Week 10: Genome Editing & Cancer Bio

Cas9 cleaves both strands of the target DNA. Which of the following could occur when cells will try to repair the damage after cleavage by Cas9? (Select all that apply.)

mutations that result in changes to the open reading frame (ORF) of the targeted gene

no change in the targeted gene

deletions of the targeted gene

the insertion of a DNA sequence into the targeted gene

loss-of-function mutations within the targeted gene

mutations that result in changes to the open reading frame (ORF) of the targeted gene

no change in the targeted gene

deletions of the targeted gene

the insertion of a DNA sequence into the targeted gene

loss-of-function mutations within the targeted gene

Transgenic models can be generated using CRISPR/Cas9 to introduce cancer-related mutations into cells within an organism. Which of the following approaches can produce a transgenic model? (Mark all that apply)

Direct nucleic acid (plasmid) injection

Patient derived xenografts (PDXs)

Viral delivery

Lipid nanoparticles

Knockin a wildtype genetic locus

Direct nucleic acid (plasmid) injection

Viral delivery

Lipid nanoparticles

All of the following are model systems that would be best to understand gene function in the context of cell differentiation or organ formation EXCEPT: 

Worm

Mice 

Yeast

Fly

Zebrafish

Yeast

T/F: CRISPR/Cas9 can be used to insert, delete, or replace DNA in any model system.

True

If you were to use CRISPR to cleave DNA at sites flanking a gene, and in this way produce a deletion of the gene, how many sgRNAs would you need?
Assume the median length of a human gene is approximately 24 Kb.

2

T/F: A cell that utilizes NHEJ to repair a double-stranded DNA break which occurred in the open reading frame of a gene is susceptible to indels resulting in a frame shift mutation and ultimately a non-functional protein.

True

T/F: CRISPR/Cas9 cannot be used to introduce mutations into specific organs such as the lungs or the brain. 

False

Defects in cell signaling can lead to a cancerous cell as a result of:

overproduction of a receptor that triggers cell division.

All of these choices are correct.

a defective signal transduction protein that stays in the activated state and triggers cell division continuously.

a defective receptor that stays in the activated state and triggers cell division continuously.

overproduction of signals that trigger cell division.

All of these choices are correct.

What properties are associated with a malignant cancer?

It is fast growing.

It invades surrounding tissue.

It is metastatic. 

All of these choices are correct.

All of these choices are correct.

Metastatic cancer cells:

have lost their adhesion to the extracellular matrix, freeing them from the original tumor.

only need to cross a single layer of capillary endothelial cells to form tumors at distant sites.

are able to leave the tumor where they originated and travel to distant locations to begin new tumors at distant sites. 

All of these choices are correct.

become malignant when they grow rapidly.

are able to leave the tumor where they originated and travel to distant locations to begin new tumors at distant sites. 

Cancer can be caused by mutations. Genetic analysis of a tumor found in a patient shows that the cell proliferation was triggered by a somatic mutation in the MYC gene, causing this gene to be inappropriately activated. The patient is concerned about passing this cancer on to the children they plan to have in the future.

Should the patient be concerned? 

No, this is not something to worry about because mutations in cancer cells cannot be passed on in cell division.

Yes, they should worry because tumor growth was triggered by a genetic change, and mutations are passed on through cell divisions.

No, they should not worry about her children because this did not occur in a germ-line cell.

No, they should not worry about her children because this did not occur in a germ-line cell.

T/F: Cancer is a disease of cell division.

True

Which of the choices would be most likely to lead to the development of cancer?

the activation of a tumor suppressor gene

the activation of a proto‐oncogene

the activation of an oncogene and the inactivation of a tumor suppressor gene

the activation of an oncogene and the activation of a tumor suppressor gene

the activation of an oncogene and the inactivation of a tumor suppressor gene

Several years ago, a man noticed a small mole on his wrist. Years later, the mole grew in size and the man was diagnosed as having metastatic melanoma.

This was likely the result of: 

a single mutation inactivating a tumor suppressor gene.

several mutations affecting proto‐oncogenes and/or tumor suppressor genes.

None of the other answer options is correct; cancers arise spontaneously, independent of mutations.

a single mutation affecting one proto‐oncogene in a cell.

several mutations affecting proto‐oncogenes and/or tumor suppressor genes.

Phosphorylated p53 is a protein that accumulates in the nuclei of cells that have damaged DNA where it functions to block the cell cycle and activate DNA repair. The p53 gene that encodes this protein is an example of a(n):

oncogene.

protein kinase.

tumor suppressor gene.

proto‐oncogene.

tumor suppressor gene.

Which of the choices could be a proto‐oncogene?

a gene encoding a cell‐surface receptor

a gene encoding a G‐protein

a gene encoding a protein kinase

All of these choices are correct. 

a gene encoding a growth factor

All of these choices are correct. 

Why are some mutations of Ras associated with cancer?

Ras is a type of second messenger.

Ras binds to growth factor receptors.

Ras activates the MAP kinase signal transduction pathway that regulates cell division.

Ras alters ion flow across the cell membrane.

Ras activates the MAP kinase signal transduction pathway that regulates cell division.