8A Mutations and Gene Expression Flashcards
Substitution mutation
One or more bases are swapped for another
Deletion mutation
One or more bases are removed
Addition mutation
One or more bases have been added
Duplication mutation
One or more bases are repeated
Inversion mutation
A sequence of bases has been reversed
Translocation mutation
A sequence of bases is moved from one location to another in the genome. Can be same or different chromosome
Hereditary mutations
If a gamete containing a mutation for a genetic disorder is fertilised the mutation will be present in the fetus
Mutagenic agent
Increase the rate of mutations
How can different mutagenic agents work?
Act as a base (changing base sequence of DNA) Alter base (cab delete or alter base) Change the structure of DNA- causes problems during DNA replication
Acquired mutations
Mutations that occur after fertilisation
Tumour
A mass of abnormal cells
What makes a cancer?
A tumour that can invade and destroy surrounding tissue
What do tumour suppressor genes normally do?
Slow cell division by producing proteins that stop cells dividing or cause them to self destruct
Apoptosis
Cells self destruct
What happens if a mutation occurs in a tumour suppressor gene?
The gene will be inactivated. Protein that suppresses cell division won’t be made, so cells are allowed to divide uncontrollably, resulting in a tumour
What to proto-oncogenes usually do?
Stimulate cell division by producing proteins that make cells divide
What happens if a mutation occurs to a proto-oncogene?
The gene becomes overactive, produces more of the protein, so cells divide uncontrollably resulting in a tumour
What is a mutated proto-oncogene called?
An oncogene
Malignant tumour
Cancerous- grow rapidly and invade and destroy surrounding tissue
Cells can break off the tumours and spread to other parts of the body in the bloodstream or lymphatic system
Benign tumours
Not cancerous- grow slower and are covered in fibrous tissue the stops the cells invading other tissues
How do benign tumours pose a risk?
Can develop into malignant tumours and can cause blockages, putting pressure on organs
Name six ways that tumour cells can differ from normal cells
Nucleus is darker and rounder or can have more than one nucleus
Irregular shape
Don’t produce all the proteins needed to function properly
No antigens on surface
Don’t respond to growth regulating processes
Divide via mitosis more frequently
What two mutations can cause the growth of a tumour?
Abnormal methylation
Increased exposure to oestrogen
How does hypermethylation lead to the development of a tumour?
Methylation = adding a methyl group
Of tumour suppressor genes
Genes are not transcribed, so translation doesn’t occur, so the proteins they produce to slow cell division aren’t made. This means cells can divide uncontrollably
How does hypomethylation lead to the development of a tumour?
Of proto-oncogenes.
Causes them to become oncogenes and produce the proteins needed for cell division at a more rapid rate
How does oestrogen lead to the development of a tumour?
Oestrogen can stimulate breast cells to divide and replicate- more cell divisions = more chance for mutations to occur
Can stimulate division- cells become more cancerous
Introduce mutations directly into DNA of certain breast cells
Stem Cells
Unspecialised cells that can develop into other types of cell
Where are stem cells found?
embryos and adult tissue such as bone marrow
Totipotent stem cells
Can mature into any cell in the body (including cells that make up the placenta)- only present in the first few stages of an embryo
Pluripotent stem cells
Can become any cell in the body except placenta cells - embryonic
Multipotent stem cells
Available from adult tissue- can differentiate into a few types of cell (e.g white and red blood cells can be developed from stem cells in bone marrow)
Unipotent stem cells
Available from adult tissue- can only differentiate into one type of cell
How do stem cells become specialised?
All stem cells contain the same genes but not all are expressed during development
mRNA is therefore only transcribed from the specific genes, and then translated into proteins
The proteins produced causes changes to occur in the cell that are difficult to reverse, so once a cell has specialised, it stays specialised
What are cardiomyocytes?
Heart muscle cells
How are cardiomyocytes made from unipotent stem cells?
Unipotent stem cells in the heart can replace old or damaged cardiomyocytes
What are the tree main sources of stem cells?
Adult stem cells
Embryonic stem cells
Induced Pluripotent stem cells
What are Induced Pluripotent Stem Cells?
Cells created by scientists in a lab
Made to express certain transcription factors in order to swtch on/ off certain genes
A way to do this is by infecting adult cells with a specially modified virus
What is the transcription of genes controlled by?
Transcription Factors
Where do transcription factors move from in eukaryotes?
The cytoplasm to the nucleus
Where do transcription factors bind to?
Specific DNA sites called promoters
Where are promoters found?
Near the start of the target gene
What are activators?
Transcription factors that stimulate or increase the rate of transcription
What are repressors?
Transcription factors that inhibit or decrease the rate of transcription
How is oestrogen used as a transcription factor?
Binds to a transcription factor called an oestrogen receptor, forming an oestrogen- oestrogen receptor complex. The complex moves from cytoplasm to the nucleus and binds to a specific Dna site near the star of the target gene. The complex acts as an activator
What is an example of stimulating transcription?
Helping RNA polymerase to bind to the start of the target gene
What is an example of inhibiting transcription?
Preventing RNA polymerase from binding
What is RNAi?
Double stranded RNA molecules stop mRNA from target genes being translated into proteins
What are the molecules involved in RNAi?
siRNA and miRNA
Where does siRNA work?
During translation
Describe the function of siRNA
mRNA transcribed and leaves nucleus for cytoplasm. In cytoplasm, double stranded siRNA associates with proteins and unwinds, producing two single strands. One strand is selected, the other is degraded
The single strand of siRNA then binds to the target mRNA as their base sequences are complementary
The proteins associated with the siRNA cut the mRNA into fragments so that it can no longer be translated
The fragments then move to a processing body, where it is degraded
Do plants have siRNA?
No, they only have miRNA
What is the function of miRNA in mammals?
Less specific than siRNA as it is not fully complementary to the target mRNA, so it can target more than one mRNA molecule.
The double strand of miRNA is broken down into two single strands by enzymes, then one single strand associates to proteins (the other is degraded)
The miRNA-protein complex physically blocks the translation of the target mRNA. The mRNA is then moved to the processing body where it can either be stored or translated
Epigenetic control
The attatchment/ removal of a chemical groups to or from DNA or histone proteins, which determine whether a gene is switched on or off
Epigenetic marks
The chemical groups that are removed/ attached to DNA or histone proteins
In simple terms, describe how epigenetic marks work?
They alter how easy it is for enzymes and other proteins needed for transcription to interact and transcribe the DNA
Why can the expression of some genes be passed on to offspring?
Epigenetic marks may still be present through generations, so the offspring can be affected by environmental changes that affected their parents or grandparents
Describe the process of increased methylation
Methyl group attaches at a CpG site (cytosine and guanine are next to each other. Increased methylation changes the DNA structure so that the transcriptional machinery can’t interact with the genes
Describe the process of decreased acetylation of histones
When acetyl groups are removed, the chromatin becomes highly condensed and genes can’t be transcribed because the transcriptional machinery can’t physically access them
What enzyme is responsible for removing the histone group?
Histone deacetylase
