8.1 Mutation Flashcards
What are the 6 types of mutations?
- Addition
- Deletion
- Substitution
- Inversion
- Duplication
- Translocation
Describe addition mutations
Addition mutations are where one or more bases are added to the DNA sequence.
Describe deletion mutations
Deletion mutations are where one or more bases are removed from the DNA sequence.
Describe substitution mutations
Substitution mutations are where bases are removed and then replaced in the DNA sequence.
Describe inversion mutations
Inversion mutations are where the order of bases in the DNA sequence are reversed.
Describe duplication mutations
Duplication mutations are where bases are repeated in the DNA sequence.
Describe translocation mutations
Translocation mutations are where a section of the DNA sequence is moved to another section of the DNA sequence.
Translocation can be within and across chromosomes.
How do mutations affect the proteins that an organism produces?
Mutations give rise to a change in the base sequence in DNA.
This could alter the amino acids that the DNA encodes.
If the amino acids in a protein are changed, the 3D structure of the protein may break down as bonds between R groups of amino acids can differ.
Explain how the DNA code being degenerate means that some mutations have no effect
Some amino acids are encoded by more than one codon.
The fact that DNA is degenerate means that a mutation in the base sequence does not necessarily affect the protein.
If one base is substituted for another base, (e.g. CAA → CAG), the mutated codon may still encode the same amino acid (e.g. both encode glutamine).
Which types of mutations cause frame shifts?
- Addition
- Deletion
- Duplication
What are the two causes of mutations?
-DNA replication - There can be be errors in the replication process causing mutations.
-Mutagenic agents - Can increase the rate at which mutations occur e.g. UV radiation, smoking etc.
What is a hereditary mutation?
When a gamete containing a mutation for a genetic disorder or type of cancer is fertilised. The mutation is present in the new fetus formed.
When a mutation occurs in a gene that controls … it can cause cancer
A gene that controls cell division
What is a tumour?
A mass of abnormal cells caused by uncontrolled cell division
What two genes control cell division?
- Tumour suppressor genes (TSG)
- Proto-oncogenes
What do tumour suppressor genes do when functioning normally?
Slow cell division by producing proteins that stop cells dividing or cause them to die (apoptosis)
What happens is TSG becomes mutated?
Cannot produce protein which slows cells dividing division so cells will divide uncontrollably
When functioning normally, what do proto-oncogenes do?
Stimulate cell division by producing proteins that make cells divide
What happens if a proto-oncogene acquires a mutation?
The gene becomes overactive which stimulates cell division uncontrollably resulting in a tumour.
What is a mutated proto-oncogene called?
Oncogene
What are the two different types of tumours?
- Malignant - cancerous
- Benign - not cancerous
What are the differences between benign and malignant tumours?
- Benign - Grow slower and covered in fibrous tissue that stops cells invading other tissues
- Malignant - Grow rapidly and invade and destroy surrounding tissues. Cells can break off tumours and spread to other parts of the body in the blood stream or lymphatic system
How does abnormal methylation cause tumour growth?
When genes that control cell division are abnormally methylated, tumours can grow. When TSG are methylated too much (hypermethylation), the genes are not transcribed. This means cells can grow uncontrollably. When proto-oncogenes are not methylated enough (hypomethylation), they produce too much protein that encourages cell division.
What is the role of oestrogen in breast cancer?
- Oestrogen can stimulate certain breast cells to divide which can cause an increased risk of mutation in the DNA replication process.
- Since oestrogen can stimulate cell division, it is thought that if cells do become cancerous, oestrogen can aid rapid replication further.
What are the two types of risk factors for cancer?
- Genetic
- Environmental
What method can be used to identify and prevent cancer?
Screening for mutations in a person’s DNA. Knowing about a person’s increased risk of developing cancer means that preventative measures can be taken.
What are stem cells?
Unspecialised cells that can specialise into other types of cell.
What are totipotent stem cells?
Stem cells that can mature into any type of body cell (found in first few cell divisions of an embryo)
What are pluripotent stem cells?
Can specialise into any type of body cell except for that of the placenta (found in embryos).
What are multipotent stem cells?
Can differentiate into a few types of cells (found in adult mammals).
What are unipotent stem cells?
Can only differentiate into one type of cell (found in adult mammals).
How does a cell become specialised?
- Certain genes are expressed so they are transcribed to mRNA which is translated to produce proteins which modify the cell making it specialised for a particular function.
- Certain genes are switched off so they are not transcribed to mRNA and proteins are not produced.
How can stem cells in bone marrow transplants help treat certain conditions?
The stem cells in the transplanted bone marrow divide and specialise to produce healthy blood cells
What are the 3 sources of stem cells?
- Adult stem cells - obtained from body tissues
- Embryonic stem cells - obtained from embryos at an early stage of development
- Induced pluripotent stem cells (iPS cells) - Adult body cells are ‘reprogrammed’ to become pluripotent
What are the ethical concerns when obtaining stem cells?
Obtaining embryos from IVF produces ethical concerns because it destroys an embryo that could become a fetus if placed in the womb. Some people think that only adult stem cells should be obtained because it does not destroy an embryo. However adult stem cells can not specialise into any body cell. Therefore, induced pluripotent stem cells could be very useful as they don’t destroy an embryo but are pluripotent.
What protein molecules control the transcription of genes?
Transcription factors
What are the two types of transcription factors?
- Activators
- Suppressors
How do activators work?
- Transcription factors move from cytoplasm to nucleus and bind to the promoter region of DNA.
- Activators stimulate the transcription of a target gene by helping RNA polymerase to bind to the start of the gene and start the process of transcription.
How do repressors work?
- Transcription factors move from cytoplasm to nucleus and bind to the promoter region of DNA.
- Repressors inhibit or decrease the rate of transcription by preventing RNA polymerase from binding to the DNA which stops transcription
How does oestrogen affect the expression of molecules?
- Oestrogen binds to a transcription factor called an oestrogen receptor
- Binding of oestrogen causes the transcription factor to change shape and it can now enter the nucleus
- The transcription factor can now bind to the promoter region of DNA and activate transcription
What are the two types of RNA interference (RNAi)?
- small interfering RNA (siRNA)
- microRNA (miRNA)
Explain how siRNA prevents translation?
- mRNA leaves the nucleus for the cytoplasm.
- Double-stranded siRNA associates with several proteins and unwinds. It is separated into two strands and one strand is destroyed (broken down).
- The single strand of siRNA is complementary to mRNA and binds to it.
- The proteins associated with the siRNA cut the mRNA into fragments.
- The fragments then move into a processing body where they are degraded (broken down).
Explain how miRNA prevents translation
One strand associates with proteins and binds to mRNA. The miRNA physically blocks the translation of mRNA. The mRNA is then moved into a processing body where it can be stored or degraded.
What are epigenetics?
Heritable changes of a person’s DNA expression by use of chemical groups rather than changing the base sequence
Can epigenetics be inherited?
Yes
What does increased methylation of DNA do?
Methyl groups are attached to DNA coding for a gene. The methyl group attaches at a CpG site (where cytosine and guanine are next to each other. Increased methylation changes the DNA structure so that transcriptional machinery can’t interact with the gene - so the gene isn’t expressed
What does decreased acetylation do?
When acetyl groups are removed from the histones, the chromatin becomes highly condensed and genes in DNA can’t be transcribed because transcriptional machinery can’t access them.
How can twin studies be used to evaluate data on the phenotype?
Any differences in phenotype between genetically identical twins must be due to environmental factors
