Topic 8A - Mutations and Gene Expression Flashcards
Define mutations.
A change to the base sequence of DNA
What do mutangenic agents do?
Increase the rate of mutation
Describe the types of mutations that can occur (6).
Substitution - one or more bases are swapped for another
Deletion - one or more bases are removed
Addition - one or more bases are added
Duplication - one or more bases are repeated
Inversion - a sequence of bases is reversed
Translocation - a sequence of bases is moved from one location in the genome to another (this could be within the same chromosome or to a different chromosome)
What may happen if any of these mutations occur?
If a mutation occurs in a gene, the sequence of amino acids in the polypeptide it codes for may change, possibly changing the 3D tertiary structure of the protein produced and thereby altering its function.
Define genetic disorders.
Inherited disorders caused by abnormal genes or chromosomes.
Define hereditary mutations.
A mutation which occurred in a gamete which was then fertilised by another gamete, and passed onto the offspring.
Define a frameshift.
A frameshift is when a shift occurs in the DNA code because of a change in the number of bases in the DNA code.
Mutations occur __________.
Spontaneously
What are some examples of mutagenic agents? (3)
Ultraviolet radiation
Ionising radiation
Carcinogens such as asbestos
How can mutagenic agents increase the rate of mutations? (3)
- Acting as a base
- Chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA. - Altering bases
- Some chemicals can delete or alter bases.
- Changing the structure of DNA
- some types of radiation can change the structure of DNA, which causes problems during DNA replication.
Define acquired mutations.
Mutations that occur in individual cells after fertilisation.
What causes the growth of a tumour?
Uncontrollable cell division caused by acquired or inherited mutations in the genes that control the rate of mitotic cell division
What are the two types of genes that control cell division?
Tumour suppressor genes
Proto-oncogenes
What do functioning tumour suppressor genes do?
They slow cell division by producing proteins that stop cells dividing or cause them to undergo apoptosis.
What is apoptosis?
Apoptosis is a type of programmed cell death. It’s where cells that are infected, damaged or have reached the end of their functional life are destroyed.
What do mutated tumour suppressor genes do?
The gene becomes inactivated so the protein the gene codes for isn’t synthesised and the cells divide uncontrollably, resulting in a tumour forming.
What do functioning proto-oncogenes do?
They stimulate cell division by producing proteins that make cells divide.
What do mutated proto-oncogenes do?
The genes can become overactive, stimulating cells to dive uncontrollably resulting in a tumour.
Define oncogenes.
A mutated proto-oncogene
Malignant tumours are _______. They grow ____ and can _____ and ____ surrounding tissues. Cells can _______ malignant tumours and spread to other parts of the body via the _________________________________.
Cancerous Rapidly Invade Destroy Break off Bloodstream and lymphatic system
Benign tumours are __________. They usually grow ______ than malignant tumours and are often covered in __________ which _______ cells invading other tissues. Bening tumours are often _______, but they can cause ____________________________________. Some benign tumours can become ________.
Not cancerous Slower Fibrous tissue Prevents Harmless Blockages and put pressure on organs Malignant
How do tumour cells differ from normal cells? (6)
- – The nucleus is larger and darker, sometimes there is more than one.
- – They have an irregular shape.
- – They don’t produce all the proteins needed to function correctly.
- – They have different antigens on their surface.
- – They don’t respond to growth regulating processes.
- – They divide by mitosis more often than normal cells.
What is methylation?
Adding a methyl group (-CH3) onto something.
Methylation of DNA is an important method of regulating ___________ - it can control whether or not a gene is _______ and ________.
Gene expression
Transcribed
Translated
What is abnormal methylation?
When methylation occurs too much or too little.
Define hypermethylation.
When too much methylation is occurring.
Define hypomethylation.
When too little methylation is occurring
What happens when tumour suppressor genes are hypermethylated?`
The methyl groups block the genes from being transcribed so the proteins they produce to slow cell division aren’t made. This means cells are able to divide uncontrollably.
What happens when proto-oncogenes are hypomethylated?
There are very little methyl groups to stop the genes from being transcribed so there is an increased production of proteins which increases the rate of cell division. This stimulates cells to divide uncontrollably
Each woman is exposed to a _______ amount of oestrogen over their lifespan, which may result in early _________ and/or late __________ if you are exposed to an ________ amount. An ________ exposure to oestrogen is also though to increase a woman’s risk of _______________________.
Variable Menstruation Menopause Increased Increased Developing breast cancer.
Describe and explain the theories linking oestrogen and breast cancer (3).
— Oestrogen can stimulate certain breast cells to divide and replicate. More cell division increases the chances of mutations occurring, and so increases the chance of cells becoming cancerous.
— Oestrogen’s ability to stimulate cell division could mean that if cells do become cancerous, their rapid replication could be further assisted by oestrogen.
— Other research suggests that oestrogen is actually able to introduce mutations directly into the DNA of certain breast cells, again increasing the chances of these cells becoming cancerous.
What factors increase a persons chance of getting cancer? (2)
- Genetic factors: some cancers are linked with specific inherited alleles. If you inherit that allele your more likely to get that type of cancer.
- Environmental factors: Exposure to radiation, lifestyle choices such as smoking, increased alcohol consumption and a high fat diet have all been linked to and increased chance of developing some cancers.
What is gene therapy?
Where faulty alleles in a person’s cells are replaced by working versions of those alleles.
What are stem cells?
Stem cells are unspecialised cells that can develop into other types of cells.
What are totipotent cells?
Stem cells that can mature into any type of body cell in an organism (including placental cells).
What are pluripotent cells?
Stem cells that can specialise into any type of body cell in an organism (excluding placental cells).
What are multipotent cells?
Stem cells that are only able to differentiate into a few different types of cells.
What are unipotent cells?
Stem cells that can only differentiate into one type of cell.
How do stem cells become specialised?
Stem cells all contain the same genes. However during development only some genes and expressed whilst others are turned off. The genes that are expressed get transcribed into mRNA, which is then translated into proteins. These proteins modify the cell - they determine the cell structure and control cell processes (including the expression of more genes, which produced more proteins). Changes to the cell produced by these proteins cause the cell to become specialised.
What are cardiomyocytes?
Heart muscle cells that make up a lot of the tissue in our hearts.
What do cardiomyocytes do in the heart?
Cardiomyocytes are replaced by new cardiomyocytes if the heart becomes damaged. This is done by a small supply of unipotent stem cells in the heart.
What stem cell therapies are in existence? (1)
- Bone marrow transplants — Bone marrow transplants can be used to replace the faulty bone marrow in patients that produce abnormal blood cells. The new stem cells will then produce healthy red blood cells.
What are the sources of stem cells? How are they extracted? (3)
- Adult stem cells — These are obtained from the body tissues of an adult. They are extracted from the bone marrow via a syringe.
- Embryonic stem cells — These are obtained from embryos at an early stage of development. Embryos are created via IVF and then extracted.
- Induced pluripotent stem cells (iPS cells) — These are created by ‘reprogramming’ specialised adult body cells so that they become pluripotent by adding transcription factors that make the adult cells express genes associated with pluripotent stem cells. The adult cells are extracted first and then the transcription factors are introduced via a specially-modified virus.
What are the benefits of stem cell therapy? (3)
- They could save lives — Stem cells could be used to grow organs.
- They could make stem cells genetically identical to a patient so new tissues wouldn’t be rejected.
- They could improve the quality of life for many people — replace damaged cells in the eyes to improve a patients vision.
What are transcription factors?
Protein molecules which control the transcription of genes.
What do transcription factors do in eukaryotes?
They move from the cytoplasm to the nucleus and bind to specific DNA sites called promoters, which are found near the start of their target genes.
How do transcription factors control the expression of genes?
They control the rate of transcription
What are activators and how do they work?
Activators are transcription factors which stimulate or increase the rate of transcription. They do this by helloing RNA polymerase bind to the start of the target gene and activate transcription.
What are repressors and how do they work?
Repressors are transcription factors which inhibit or decrease the rate of transcription. They do this by binding to the start of the target gene, preventing RNA polymerase from binding and therefore stopping transcription.
Why are not all cells affected by oestrogen?
Only cells with oestrogen receptors are affected by oestrogen.
How are oestrogen-oestrogen receptors complexes formed?
When oestrogen binds to a transcription factor called an oestrogen receptor.
What do oestrogen-oestrogen receptors do?
They move from the cytoplasm into the nucleus where they bind to specific DNA sites near the start of the target gene. The complex acts as an activator and helps RNA polymerase bind to the start of the target gene. However, in some genes the complex acts as a repressor and helps prevent transcription from occurring.
What is RNAi?
Small lengths of non-coding RNA.
What does siRNA do to control gene expression?
Once mRNA has been transcribed, it leaves the nucleus for the cytoplasm. In the cytoplasm, double-stranded siRNA associates with several proteins and unwinds. One of the resulting single strands of siRNA is selected and the other strand is degraded. The single strand of siRNA then bonds to the target mRNA. The base sequence of the siRNA is complementary to the base sequence in the sections of the target mRNA. The proteins associated with siRNA cut the mRNA into fragments - so it can no longer be translated. The fragments then move into a processing body, which contains ‘tools’ to degrade them.
What does miRNA do in mammals to control gene expression?
miRNA is processed into a double strand and then two single strands by enzymes in the cytoplasm. One strand associates with proteins and bonds to target mRNA in the cytoplasm. The miRNA-protein complex physically blocks the translation of the target mRNA. The mRNA is then moved into a processing body,!where it can either be stored or degraded. When it’s stored it can be returned and translated at another time.
What does miRNA look like when it is first transcribed?
It exists as a long, folded strand that is then processed into a double strand and then into two single strands.
What does miRNA do in plants to control gene expression?
miRNA is processed into a double strand and then two single strands by enzymes in the cytoplasm. One strand associates with proteins and bonds to target mRNA in the cytoplasm. The base sequence of the miRNA is complementary to the base sequence in the sections of the target mRNA. The proteins associated with miRNA cut the mRNA into fragments - so it can no longer be translated. The fragments then move into a processing body, which contains ‘tools’ to degrade them.
What does siRNA look like when it is first transcribed?
Double-stranded.
siRNA is _________ complimentary.
miRNA in plants is _________ complimentary.
miRNA in mammals is _________ complimentary.
Perfectly
Perfectly
Partially
