A-level Biology - 3.2.11 Mutation and Cancer
A gene mutation is a change in the DNA base sequence of a gene. This can affect the production or function of proteins, potentially leading to disorders such as cancer if the mutation occurs in genes that regulate cell growth and division.
What is a gene mutation?
Changes in DNA base sequence of chromosomes
Key Terms
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
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| Term | Definition |
|---|---|
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 |