Topic 7.2 Factors affecting gene expression Flashcards
Define cell differentiation
the process by which a cell becomes specialised for a particular function
What are transcription factors?
proteins that bind to the DNA in the nucleus and affect the process of transcribing the genetic material
What do gene probes do?
allow a particular section if DNA or mRNA to be identified
What is the most common way of controlling gene expression?
switching on and off the transcription of certain genes
What is transcription?
the process by which the genetic code of DNA is copied to a complementary strand of RNA (mRNA) before protein synthesis can take place
What are promoter sequences?
specific regions on the DNA to which transcription factors bind to stimulate transcription
Where are promotor sequences usually found?
just above the starting point for transcription upstream of the gene (5’ end)
What are enhancer sequences?
specific regions on the DNA to which transcription factors bind and regulate the activity of the DNA by changing the structure of the chromatin, making it more or less available to RNA polymerase so either stimulating or preventing transcription
What is an open chromatin structure linked to?
active gene expression
What is a closed chromatin structure linked to?
gene inactivity
What is pre-mRNA?
the mRNA that is transcribed directly from the DNA before it has been modified
What are spliceosomes?
enzyme complexes that act on pre-mRNA, joining exons together after the removal of introns
Define DNA methylation
the addition of a methyl (-CH3) group to a cytosine in the DNA molecule next to a guanine (CpG site) in the DNA chain and prevents transcription
What is DNA demethlyation?
the removal of a methyl group from methylated DNA allowing genes to become active so they can be transcribed
What is chromatin?
the DNA/protein complex that makes up chromosomes, included the protein histones
How does DNA methylation silence genes?
the methyl group changes the arrangement of the DNA molecule so prevents transcription from taking place
Define heterochromatin
densely supercoiled and condensed chromatin where the genes are not available to be copied to make proteins
Define histone acetylation
the addition of a acetyl group (-COCH3) to one of the lysines in the histone structure, which opens up the structure and allows genes in that area to be transcribed
Define histone methylation
the addition of a methyl group (-CH3) to a lysine in the histone structure and depending on the position of the lysine, methylation may cause activation or inactivation of the DNA region
What is meant by totipotent?
describes an undifferentiated cell that can form any on of the different types of cell needed for an entire new organism
Define pluripotent
describes an undifferentiated cell that can form most of the cell types needed for an organism except the placenta
What are embryonic stem cells?
the undifferentiated cells of the human embryo which have the potential to develop into many different types of specialised cell
What are somatic/adult stem cells?
undifferentiated cells that are found among differentiated cells in a tissue or organ that can differentiate when needed to produce any one of the major cell types found in that particular tissue or organ
Define multipotent
a cell that can form a very limited range of differentiated cells within a mature organism
Define therapeutic cloning
an experimental technique used to produce embryonic stem cells from an adult cell donor
Describe the process of therapeutic cloning
- remove nucleus from adult cell from the patient and transfer to a human ovum which has had its nucleus removed
- mild electric shock fuses the nucleus with the new cell and triggers development
- the new pre-embryo cell develops and divides which produces embryonic cells with the same genetic material as the patient
- embryonic stem cells cultured in a suitable environment to differentiate into required tissue
- differentiated cells transferred to patient without rejection problems
In therapeutic cloning, what additional factor must be considered in the treatment of genetic diseases?
the adult stem cell nucleus would need to be genetically modified before being added to the ovum, otherwise the cultured stem cells would carry the gene mutation
Identify the negatives of stem cell therapy
- use of embryo
- risks in the development of cancers
- e.g. evidence bone marrow transplants used to overcome leukaemia puts patients at a higher risk for developing other cancers
Identify the positives/benefits of stem cell therapy
- no cures for many conditions that stem cell therapy could solve
- gives the ability to produce tailor-made cells to take over the function of damaged ones
- avoids risk of rejection
What are induced pluripotent stem cells?
iPS cells are adult cells that have been reprogrammed by the introduction of new genes to become pluripotent again
Give the benefits of iPS
- overcomes ethical objections of using embryonic tissue
- treats a wide range of diseases caused by faulty cells
What are the negatives of using iPS?
- tendency to becomes cancerous very quickly
- persuading cells to become pluripotent is very difficult
- differentiating the cells is also very difficult
Give examples where induced pluripotent cells could be used to cure diseases
- parkinson’s disease
- type 1 diabetes
- damaged nerves
- organs for transplant
How would iPS cure Parkinson’s disease?
- replace lost brain cells
- restore dopamine production
How would iPS cure Type 1 diabetes?
-give patients a working pancreas so blood glucose control
Is iPS used in the medical world?
no they have only done studies on animals
Name the 4 ethical principles
- respect for autonomy, respect for individuals (not performing procedures without consent)
- beneficence, the aim of doing good (e.g. giving medicine to relieve suffering)
- non-maleficence, to do no harm
- justice, treat everyone equally and fairly share resources
State the similarities between embryonic stem cells and induced pluripotent stem cells (iPS)
- both have the potential to divide indefinitely
- both have the potential to divide into a number of cell types
State the differences between embryonic stem cells and induced pluripotent stem cells (iPS)
- no/less ethical objections using iPS
- iPS were adult cells, embryonic taken from morula/inner cell mass
- iPS have a gene added
- iPS can form adults cells whereas embryonic form younger cells
- rejection issues with embryonic cells, patient-matched cells produced from iPS
Describe epigenetic modification
- changes that affect gene expression/activation
- e.g. DNA methylation, histone acetylation
- involved in differentiation/ change in function
