Mutations and Gene Expression- A15 Flashcards
What are stem cells?
Unspecialised cells that can develop into other types of cell. They keep dividing to produce more stem cellls, which then differentiate to become specialised
What types of stem cells are found in embryos?
-totipotent: can differentiate into any type of body cell in an organism(including placental cells). They’re only present in mammals in the first few divisions of an embryo
-pluripotent: can mature into any type of body cell but have lost the ability to develop into placental cells
What type of stem cells are found in adult mammals?
-multipotent: can differentiate into any few different types of cell e.g. multi potent stem cells in bone marrow can differentiate into red and white blood cells
-unipotent: can only differentiate into one type of cell e.g. there is a type of unipotent stem cell in the heart that can only differentiate into cardiomyocytes
Describe the process of differentiation.
-stem cells become specialised because during their development they only transcribe and translate part of their DNA
-stem cells all contain the same genes, but during development not all of them are transcribes and translated(expressed).
-under one set of conditions, certain genes are expressed and others are switched off, and vice versa.
-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 produce more proteins)
-changes to the cell produced by these proteins cause the cell to become specialised.
-this is difficult to reverse, so. Once a cell has specialised, it stays specialised.
What are cardiomyocytes?
Heart cells that cannot divide to replicate themselves
What is there a small supply of in the heart to replace old or damaged cardiomyocytes?
Unipotent stem cells
What are induced pluripotent stem cells?
-Specialised adult body cells are reprogrammed to become pluripotent
-adult cells are made to express a series of protein transcription factors that are normally associated with pluripotent stem cells
-protein transcription factors cause the adult body cells to express genes that are associated with pluripotency
How can a modified virus introduce protein transcription factors to an adult cell?
-protein transcription factors can be introduced o adult cells by infecting them with a modified virus, which contains genes coding for the protein transcription factors within it’s genetic material
-virus infects cell which incorporates the PTF genes into the cell’s DNA, which is then expressed, producing PTF
-iPS cells are useful in research and medicine in the future. More research must be done into how similar they actually are to true pluripotent embryonic stem cells before they can be properly utilised.
What are the ethical considerations with stem cells?
-obtaining stem cells from an embryo result in destruction of an embryo - destroying a potential life
-could take stem cells from an unfertilised egg that has been stimulated to divide - can’t survive past a few days in the womb
-some people say only adult stem cells should be used but as they are multipotent, they aren’t as useful.
What are the benefits of stem cell therapy?
-could save many lives - organ transplants(not iPS) so still chance of rejection)
-if iPS are used then possible o make new tissues or organs for people which are genetically identical to their cells so less chance of rejection
-improve quality of life for people - use to replace damaged cells in people with disease
What is a risk of stem cell therapy?
-stem cells may divide out of control, leading to a tumour.
What are mutations?
-a change to the base sequence of DNA
-can be caused by errors during DNA replication
-rate of mutations can be increased by mutagenic agents
What is translocation?
-a sequence of bases is moved from one location in the genome to another
-this could be movement within the same chromosome or movement to different chromosomes
How can some mutations cause genetic disorders?
if a gamete containing a mutation for a type of cancer or a genetic disorder is fertilised, the mutations will be present in the foetus - hereditary mutations - passed from parent onto offspring
How does a mutagenic agent act as a base?
-chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA
How do mutagenic agents alter bases?
some chemicals can delete or alter bases
How do mutagenic agents change the structure of DNA?
some types of radiation can change the structure of DNA, which causes problems during DNA replication
What is transcription?
Transcription is when a gene is copied from DNA into messenger RNA(mRNA). The enzyme responsible for this is called RNA polymerase.
What is the name of the proteins that control transcription?
transcription factors
What is the role of transcription factors?
-in eukaryotes, TF move from the cytoplasm into the nucleus
-then bind to specific DNA sites called promotors, which are found near the start of their target genes
-TF control expression by controlling the rate of transcription
What are the two types of transcription factor and what is their role?
-activators and repressors
-activators - increase the rate of transcription - they activate RNA polymerase by helping the enzyme bund and increase transcription
-repressors….
