3.8.1 and 3.8.2 control of gene expression Flashcards
3.8.1 control of gene expression
what are the 3 main causes of mutation
- spontaniosly , unavoidable , random process
- chemicals / mutagenic compounds e.g from smoking
- radiation - from compounds
what are mutagens give two examples
things that can cause mutations
nitrogen dioxide , benzopyrene
what is a frame shift
the whole bases move , coding for diffrent amino acids as they are non-overlapping , codons are moved down
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Happen spontaneously
Natural, unavoidable
Random process
Cells have proofreading mechanisms to correct these errors but occasional errors go uncorrected.
The mutation rate varies from species to species, but is around 2 mutations per 100,000 genes per generation.
what is a silent mutation
when a mutation does not effect the protein that is formed
what is a nonsense mutation
when a codon is replaced with a stop codon
what is a missense
there are two
conservative - which does not change the property e.g if its non- polar
non-conservative - when the charactistic changes
how is it possible to have a mutation that has no effect on an organism’s phenotype ?
- silent mutation
- DNA mutations may occure in introns
what are chromosome mutations
non-disjunction which may cause a pheonotype of down syndrome . therefor more gene are going to be switched on which may cause too nuch proteins or enzymes to be made
Nondisjunction is the failure of the chromosomes to separate, which produces daughter cells with abnormal numbers of chromosomes.
what is development
Development involves the specialisation of cells and arranging them into functional units.
what is becoming adapt
cellular differentiation
what is it called when a sperm cells fuses with a egg cell
zygote
after a zygote has formed what is formed next and what type of cell e.g toti / uni potent
morula (about 16 cells )
totipotent
what can totipotent cells make
everycell in the body
that includes placenta and amniotic sac
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In an adult, all cells are specialised.
They have already been through the process of differentiation and cannot transform into another type of cell.
Only embryonic stem cells have the capacity to become any type of cell.
We call this ability….
totipotency
what is the definition of totipotency
Totipotent cells have the ability to develop into any cell found in the human body.
why is totipotency usefull
This is obviously useful during embryo development, as we start off as a single cell, but are eventually a collection of millions of different cell types.
when a cell specialises what happens to it
the specialisation is irreversible.
and the potential is less
what are multipotent cells
they are called adult stem cells and they can diffrintiate down a linearage
why is totipotency usefull during embryo development
as we start off as a single cell, but are eventually a collection of millions of different cell types.
what happens when a cell becomes fully specialised . e.g liver cell or brain cell
certain genes are turned off or on depending on there function and cannot be turned on again , however the gene is still there.
during the process of differentiation the what cellular functions change
- size
- shape
- metabolism
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in mammals differentiation is generally not reversible. however , it can be reversed in plants.
Stem cells from a developing embryo can develop into any cell type….
......so a patient with paralysis or brain damage could benefit if stem cells could be instructed to grow into new nerve cells.
cells that can differentiate are called
mammals _____
plants ________
mammels : stem cells
plants : meristematic
how can bone marrow transplants be used to help patients with leukaemia
Because bone marrow contains stem cell that can differentiate into blood cells…..
…..bone marrow transplants can help a patient with leukaemia develop healthy blood cells.
Stem cells from adult bone marrow have LIMITED uses though.
what is leukaemia
Leukaemia is cancer of the blood. The blood cells grow out of control, and abnormally. With abnormal white blood cells, a person with leukaemia can’t fight off disease.
stem cells are diffrent from other cells of the body because stem cells can both:
- self renew : make copys of them selves
- differentiate : spesilise for a spesific role
draw a diagram of a stem cell self renewing and differentaiting
two arrows from a stem cell
1st arrow pointing to an exact copy of the stem cell
2nd arrow pointing to a specialised cell
what is the definiton of :
potency
A measure of how many types of specialized cell a stem cell can make
what is the definiton of :
tetopotent
Totipotent- Can make all the specialized cells in the body, and the cells in the extra-embryonic membranes (chorion, amnion, placenta). Embryonic cells within the first couple of divisions are totipotent
what is the definiton of :
pluripotent
Can make all types of specialized cells in the body Embryonic stem cells are pluripotent
what is the definiton of :
multipotent
Can make multiple types of specialized cells, but not all types Tissue stem cells are multipotent
what is the definiton of :
unipotent
Can differentiate along only one lineage, and can produce only 1 type of cell
list the order of potency in order from highest to lowest :
Multipotent
Totipotent
Pluripotent
Unipotent
Totipotent > Pluripotent >Multipotent > Unipotent
why is it that some genes are never switched off and give examples
There are some genes that all cells express. These contain the instructions for essential processes, e.g:
Enzymes involved in respiration
Enzymes involved in membrane/organelle synthesis
tRNA production
what type of cell is insulin made from / expressed
beta - cells
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In unicellular and simple multicellular organisms each cell is capable of performing all functions.
Not so in more complex organisms.
All cells are derived by mitosis and so contain the same instructions, yet they develop differently and differentiate, i.e. they become specialised for particular functions.
Once differentiated they lose:
ability to divide.
totipotency i.e. ability to do everything.
Structure of specialised cells suits their function.
where can you find embryonic stem cells
blastocyst - a very early embryo
give a description of totipotent cells in the embryo
Found in the embryo in very early development (1-5 days). Can form all the tissues in the body, as well as the extra-embryonic membranes (chorion and amnion)
give the general featurs of stem cells
self renew
divide rarely
high potency
rare
give the general featurs of more spesilised cells (progenitors)
multipotent
divide rapidly
non self renewal
what are specialized cells
they are cells that can no longer diffrientate
where are blood stem cells found
bone marrow
what is the use of having multipotent cells
they replace cells that are damaged or unhealthy . because they are limmited to the number of cells they can diffrentiate to
give examples of unipotent cells
cardiomyocytes - form cardiac mucle
they have there own precurser stem cells
how can embryonic stem cells be used for medical applications ?
calls taken from an embryo can be cultivated to produce more embyo cells , these cells can then be specilised under spesific conditions to produce specilised cells.
what are the four main sources of stem cells
Embryonic Stem Cells:
Come from the embryo early in development. (Pluripotent)
Umbilical Cord Stem Cells:
Derived from umbilical cord blood, similar to adult stem cells.( Multipotent)
Placental Stem Cells:
Found in the placenta. (Multipotent)
Adult Stem Cells:
Despite the name, are found in the body tissues from the foetal stage of development into and throughout adulthood. (Multipotent)
describe the process of cultivating and spesilising stem cells
- embryonic stem cells taken from
the inner cell mass - culture in the lab
to grow more cells - they then diffrentiate diffrently in diffrent conditions
The big challenge for scientists is to learn how to control these fascinating cells. If we could force embryonic stem cells to make whatever kind of cell we want, then we would have a powerful tool for developing treatments for disease. For example, perhaps we could grow new insulin-producing cells to transplant into a patient with diabetes.
what does IPS stand for
what is it trying to do
how would it work
induced pluripotent stem cells
the ability to take adult cells and turn them into stem cells
- reprogramming : proteins called transcription factors are added that ‘switch on’ the long dormant genes nessery for a cell to be pluripotent
- differentiation : given the right chemical stimulus a cell can be encouraged to specilise into a complimentory diffrent type of cell
what are the benifits of using stem cells
great potential to treat a wide variety of diseases from diabetes and paralysis
organs developed from a patient’s own stem cells reduces the risk of organ rejection and the need to wait for an organ donation
adult stem cells are already used successfully in a variety of tratments acting as proof of benefits
what are the risks / issues of using stem cells
stem cells cultured in the lab could become infected with a virus which could be transmitted to the patient
there is a risk of cultured stem cells accumulating mutations that can lead to them develpoing into cancer cells
low number of stem cells donors
what are the social issues of using stem cells
it is possible for embryonic stem cells to be collected before birth (from amniotic fuild) or after birth (umbilical cord blood ) and stored by a clinic - but this can be expensive and isn’t an option for everyone
a lack of peer-reviewed clinical evidance of the success of stem cell tratment
educating the public sufficientlyabout what stem cells can and cannot be used for.
what are the ethical issues of using stem cells
stem cells may be sourced from unused embryos produced in ivf treatment - is it right to use them ? who gives permission ?
is it right to create embryos through cloning and then destroy them ? who owns the embryo ?
should an embryo be trated as a person with human rights ? or as a commodity ?
compare an embryonic cell with a liver cell and how there genes are activated
An embryonic stem cell will have all genes turned on.
A specialised liver cell will have the genes that code for the function of a liver cell switched on, as shown on the right, others switched off.
What are transcription factors?
They are proteins which move in from the cytoplasm and bind to DNA at specific sites called PROMOTERS, which are found near the start of a target gene ( about 100 base pairs upstream)
what do transcription factors do
Transcription factors enable RNA Polymerase to attach to the start of the gene and BEGIN TRANSCRIPTION:
waht are the two types of transcription factors
ACTIVATORS – they help RNA polymerase bind and activate transcription.
REPRESSORS and decrease the rate of transcription because they slow or prevent RNA polymerase from binding
transcription factors ,true or false :
All transcription factors are present in all cells
false
transcription factors ,true or false :
They are made of carbohydrates
false
transcription factors ,true or false :
They bind to promotors
true
transcription factors ,true or false :
All transcription factors are activators
false
transcription factors ,true or false :
Some are present in particular cells
true
transcription factors ,true or false :
Some are present at a particular stage of development
true
transcription factors ,true or false :
They are all created in an inactive form and then are activated by other molecules
false
transcription factors ,true or false :
They are only made in the nucleus
false
describe the structure of a DNA nucliotide
phosphate group , deoxyribose suger , nitrogenous bases
where does transcription take place
in the nucleious of the cell
define an exon
it is the coding region of the genone
name the enzyme involved in joining adjasent RNA nucleotides in transcription
RNA polymerase
why is the genetic code described as degenerate
as despite a mutation many codons can code for a singular amino acid
there are many codons that code for the same amino acid
name 4 types of mutation
point mutation
deleation
addition
insertion
substitution
translocation
how does oestrogen regulates transcription
- oestrogen is lipid soluable and there for diffuses through the cell surface membrrane
- oestrogen binds to the receptor of the transcription factor
- the transcription factor changes shape because of this
- transcription factor binds to promotor region and causes an increase or decrease in transcription of that gene
is oestrogen an activator or represor
its both
oestrogen binds with a transcription factor to make what
oestrogen-oestrogen
waht are the two main ways in which epigenetics are caused
DNA methilation
histone acetilation
what are some main causes of epigentics
diet
pollution
smoking
alcohol
radiation
chemical
enviroment
medicine
microbiomes
exercise
financial stress
drugs and abuse
disease
seasonal correlations
mental state
social interactions
where does the methyl group attatch to ?
the cytosine nucliotide
where does the acetyl groups bind to
they bind to the histone tails
what does methylation of cytosine do
it causes the DNA molecule to coil around the histones more , this makes it harder for transcription factors to bind and or polymerase to act
this silences / reduces transcription
what does histone modification do
DNA is negativly charged , acetyl groups (which are negative) bind to the histones , this shares the charge which weakens the bond between the DNA and histone.
also attacting proteins that condense the DNA - histone complex
this causes the DNA to be less coiled around the DNA , more transcription factors bind which can lead to an increase in translation
how many genes are there all together
around 20,000
how can epigenetics cause cancer
by increasing/decrease the transcription of or the tumour suppresor gene or the proto onco gene
what is HDAC and what does it do
HDAC ( histone deacetylase) inhibitors
they block the enxyme which removes acetyle groups off histones , this then causes the gene to be more expressed increasing transcription
’ epigenetic involves permanent changes to the DNA that can be passed on from parent to offspring ‘
evaulate this statment :
true - epigenetic changes in the DNA can be heritable (transgenarational inheritance )
flase - enviromental factors may add or remove them
what is the name given to chromatin that is tightly wounded
heterochromatin
what is the name given to chromatin that is loosly wounded
euchromatin
draw out a methyl group
CH3 +
draw out a acetyl group
CH3CO -
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Incorrect activation of a normally inactive gene linked with cancer e.g. tumour suppressor gene / oncogenes
Patients with colorectal cancer had less DNA methylation that normal = higher than normal gene activity (oncogenes turned on/overexpressed)
describe the protoncogene
proto-oncogene, stimulates cell division (like the accelerator on a car)
describe the tumour supressor gene
Genes normally control cell division and division is halted by tumour suppressor genes when sufficient cells have been produced for growth and repair (like the brakes on a car).
describe what small interfearing RNA is
In eukaryotes and some prokaryotes, translation of the mRNA produced from target genes can be inhibited by RNA interference (RNAi)
Small, double-stranded RNA molecules called small interfering RNA (siRNA) bind to mRNA that has been transcribed from target genes (the genes to be ‘silenced’) as their base sequence is complementary
Each siRNA is attached to a protein complex which is able to breakdown the mRNA that has been transcribed from target genes (the genes to be ‘silenced’)
Therefore, the mRNA is unable to be translated into proteins
describe how RNA interface works
Double stranded RNA (dsRNA) is produced by RNA-dependent RNA polymerases (RDRs)
dsRNA is hydrolysed into smaller fragments, roughly 23 nucleotides long, called small interfering RNAs (siRNAs)
In the cytoplasm, siRNAs bind to protein complexes which use energy from ATP to separate the two strands of the siRNA
This exposes the nucleotide bases so they are able to pair with bases from an mRNA molecule
Once the target mRNA leaves the nucleus and enters the cytoplasm, single-stranded siRNA binds to the target mRNA throughcomplementary base pairing
The mRNA molecule is cut into fragments by theenzyme/protein complexassociated with the siRNA
Cut mRNA cannot be translated and thereforewill not produce proteins
After the target mRNA has been cut up into fragments, the fragments are broken down into RNA nucleotides by enzymes
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siRNAs created againstviral genetic material will signal for their degradation and stop the virus from using the host’s cellular machinery to replicate itself
siRNAs can be used in cancer treatment by targetingoncogenesthat have been expressed or upregulated
This reduces the number of proteins produced that can lead to cancer or that maintain cancerous growth
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When a CH3 ( methyl) group is joined onto a something we say that METHYLATION has occurred.
Methylation of DNA is a way of regulating gene expression by controlling whether TRANSCRIPTION or TRANSLATION occurs.
If too much or too little METHYLATION occurs there can be problems.
HYPER = Too much HYPO = Low
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When functioning normally proto oncogenes stimulate cell division by producing proteins that make the cell divide.
If a mutation occurs in a proto oncogene, the gene can become overactive and stimulate the cells to divide uncontrollably. This mutated proto oncogene is called an ONCOGENE and can lead to CANCER
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When functioning normally these inhibit and slow down cell division by producing proteins that stop cells dividing or cause them to self destruct ( apoptosis)
If a mutation occurs a tumour can develop.
what are transcription factors made of
proteins
