Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Stem Cell and Cancer > L12 - Oncogenes > Flashcards

L12 - Oncogenes Flashcards

1
Q

What is the suspected cause of human cancers?

A

Tumour viruses

In reality only a minority of tumours are virally-induced

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the characteristics of viral genomes?

A

Very simple – only a few genes
Enough to drive tumour phenotype
Potent genes to perturb complex regulatory circuitry of the host cell they infect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What experiment did Peyton Rous undertake?

A
  1. Chicken with sarcoma in breast muscle
  2. Removed sarcoma and broke up tissue into small chunks
  3. Ground up sarcoma with sand
  4. Collected filtrate that passed through fine pore filter
  5. Injected filtrate into young chicken and observe sarcoma formation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What did Peyton Rous experiment show?

A

Showed the carcinogenic agent was very small as it could pass through filter
RSV - Rous Sarcoma Virus
- Caused sarcoma formation in injected chicken – tumour always appeared after a set

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What provided the opportunity to induce cancer?

A

RSV capable of multiplying within chicken tissues  virus can be recovered in big amounts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How can RSV transform infected cells in culture?

A

Chicken embryo fibroblasts infected with RSV show traits associated with cancer cells
The cells showed cell transformation - conversion of a normal cell into cancer cell
Showed cancer was a disease of malfunctioning cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What traits do chicken embryo fibroblasts show when infected with RSV?

A

Foci (clusters) appear after infection

Similar metabolism to cells isolated from tumours

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the two explanations of why the transformation phenotype is transmitted from infected cells to descendants?

A

RVS particles transformed the progenitor cells and their descendants
- Virus must be present all the time to maintain transformed phenotype
RVS only needed to transform progenitors, which then transmit phenotype to descendants
- Virus only needs to be present at the beginning

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What experiment was undertaken to decide which explanation for how the transformation phenotype is transmitted from infected cells to descendants was correct?

A

Temperature sensitive RSV mutant - function at permissive temperature
Transformed state lost when cells kept at non-permissive temperature
Transformed state regained when permissive temperature reached
- Continued actions of viral temperature sensitive protein required to maintain transformed phenotype

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What were the conclusions from the temperature sensitive RSV mutant experiments?

A

Viral transforming gene required to both initiate and maintain transformed phenotype

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the properties of transformed cells?

A

Altered morphology - rounded shape
Loss of contact inhibition – can grow over one another
Ability to grow without attachment - anchorage independence
Ability to proliferate indefinitely – immortalisation
Reduced requirement for mitogenic growth factors
High saturation density in culture dish
Inability to halt proliferation in the absence of growth factors
Increased uptake of glucose
Tumorigenicity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How was it worked out which gene was responsible for RSV induced transformation?

A

RSV viral constituents – gag, pol, env and unknown
When either one of the genes removed the virus was
- Unable to replicate
- Able to transform cells
When the unknown gene was removed the virus
- Able to replicate
- Unable to transform cells
Shows a single gene (unknown) is required for transformation (not for viral replication)
- Unknown – src

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the RSV viral constituents?

A

gag, pol, env and src

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What was used to understand origins, functions and follow src in infected cells?

A

Src specific DNA probe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the two types of src?

A

C-src – cellular src - present in genome of normal organisms, acts as a proto-oncogene
- Genomes carry a agene that has the potential, under certain circumstances to induce cell transformations and thus cancer
V-src - viral src - acts as an oncogene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the two hypothesis for the causes of cancer?

A

Activation of endogenous retrovirus

Induced by mutagens – physical or chemical agents that can mutate growth controlling genes

17
Q

Do non-viral oncogenes exist in chemically transformed cells?

A

Chemically transformed cells carry mutated genes –> responsible for aberrant growth of these cells
Donor tumour DNA carried one or several genetic elements able to convert a normal cell into a tumorigenic one

18
Q

How do you identify the mutant genes responsible for aberrant growth of transformed cells?

A

Transfection

  1. Chemically transformed mouse fibroblasts
  2. DNA transfection using calcium phosphate co-precipitation procedure
  3. Injected into normal mouse fibroblasts
  4. Formation of a focus of transformed cells
  5. Injection of transformed cells into mouse host leading to tumour
19
Q

Does fibroblast transformation involve one or more genes?

A

Only 0.1% of donor mouse DNA became established in recipient cell genome
Low probability of 2 independent genes meaning only 1 gene responsible for transformation
- Similar experiments done with human tumour cells

20
Q

Oncogenes detected by transfection were derived from?

A

Pre-existing normal cellular genes lacking oncogenic function

  • Were converted by the chemical transformation
  • Same scenario that happens with viral oncogenes
21
Q

Could the same group of proto-oncogenes be activated by viruses or mutagens?

A

Yes
DNA probes for retroviral associated oncogenes used on chemically transformed cells
- Many proto-oncogenes found in activated, oncogenic form in human tumour genomes

22
Q

How can proto-oncogenes be converted to active oncogenes?

A

Activated by genetic changes

23
Q

How was H-ras detected?

A

By transfection of human bladder carcinoma DNA

No gene amplification as only present in 1 copy

24
Q

What method was used to find the difference between an oncogene and proto-oncogene?

A

Ras oncogene isolated from transformed cells – by molecular cloning
Ras proto-oncogene isolated from normal cells
A similar size fragment from both types of cells
- To find out the difference in size – fragment recombination
- Looked to see if hybrid gene was able to transform the cells
– Narrowed down the section responsible for the difference in behaviour

25
Q

What was the difference between oncogene and proto-oncogene for H-ras?

A

One single change in amino acid – glycine swapped for valine

26
Q

Many human tumours were found to carry point mutations in one of 3?

A

Ras genes

- H-ras, K-ras and N-ras

27
Q

What is the Ras signalling cycle?

A

Small GTPases

Cycle between active GTP-bound and inactive GDP-bound

28
Q

What is the Ras signalling cycle mediated by?

A

GEF - guanine nucleotide exchange factors

GAP - GTPase-activating proteins

29
Q

When Ras G12V mutant is present what happens?

A

Unable to hydrolyse GTP to GDP
Ras is constitutively active
Leads to activation of downstream pathways resulting in more proliferative cells

30
Q

Myc is over expressed in?

A

70% of human tumours

31
Q

What are the 3 members of the myc family?

A

C-myc, N-myc, L-myc

32
Q

Conversion of myc protooncogene to oncogene occurs via which 3 mechanisms?

A

Gene amplification
Chromosomal translocation
Pro-virus integration

33
Q

Myc proteins in the nucleus leads to?

A

Growth promoting transcription factors

34
Q

What is the chromosomal translocation method of myc oncogene formation?

A

C-myc under control of foreign transcriptional promoter –> Burkitt lymphoma
Structurally normal myc protein but abnormally high amounts

35
Q

What is the gene amplification method of myc oncogene formation?

A

N-myc amplification –> 30% childhood neuroblastoma
Expression driven by normal promoter
Increased levels of gene product

36
Q

What is the pro-virus integration method of myc oncogene formation?

A

Insertional mutagenesis
Viral transcriptional promoter disrupts mechanisms controlling myc expression –> Avian leukosis virus
- Increased expression and high levels of myc protein
80% ALV-induced leukaemia –> integration of ALV pro-virus adjacent to myc proto-oncogene

37
Q

Structural changes in what protein can lead to oncogenes?

A

De-regulation of the epidermal growth factor receptor

38
Q

What structural changes in EGF receptor can lead to cancer?

A

Over expression of EGF receptor
- Can lead to ligand independent or ligand dependent signalling
Mutations in EGF receptor
- Extracellular function of receptor lost
- Receptor constitutively active

39
Q

What 3 mechanisms can proto-oncogenes be activated by?

A

Ras: point mutations –> G12V substitution –> constitutively active protein
Myc: gene amplification, chromosomal translocation, insertional mutagenesis
EGFR: structural changes

Stem Cell and Cancer (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions