7.2 Factors affecting gene expression Flashcards
why does cell differentiation take place
to form different tissues and organs, and so different cells can go on to produce proteins specific to their cell types
how do scientists measure different degrees of cell differentiation
gel electrophoresis
how would a scientists find a known gene out of all the genes present in the DNA of a cell
- they use gene probes, which allow a specific section of DNA and mRNA in a cell to be identified
- the gene probe finds the unique sequence of nucleotides in DNA that make up the gene by using RNA with a complimentary sequence
describe the process of using gene probes to find a specific sequence of DNA or mRNA
- DNA from the cells under investigation is heated to break hydrogen bonds
- fluorescently labelled mRNA for the required gene is added (the probe)
what determines the type of cell and its function in the body
- the proteins present in a cell and the quantities of different proteins
what is transcription
the process by which the genetic code of DNA is copies into a complimentary strand of RNA before protein synthesis takes place
why is mRNA transcription an effective point to control gene expression
- because a single mRNA strand results in the production of many protein molecules
what is a transcription factor
proteins that bind to the DNA in the nucleus and affect the process of transcribing genetic material
what is a promoter sequence and where are they found
- the part of the DNA that the transcription factor binds to
- usually found just above the point of transcription
- some of them stimulate DNA transcription, by binding to the promoter sequence, by making transcription start from that point
what is an enhancer sequence, what happens when it is bound to
- a region on the DNA sequence that the transcription factor binds to
- when they bind here, they regulate the activity of DNA by changing the structure of the chromatin and deciding how open it is to RNA polymerase
- when its very open, the gene is active and whet it’s closed, it’s not active
- they can stimulate or prevent the transcription of a gene
what is pre-mRNA, and what are the modifications made to it
- the RNA that’s produced in the nucleus from transcription usually gets modified before it lines up on the ribosomes
- the introns are removed and sometimes some exons are removed, then they’re rejoined together by spliceosomes
what is RNA splicing
when spliceosomes join together the same exons in a variety of ways, so a single gene can produce different versions of functional mRNA that code for different amino acids which in turn produce different polypeptide chains
how is a protein modified
- protein modification can take place after they have been synthesised by being shortened or lengthened by enzymes to give a variety of other proteins
what is epigenetics
- a new area of research in biology
- studied genetic control by factors other than base sequences on DNA
what are the three intracellular systems that interact to control genes
- DNA methylation
- histone modification
- non-coding RNA
what’s a histone
a protein that provides structural support for chromatin
what is DNA methylation
- widely used mechanism in epigenetics
- addition of a methyl (CH3) group to cytosine, SILENCES a gene/ sequence
- methyl group is added by methyltransferase
- it can also modify the structure of histones
- methyl group changes structure of DNA molecule so transcription can’t occur
what is DNA demethylation
- the removal of a methyl group
- enables the gene to become active so they can be transcribed
what’s the problem with DNA methylation / demethylation
- researchers are finding that its associated with diseases, including a number of human cancers
describe a histone
- positively charged proteins
- DNA helices wind around histones to form chromatin, which makes up chromosomes
- the histones determine the structure of chromatin
what is histone acetylation
- an acetyl group (COCH3) is added to one of the lysines in a histone
- this opens up the structure and activates chromatin, allowing the genes to be transcribed
what is histone methylation
- a methyl group is added to lysine in a histone
- depending on the position of the lysine, methylation can cause activation or inactivation of the DNA
- however it is often linked to the silencing of a gene/ chromosome
what does non-coding RNA do
- they affect the transcription of DNA or modify the products of transcription
- genes or whole chromosomes can be silenced by ncRNAs
why does cell differentiation occur and what is it a result of
- it is a result of epigenetic modification to the genetic material of the cell
- it ensures a wide range of proteins are made within the cell as it differentiates
- it is a result of DNA methylation or demethylation or histone modification
define the following:
1. totipotent cell
2. pluripotent cell
3. multipotent cell
- undifferentiated cells that can form any of the different cell types
- undifferentiated cells that can form most of the different cell types
- cells that can form a limited range of the different cell types
whats cleavage (hehe)
- first stage of embryonic development
- forms a small mass of undifferentiated cells forming a hollow sphere (blastocyst)
- takes place as zygote moves along the oviduct towards the uterus
in terms of differentiation, what are the following stages of embryonic cell development:
1. embryonic stem cells
2. blastocyst
3. zygote
4. cells in umbilical cord
- totipotent
- pluripotent
- totipotent
- pluripotent stem cells
describe the process of the early stages of development
- cleavage results in a blastocyst (5-6 days), inner layer is pluripotent, outer layer forms placenta
- zygote moves along the oviduct towards uterus
- one large zygote forms a large number of small cells in early embryo (embryonic stem cells)
- earliest cells in embryo are totipotent
how do we use umbilical cord stem cells
- blood drained from umbilical cord and placenta is frozen and is a rich source if pluripotent stem cells
- used by the child or family members throughout life
- can’t happen for everyone because they would be too expensive to store
describe adult stem cells and what else are they called
- found among normal cells, stay undifferentiated until needed to produce a major cell type in the tissue or organ that they’re held in
- kept in bone marrow
- also called somatic stem cells
why aren’t adult stem cells used widely
- only a small number of adult stem cells in each tissue
- difficult to extract and most form a limited range of cells (multipotent)
- difficult to grow in the laboratory
how do undifferentiated cells form different cell types in cell development
- cells are predestined days after conception
- what they become is linked to their position in the embryo
- if they’re removed and grown externally, they will still produce the same cell type
- scientists are still unsure of the mechanism
- once cells are differentiated, they cannot return back to being undifferentiated
describe the evidence for cell determination
- the idea that cell determination occurs irreversible at an early stage was disproved by transplanting tiny patches of tissue from one area of an early embryo to another
- the cells formed the tissue linked to their new position, not their original position
- same experiment was completed with a slightly older embryo and scientists saw that cell determination was complete and cells differentiated to form the cells linked to their old position instead
how are the changes from embryonic stem cells to stem cells in the blastocyst to fully differentiated somatic cells brought about
- during cell differentiation some parts of the chromosome undergo supercoiling to prevent the genes being transcribed and other areas uncoil to open up and be transcribed.
- some genes are activated and some are silenced and its the combination of each of these factors that results in the characteristics in mature cells
what is an example of epigenetic control in human development
- fetal haemoglobin (2A, 2G) has a stronger affinity to oxygen than adult haemoglobin (2A, 2B)
- during human development, different versions of globin genes are switched on and off
- levels of globin chains change through the 40 weeks in pregnancy
- genes controlling fetal gamma globin are silenced around birth and those for beta globin are activated
how are adult stem cells used to make new body parts
- stem cells from the patient are seeded onto framework, which may be collagen based and from or donor or completely synthetic
- ## stem cells grow to form the required cells and new body part is returned to patient with no risk of rejection
what is therapeutic cloning
- an experimental technique that scientists aim to use to produce large quantities of healthy tissue to treat people with Alzheimer’s or type 1 diabetes etc.
describe the process pf therapeutic cloning
- produce healthy cloned cells from the patient by removing the nucleus from their normal cell and transfer to a human ovum that has had its nucleus removed
- newly formed pre-embryo develops and divides to produce embryonic cells with the same genetic information as the patient
- embryo is used as a source of stem cells
- stem cells are harvested, embryo is destroyed
- embryonic stem cells are cultured in a suitable environment so they differentiate into the required tissue
what is a problem with therapeutic cloning
- nucleus from the patients normal cells would have to be modified before being added to empty ovum, or the DNA would still carry the genetic mutation causing the disease
what are the potential pitfalls of stem cell therapy
- no one is quite sure how genes are switched on and off to form particular types of tissue
- there are concerns that stem cells could cause the development of cancers in the body
what are the advantages of stem cell therapy
- there are no cures for the many conditions that stem cell therapy may solve
- the ability to produce tailor-made cells to take over the function of damaged cells would revolutionise medicine
what drugs to people take after having an organ transplant
- immunosuppressant drugs
what’s the big advantage of embryonic stem cell therapy over other stem cell types
- they do not face the risk of rejection
how did iPS cells come about
- researchers took adult mouse cells and used genetic engineering techniques to make them pluripotent again
are the benefits of of iPS cells
- they overcome ethical objections to using embryonic tissue
- there is no risk of rejection if cells from an individual are used to make their own stem cells
who could benefit from stem cell therapy
- people with Parkinson’s disease
- those with type 1 diabetes
- those with damaged nerves, e.g. spine injuries, paralysed
- those in need for organ transplants
how would stem cell therapy help those with Parkinson’s disease
- uncontrollable tremors, body can’t move normally
- stem cell transplants can replace lost brain cells to restore dopamine production
- mature fetal cells have been transplanted into brains of adult humans, and produced dopamine for many years
- very hard to obtain fetal cells
How would stem cell therapy help those with type 1 diabetes
- cells stop producing insulin
- blood glucose concentration is uncontrolled
- Stem cell therapy can give them working pancreas cells and restore insulin production
- mouse embryonic stem cells were transplanted into mice with diabetes and it improved control of blood glucose
How would stem cell therapy help those with damaged nerves
- damaged nerve cells do not regrow, so those with major injury to their spines may be permanently paralysed
- embryonic stem cells have been transplanted into mice with damaged spines, and it has improved control of movement and limbs
what are the 4 ethical principles
- respect for autonomy - do not perform procedures on people unless you have their consent
- Beneficence - The aim of doing good, give medicine to relieve suffering
- Non-maleficence - do no harm
- Justice - Treat everyone equally, avoid discrimination
for those who are in support of embryonic stem cell use, what do they say about the ethical arguments
- the vast majority of embryos do not make it past the early stages of development to form living babies, so using a small number of early embryos is acceptable
- once a enough willingly donated embryos are received, it will reduce use of new embryos
- adult stem cells do not provide a good alternative, they are limited in terms of cell differentiation
for those who are against embryonic stem cell use, what do they say about the ethical issues
- it’s wrong it is abuse of human rights
- religious groups believe its is wrong to use a potential human life
- it is a potential human so it should have the same human rights as a fully grown adults
what is the ethical argument against therapeutic cloning
- they believe it can be taken further with cloned embryos implanted into a uterus as an act of human cloning
what are the ethical arguments against use of iPS cells, and what is the biggest issue it faces
- there are no ethical arguments
- they are more difficult to grow and manipulate than pluripotent embryonic stem cells
