3.8.1 Control of Gene Expression Flashcards
What is a mutation
A change to the sequence of DNA bases or to the amount of DNA in a chromosome
What are some causes of DNA mutation
Ionising radiation (alpha particles, x rays, uv rays) chemicals (nicotine and other mutagenic agents)
What is a substitution
When one DNA base (eg T) is replaced with another (eg C)
Explain how a substitution can be a “silent” mutation
If the mutation changes a codon to a different codon that codes for the same amino acid (due to the degnerate nature of the code) then the mutation will not affect the polypeptide produced
Why are insertion or deletion mutations usually quite damaging
They cause a frame shift that means all codons following are affected
How can epigenetic changes affect the functioning of the genome?
Methylation of DNA can prevent transcription. Acetylation of histones causes DNA to be loosely associated so allows more transcription
What is gene expression controlled by ?
Altering the rate of transcription of genes
What are transcription factors ?
Proteins that bind to DNA and activate or deactivate genes increasing or decreasing the rate of transcription. They often bind to promoter regions of the DNA which is a section of DNA just upstream of the gene where RNA polymerase binds
Describe how oestrogen can activate transcription
It is a steroid hormone and can diffuse across the phospholipid bilayer. It binds to an oestrogen recetpor inside the cell causing a conformational change that reveals a DNA binding site. The hormone-receptor complex moves to the nucleus and binds to the promoter region of a gene activating transcription
What can epigenetic control determine ?
Whether certain genes are expressed, altering the phenotype
How does increased methylation of DNA repress a gene?
A methyl group is attached to the DNA coding for a gene(cytosine base). Increased methylation changes the DNA structure so that chromatin packs more tightly making it harder for transcription factors and RNA polymerase to bind. Hence there is reduced transcription
How does modification of histones affect gene expression ?
When histones are acetylated, the chromatin is less condensed so transcription proteins can bind to the DNA allowing genes to be transcribed. When acetyl groups are removed, the chromatin is highly condensed so genes in the DNA cannot be transcribed
What are histones ?
Proteins that DNA wraps around to form chromatin which makes up chromosomes
what is heterochromatin
tightly packaged chromatin associated with silenced genes
what is euchromatin
loosely packaged chromating associated with actively transcribed genes
How are epigenetic changes to a cells gene expression passed on
When a cell divides and replicates the changes are passed on to the daughter cells
What are stem cells ?
unspecialised cells that can develop into other types of cells
What is differentiation ?
the process by which a cell becomes specialised
What is totipotency ?
the ability of a stem cell to produce all cell types, including all the specialised cells in an organism and extra embryonic cells
What is pluripotency ?
the ability of a stem cell to produce all the specialised cells in an organism but not extra embryonic cells because the genes for these cell types have become inactivated
Where might you find a multipotent stem cell
In the adult body. For example bone marrow cells are multipotent and can differentiate into many types of blood cell
Where are totipotent and unipotent stem cells present ?
In the first few cell divisions of an embryo
What is an IPSC?
Induced Pluripotent Stem Cell. An adult cell can be induced to go back to a pluripoten state (this is done by artificially activating a few genes)
How do stem cells become specialised ?
different genes in their DNA become activated or inactivated. This may occur through epigenetic mechanisms
What are the advantages of patient stem cells over donor stem cells ?
Less risk of infection, no risk of rejection, no need to take immunosuppressant drugs as it is genetically identical to the patients cells
Why are there regulatory authorities for human embryo research ?
decide on max age of embryo allowed for research, stopping of cloning, judging what is acceptable by following codes of practice, checking the source of the stem cell is acceptable
How can stem cells be used in medicine ?
To replace damaged tissues, to study medicines or organs in vitro
What are the potential benefits of stem cell therapies ?
They could save many lives as stem cells can be used to grow organs for people waiting for transplants. They could improve the quality of life for many people
Give ethical issues raised by the use embryonic stem cells
Embryos have the right to life as they are a genetically unique individual, cannot consent. Some people have fewer objections to stem cells that have been artificially activated as the cells couldn’t survive past a few days anyway.
What is a cancer
A group of cells that divide in an uncontrolled fashion
Give features of a benign tumour
Cells generally stick gogether and are surrounded by a capsule. The are relatively normal in appearance and well differentiated. They have localised effects, can often be removed by surgery and rarely reoccur after treatment
Give features of a malignant tumour
Cells grow rapidly, are highly mutated and don’t stick together. They form metastases that spread around the body causing secondary tumors. They are treated with chemotherapy and immunotherapy and reoccur more frequently after treatment
What is a tumor supressor gene
A gene that normally detects DNA damage or acts to halt progression of the cell cycle
How could a tumour supressor gene be inoolved in cancer
If these genes are mutated to becom inactive or are epigenetically silenced (via methylation) then this would cause and increased rate of cell division
What is a proto-oncogene
In their normal form proto-oncogenes stimulate cell division but in response to controlled signals
What is an oncogene and how are they involved in cancer
Mutated proto-oncogenes that constatntly stimulate cell division. This could be because of mutation or elevated expression because of less methylation of the gene or more acetylation of histone proteins
How is oestrogen related to cancer
Oestogen activates transcription factors that may cause increased expression of proto-oncogenes leading to more cell division. Over time it is thought that high lifetime exposure to oestogen may lead to higher relative risk of some cancers
What is the Human Genome Project ?
A 13 year long project that identified all of the genes found in human DNA
How have scientists used data which is stored in databases from the Human Genome Project?
To identify genes and so proteins that are involved in disease. This information is used to create new drugs that target the identified proteins
