7.2 Flashcards
what is cell differentiation
the process by which a cell becomes specialized for a particular function
why are gene probes important
they identify particular sections of DNA and mRNA
how does a gene probe work
the gene probe finds the unique sequence of nucleotides in the DNA using RNA with a complementary sequence
then it is isolated and heated to break hydrogen bonds and a florescent label mRNA is added so that the gene can be identified
how can gene probing be used to show that all genes are present in cells but not all are expressed
by comparing the DNA and RNA gene probing for proteins expressed in some cells and not all
define transcription
the process by which the genetic code of the DNA is copied to a complementary strand of (m)RNA
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
specific regions of DNA found just above the starting point for transcription, upstream from the gene that transcription factors bind to in order to stimulate transcription
what are enhancer sequences
specific regions of DNA found anywhere in the base sequence which transcription factors bind to in order to either stimulate or prevent transcription of a gene
how does a enhancer sequence stimulate or prevent transcription of a gene
they change the structure of chromatin so it becomes more or less open to RNApolymerase
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
what is the point of RNA splicing
a single gene may produce several versions of functional mRNA transcribed from the same section of DNA, these different mRNA sequences code for different arrangements of amino acids, different polypeptides and different proteins
how does RNA splicing occur
spliceosome removes an intron from in between two exons on a pre-mRNA molecule, the removed intron forms a loop and the 2 exons join together to create mature mRNA
define DNA methylation
the addition of a methyl group to a cytosine in the DNA molecule next to a guanine in the DNA chain
what does DNA methylation do
stops the transcription of a gene and modifies the structure of the histones
what enzyme is involved in DNA methylation
methyltransferase enzyme
define DNA demethylation
the removal of the methyl group from the methylated DNA enabling the DNA to become active so that it can be transcribed
what are histones
positively charged proteins which DNA helices winds around
what is chromatin
the DNA/protein complex that makes up chromosomes
what is heterochromatin
densely supercoiled and condensed chromatin where the genes are not available to be copied to make proteins
why does chromatin allow transcription to take place whereas heterochromatin does not
active chromatin is more loosely held together with uncoiled regions of DNA opening up more genes for transcription whereas heterochromatin is densely supercoiled so no genes are available for transcription
what is histone acetylation
an acetyl group (COCH3) is added to one of the lysines in the histone structure which opens up the structure and activates the chromatin allowing genes in that area to be transcribed
what is histone methylation
the addition of a methyl group (CH3) to lysine in the histone, can cause activation or deactivation of the DNA
what is the non-coding RNA (ncRNA) often used for
affects the transcription of the DNA code and modifies the products of transcription
how does ncRNA affect the X chromosome in females
X chromosomes in females are inactivated at random, active Xist gene produces Xist it causes the X chromosome to supercoil and condense to form a stable inactive Barr body
why are X chromosomes inactivated in some female cells
to maintain the balance of gene products in males
why does cell differentiation occur
unspecialized cells switch different genes on and off so that they can become more specialized
what can cause epigenetic changes
response to internal stimuli or changes outside the cell which effects the inside of the cell
define totipotent and give an example
undifferentiated cell which can form any one of the different cell types needed for a new organism (embryo)
define embryonic stem cell
undifferentiated cells of early human embryo with potential to develop into any specialized cell
define pluripotent and give an example
undifferentiated cell that can form most cell types needed for a new organism (stem cells)
what are somatic stem cells/adult stem cells
undifferentiated cells found in organs and tissues that can differentiate when needed to produce any one of the major cells found in that tissue/organ
define multipotent
a cell that can form a very limited range of differentiated cells within a mature organism
how is the formation of a cleavage different to regular cell division
cells divide repeatedly without interphase growth between divisions
what does the cleavage result in the formation of
a mass of small, identical and undifferentiated cells forming a hollow sphere known as a blastocyte
explain how potency changes as an embryo develops
earliest embryonic stem cells are totipotent but by the blastocyst when the embryo implants on the uterus the inner cells are pluripotent
where can pluripotent stem cells be taken from at birth
blood that drains from the placenta and umbilical cord
why would taking a babys pluripotent stem cells be beneficial
the stem cells will be available for the childs lifetime for stem cell therapy
what are the limitations of taking a baby pluripotent stem cells
it would take a lot of storage space
it would be expensive
precursor cells of conditions such as leukemia are already present in the blood at birth
how is cell determination related to its position and age of the cell (experiment)
early ‘skin’ cell from embryo transferred to early ‘brain’ cell and became brain tissue
older ‘skin’ cell from embryo transferred to early ‘brain’ embryo and formed skin tissue in the brain
why do fetuses have higher affinity for oxygen than adult human
adult human hemoglobin contains 2 alpha and 2 beta globin chains whereas embryos contain 2 alpha and 2 gamma globin chains
what are the issues of stem cell therapy
difficult to control the differentiation of cells
successful transplants have developed cancer
ethical objections of the use of embryonic stem cells
how are adult stem cells used to make organs
stem cells from the patient are seeded onto a framework which may be collogen based or completely synthetic and the stem cells grow to form the required cells then can be returned to the patient with no chance of rejection
why are adult stem cells better than embryonic stem cells
adult stem cells won’t be rejected and there are no ethical concerns
what is somatic cell/therapeutic cloning
an experimental technique used to produce embryonic stem cells from an adult cell donor
how is somatic cell/therapeutic cloning done (theoretically)
- produce healthy clones of cells from patient
- remove nucleus from cloned patient cells and put the nucleus in a human ovum which has had its nucleus removed
- mild electric shock to fuse nucleus and trigger development
- pre-embryo starts to develop and divide
- stem cells harvested from the embryo
- cells cultured in suitable environment differentiate into the required tissue
- transfer tissue/organ to patient
what is the main reasons for why somatic cell/therapeutic cloning is not used in everyday medical procedures
it is still unknown the exact triggers of that control cell differentiation
ethical issues - the patient nucleus must be genetically modified to be fused with ovum to stop genetic mutation
what are the reasons for stem cell therapy
gives cures to many conditions which currently have no cure
tailor-made cells would revolutionise medicine
what are induced pluripotent stem cells (IPSC)
adult cells that have been reprogrammed by the introduction of new genes to become pluripotent again
what are the advantages and disadvantages of induced pluripotent stem cells (IPSC)
+/ overcomes ethical objections
no risk of rejection
regenerate on their own
-/ not easy to differentiate into the tissue you want
it is hard to make cells become pluripotent and not always successful
it is unknown how long they will remain pluripotent
have shown potential to become cancerous
what are the 4 main ethical concerns with stem cell therapy
respect for autonomy - consent
beneficence - research for good purposes
non maleficence - do not harm
justice - share resources equally
