3.8.2.3 - CANCER

Question 1

the KRAS gene codes for a protein called K-Ras. the protein relays signals from outside a cell to a cell’s nucleus, stimulating cell division. an alteration in the KRAS gene produces an oncogene which can cause a tumour to develop.

suggest and explain how an alteration in the KRAS gene can cause a tumour to develop (3)

Answer 1

1. mutation in KRAS gene OR change in base sequence of KRAS base sequence
2. change in protein produced
3. results in rapid uncontrollable cell division

Question 2

describe how altered DNA may lead to cancer (6)

Answer 2

1. DNA altered by mutation
2. mutation changes base sequence
3. of tumour suppressor gene/proto-oncogene
4. change protein structure/non-functional protein produced
5. TSG genes produce proteins that inhibit cell division
6. mitosis
7. uncontrolled cell division
8. malignant tumour

Question 3

explain why fragments of DNA from cancer cells may be present in blood plasma (2)

Answer 3

1. cancer cells die/break open
2. releasing DNA

Question 4

explain why cancer is more likely to be treated successfully if the disease is detected at a very early stage (2)

Answer 4

1. fewer cancerous cells/smaller tumours
2. less spread/fewer locations to treat

Question 5

explain how examining mRNA enables scientists to discover whether cancer is present (3)

Answer 5

1. mRNA base sequence has changed
2. so gene has mutated
3. cancer gene active/TSG inactive

Question 6

explain how the methylation of tumour suppressor genes can lead to cancer (3)

Answer 6

1. methylation prevents transcription of gene
2. protein not produced that prevents cell division]
3. no control of mitosis

Question 7

explain why tumour area may not be the best indicator of tumour size and suggest a more reliable measurement (2)

Answer 7

1. tumour may be different depths
2. measure tumour volume/mass/weight

Question 8

drugs are used to treat cancer. at what phase in the cell cycle would each of the following drugs act?

1. a drug that prevents DNA replication (1)
2. a drug that prevents spindle fibres shortening (1)

Answer 8

1. interphase
2. anaphase

Question 9

some tumours are benign and some are malignant.

give one way in which a benign tumour differs from a malignant tumour (1)

Answer 9

1. benign does not cause cancer
2. does not invade other tissues causing damage
3. with benign, pieces do not break off and start new tumours elsewhere in the body (metastasis)

Question 10

describe two ways in which both types of tumour may cause harm to the body (2)

Answer 10

1. may damage organ concerned
2. may cause blockages
3. may damage/exert pressure on other organs

Question 11

explain the link between sunbathing an skin cancer (2)

Answer 11

1. sun’s radiation contains ultra violet radiation
2. causes mutation of genes which control division

Question 12

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

Answer 12

because fair skin has less melanin which protects against UV radiation

Question 13

suggest why people with a family history of cancer are at a greater risk of cancer than those with no family history of cancer (1)

Answer 13

because cancer has a genetic component/may have inherited gene which causes/gives predisposition to cancer

Question 14

describe what is meant by a malignant tumour (3)

Answer 14

1. mass of unspecialised cells
2. uncontrolled cell division
3. metastasis - break off and form new tumour

Question 15

explain why it is important to destroy all the cancer cells in a tumour (2)

Answer 15

1. cells can metastasise
2. remaining cells continue to divide forming a secondary tumour