A-LevelBiologyInherited change9700/21 · Oct/Nov 2020 · Q69 Marks

(a) Mutations in body cells can sometimes result in a tumour. Some tumours are cancerous.

(a)(i)Outline how mutations can result in the development of a tumour.[2]
(a)(ii)Tumour cells have antigens on their cell surface that are not present on non-tumour cells. These antigens are the result of gene mutations and are known as tumour specific antigens (TSA). One type of TSA differs in structure from the protein found on the cell surface of non-tumour cells by a single amino acid. Explain how a gene mutation could result in the production of this TSA.[2]
(b)(i)Immunotherapy is a form of treatment for cancer which aims to stimulate the immune system to destroy tumour cells. One form of immunotherapy for cancer uses a vaccine which contains one specific type of TSA. Describe how vaccination with a specific type of TSA could lead to the destruction of tumour cells by T-lymphocytes in the body.[3]
(b)(ii)Vaccines that contain tumour cells instead of a TSA are being developed for use during immunotherapy. Tumour cells are removed from a patient's body and used in a vaccine for the patient. Suggest one advantage and one disadvantage of using a patient's tumour cells in a vaccine rather than a TSA. advantage ________________________________________________________ disadvantage _____________________________________________________[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[2] in context of mutations in genes any two from: uncontrolled, (cell) division / mitosis; cell cycle not regulated ; programmed cell death does not occur / cell becomes immortal ; uncontrolled growth not suppressed ; ref. to mass of abnormal cells ; AVP; e.g. cell cycle checkpoints impaired proto-oncogenes become oncogenes tumour suppressor genes switched off
[2] any two from: ref. to change of a single, nucleotide / base (in sequence of DNA) or one base substitution (mutation) ; change in one, DNA triplet / mRNA codon ; ref. to tRNA with a different anticodon / tRNA brings a different amino acid ; idea that different primary structure leads to different tertiary structure ;
[3] any three from: vaccination stimulates an immune response ; antigen presentation, qualified; e.g. TSA engulfed by, phagocyte / named phagocyte antigen binds to, specific / complementary, receptor, on, T-lymphocyte / cytotoxic T cell / killer T cell ; clonal expansion; A described e.g. divides by mitosis to form a clone (receptor on) cytotoxic T cell / killer T cell, binds to TSA on tumour cell; release of, perforin / hydrogen peroxide (to kill cell); A other named e.g. granzymes AVP; e.g. causes lysis of the cell
[2] advantage any one relevant e.g. tumour cells may have more than one TSA ; stimulate a specific immune response to each TSA; idea that TSA on patient's tumour cells has the appropriate antigen idea that personalised treatment so more effective disadvantage any one relevant e.g. high cost of personalised treatment ; immune system may not recognise TSA on own body cell as, foreign / non-self, the cells in the tumour may not have the TSA in the vaccine ; patient's tumour may not be large enough to obtain enough cells for treatment ; patient needs surgery to obtain (large quantity of) cells; AVP; e.g. suggestion that tumour cell may settle in a part of the body and not be destroyed