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Concepts of Disease > Cancer 3 > Flashcards

Cancer 3 Flashcards

1
Q

What factors support hte multi-hit model of carcinogenesis?

A
  • Genetic homogeneity in cells from given tumour
  • Cancer incidence increases with age
  • In vivo evidence of cooperative effects of mutations to drive cancer
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2
Q

How does colorectal cancer support hte multihit model of carcinogenesis? (3 marks)

A
  • Polyps arise in colon epithelium due to loss of tumour suppressor gene APC (encodes growth inhibiting protein)
  • At this point polyp normally benign but can become cancerous - an adenoma - when mutations occur
  • Can occur over 10-20 years
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3
Q

How does a polyp go from an adenoma to a malignant tumour?

(5 marks)

A
  1. Excessive epithelial proliferation = oncogene (Ras activated)
  2. Small tumour
  3. Large tumour (1/3 tumour suppressor genes lost - p53 gone)
  4. Tumour becomes invasive
  5. Metastasis
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4
Q

What is the difference between ‘driver’ mutations and ‘passenger’ mutations?

A

Driver mutations: occur in genes that’ll give a growth advantage

Passenger mutations: are silent and have no impact on gene product

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5
Q

What are ‘indogenous’ mutations?

A

Normal mistakes in DNA which can be repaired

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6
Q

Is inflammation an enabling characteristic?

A

Yes x

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7
Q

How does radiation affect DNA and cause cancer?

(4 marks)

A
  • High radiation hits molecule, changes it from neutral to electrically charged
  • Damages DNA directly due to radiolysis of water
  • Radiolysis causes H2O2, hydroxy radical and superoxide radical to be generated
  • H2O2 most dangerous as stays stable for longer to interact with DNA
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8
Q

What are risk factors increase experiencing gamma radiation? (3 marks)

A
  • Exposure to X-rays
  • Living at high altitude
  • Plane travel
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9
Q

How does UV radiation lead to the misread of a DNA strand?

(3 marks)

A
  • Double bonds in DNA absorb UV causing it to bend and kink
  • Due to formation of pyrimidine dimer - specially cyclobutane
  • Pyrimidine dimers are responsible for at least 80% of UVB induced mutations
  • Normally have mechanism to trigger apoptosis in cell but those damaged by UVB avoid being killed by apoptosis
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10
Q

How do chemical carcinogens work? (2 marks)

A

HAve an electrophilic version of carcinogen which reacts with a nucleophilic site in purine and pyrimidine rings of nucleic acids

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11
Q

How do direct acting carcinogens work?

A
  • Exist in highly readily active forms
  • React with N+ and O2+ atoms in DNA
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12
Q

How do indirect acting carcinogens work? (4 marks)

A
  • Exist in unreactive forms - water solube and can dissolve
  • Get an electrophilic centre made by enzyme modifications by cytochrome P450 enzyme
  • Converted via metabolism inot carcinogenic agent
  • Interacts with DNA to form adducts and DNA becomes unstable
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13
Q

What is a DNA adduct?

A

Segemnt of DNA bound to cancer causing chemical

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14
Q

Where do aromatic amines come from ad how can they lead to cancer formation?

(4 marks)

A
  • From cooked meats
  • 2 amino acids converted by cytochrome P450
  • This interacts with guanine to form huge adduct makes base unstable
  • Base comes out of DNA and DNA is misread
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15
Q

What is the name of the carcinogen found in cigarette smoke?

A

Benzo[a]pyrene

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16
Q

Outline the process of lung cancer caused by benzo[a]pyrene.

(5 marks)

A
  • Benzo[a]pyrene
    • (encounter P450 enzyme CYP1A1 - exp in lung tissue)
  • BP diol epoxides
  • Forms adducts with purine bases
  • G to T transversions
  • Error prone DNA replication
  • Could lead to lung cancer
17
Q

What does neoplasm/plastic mean?

A
  • Abnormal growth of cells
  • Neoplastic diseases are any that cause tumour growth - benign or malignant
18
Q

What is the virus causative of cervical cancer?

A

Human papillomavirus

  • Produces a viral protein that blocks tumour suppressor actin.
  • Done by protein-protein interactions
19
Q

How can a retrovirus be tumour causing?

A
  • Replicates and integrates its viral genome into host DNA and uses host cell machinery to make viral proteins
  • Will mutate normal genes that have a dominant effect in the cell
20
Q

How can bacteria be tumour causing?

A
  • Can cause chronic inflammation that helps promote cancer
21
Q

How does ROS contribute to cancer formation?

A
  1. Produced from oxidative respiration and lipid peroxidation (normal forms of metabolism)
  2. Breathing generates ROS intermediates
  3. In respiration O2- is made from reduction of NADH which makes less reactive superoxide radical
22
Q

Give examples of endogenous reactions that may generate mutations and cause cancer.

A
  • Pathogen killing by immune cells (by macrophages)
  • Enzyme reactions
  • Carcinogens from natural endogenous molecules being metabolised e.g. oestrogen - potent driver of cell proliferation
23
Q

What is the most common chemical reaction that causes cancer?

A

Deamination of cytosine to uracil

Concepts of Disease (20 decks)

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