1. Higher Human Biology Unit 1 – Human Cells
Section 3 – Gene Expression

2. Protein Synthesis - What Can You Remember?
What are the building blocks of proteins?
What holds these subunits together?
What is another name for a protein molecule
List as many functions of proteins that you can remember
Describe how and enzyme works
What does the term genotype mean?
What dies the term phenotype mean?
List the steps of protein synthesis
Amino Acids
Peptide bonds
polypeptide
Enzymes, antibodies, hormones structural
Specific, Substrate, active site, unchanged, optimum conditions – temp and pH, denatured
combination of alleles an organism has for particular characteristic
the physical appearance of these characteristics

3. a – Gene Expression We will be learning…
Define the term gene expression
State that transcription and translation involve three types of RNA (mRNA, tRNA, and rRNA)
Describe the structure and function of the three types of RNA.
Describe the process of Transcription.
State that mRNA carries a copy of DNA code from the nucleus to the ribosome
State that tRNA has an anticodon at one end and an attachment site for a specific amino acid at the other
State that tRNA carries the specific amino acid to the ribosome
Describe the structure of the ribosome as being made up of rRNA and protein

4. What makes a cell function the way that it does?
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
A cell’s genotype is determined by the particular set of genes that an individual has.
A gene is a specific sequence of nucleotides that code for a particular characteristic.
mRNA
U C U C C A A C U G C U U
codon
ser
pro
thr
ala
Ribosome
Translation
Overview of gene expression
Protein

5. Gene Expression & types of RNA
Gene expression is the process by which specific genes are activated to produce a required protein.
Every cell in a multi-cellular organism contains every gene needed to make every protein that that organism will ever make. However, in any cell, only a very small number of these genes are ever expressed. Each cell is specialised to carry out a certain task and will therefore only need to express certain genes.

6. Protein Synthesis Proteins are made in the cytoplasm
A messenger is required to pass information from the DNA in the nucleus to the cytoplasm
This is messenger RNA (mRNA)
It is formed (transcribed) from free RNA nucleotides in the nucleus
This process of transcription.

7. Types of RNA RNA is a nucleic acid of similar
structure to DNA. There are three
types of RNA involved in translation and transcription. Each of which play a significant
role in protein synthesis; mRNA, tRNA
and rRNA.
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)

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

9. mRNA Structure Single stranded Ribose sugar Uracil pairs with adenine
mRNA is formed in the nucleus from free nucleotides and carries a copy of the DNA code from the nucleus to the ribosome
Single stranded
Ribose sugar
Uracil pairs with adenine

10. tRNA Structure
tRNA molecules collect specific amino acids and bring them to the ribosome to build proteins.
Each tRNA molecule has a sequence of three bases called an anticodon. These are complementary to codons on the mRNA molecule.

11. Structure of the Ribosome - rRNA
rRNA molecules combine with proteins to create the ribosome – the organelle responsible for assembling proteins following the DNA code.
Blue = Proteins
Orange = rRNA subunit 1
Yellow = rRNA subunit 2

12. Differences Between DNA and RNA
How many strands?
What sugar is present?
What bases are present?
Where is it located?
What is its function? 2 1
Deoxyribose
Ribose
A, T, C, G
A,U, C, G
Both Nucleus and Cytoplasm
Nucleus of Cells
Genetic and Hereditary material of the cells
Synthesis of proteins

13. Transcription - Nucleus
Transcription is the synthesis of mRNA from a section of DNA. A single stranded Messenger RNA (mRNA) must be Transcribed from a single strand of double stranded DNA.
Transcription of a gene starts from a region of DNA known as the promoter.
Terminator: End of a gene
Promoter: Start of a gene

14. RNA Polymerase binds onto the promoter region of the DNA strand
The DNA strand unwinds and unzips.
The mRNA strand is synthesized which is complementary to template DNA strand.
RNA Polymerase can only add nucleotides to the 3’ end of the growing mRNA molecule.
The mRNA strand elongates until the terminator sequenced is reached.
The resultant mRNA strand becomes separated from its DNA template is called the primary transcript.
Click here for an overview of protein synthesis

15. Now try the card sort for Transcription

16. Codon on mRNA
Since there are only 4 bases present in DNA and approximately 20 amino acids that are present in proteins such as enzymes they cannot simply code for each other in a 1:1 ratio.
Bases are placed into triplets called codons and these groups of three code for an amino acid.
Each triplet of bases on mRNA is called a codon

17. b – RNA Polymerase We will be learning…
Describe the role of RNA polymerase in transcription of DNA into primary mRNA transcripts
Describe the process of Translation.
Describe what is meant by a Primary Transcript.
State that uracil is complimentary to Adenine in RNA
Describe the process and products of RNA splicing.
State that introns are non-coding regions that are removed from the primary transcript
State that exons are coding regions and are joined together to form the mature transcript

18. RNA polymerase This enzyme is responsible for transcription.
RNA polymerase binds at the promoter and unwinds the DNA.
RNA polymerase adds nucleotides onto the 3’ end of the growing mRNA molecule.
Due to the base-pairing rules the mRNA produced will be complementary to the DNA.
The molecule elongates until it reaches the terminator sequence.
The molecule produced is called the primary transcript.

19. Uracil is complimentary to Adenine

20. d – RNA Splicing Explain how one gene can code for many proteins.
We will be learning…
Explain how one gene can code for many proteins.
Describe splicing and post translational modification.
State that different mature mRNA transcripts are produced from the same primary transcript

21. Modification of the Primary Transcript
Not all the regions in a genome are required to produce the final protein.
These non-coding regions are called introns.
The coding regions are called exons.
Primary transcript

23. 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.

24. Alternative RNA Splicing
More than one mRNA strand can be produced from the primary transcript. Depending on circumstances, alternative segments of RNA may be treated as the exons and introns.
This means that the primary transcript has the potential to produce several mRNA strands each with a different sequence of base triplets, each coding for a different polypeptide e.g. one gene can code for several different proteins e.g. different antibodies.

25. c – tRNA - Cytoplasm
We will be learning…
State that tRNA is involved in the translation of mRNA into a polypeptide at the ribosome.
Explain the relationship between a codon and an anticodon
Explain the genetic code and be able to translate between DNA, mRNA and tRNA.
State that peptide bonds join the amino acids together.
Explain that tRNA leaves the ribosome as the polypeptide forms

26. Transfer RNA - tRNA
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. tRNA is involved in the translation of mRNA into a polypeptide at the ribosome.
It is folded into a 3D structure, held together by hydrogen bonds. Each molecule of tRNA has a triplet of bases exposed. This triplet is known as an anticodon, corresponds to a particular amino acid.
The tRNA picks up its appropriate amino acid and takes it to the ribosome to be matched with the mRNA.

28. tRNA - Picking up Amino Acids
The anticodon corresponds to a particular amino acid. Each tRNA molecule picks up the appropriate amino acid from the cytoplasm at its site of attachment. There are 20 different amino acids.

29. The codon on the mRNA strand is complimentary to the anticodon on the tRNA molecule

30. Translation (RNA to protein)
- every 3 bases forms a CODON
- these correspond to an amino acid
Transfer RNA (tRNA) is found in the cytoplasm
It brings amino acids to the ribosome
tRNA has triplets of bases - ANTICODONS
Anticodons match up with complimentary CODONS on the mRNA

31. Each codon is code for one amino acid.
Translation
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 code for one amino acid.

32. tRNA leaves the ribosome as the polypeptide forms
tRNA leaves the ribosome as the polypeptide forms. Peptide bonds join the amino acids together to form the polypeptide.

33. Ribosomes are small, roughly spherical structures found in all cells.
Some occur freely in the cytoplasm, others are found attached to endoplasmic reticulum

34. Ribosomes are the site of translation of mRNA into protein
Ribosomes are the site of translation of mRNA into protein. The ribosome becomes attached to one end of the mRNA molecule about to be translated. Inside the ribosome there are sites for attachment of tRNA molecules, two at a time. Weak hydrogen bonds form between the anticodon of the tRNA and the codon of the mRNA. When the second tRNA molecule repeats this process, the first two amino acids molecules are brought into line with one another. The two amino acids become joined together by a strong peptide bond. The first tRNA becomes disconnected from its amino acid and from the mRNA then leaves the ribosome.

35. They contain the enzymes essential for protein synthesis.
Ribosomes
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.

36. 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.

37. Translation
The ribosome binds to the 5’ end of the mRNA so that the start codon (AUG) is in site P.
Next a tRNA carrying a new amino acid becomes attached to site P.
The mRNA codon at site A bonds complementary anticodon on the appropriate tRNA bearing the correct amino acid.
A peptide bond then forms between these two amino acids.
5. The ribosome then moves along one codon.
6. The tRNA from Site P is moved to Site E and released.
7. Steps 3-6 then repeat until it reaches a stop codon (UAA, UAG or UGA).

38. Can we Make a Protein?
Use the following DNA strand to carry out transcription. You will need to convert the information into mRNA and then into Amino acids.
C T A G A A C C G T G T C G A A G T G T G G T G - DNA
GAU CUU GGC ACA GCU UCA CAC CAC - mRNA
Asp – Leu – Gly – Thr – Ala – Ser – His – His – Amino Acid

39. e – Amino Acids
We will be learning…
State that amino acids are linked by peptide bonds to form polypeptides
Describe how polypeptide chains fold to form 3D shapes of proteins held together by hydrogen bonds and other interactions between individual amino acids e.g. sulfur bridges
Describe the structure of proteins and how this relates to their function.
Describe the different types of protein.

40. Peptide Bonds in the Polypeptide Chain
The amino acids continue to align by forming peptide bonds and disconnecting. The growing chain of amino acids is known as a polypeptide chain. The completed polypeptide chain consisting of very many amino acids is then released into the cytoplasm. The tRNA and mRNA are reused.
The polypeptide may then be folded and rearranged to become the final protein. Sometimes several polypeptide chains combine to form the complete protein.
The mRNA is then fully translated to form a protein

41. Coiling and Folding of the Polypeptide
When a protein is made on the ribosome that is attached to the endoplasmic reticulum (ER), the polypeptide is ‘injected’ into the ER and then coiled and folded. The protein is then passed to the golgi apparatus for packaging (e.g. adding a carbohydrate part to make it into a glycoprotein which is a conjugated protein) and secretion from the cell
Proteins synthesised in free ribosomes are for use within the cell; protein made in ribosomes attached to the ER are for export.

42. Protein made in
Ribosomes attached
To endoplasmic
Reticulum is for
export
Protein made
In free
Ribosomes is
For use
Within the
cell

43. Post Translational Modification
Following translation, further modification can occur in addition to folding and coiling. In order for the protein to be able to perform its function.
Cleavage – the protein may need to be cut (cleaved) to become active e.g. insulin
Molecular Addition - the protein can be modified by adding a carbohydrate or phosphate group e.g. mucus or regulatory proteins respectively.

44. Bonding in Polypeptide/Proteins – Peptide Bonds
1. Peptide bonds – Primary Structure
The product – POLYPEPTIDE CHAIN (eventually a protein)
Proteins are build up of sub-units called amino acids. These are joined together by chemical links called peptide bonds.
AA1
AA2
tRNA
tRNA
The sequence of amino acids determines the protein’s structure and function. U C G A G C A G C U C G A G G

45. Secondary Structure Bonding in Polypeptide/Proteins – Hydrogen Bonding/Other Linkages
2. Hydrogen bonds
Weak hydrogen bonds form between amino acids in a polypeptide chain causing the chain to coil into a spiral.
3. Other linkages
There are different cross-connections that bridges sulfur atoms with hydrogen bonds. These are important because they determine the final structure of the protein and so determine the function of the protein. They lead to the formation of fibrous or globular proteins.

46. Types of Proteins
Hydrogen bonds form between certain amino acids causing the chain to become coiled or folded
Also, various types of cross connections form including ‘bridges’ between sulphur atoms

47. Fibrous Proteins
Fibrous proteins are formed by several spiral-shaped polypeptide molecules link together giving it a rope-like structure. Responsible for the strength and flexibility of the skin, ligaments and tendons.
Example:
Collagen – found in
bone providing inelastic,
rigid support.

48. Globular Protein Enzymes Transport proteins Hormones Antibodies
Globular proteins are formed with polypeptide chains fold into a spherical shape. This type of protein are vital for all living cells and perform many functions:
Enzymes
Transport proteins
Hormones
Antibodies

49. Conjugated Protein
These proteins are globular but also consist of a non-protein chemical.
Examples:
GLYCOPROTEIN - made up of protein and a carbohydrate. For example, mucus that helps lubricate and protect parts of the body.
HAEMOGLOBIN – pigment that transports oxygen in blood. Consists of the protein globin and haem (non-protein containing iron).

50. Review
Name the molecule that carries the instructions for making proteins.
Where are proteins made in the cell?
What are the sub-units of proteins?
How are these sub-units joined together?
What are the two shapes of protein?
Give examples of each.
DNA
In the cytoplasm by the ribosome
Amino acids
Peptide bonds
Fibrous and globular
Fibrous - Collagen, elastin, keratin, actin/myosin
Globular – hormones, antibodies, enzymes
Conjugated - haemoglobin 50 50

51. Examples of proteins Protein name Type of protein Role
Collagen
Fibrous
Found in skin
Actin
Muscle cell filaments
Myosin
Amylase (Enzyme)
Globular
Breakdown of starch into maltose
Testosterone (Hormone)
Produces male gender characteristics
Haemoglobin
Conjugated globular
Found in red blood cells. Carries oxygen.
Polypeptide chains
Become arranged in long parallel strands e.g. tendons
Become folded into a spherical shape e.g. enzymes
Become folded together into a spherical shape which incorporates another chemical e.g. haemoglobin

52. Now try the following
Describe what is meant by the primary structure of proteins.
Name the bond between amino acids.
What additional bond(s) gives secondary structures their shape?
Simply the sequence of amino acids in a polypeptide chain
Peptide bond
Weak Hydrogen bonds and Sulfur bridges

53. Now I can….. a Define the term gene expression
State that transcription and translation involve three types of RNA (mRNA, tRNA, and rRNA)
Describe the structure and function of the three types of RNA.
Describe the process of Transcription.
State that mRNA carries a copy of DNA code from the nucleus to the ribosome
State that tRNA has an anticodon at one end and an attachment site for a specific amino acid at the other
State that tRNA carries the specific amino acid to the ribosome
Describe the structure of the ribosome as being made up of rRNA and protein b
Describe the role of RNA polymerase in transcription of DNA into primary mRNA transcripts
Describe the process of Translation.
Describe what is meant by a Primary Transcript.
State that uracil is complimentary to Adenine in RNA
Describe the process and products of RNA splicing.
State that introns are non-coding regions that are removed from the primary transcript
State that exons are coding regions and are joined together to form the mature transcript

54. Now I can….. d Explain how one gene can code for many proteins.
State that tRNA is involved in the translation of mRNA into a polypeptide at the ribosome.
Explain the relationship between a codon and an anticodon
Explain the genetic code and be able to translate
between DNA, mRNA and tRNA.
State that peptide bonds join the amino acids together.
Explain that tRNA leaves the ribosome as the polypeptide forms d
Explain how one gene can code for many proteins.
Describe splicing and post translational modification.
State that different mature mRNA transcripts are produced from the same primary transcript

55. Now I can….. e
State that amino acids are linked by peptide bonds to form polypeptides
Describe how polypeptide chains fold to form 3D shapes of proteins held together by hydrogen bonds and other interactions between individual amino acids e.g. sulfur bridges
Describe the structure of proteins and how this relates to their function.
Describe the different types of protein.
State that Phenotype is determined by proteins produced as the result of gene expression

56. CfE HH 2017 B Q12 Answer the following:
Labelled diagrams may be used where appropriate – 9 marks each
B Describe the structure of RNA and the process of transcription

58. CfE HH 2016 A Q3 C

59. CfE HH 2016 B Q2

61. CfE HH 2015 A Q2 C

62. CfE HH 2015 A Q3 B

63. Sugar-phosphate backbone
a – Gene Expression
Word
Meaning
Gene Expression
transcription and translation of a gene to synthesise proteins
Transcription
copying of DNA sequences to make a primary transcript
mRNA
carries a copy of the DNA code from nucleus to ribosome
tRNA
transfers specific amino acids to the mRNA on the ribosomes in the cytoplasm
rRNA
type of RNA that makes up ribosomes
Ribosome
site of protein synthesis; composed of rRNA and protein
Anticodon
sequence of three bases on tRNA that codes for a specific amino acid
Codon
sequence of three bases on mRNA that codes for a specific amino acid
Amino acid
unit of polypeptide structure
Genetic Code
total genetic material present in an organism
Sugar-phosphate backbone
strongly bonded strand of DNA

64. b – RNA Polymerase Word Meaning RNA Polymerase Translation
enzyme involved in synthesis of primary transcripts from DNA
Translation
production of polypeptide at a ribosome using information encoded in Mrna
Primary Transcript
molecule made when DNA is transcribed
Uracil
RNA base not found in DNA
RNA Splicing
joining of exons following the removal of introns from a primary transcript
Introns
non-coding sequence of DNA
Exons
sequence of DNA that codes for protein
Mature Transcript
Modified mRNA strand
Attachment Site
site on a transfer RNA molecule to which a specific amino acid binds

65. C - tRNA Word Meaning Polypeptide Peptide bonds
short strand of amino acids
Peptide bonds
strong chemical link between amino acids in the primary structure of a polypeptide

66. Post Translational Modification
d – RNA Splicing
Word
Meaning
Promoter
A region of DNA in a gene where transcription is initiated.
Post Translational Modification
changes made to polypeptides following translation

67. Molecular Interactions
e – Amino Acids
Word
Meaning
Hydrogen Bonds
weak chemical link joining complementary base pairs in DNA
Fibrous Protein
Long elongated rope-like structures that provide structural support for cells and tissues
Globular Protein
have a compact and relatively spherical structure
Conjugated Protein
Globular protein with non-protein part
Molecular Interactions
various chemical links (e,g. sulfur bridge, ionic bond, van der Waals forces) joining amino acids and giving protein molecules their shape
Phenotype
outward appearance of an organism
Genotype
your complete heritable genetic identity