mutations, gene expression & cancer

Question 1

Explain what is meant by the terms totipotent and pluripotent.

Answer 1

• totipotent cells can give rise to a complete human/all cell types;
• pluripotent can only give some cell types;

Question 2

Explain how cells produced from stem cells can have the same genes yet be of different types.

Answer 2

• {not all / different} genes are switched {on / off} /active / activated ;
• correct and appropriate reference to factors /mechanisms for gene switching ;
• e.g. reference to promoters / transcription factors

Question 3

Describe the mechanism by which a signal protein causes the synthesis of mRNA.

Answer 3

• signal protein {binds to / joins to / interacts with / activates}
• receptor on surface membrane;
• messenger molecule moves from cytoplasm and enters nucleus;
• {produces / activates} transcription factor;
• binds to promoter region;
• RNA polymerase transcribes target gene;

Question 4

Explain how oestrogen enables RNA polymerase to transcribe its target gene.

Answer 4

• Oestrogen diffuses through the cell membrane;
• attaches to ERα receptor;
• ERα receptor changes shape;
• ERα receptor leaves protein complex which inhibited it’s action;
• oestrogen receptor binds to promoter region;
• enables RNA polymerase to transcribe target gene.

Question 5

Compare the structure of dsRNA and DNA.

Answer 5

• Similarities; 2 max
• Polynucleotides/polymer of nucleotides;
• Contain Adenine, Guanine, Cytosine;
• Have pentose sugar/5 carbon sugar;
• Double stranded/hydrogen bonds/base pairs.

• Differences; 2 max
• dsRNA contains uracil, DNA contains thymine;
• dsRNA contains ribose DNA contains Deoxyribose;
• dsRNA is Shorter than DNA; fewer base pairs in length;

Question 6

Explain how the methylation of tumour suppressor genes can lead to cancer.

Answer 6

• Methylation prevents transcription of gene;
• Protein not produced that prevents cell division / causes cell death / apoptosis;
• No control of mitosis.

Question 7

Describe how alterations to tumour suppressor genes can lead to the development of tumours.

Answer 7

• (Increased) methylation (of tumour suppressor genes);
• Mutation (in tumour suppressor genes);
• Tumour suppressor genes are not transcribed/expressed
• OR
• Amino acid sequence/primary/ tertiary structure altered;
• (Results in) rapid/uncontrollable cell division;

Question 8

Describe what is meant by a malignant tumour.

Answer 8

• mass of undifferentiated / unspecialised / totipotent cells;
• uncontrolled cell division;
• (not ‘repeated’)
• metastasis / (cells break off and) form new tumours /
• spread to other parts of body;

Question 9

Describe how altered DNA may lead to cancer.

Answer 9

• (DNA altered by) mutation;
• (mutation) changes base sequence;
• of gene controlling cell growth / oncogene / that monitors cell division;
• of tumour suppressor gene;
• change protein structure / non-functional protein / protein not formed;
• (tumour suppressor genes) produce proteins that inhibit cell division;
• mitosis;
• uncontrolled / rapid / abnormal (cell division);
• malignant tumour;

Question 10

Describe how alterations to tumour suppressor genes can lead to the development of tumours.

Answer 10

• (Increased) methylation (of tumour suppressor genes);
• Mutation (in tumour suppressor genes);
• Tumour suppressor genes are not transcribed / expressed OR Amino acid sequence / primary structure altered;
• (Results in) rapid/uncontrollable cell division;

Question 11

Define epigenetics

Answer 11

• Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.

Question 12

Describe the difference between malignant and benign tumours (1)

Answer 12

1. Malignant tumours metastasise (spread)
   WHEREAS benign tumours do not metastasise

Question 13

What do tumour suppressor genes do? (1)

Answer 13

1. Slows cell division