some pupils will……
Explain the importance of splicing.

36. Protein synthesis
Protein synthesis by gene expression has 2 main stages……… 1. Transcription 2. Translation

37. Transcription
Transcription is the synthesis of mRNA from a section of DNA.
It takes place in the nucleus and involves the synthesis of mRNA from the information contained on the gene.
For transcription to occur you need:
DNA template
Supply of RNA nucleotides
Enzyme DNA polymerase
ATP (energy)

38. Stages of Transcription
Promoter: Start of a gene 3’ 5’
Terminator: End of a gene
Transcription of a gene starts from a region of DNA known as the promoter.

39. RNA polymerase
This enzyme is responsible for transcription. RNA polymerase binds at the promoter and unwinds the DNA by breaking the hydrogen bonds between the base pairs from the 3’ end. Sugar phosphate bonds form between the ribose sugar of one RNA nucleotide and the phosphate group of the next. 5’ 3’ 5’ 3’
RNA polymerase

40. 3’ 5’ 3’ 3’ 5’ 5’
The molecule elongates until it reaches the terminator sequence.
The molecule produced is called the primary transcript.
Primary transcript of mRNA forming

41. 3’ 5’ 5’ 3’
Completed primary transcript of mRNA released.
Due to the base-pairing rules the mRNA produced will be complementary to the DNA.
RNA polymerase released

43. Modification of the primary transcript
Not all the regions in a eukaryotic gene are required to produce the final protein.
These non-coding regions are called introns.
The coding regions are called exons.

44. RNA splicing
After the mRNA has been transcribed the introns are removed.
The remaining exons are spliced together to form a continuous sequence.
This is called the mature transcript.
The mature transcript then leaves the nucleus to travel to the cytoplasm.

45. Primary transcript
Primary transcript
Mature transcript

46. Success Criteria All pupils will…..
State the two main stages of protein synthesis.
Most pupils will…..
Describe the stages of transcription.
Some pupils will……
Explain the importance of splicing.

47. Translation

48. Starter questions 1. What is required for transcription to occur?
DNA template, Supply of RNA nucleotides, Enzyme DNA polymerase, ATP (energy)
2. What enzyme is used in transcription?
RNA polymerase
3. What direction does this enzyme unzip the RNA?
3’ to 5’
4. What is the difference between and intron and an exon?
Introns are non-coding and exons are coding

49. What are the stages of protein synthesis?
Learning Intention
What are the stages of protein synthesis?

50. Success Criteria All pupils will…..
State the type of RNA used in translation
Most pupils will…..
Describe the process of translation using a diagram.
Some pupils will……
Explain why translation must occur.

51. Genetic code
Translation is the synthesis of protein following the code with in the mature mRNA transcript.
The mRNA is made of sequences of three nucleotides (a triplet of bases) called codons.
Each codon is the code for one amino acid.

53. A further type of RNA is found in the cell’s cytoplasm.
This is called tRNA (transfer RNA) and is made of a single chain of nucleotides.
It is folded into a 3D structure, held together by hydrogen bonds.

54. Each tRNA has an attachment site for a specific amino acid and a triplet of bases known as an anticodon.
Many different types of tRNA are present in cell, one or more for each type of amino acid.
The tRNA picks up its appropriate amino acid and takes it to the ribosome to be matched with the mRNA.

56. Translation Translation occurs on ribosomes.
It involves the information on the mature transcript of mRNA being translated to form a polypeptide chain.

57. Ribosomes
Ribosomes are small, roughly spherical structures found in all cells.
They contain the enzymes essential for protein synthesis.
The ribosome’s function is to bring the tRNA molecules bearing amino acids in contact with the mRNA.

58. Site P – holds the tRNA carrying the growing polypeptide chain
Site P – holds the tRNA carrying the growing polypeptide chain. Site A – holds the tRNA carrying the next amino acid to be joined to the chain.
Site E – releases the empty tRNA once it has dropped off its amino acid.

59. Translation
The ribosome binds to the 5’ end of the mRNA so that the start codon (AUG) is in site P.

60. Translation
2. Next a tRNA picks up specific amino acids from the cytoplasm and brings them to the ribosome.

61. Translation
3. The ribosome holds the codon and anticodon together (by hydrogen bonds) until the amino acids on the adjacent tRNA molecules become joined together by peptide bonds.

62. Translation
4.The freed tRNA molecule is released into the cytoplasm to pick up another amino acid.

63. Translation
5. The ribosome moves along the tRNA until it reaches the stop codon and the pollypeptide chain is released.

64. Video

65. Success Criteria All pupils will…..
State the type of RNA used in translation
Most pupils will…..
Describe the process of translation using a diagram.
Some pupils will……
Explain why translation must occur.

66. One gene…many proteins

67. Is there only one gene for one protein?
Learning Intention
Is there only one gene for one protein?

68. Success Criteria All pupils will….. State Most pupils will….. Describe
Some pupils will……
Explain

69. One gene…many proteins
The same gene can be used to make several different proteins by:
Alternative RNA splicing
Post-translational modification

70. 1. Alternative RNA Splicing
Previously we learned that the primary transcript is separated into exons and introns and the exons are spliced together to make the mature transcript.
Under certain conditions alternative segments of RNA may be treated as exons and introns.
In other words one gene can produce several different mature mRNA transcripts.
And therefore, several different proteins.

71. Primary transcript
Alternatively spliced mature mRNA transcripts
Different proteins are formed

72. 2. Post-translational modification
Once translation is completed, proteins can be modified by:
Cleavage
Addition of other molecules

73. (a) Cleavage
A single poly-peptide chain can be cleaved (cut) by enzymes to make it active. Insulin is an example of the protein modified in this way. A central section of the “pro-insulin” molecule is removed to make insulin.

74. Inactive “pro-insulin”
Active insulin
Redundant central section

75. (b) Addition of other molecules
Carbohydrates and phosphate groups can be added to proteins. Mucus is a glycoprotein made by the addition of a protein and a carbohydrate.

76. Some regulatory proteins need phosphate groups added to them to make them active. e.g. p53 is a regulator involved in DNA repair. Normally it is inactive. When phosphate is added it becomes active.

77. Overview of gene expression
Nucleus
A G A G G T T G A C G A A
T C T C C A A C T G C T T
DNA
Transcription
mRNA
U C U C C A A C U G C U U
codon
Overview of gene expression
ser
pro
thr
ala
Ribosome
Translation
Protein