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Nucleic Acids > Cancer > Flashcards

Cancer Flashcards

1
Q

What is the definition of cancer?

A

A group of diseases that includes solid tumours at almost any site of the body and leukaemias

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2
Q

What differentiates cancer from most other diseases?

A

It is a disease of the body’s own cells

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3
Q

What is cancer caused by?

A

Uncontrollable division of abnormal cells

The cells behave abnormally as they have lost the ability to regulate when they need to grow and divide

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4
Q

Why are the most common cancers lung and skin cancer?

A

These occur in tissues where cell death and replacement is the most frequent

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5
Q

What are the 4 features of cancer cells?

A
  1. uncontrolled cell division
  2. change in morphology (shape) of the cells
  3. Dedifferentiation of cells
  4. Cell migration into adjacent as well as distant tissues
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6
Q

What is meant by dedifferentiation of cells?

A

This involves cells regressing from a specialised form to a similar state resembling that of stem cells

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7
Q

What are the 3 characteristics of cancer cells grown in the lab?

A
  1. uncontrolled growth
  2. loss of contact inhibition
  3. cells are immortal
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8
Q

What would happen to normal cells once they had filled the surface of a petri dish?

A

They stop growing due to sending each other signals when they are touching each other and have formed a layer

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9
Q

What would happen if normal cells that had filled the petri dish were diluted and placed in a larger dish?

A

The cells would continue dividing

They would eventually stop dividing altogether as they have a finite lifespan

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10
Q

What is meant by ‘loss of contact inhibition’ in cancer cells?

A

Cancer cells do not stop growing once they have filled the petri dish

They begin to pile on top of each other

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11
Q

What is meant by cancer cells being ‘immortal’?

A

They continue to grow without dying off

They do NOT have a finite lifespan

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12
Q

What is a metastatic cancer?

A

A cancer that has spread from the primary site of origin into different areas of the body

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13
Q

What is metastasis?

A

The spread of cancer cells to new areas of the body

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14
Q

What are the 4 stages in cancer development?

A
  1. single hyperproliferative cell
  2. early adenoma
  3. late adenoma
  4. carcinoma
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15
Q

When does hyperproliferation occur in the 1st stage of cancer development?

A

It occurs when there is an abnormally high rate of cell proliferation by rapid division

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16
Q

What are the characteristics of an early adenoma?

A

It is a small clump of cells

It is a non-cancerous tumour that does not have the ability to spread to other parts of the body

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17
Q

How is the late adenoma formed?

A

The cells continue to divide uncontrollably and pile on top of each other

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18
Q

What are the characteristics of a carcinoma?

A

The cancer cells have begun to invade the local tissue

They can now enter blood vessels and be transported around the body

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19
Q

What are the series of mutations which lead to tumour formation?

A

Mutations may encourage the growth of cells to form a malignant tumour

Further mutations may cause the tumour to become metastatic

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20
Q

How many mutations must occur in order for cancer to develop?

A

There must be multiple mutations in several key genes

Cancer does not occur from a single gene mutation

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21
Q

Cancer only occurs when mutations occur in which 3 types of genes?

A
  1. proto-oncogenes and oncogenes
  2. tumour suppressor genes
  3. DNA repair genes
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22
Q

What is the role of proto-oncogenes?

A

They are growth promoting genes that tell cells when to grow and divide

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23
Q

What is the difference between a proto-oncogene and an oncogene?

A

A proto-oncogene is a normal gene, that when mutated becomes an oncogene, which contributes to cancer

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24
Q

What do mutations in proto-oncogenes lead to?

A

It increases activity of the oncogenes and leads to inappropriate switching on of cell division

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25
Q

What is the role of tumour suppressor genes?

A

They are growth-inhibiting genes that maintain a cell in a non-dividing state

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26
Q

What happens when there is a mutation in a tumour suppressor gene?

A

It leads to uncontrolled cell division

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27
Q

What is the role of DNA repair genes?

A

They repair any damage to DNA

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28
Q

Why is cancer more frequently seen in older people?

A

The process of accumulating mutations in several genes takes many years

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29
Q

What is a malignant cancer?

A

Malignant cancer cells form a cancer at the original organ

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30
Q

How does a malignant cancer spread around the body?

A

The malignant cancer cells will develop more mutations and form a metastatic tumour

This can then spread to other organs through the bloodstream

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31
Q

What are the 2 types of point mutations?

How many nucleotides do they tend to affect?

A

Missense and nonsense mutations

They affect only one or very few nucleotides in a gene sequence

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32
Q

What is a missense mutation?

A

When a single nucleotide is changed and the codon now codes for a different amino acid

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33
Q

What is a nonsense mutation?

A

When a single nucleotide is changed and the codon becomes a stop codon

This results in a truncated protein product

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34
Q

What is an insertion/deletion mutation?

A

The addition or loss of nucleotides, from a single base pair to huge swathes of chromosome

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35
Q

What happens if a multiple of 3 is inserted/deleted?

What if it is not a multiple of 3?

A

If a multiple of 3 bases is added or deleted, it causes an amino acid to be inserted or deleted

If it is not a multiple of 3, it causes a frameshift mutation

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36
Q

What is gene amplification?

A

An increase in the number of copies of a gene without a proportional increase in other genes

37
Q

What does gene amplification result from?

A

The duplication of a region of DNA that contains a gene

This occurs through errors in DNA replication and repair machinery

38
Q

What are the most common genetic changes found in human cancer cells?

A

Translocations

39
Q

What is a translocation?

A

A chromosome abnormality caused by a rearrangement of parts between non-homologous chromosomes

40
Q

In which ways can translocations cause cancer?

A
  1. a gene may be moved to a more transcriptionally active region of the new chromosome
  2. two genes may be recombined into a new gene through fusion
41
Q

What is aneuploidy?

A

Any departure from the normal structure or number of chromosomes

e.g. trisomy

42
Q

What are the two different things that a mutation can do to a gene?

A
  1. disrupt the coding sequence sufficiently to stop the protein from functioning normally, if at all
  2. make the protein more active
43
Q

In cancer cells, how does the number of mutations affect how the cancer progresses?

A
  1. initial mutation occurs in a single cell
  2. as the cell expands, other mutations will be picked up
  3. some mutations incur a growth advantage
  4. more mutations continue to develop as the cell grows
44
Q

What is the genetic instability in cancer cells caused by?

A

Exposure to carcinogens or mutations in DNA repair genes

45
Q

What are the 3 things that mutation induction requires?

A
  1. chemical modification of DNA and/or
  2. replication of DNA
  3. resulting in misincorporation by DNA polymerase
46
Q

How may DNA polymerase usually make mistakes and what do they result in?

A

DNA polymerase naturally makes mistakes which result in the accumulation of genetic variation or polymorphisms in coding and non-coding sequences of the genome

Some of these changes are deleterious mutations

47
Q

What increases the tendency of polymerases to make mistakes?

A

The presence of chemical modifications in DNA

48
Q

How may chemical modifications of nucleotides arise?

A
  1. through environmental influence

2. through endogenous reactive molecules, such as free radicals

49
Q

How are normal cells induced to divide?

A

By positive growth factors binding to receptors on the cell surface

50
Q

What happens when a positive growth factor binds to a receptor on the cell surface?

A

The internal portion of the growth factor receptor is activated

This activates a cascade of intracellular signalling proteins

The signal reaches the nucleus and initiates transcription of genes involved in regulating the cell cycle

51
Q

How are normal cells prevented from dividing?

A

Through negative growth factors

These are produced by growing tissues when sufficient cell division has taken place

52
Q

How do negative growth factors affect the cell after binding to receptor proteins on the cell surface?

A

They initiate a signalling cascade that shuts down the cell cycle

This results in the cell entering a quiescent/dormant state

53
Q

What are the other key properties of normal cells?

A
  1. they have a finite lifespan
  2. they have a self-destruct mechanism called apoptosis
  3. they have no influence on blood vessel formation
  4. they are tightly joined together and are immobile
  5. they are genetically stable
54
Q

What are the 5 key properties of cancer cells?

A
  1. independent of positive growth factors
  2. resistant to negative growth factors
  3. resistant to apoptosis
  4. angiogenic
  5. invasive and metastatic
55
Q

What is meant by cancer cells being angiogenic?

A

They have the ability to cause blood vessels to form nearby

As the tumour grows, the increasing number of cells requires more blood vessels to supply O2 and nutrients

56
Q

What is the difference between a cancer cell being invasive and it being metastatic?

A

They are invasive when they begin to invade surrounding tissues

They are metastatic when they exist in other tissues other than the ones in which they first developed

57
Q

What is a cancer syndrome?

A

When cancer develops from mutated genes that have been genetically inherited

58
Q

What types of cancer tend to be common in certain families?

Inherited predispositions account for what % of all cancers?

A

Colon and breast cancers

Inherited predispositions account for 5% of all cancers

59
Q

What are examples of biological agents and the cancers which they cause?

A

Hepatits B and C - liver cancer

Human papilloma virus - cervical cancer

H.pylori - stomach cancer

60
Q

What are examples of chemical agents and the cancers they cause?

A
  1. cigarette smoke - lung, bladder and others

2. Heterocyclic amines in cooked meat - colon cancer

61
Q

What are examples of physical agents and the cancers they cause?

A

UV in sunlight - skin cancer

X-rays and gamma-rays - radiotherapy related leukaemia

62
Q

What is a carcinogen?

A

Any agent that significantly increases the risk of developing cancer

63
Q

Why are most carcinogens described as ‘genotoxic’?

A

Genotoxicity describes the property of chemical agents that damage the genetic information within a cell, causing mutations

64
Q

How do non-genotoxic carcinogens cause cancer?

A

They induce cell division and DNA replication without being mutagenic

65
Q

What other word can be used to describe genotoxic carcinogens?

A

Mutagens

All mutagens are genotoxic, but not all genotoxic substances are mutagens

66
Q

How do carcinogens increase the chance of cancer occurring?

A

They increase cell proliferation, so increase the chances of mutations occurring

67
Q

What type of study must be carried out to show that a chemical is carcinogenic in humans?

A

Epidemiology studies

This involves looking for an association between the exposure to the chemical and the incidence of cancer

68
Q

What are the 2 types of epidemiology studies?

A
  1. case-control studies

2. prospective (cohort) studies

69
Q

What is involved in a case-control study?

A

Comparing diseased groups with matched control groups

Looking for factors that are more common in people with the disease

70
Q

What is important to consider when preparing a case-control study?

A

Variation should try to be reduced between the disease and control group

e.g. same gender, same age, come from the same city

71
Q

How can the results of a case-control study show strong evidence?

A

If the study is repeated many times in different places and the results are repeated

72
Q

What is involved in a prospective (cohort) study?

A

A population is followed over time to confirm that a disease is linked to a suspected cause

73
Q

What types of people are involved in a cohort study and what type of data is collected?

A

Healthy people are followed and split into an exposed and unexposed group and exposure data is collected

This establishes whether there is an association between exposure and disease

74
Q

What are the pros and cons of a cohort study?

A

It is less susceptible to bias and more effective but…

It takes longer

75
Q

How many carcinogens are in cigarette smoke and how do they cause cancer?

A

It contains over 50 chemical carcinogens

These react with DNA to cause DNA damage

76
Q

What is benzopyrene?

How does it affect DNA?

A

It is a polycyclic aromatic hydrocarbon found in tobacco smoke

It binds to deoxyguanosine to form a DNA adduct

77
Q

What does the presence of a DNA adduct lead to?

A

Increased chance of mutation

78
Q

What is significant about benzopyrene containing aromatic rings?

A

It is not soluble in water so it is difficult for the body to excrete

79
Q

What happens once benzopyrene has bound to guanine?

A

DNA polymerase is unable to recognise guanine

This means the wrong base is inserted opposite guanine

80
Q

What does a non-melanoma skin cancer develop from?

A

They develop in the epidermis (outermost layer of skin)

81
Q

What is the difference between a squamous cell carcinoma and a basal cell carcinoma?

A

SC - starts in the cells lining the upper epidermis

BC - starts in the cells lining the bottom of the epidermis

They are both non-melanoma

82
Q

How common and curable are non-melanoma skin cancers?

A

Quite common and often curable

There is a much lower risk that the cancer will spread to other parts of the body

83
Q

Where does melanoma skin cancer develop from?

A

Skin cells called melanocytes

84
Q

Why is melanoma skin cancer more dangerous than non-melanoma?

A

It is more fatal and can spread to other organs easily

There is a chance of melanoma returning once it has been treated

85
Q

How does UV-B damage DNA and cause potentially mutagenic damage?

A

It puts energy into the DNA molecule to break the sugar-phosphate backbone

It may change some of the bases

86
Q

What is the thymine dimer?

A

Energy from UV-B radiation causes covalent bonds to form between adjacent thymine molecules

DNA polymerase cannot recognise the thymine in this state

87
Q

How do different genotoxic agents (mutagens) affect DNA?

A

They can modify DNA in different ways

This leads to lots of different mutational outcomes which vary in severity

88
Q

What are DNA lesions?

A

Sites of damage in the base-pairing or structure of the DNA molecule

89
Q

What are the 5 tips to avoid getting cancer?

A
  1. don’t smoke
  2. drink in moderation
  3. avoid too much time in the sun
  4. eat a balanced diet with lots of fruit and vegetables and not too much sugar or red meat
  5. maintain a healthy weight

Nucleic Acids (4 decks)

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