CRISPR-Cas 9 VCE Biology 3/4

Unit 3 AOS 1 /Cards include: Agricultural applications of CRISPR-Cas9 and CRISPR-Cas9 basics

CRISPR-Cas9

A bacterial immune system and a genome-editing tool that cuts DNA at precise locations.

What is a CRISPR-Cas9 knock-out?

Disabling a gene, often when DNA repair introduces changes that disrupt its sequence.

What is a CRISPR-Cas9 knock-in?

Inserting a new gene or allele into an organism’s genome.

What is a bacteriophage?

A virus that infects bacteria by inserting genetic material and hijacking the cell to replicate.

How do bacteria use CRISPR-Cas9 naturally?

They store fragments of viral DNA and use them to recognise and cut matching viral DNA during later infections.

What is a CRISPR sequence?

A region of the bacterial chromosome containing viral-DNA spacer sections separated by repeat sections.

What are spacers in a CRISPR sequence?

Stored fragments of bacteriophage DNA that provide a record of past infections.

What happens during the exposure stage?

Cas1-Cas2 enzymes cut a short viral DNA sequence, which becomes a new spacer in the CRISPR sequence.

What role does the Cas1-Cas2 complex play?

It captures a fragment of viral DNA for storage as a CRISPR spacer.

What happens during the expression stage?

Spacer sequences are transcribed into guide RNA, which forms a targeting complex with Cas9.

What is guide RNA (gRNA)?

RNA that guides Cas9 to DNA complementary to its sequence.

What is the role of Cas9?

It is an endonuclease that cuts both strands of matching target DNA.

What is a PAM site?

A short DNA sequence recognised by Cas9 that helps it locate suitable target sites.

How does PAM help protect bacterial DNA?

The notes state bacterial DNA lacks the relevant PAM site, helping prevent Cas9 from cutting it.

What happens during the extermination stage?

The CRISPR-Cas9 complex finds matching viral DNA near a PAM site and Cas9 cuts both strands.

What are the main steps in CRISPR-Cas9 gene editing?

Design complementary guide RNA, combine it with Cas9, deliver the complex to target cells, cut target DNA, then allow cellular repair.

How can DNA repair produce a knock-out?

Random nucleotides may be introduced during repair, changing the gene sequence and inactivating it.

How can DNA repair produce a knock-in?

A scientist supplies a new gene or allele that may be incorporated during repair.

Give two research uses of CRISPR-Cas9.

Locating a gene with fluorescently tagged Cas9 and disrupting gene expression to investigate gene function.

Give two potential medical uses of CRISPR-Cas9.

Replacing a harmful allele with a healthy one, or modifying genes associated with disease.

Give two agricultural uses of CRISPR-Cas9.

Introducing pest or herbicide resistance and altering genes to increase crop growth or yield.

Name two limitations or risks of CRISPR-Cas9.

Knock-in may be inconsistent; off-target cuts or unintended effects may occur.

What ethical issues can arise from editing human embryos?

Consent and respect, non-maleficence due to unknown risks, integrity, beneficence, and justice in access.

What is CRISPR-Cas9 used for in crop improvement?

Editing plant DNA at specific locations to alter traits and potentially improve photosynthesis and yield.

What is a CRISPR knock-out in crops?

Deleting or disabling a gene.

What is a CRISPR knock-in in crops?

Inserting a new gene or allele into the plant genome.

Why is improving crop yield important?

Food demand is increasing as the world population grows, while climate change makes growing conditions more difficult.

Why are many common crops vulnerable to photorespiration?

Crops such as wheat, rice, fruits and vegetables are C3 plants, which are susceptible especially in hot or dry conditions.

How might CRISPR improve photosynthetic efficiency in C3 plants?

It may improve Rubisco efficiency or reduce photorespiration, making plants more like C4 or CAM plants.

How could CRISPR increase resistance to infection?

By editing genes to increase a crop plant’s resistance to pathogens.

How could CRISPR improve fruit and vegetable storage?

By editing traits to improve shelf life.

Give four other possible CRISPR crop-yield improvements.

More compact plants, larger wheat grains, a longer flowering/fruiting period, and improved disease resistance.

What is crop yield?

The amount of product harvested.

What is a potential overall benefit of CRISPR crop editing?

Greater photosynthetic efficiency and/or higher crop productivity.