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AQA A Level Biology > 3.2.11 Mutation and Cancer > Flashcards

3.2.11 Mutation and Cancer Flashcards

1
Q

What is a gene mutation?

A

Changes in DNA base sequence of chromosomes

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2
Q

Name 2 types of errors that occur

A
  • Substitution
  • Deletion
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3
Q

What is deletion?

A

When one base is deleted

e.g. ATGCCT becomes ATCCT (G is deleted)

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4
Q

What is substitution?

A

When one base is substituted with another

e.g. ATGCCT becomes ATTCCT (G is swapped for T)

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5
Q

Name 3 types of substitution

A
  • Nonsense mutation
  • Missense mutation
  • Silent mutation
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6
Q

What is a nonsense mutation?

A

Occurs if base change = stop codon

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7
Q

What is a missense mutation?

A

Occurs if base change = different amino acids being coded for

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8
Q

What is a silent mutation?

A

Substituted base, although different = codes for same amino acid

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9
Q

Why will not all substitution mutations lead to a change in the amino acid sequence of a protein?

A

Due to the degenerate nature of genetic code, some amino acids are coded for by more than one DNA triplet

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10
Q

Why will deletions always lead to changes in amino acid sequence?

A

From point of mutation base sequence changes/causes frame shift

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11
Q

What do mutagenic agents do?

A

Increases the frequency of mutations

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12
Q

Give an example of a mutagenic agent

A

e.g. UV radiation, ionising radiation, some chemicals and some viruses

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13
Q

Mutations occur _____

A

spontaneously

e.g. when DNA is misread during replication

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14
Q

What are acquired mutations?

A

Mutations that occur in individual cells after fertilisation

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15
Q

Describe how mutations can cause a tumour

A
  1. If mutations occur in genes that control rate of cell division (by mitosis) = uncontrolled cell division
  2. Uncontrolled cell division = tumour (mass of abnormal cells)
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16
Q

What is cancer?

A

Tumours that invade and destroy surrounding tissue

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17
Q

Name the 2 types of gene that control cell division

A
  • Tumour suppressor genes
  • Proto-oncogenes
18
Q

How can tumour suppressor genes be inactivated?

A

If mutation occurs in DNA sequence

19
Q

When functioning normally, what do tumour suppressor genes do & how?

A

Slow cell division by producing proteins that stop cells dividing or cause them to self-destruct

20
Q

Describe how a mutation may affect tumour suppressor genes & what this can lead to

A
  1. Mutation prevents transcription of gene
  2. Protein isn’t produced so doesn’t inhibit cell division
  3. No control of mitosis (cells divide uncontrollably) = tumour
21
Q

How can the effect of proto-oncogene be increased?

A

If mutation occurs in DNA sequence

22
Q

What is a mutated proto-oncogene called?

A

Oncogene

23
Q

When functioning normally, what do proto-oncogenes do & how?

A

Stimulate cell division by producing proteins that make cell divide

24
Q

Describe how a mutation may affect proto-oncogenes & what this can lead to

A
  1. Proto-oncogenes become oncogenes
  2. Oncogene stimulate rapid cell division without growth factor (divide uncontrollably = tumour)
  3. Oncogene cause production of excess growth factor
25
Q

Tumours can develop for years without ______ _______ & can become ____ before they’re ______

A

Tumours can develop for years without obvious symptoms & can become large before they’re discovered

26
Q

Name the 2 types of tumours

A
  • Malignant tumour (cancerous)
  • Begin tumours (not cancerous)
27
Q

Describe malignant tumours

A
  • Mass of undifferentiated cells
  • Uncontrolled cell division
    • Usually grow rapidly and invade and destroy surrounding tissues
  • Cells break off tumours and spread to other parts of body (in bloodstream and lymphatic system)
28
Q

Describe begin tumours

A
  • Grow slower than malignant tumours & often are covered in fibrous tissues that stop cells invading other tissues
  • Often harmless but can cause blockages & put pressure on organs
  • Some benign tumours can become malignant
29
Q

Name 6 ways tumour cells can differ from normal cell

A
  1. Irregular shape
  2. Nucleus is larger and darker (& sometimes have more than 1 nucleus)
  3. Don’t produce all proteins needed to function correctly
  4. Different antigens on their surface
  5. Don’t respond to growth regulating processes
  6. Divide by mitosis more frequently
30
Q

What are cancer treatments that target the cell cycle designed to do?

A
  • Designed to control rate of cell division in tumour cells by disrupting the cell cycle
  • This kills tumour cells
31
Q

Treatments don’t… & so they…

A
  • Treatments don’t distinguish tumour cells from normal cells
  • So they kill normal body cells that are dividing
32
Q

Why are cancer treatments more likely to kill tumour cells?

A

Tumour cells divide much more frequently than normal cells

33
Q

Name 2 cell cycle targets of some cancer treatments

A
  • G1 (cell growth and protein production)
  • S phase (DNA replication)
34
Q

Describe how cancer treatments targeting the G1 work

A
  • Some chemical drugs (chemotherapy) prevent synthesis of enzymes needed for DNA replication
  • If these aren’t produced = cell is unable to enter synthesis phase (S)
  • ∴ cell cycle is disrupted and forces cell to kill itself
35
Q

Describe how cancer treatments targeting the S phase work

A
  • Radiation and some drugs damage DNA
  • At several points in cell cycle (e.g. just before and during S phase) DNA in cell is checked for damage
  • If severe damage detected = cell kills itself to prevent further tumour growth
36
Q

Explain the link between sunbathing and skin cancer (2)

A
  • Sun’s radiation contains UV radiation
  • Causes mutation of genes which control cell division
37
Q

Suggest why fair-skinned people are at a greater risk of skin cancer than dark-skinned people when sunbathing (1)

A

Little melanin = little protection against UV radiation (can easily burn)

38
Q

Cancer Treatments

At what phase in the cell cycle would a drug that prevents the spindle fibre shortening act?

A

Anaphase

39
Q

Cancer Treatment

Describe how a drug affecting spindle activity would work (3)

A
  • Affects mitosis
  • As chromosomes cannot attach to spindle / chromatids cannot separate on spindle
  • Cell division slows down
40
Q

Explain how a drug that inhibits the enzyme DNA polymerase might be effective against some types of cancer (2)

A
  • Stops DNA replication
  • New strand not formed (nucleotides not joined together)
41
Q

Suggest why cancer treatments should not be given too frequently even though it means they’ll kill more cancer cells (3)

A
  • Too many healthy cells killed
  • Take time to replace
  • Patient will have side effects
42
Q

Human cells contain genes that control their growth and division. Explain in detail how a gene mutation could lead to cancer. (6)

A
  1. Change in base sequence
  2. Substitution / deletion
  3. Transcription changed
  4. Amino acid sequence changed / different protein
  5. Loss of function
  6. Uncontrolled cell division

AQA A Level Biology (41 decks)

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