3.2.11 Mutation and Cancer Flashcards
What is a gene mutation?
Changes in DNA base sequence of chromosomes
Name 2 types of errors that occur
- Substitution
- Deletion
What is deletion?
When one base is deleted
e.g. ATGCCT becomes ATCCT (G is deleted)
What is substitution?
When one base is substituted with another
e.g. ATGCCT becomes ATTCCT (G is swapped for T)
Name 3 types of substitution
- Nonsense mutation
- Missense mutation
- Silent mutation
What is a nonsense mutation?
Occurs if base change = stop codon
What is a missense mutation?
Occurs if base change = different amino acids being coded for
What is a silent mutation?
Substituted base, although different = codes for same amino acid
Why will not all substitution mutations lead to a change in the amino acid sequence of a protein?
Due to the degenerate nature of genetic code, some amino acids are coded for by more than one DNA triplet
Why will deletions always lead to changes in amino acid sequence?
From point of mutation base sequence changes/causes frame shift
What do mutagenic agents do?
Increases the frequency of mutations
Give an example of a mutagenic agent
e.g. UV radiation, ionising radiation, some chemicals and some viruses
Mutations occur _____
spontaneously
e.g. when DNA is misread during replication
What are acquired mutations?
Mutations that occur in individual cells after fertilisation
Describe how mutations can cause a tumour
- If mutations occur in genes that control rate of cell division (by mitosis) = uncontrolled cell division
- Uncontrolled cell division = tumour (mass of abnormal cells)
What is cancer?
Tumours that invade and destroy surrounding tissue
Name the 2 types of gene that control cell division
- Tumour suppressor genes
- Proto-oncogenes
How can tumour suppressor genes be inactivated?
If mutation occurs in DNA sequence
When functioning normally, what do tumour suppressor genes do & how?
Slow cell division by producing proteins that stop cells dividing or cause them to self-destruct
Describe how a mutation may affect tumour suppressor genes & what this can lead to
- Mutation prevents transcription of gene
- Protein isn’t produced so doesn’t inhibit cell division
- No control of mitosis (cells divide uncontrollably) = tumour
How can the effect of proto-oncogene be increased?
If mutation occurs in DNA sequence
What is a mutated proto-oncogene called?
Oncogene
When functioning normally, what do proto-oncogenes do & how?
Stimulate cell division by producing proteins that make cell divide
Describe how a mutation may affect proto-oncogenes & what this can lead to
- Proto-oncogenes become oncogenes
- Oncogene stimulate rapid cell division without growth factor (divide uncontrollably = tumour)
- Oncogene cause production of excess growth factor
Tumours can develop for years without ______ _______ & can become ____ before they’re ______
Tumours can develop for years without obvious symptoms & can become large before they’re discovered
Name the 2 types of tumours
- Malignant tumour (cancerous)
- Begin tumours (not cancerous)
Describe malignant tumours
- 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)
Describe begin tumours
- 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
Name 6 ways tumour cells can differ from normal cell
- Irregular shape
- Nucleus is larger and darker (& sometimes have more than 1 nucleus)
- Don’t produce all proteins needed to function correctly
- Different antigens on their surface
- Don’t respond to growth regulating processes
- Divide by mitosis more frequently
What are cancer treatments that target the cell cycle designed to do?
- Designed to control rate of cell division in tumour cells by disrupting the cell cycle
- This kills tumour cells
Treatments don’t… & so they…
- Treatments don’t distinguish tumour cells from normal cells
- So they kill normal body cells that are dividing
Why are cancer treatments more likely to kill tumour cells?
Tumour cells divide much more frequently than normal cells
Name 2 cell cycle targets of some cancer treatments
- G1 (cell growth and protein production)
- S phase (DNA replication)
Describe how cancer treatments targeting the G1 work
- 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
Describe how cancer treatments targeting the S phase work
- 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
Explain the link between sunbathing and skin cancer (2)
- Sun’s radiation contains UV radiation
- Causes mutation of genes which control cell division
Suggest why fair-skinned people are at a greater risk of skin cancer than dark-skinned people when sunbathing (1)
Little melanin = little protection against UV radiation (can easily burn)
Cancer Treatments
At what phase in the cell cycle would a drug that prevents the spindle fibre shortening act?
Anaphase
Cancer Treatment
Describe how a drug affecting spindle activity would work (3)
- Affects mitosis
- As chromosomes cannot attach to spindle / chromatids cannot separate on spindle
- Cell division slows down
Explain how a drug that inhibits the enzyme DNA polymerase might be effective against some types of cancer (2)
- Stops DNA replication
- New strand not formed (nucleotides not joined together)
Suggest why cancer treatments should not be given too frequently even though it means they’ll kill more cancer cells (3)
- Too many healthy cells killed
- Take time to replace
- Patient will have side effects
Human cells contain genes that control their growth and division. Explain in detail how a gene mutation could lead to cancer. (6)
- Change in base sequence
- Substitution / deletion
- Transcription changed
- Amino acid sequence changed / different protein
- Loss of function
- Uncontrolled cell division
