GENE MUTATIONS

• Use information in the diagram to suggest how the binding of interferon gamma to its receptor protein leads to the production of phosphorylated STAT1.? (2)

  Binding of the interferon gamma changes shape/ tertiary structure of receptor

  Activates enzyme

  Use of ATP (to phosphorylate STAT1)
•  Name the two transcription factors in the diagram.? (2)

  Phosporylated STAT1

  IRF protein
•  The regulation of the formation of helper T cells by interferon gamma is an example of positive feedback.

  Explain why it is an example of positive feedback. (2)?

  Causes more t-helper cells to form

  SO more interferon gamma production by helpter T cells
• The IRF gene can be a tumour suppressor gene.

  Use the information in the diagram to explain how the IRF gene acts as a tumour suppressor gene. (3)?


  Tumour suppressor gene - slows cell division WHICH cause death of damaged tumours or cancer cells

  IRF gene leads to formation of IRF protein that binds to gene B

  Gene B causes death of damaged mutated cells or slows division
• A mutation of a tumour suppressor gene can result in the formation of a tumour. Explain How? (2)

  Tumour suppressor gene if its inactivated - it'll be unable to control or slow down cell division

  Rate of cell division will be too fast
• Not all mutations result in a change to the amino acid sequence of the encoded polypeptide.

  Explain why. (1)?

  Genetic code is degenerate

  OR mutation in INTRON
• Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide.

  Scientists have produced a monoclonal antibody that stops this stimulation.

  Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour. (3)?

  Antibody has a specific tertiary structure / binding region

  Complementary shape to receptor protein OR Gf

  WHICH prevents GF binding to receptor
• Describe what happens in

  (i)      metaphase? (2)

  Spindle formed and chromatids attach to spindle

  Chromosomes line up at equator / move to the middle
• Describe what happens in

  (i)      anaphase (2)?

  Chromosomes split/ chromosomes pulled apart

  To opposite sides/ poles of cell
• Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cells completing the cell cycle in a short time (1)?

  Rapid cell replication
• Mikanolide is a drug that inhibits the enzyme DNA polymerase. Explain why this drug may be effective against some types of cancer. (2)?

  prevents DNA replication - so slows mitosis/ cell division

  New strand not formed
• Oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells. Explain how an activated oestrogen receptor affects the target cell. (2)?

  Receptor binds to promoter region which stimulates RNA polymerase

  Transcribes gene/ increases transcription
•  Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body?

  Other cells do not have oestrogen receptors
• Some tumours are benign and some are malignant.

  (i)      Give one way in which a benign tumour differs from a malignant tumour.(1)?


  benign does not cause cancer

  Does not invade other tissues causing damage

  Benign cancer - pieces that break off do not start new tumours elsewhere in body (metastasis)
•  Describe two ways in which both types of tumour may cause harm to the body. (2)?

  May damage organ concerned

  May cause blockages

  May damage/ put pressure on other organs
•  Explain the link between sunbathing and skin cancer (2)?

  Sun radiation contains UV radiation

  This causes mutation of genes which control division
• Suggest why fair-skinned people are at a greater risk of skin cancer than dark-skinned people when sunbathing (1)?

  Because fair skin has little melanin which protects against UV radiation
•  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)?

  Cancer may have a genetic component which gives predisposition to members of family - so can be inherited
• The grandparents, A and B, had two children, girl C and boy D. Explain how the phenotypes of these children provide evidence that Li-Fraumeni syndrome is:  caused by a dominant allele? (3)

  C = GIRL WITHOUT CANCER D= BOY WITH CANCER?


  Daughter C does not have condition

  Parents must have been carriers of healthy recessive

  ALSO if recessive then parents = homozygous (which means all children affected)
• The grandparents, A and B, had two children, girl C and boy D. Explain how the phenotypes of these children provide evidence that Li-Fraumeni syndrome is: not sex-linked?


  Father would pass on X - chromosome to daughter

  But she is not affected
• This family’s history of cancer was investigated when person E asked for genetic counselling. At the time she was 25 years old. What advice could a genetic counsellor give her about her probability of developing cancer? (2)?

  IS 25 - only forms at young age so she will not be at risk of developing cancer

  BUT if heterozygous = 50% chance of carrying allele

  if Homozygous - serious risk of cancer
• Li-Fraumeni syndrome is caused by a mutation affecting a tumour suppressor gene called TP53. This gene codes for a protein that initiates the death of cells where damaged DNA cannot be repaired. The mutated TP53 gene leads to the production of a non-functional protein. Suggest how the non-functional protein may lead to cancer.? (3)

  Mutation changes DNA of cell

  Damaged DNA not repaired

  Mutation leads to loss of control - uncontrolled cell division
•   Suggest how a mutation can lead to the production of a protein that has one amino acid missing.? (2)

  Loss of 3 BASES/ TRIPLET
• Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder such as Ellis-van Creveld syndrome. (2)?

  Change in tertiary shape/ active site

  SO faulty non-functional protein
• One hypothesis for the cause of cancer of the colon (large intestine) is that Clostridium bacteria present in the gut can convert bile steroids into cancer-causing substances.

  (a)     Explain the presence of bile in the colon. (2)?

  Secreted by liver/ released by gall bladder into the duodenum/ small intestine

  Bile passes unchanged from small intestine to colon
• Human cells contain genes that control their growth and division. One of these genes codes for a protein that prevents cell division. The substances formed from bile steroids by Clostridium bacteria may cause gene mutation. Describe and explain how these substances could cause colon cancer (4)?

  Changes in code/ base sequence -

  Leads to: addition/ deletion/ substitution

  causes changes in mRNA/ transcription

  protein structure/ amino acid structure has also changed

  It is now at a loss of function

  AND there is uncontrolled cell division
• Explain how the structure of DNA is related to its functions. (6)?

  Double stranded/ helix provides strength and stability + protects bases so protects hydrogen bonds as well

  Long/ large molecule so can store lots of information

  Helix - so compact

  Base sequence allows information to be stored

  Base sequence codes for amino acids

  Double stranded so replication can occur semi-conservatively (strands act as templates)

  Weak hydrogen bonds for replication - strand separation

  Many hydrogen bonds so stable and strong
•  More cancer cells could be destroyed if the drug was given more frequently.

  Suggest why the drug was not given more frequently.?

  Could lead to more healthy cells being killed

  SO will take time to replace - increase in number

  Person may have damaging side effects
• Describe how altered DNA may lead to cancer.(6)?

  DNA altered by mutation

  Mutation changes base sequence

  Of gene controlling cell growth/ oncogene

  Of tumour suppressor genes

  Change protein structure

  Tumour suppressor genes produce proteins that inhibit cell division

  Mitosis

  Uncontrolled rapid cell division

  which LEADS TO a malignant tumour
•  Explain why fragments of DNA from cancer cells may be present in blood plasma?

  Cancer cells die and break open

  Releasing DNA
• Explain why the nucleic acid on the test strip will only bind to altered DNA (2)?

  Normal and altered DNA have different base sequences

  SO DNA only binds to complementary sequence
• This test strip will allow cancers to be detected at a very early stage. Explain why cancer is more likely to be treated successfully if the disease is detected at a very early stage?

  Fewer cancerous cells

  Less cell damage and less spread
•  Explain how examining mRNA (line 7) enables scientists to discover whether cancer is present.?

  mRNA base sequence has changed

  DNA structure is different/ has mutated

  TSG - inactive
• Treatment with isoniazid leads to the osmotic lysis of this bacterium. Use information in the diagram to suggest how.?


  Cell wall not formed/ production inhibited

  Lower water potential in bacterium

  Water enters and causes lysis/ expansion/ pressure
• Human cells also produce fatty acids. Isoniazid does not affect the production of these fatty acids.

  Use information in the diagram to suggest one reason why isoniazid does not affect the production of fatty acids in human cells?

  Human cells lack enzyme B / have a different enzyme / produce different fatty acids / use different substrates
• A mutation in the gene coding for enzyme B could lead to the production of a non-functional enzyme. Explain how.?

  Change in base sequence of DNA leads to change in amino acid sequence/ primary structure of enzyme

  Change in hydrogen bonds leads to changes in tertiary structure // changes of active site in enzyme

  Substrate not complementary - cannot bind to enzyme
• Explain how this mutation leads to the formation of non-functioning PAH.?

  Changes in amino acid sequence/ primary structure

  Changes in hydrogen bonding which alters the tertiary structure of enzyme - impacts the active site

  Substrate not complementary - so no enzyme-substrate complexes form
• One mutation causing phenylketonuria was originally only found in one population in central Asia. It is now found in many different populations across Asia. Suggest how the spread of this mutation may have occurred. (1)?

  Migration/ founded effect/ interbreeding
• What name is used for the non-coding sections of a gene?

  Introns
• During which part of the cell cycle are gene mutations most likely to occur? and why?

  Interphase/ S phase

  because DNA replication occurs + longest stage