CASE STUDY

Question 1

How does a mutation in the β-globin gene lead to a change in the structure and function of haemoglobin?

Answer 1

• Changes DNA base sequence
• Different codon in mRNA
• Different amino acid in polypeptide chain
• Affects folding, producing haemoglobin S with abnormal function

This mutation can lead to sickle cell disease.

Question 2

How can a change in amino acid sequence affect the tertiary structure of a protein?

Answer 2

• Alters R group interactions
• Changes hydrogen bonds
• Changes ionic bonds
• Affects overall shape and function

The tertiary structure is crucial for protein functionality.

Question 3

Outline the process of transcription and translation leading to haemoglobin production.

Answer 3

• RNA polymerase binds to DNA
• Synthesizes complementary mRNA
• mRNA exits nucleus and attaches to ribosome
• tRNA delivers amino acids according to codon–anticodon pairing
• Amino acids joined by peptide bonds to form polypeptide

This process is essential for protein synthesis.

Question 4

Why are sickle-shaped red blood cells less effective at transporting oxygen?

Answer 4

• Rigid and less flexible
• Can block capillaries
• Reduce oxygen delivery to tissues

This leads to various health complications.

Question 5

What is the role of the BCL11A gene in regulating fetal haemoglobin production?

Answer 5

• Suppresses expression of fetal haemoglobin genes after birth
• Reduces HbF production when active

This regulation is crucial for normal hemoglobin function.

Question 6

How can gene expression be altered to increase fetal haemoglobin levels?

Answer 6

• Reduce or disrupt BCL11A expression
• Allows fetal haemoglobin genes to be expressed

This can lead to therapeutic approaches for sickle cell disease.

Question 7

Explain how changes in gene expression can lead to changes in phenotype.

Answer 7

• Alters proteins produced
• Changes cell function
• Leads to observable phenotype changes

Gene expression is a key factor in phenotypic variation.

Question 8

Describe how CRISPR-Cas9 can be used to disrupt the BCL11A gene.

Answer 8

• gRNA matches BCL11A gene sequence
• gRNA directs Cas9 to target DNA
• Cas9 creates double-strand break
• DNA repaired by NHEJ, introducing mutations

This reduces BCL11A activity and increases fetal haemoglobin production.

Question 9

What are the roles of gRNA, Cas9, and PAM sequence in gene editing?

Answer 9

gRNA (guide RNA): binds to the complementary target DNA sequence and guides Cas9 to the correct location.
Cas9: a nuclease that cuts both strands of DNA at the target site.
PAM sequence: a short DNA sequence required for Cas9 to bind and initiate cutting.

These components are essential for the CRISPR-Cas9 mechanism.

Question 10

Distinguish between knock-out and knock-in mutations in the context of CRISPR.

Answer 10

• Knock-out: disrupts a gene to stop its function
• Knock-in: inserts or replaces DNA to add or modify a gene

These strategies are used for different genetic modifications.

Question 11

Outline the steps involved in using CRISPR to treat sickle cell disease.

Answer 11

• Remove stem cells from patient
• Use CRISPR to target and disrupt BCL11A
• Return modified cells to patient
• Cells produce increased fetal haemoglobin

This approach aims to alleviate symptoms of sickle cell disease.

Question 12

Describe the trend in fetal haemoglobin levels before and after treatment.

Answer 12

Fetal haemoglobin levels increase significantly after CRISPR treatment in all patients

This indicates the effectiveness of the treatment.

Question 13

Use data to support the conclusion that CRISPR treatment is effective.

Answer 13

All patients show a higher percentage of HbF after treatment compared to before

This data reinforces the treatment’s success.

Question 14

Identify one limitation of the data and explain its impact on reliability.

Answer 14

Small sample size reduces reliability

This limits confidence in applying results to a larger population.

Question 15

Define recombinant plasmid and explain its role in genetic modification.

Answer 15

A recombinant plasmid is a plasmid that contains a gene of interest

It is used to transfer the gene into a host cell.

Question 16

Describe how the Bt gene is inserted into maize plants.

Answer 16

• Cut Bt gene from bacterial DNA using restriction enzymes
• Insert into plasmid using DNA ligase
• Transfer plasmid into plant cells using Agrobacterium

This process is crucial for creating Bt maize.

Question 17

Explain the role of Agrobacterium tumefaciens in this process.

Answer 17

Agrobacterium transfers the recombinant plasmid into plant cells

It acts as a vector to introduce foreign DNA.

Question 18

How does expression of the Bt gene lead to insect resistance?

Answer 18

The Bt gene is expressed in the plant to produce a toxin protein.
When insect larvae feed on the plant, the toxin damages cells in their gut lining.
This disrupts digestion and kills the insects, providing resistance.

This mechanism is vital for pest control.

Question 19

Compare insect damage and crop yield between Bt maize and non-modified maize.

Answer 19

• Bt maize: 9% insect damage, 7.8 tonnes/ha yield
• Non-modified maize: 62% insect damage, 6.2 tonnes/ha yield

This comparison highlights the effectiveness of Bt maize.

Question 20

Use data to justify whether Bt maize is more effective than non-modified maize.

Answer 20

Bt maize has significantly lower insect damage and higher yield

This indicates improved crop performance.

Question 21

Explain the relationship between insect damage and crop yield.

Answer 21

Lower insect damage results in less plant tissue loss

This allows greater growth and increases crop yield.

Question 22

Evaluate the effectiveness of CRISPR as a treatment for sickle cell disease.

Answer 22

• Increases fetal haemoglobin levels
• Reduces symptoms
• Limitations include potential off-target effects

This evaluation considers both benefits and risks.

Question 23

Identify one biological limitation of CRISPR gene editing.

Answer 23

Off-target mutations may occur, affecting unintended genes

This can lead to harmful effects.

Question 24

Outline one ethical concern associated with gene editing in humans.

Answer 24

Concerns about long-term effects and modifying human genetics

Ethical considerations are crucial in gene editing discussions.

Question 25

Describe one **advantage** and one **disadvantage** of **Bt maize**.

Answer 25

* Advantage: reduces insect damage and increases yield * Disadvantage: may lead to resistant insect populations ## Footnote These factors influence agricultural practices.

Question 26

Distinguish between **GMO** and **transgenic organism** using **Bt maize** as an example.

Answer 26

* GMO: altered DNA * Transgenic: contains a gene from another species (bacteria) ## Footnote Bt maize is a specific example of a transgenic organism.

Question 27

How does **CRISPR gene editing** alter gene expression rather than the gene itself?

Answer 27

CRISPR disrupts the regulatory gene BCL11A, increasing fetal haemoglobin expression without altering the structural gene ## Footnote This reduces repression of fetal haemoglobin genes, leading to changes in protein production.

Question 28

Why does increasing **fetal haemoglobin** reduce symptoms of sickle cell disease?

Answer 28

Fetal haemoglobin does not form fibres under low oxygen conditions, preventing sickle-shaped red blood cells ## Footnote This improves oxygen transport and reduces symptoms.

Question 29

Describe how the **structure of haemoglobin** relates to its function in oxygen transport.

Answer 29

Haemoglobin has a specific tertiary and quaternary structure that allows efficient oxygen binding ## Footnote Changes to this structure can reduce its ability to carry oxygen.

Question 30

Explain why a **single base substitution** can have a large effect on phenotype.

Answer 30

It can alter a codon, leading to a different amino acid, changing protein folding and function ## Footnote This results in a different phenotype.

Question 31

How can a change in one **amino acid** lead to aggregation of haemoglobin molecules?

Answer 31

It can alter R group properties, causing haemoglobin molecules to stick together and form fibres ## Footnote This affects the overall structure and function of the protein.

Question 32

What role do **R group interactions** play in haemoglobin structure?

Answer 32

They form hydrogen bonds, ionic bonds, and disulfide bridges, stabilizing protein structure ## Footnote These interactions determine the protein's folding.

Question 33

Why is **NHEJ** used to disrupt BCL11A rather than HDR?

Answer 33

NHEJ is faster and does not require a template, introducing mutations that disrupt the gene ## Footnote This makes it suitable for knock-out of BCL11A.

Question 34

What is one advantage of editing **stem cells** outside the body before reinsertion?

Answer 34

Cells can be checked for successful editing before reinsertion ## Footnote This reduces risk and increases treatment effectiveness.

Question 35

What is one **risk of CRISPR** gene editing in this treatment?

Answer 35

Off-target mutations may occur, potentially disrupting other genes ## Footnote This could lead to harmful effects.

Question 36

Why might targeting a **regulatory gene** (BCL11A) be more effective than editing the β-globin gene directly?

Answer 36

Targeting BCL11A increases fetal haemoglobin production, which naturally reduces sickling ## Footnote This may be more effective than directly fixing the mutation.

Question 37

Why do different patients show different **HbF levels** after treatment?

Answer 37

Differences may be due to variation in editing efficiency or biological differences between patients ## Footnote This highlights the variability in treatment response.

Question 38

Identify one **variable** that should be controlled in the experiment.

Answer 38

Environmental conditions or treatment procedures ## Footnote This ensures valid results.

Question 39

Does the data show **causation or correlation**?

Answer 39

The experiment suggests causation, as CRISPR treatment directly increases HbF levels ## Footnote This indicates a direct relationship.

Question 40

Predict what would happen to **sickling rates** as HbF increases.

Answer 40

Sickling of red blood cells would decrease ## Footnote This is due to the protective effect of fetal haemoglobin.

Question 41

How does inserting the **Bt gene** result in protein expression in plant cells?

Answer 41

The inserted Bt gene is transcribed into mRNA and translated into a toxin protein ## Footnote This protein is expressed in plant cells.

Question 42

Why does the **Bt protein** specifically affect insect gut cells but not humans?

Answer 42

The Bt protein specifically binds to receptors found in insect gut cells. These receptors are not present in humans, so the toxin cannot bind or damage human cells. Therefore, it only affects insects and is safe for humans. ## Footnote This specificity makes it safe for human consumption.

Question 43

What might happen if insects develop **resistance** to Bt toxin?

Answer 43

Effectiveness of Bt crops may be reduced over time ## Footnote This could lead to increased pest problems.

Question 44

Suggest one **environmental impact** of widespread Bt crop use.

Answer 44

May reduce biodiversity or affect non-target organisms ## Footnote This raises concerns about ecological balance.

Question 45

Evaluate whether **CRISPR** is a sustainable long-term treatment.

Answer 45

Promising as it targets the cause of disease, but long-term effects and risks must be considered ## Footnote Sustainability depends on ongoing evaluation.

Question 46

Explain one **ethical issue** specific to editing human stem cells.

Answer 46

Concerns about long-term effects and genetic modification ## Footnote This raises questions about consent and future implications.

Question 47

Compare **CRISPR treatment** to traditional treatments.

Answer 47

CRISPR targets the genetic cause, while traditional treatments only manage symptoms ## Footnote This represents a significant shift in treatment approaches.

Question 48

Explain the relationship between **DNA, RNA, and protein** using the sickle cell example.

Answer 48

A mutation in DNA changes mRNA during transcription, leading to a different amino acid sequence during translation ## Footnote This alters protein structure and function, resulting in a changed phenotype.

Question 49

How can **biotechnology** modify phenotype by altering gene expression?

Answer 49

It can alter gene expression or DNA sequences, changing the proteins produced ## Footnote This results in a change in phenotype.

Question 50

Compare **CRISPR gene editing** and recombinant DNA technology.

Answer 50

CRISPR edits DNA directly at a specific location ## Footnote Recombinant DNA involves inserting genes using vectors such as plasmids.

Question 51

Explain how a mutation in the beta-globin gene leads to sickle cell disease?

Answer 51

The point mutation in the beta-globin gene substitutes glutamic acid with valine, which produces abnormal hemoglobin polymerase causing red blood cells to become sickle-shaped.

Question 52

Analyse how sickle-shaped red blood cells affect oxygen transport and blood cells.

Answer 52

Due to the rigid and less flexible shape of a sickle cell, it becomes less effective to transport oxygen, as this shape blocks capillaries and reduces oxygen delivery to tissues

Question 53

Evaluate the importance of fetal hemoglobin (HbF) in treating sickle cell diseases.

Answer 53

The importance of hemoglobin is that it does not form fibres under low oxygen & increases oxygen, preventing sickle cell blood & increasing oxygen transportation .

Question 54

Describe the role of the BCL11A gene in haemoglobin regualtion?

Answer 54

The role of BCL11A is to suppress the expression of fetal Haemoglobin genes after birth and allow the b-globin to be dominant and expressed.

Question 55

Explain how CRISPR-Cas9 can be used to treat sickle cell disease?

Answer 55

CRISPR disables BCL11A, so the production of hemoglobin can produce more oxygen.

Question 56

Analyse the data showing increased HbF after CRISPR treatment. What conclusion can be drawn ?

Answer 56

Post-treatment can cause the elevated fetal hemoglobin in the blood, which indicates the effectiveness of CRISPR revealed suppression of BCL11A reactivating fetal hemoglobin production

Question 57

Explain how Bt toxin affects insect pests but not humans?

Answer 57

Modified genes = Bt toxin binds to a specises receptors present in the insect mid gut causing lises humans lack these receptors & have different digetic condtions so the toxin is harmless to humans

Question 58

Evaluate the advantages and disadvantages of genetically modified crops.

Answer 58

Advantage - Increase yield Disadvantage - Ethical concerns

Question 59

Evaluate one advantage and one ethical concern of CRISPR gene editing?

Answer 59

- By using CRISPR we can target a specific sequence. - Ethical concern is long-term biological effects.

Question 60

Explain how Bt Maize is produced using genetic engineering?

Answer 60

The Bt toxin gene is cloned into a plasmin & introduces into maize cells using agro-bacterium by immediate transformation, enabling the plant to expose the insexidul bt protein.