3.2.11 Mutation and Cancer

Question 1

What is a gene mutation?

Answer 1

Changes in DNA base sequence of chromosomes

Question 2

Name 2 types of errors that occur

Answer 2

• Substitution
• Deletion

Question 3

What is deletion?

Answer 3

When one base is deleted

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

Question 4

What is substitution?

Answer 4

When one base is substituted with another

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

Question 5

Name 3 types of substitution

Answer 5

• Nonsense mutation
• Missense mutation
• Silent mutation

Question 6

What is a nonsense mutation?

Answer 6

Occurs if base change = stop codon

Question 7

What is a missense mutation?

Answer 7

Occurs if base change = different amino acids being coded for

Question 8

What is a silent mutation?

Answer 8

Substituted base, although different = codes for same amino acid

Question 9

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

Answer 9

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

Question 10

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

Answer 10

From point of mutation base sequence changes/causes frame shift

Question 11

What do mutagenic agents do?

Answer 11

Increases the frequency of mutations

Question 12

Give an example of a mutagenic agent

Answer 12

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

Question 13

Mutations occur _____

Answer 13

spontaneously

e.g. when DNA is misread during replication

Question 14

What are acquired mutations?

Answer 14

Mutations that occur in individual cells after fertilisation

Question 15

Describe how mutations can cause a tumour

Answer 15

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)

Question 16

What is cancer?

Answer 16

Tumours that invade and destroy surrounding tissue

Question 17

Name the 2 types of gene that control cell division

Answer 17

• Tumour suppressor genes
• Proto-oncogenes

Question 18

How can tumour suppressor genes be inactivated?

Answer 18

If mutation occurs in DNA sequence

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

How can the effect of proto-oncogene be increased?

Answer 21

If mutation occurs in DNA sequence

Question 22

What is a mutated proto-oncogene called?

Answer 22

Oncogene

Question 23

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

Answer 23

Stimulate cell division by producing proteins that make cell divide

Question 24

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

Answer 24

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

Question 25

Tumours can develop for years without ______ \_\_\_\_\_\_\_ & can become ____ before they're \_\_\_\_\_\_

Answer 25

Tumours can develop for years without _obvious_ _symptoms_ & can become _large_ before they're _discovered_

Question 26

Name the 2 types of tumours

Answer 26

* Malignant tumour (cancerous) * Begin tumours (not cancerous)

Question 27

Describe malignant tumours

Answer 27

* 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)

Question 28

Describe begin tumours

Answer 28

* 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

Question 29

Name 6 ways tumour cells can differ from normal cell

Answer 29

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

Question 30

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

Answer 30

* Designed to control rate of cell division in tumour cells by disrupting the cell cycle * This kills tumour cells

Question 31

Treatments don't... & so they...

Answer 31

* Treatments don't distinguish tumour cells from normal cells * So they kill normal body cells that are dividing

Question 32

Why are cancer treatments more likely to kill tumour cells?

Answer 32

Tumour cells divide much more frequently than normal cells

Question 33

Name 2 cell cycle targets of some cancer treatments

Answer 33

* G1 (cell growth and protein production) * S phase (DNA replication)

Question 34

Describe how cancer treatments targeting the G1 work

Answer 34

* 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

Question 35

Describe how cancer treatments targeting the S phase work

Answer 35

* 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

Question 36

Explain the link between sunbathing and skin cancer (2)

Answer 36

* Sun's radiation contains UV radiation * Causes mutation of genes which control cell division

Question 37

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

Answer 37

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

Question 38

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

Answer 38

Anaphase

Question 39

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

Answer 39

* Affects mitosis * As chromosomes cannot attach to spindle / chromatids cannot separate on spindle * Cell division slows down

Question 40

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

Answer 40

* Stops DNA replication * New strand not formed (nucleotides not joined together)

Question 41

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

Answer 41

* Too many healthy cells killed * Take time to replace * Patient will have side effects

Question 42

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

Answer 42

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