8.2 Gene expression Flashcards
What is cell differentiation?
becoming specialised for a specific function
What is an example of a gene that is permenantly switched on?
resp enzyme genes
protein synthesis genes
What are examples of genes that are permenantly switched off?
insulin production in salivary glands
adrenaline production in skin cells
What is an example of a gene that can be switched and off as needed?
Lac operon = codes for enzyme that digests lactose in bacteria
switches on when lactose is present to resp it
siwtches off when no lactose is present
What are stem cells?
undifferentiated cell that can continuely divide and replicate
What are the 4 types of stem cells?
totipotent
pluripotent
multipotent
unipotent
What is a totipotent stem cell?
stem call can differentiate and divide into ANY type of cell
What is an example of a totipotent stem cell?
zygote in animal cells
all plant cells
What are pluripotent stem cells?
stem cells that can differentiate and divide into ALMOST any cell type
What is an example of pluripotent cells?
embryonic cells
What is a multipotent stem cell?
stem cell that differentiates and divides into a LIMITED no of cell types
What are examples of multipotent stem cells?
adult somatic cells
bone marrow cells
What are unipotent stem cells?
stem cells that differentiate and divide into ONE type of cell
What are examples of unipotent cells?
adult body tissue
skin cells
What does iPS stand for?
induced pluripotent stem cells
What are iPS cells?
unipotent cells that have had their genes and transcription factors induced to form pluripotent cells that limitlessly divide
How are iPS cells made?
inducing specific genes (turning them on)
inducing transcription factors (switching them on)
so that they express themselves to form pluripotent cells
What are the use of iPS cells?
to treat human disorders
What cell types can iPS differentiate into?
neural cells
muscle cells
organs
blood cells
bone cells
What conditions can iPS treat?
leukemia = replace blood cells
burns = skin replacement and grafting
Type 1 diabetes = replace beta cells
damage from heart attack = replace cardiac cells
oesteoparosis = replace bone cells
What are the issues of using iPS to treat human disorders?
doesnt always work
risk of cancer
ethical issues of using embryonic cells
How can iPS lead to a risk of cancer?
they can divide limitlessly so there is a risk of uncontrolled mitosis forming tumours
What is the issue of using embryonic stem cells for treatments of disorders?
use therapeutic clones = they take the cells from the embryo, differentiate the cells and then destroy the embryo
What must happen for transcription to occur?
must be triggered by a protein (transcription factor) for the gene to be expressed as a protein
Where does the transcription factor bind to on DNA?
the promoter region
What is the promoter region of DNA?
the specific sequence of bases at the start of DNA
What does it mean that oestrogen is a steroid hormone?
it is lipid soluble and can pass through the membrane by simple diffusion
What is the role of a transcription factor?
bind to the promoter site on DNA to initiate transcription
Describe how oestrogen initiates transcription
- oestrogen binds to transcription factor that is already in the cytoplasm by it receptor site
- the binding of oestrogen causes the transcription factor to change shape so that it is complimentary in shape to the promoter region on DNA
- transcription factor enters nucleus via nucleur pore
- transcription factor binds to promoter region on DNA and stimulates RNA polymerase
What is epigenetics?
the ability to control gene expression by switching genes on or off by epigenetic markers
What does epigenetics show?
how environmental factors can make changes to the function of your genes and your gene expression
What happens when monozygotic twins increase in age?
their appearance becomes increasingly different to each other - different phenotypes as different genes are expressed because they have different epigenetic markers as a result of different environments and lifestyles as they grow up
What are the 2 epigenetic modifications?
DNA methylation
Histone modification
What is DNA methylation?
addition of a methyl group to a base (normally cytosine)
How can heavy DNA methylation reduce transcription?
reduces the recognition by transcription factors to bind to
so they are less likely to be transcribed
What is histone modification?
histones are proteins made of amino acids
the amino acids can be methylated, phosphorylated and methylated
this determines how tightly packed the nucleosome is
How is transcription reduced by histone modification?
if the nucleosome is more tightly packed, the genes are hidden and are inaccessible to transcription factors
How do silencing epigenetic markers work to switch genes off?
- it is the result of histone methylation = higher affinity between DNA and histones
- chromatin is more condensed
- gene is less accessible to transcription factors
- gene is less likely to be express = switched off
How do activating epigenetic markers work to switch on genes?
- it is the result of histone acylation = lower affinity between DNA and histones
- loose packing of the nucleosome
- chromatin is less condensed
- gene is more accessible to transcription factors
- gene is more likely to be expressed = switched on
What is dsRNA?
double stranded RNA
What is siRNA?
small interferring RNA
What is RNA interference (RNAi)?
translation is inhibited by cutting up the mRNA before translation so the gene is silenced
What is the process of gene silencing by RNA interference?
- enzyme cutes dsRNA into smaller siRNA molecules by hydrolysing phosphodiester bonds
- one of the siRNA strands combines with an enzyme
- siRNA guides enzyme to mRNA so it can complementary base pair with a specific section of mRNA
- enzyme is correctly positioned to cut mRNA into smaller pieces
- mRNA can not be translated at the ribosome and the gene is silences as the gene protein is not found
What do cells loose the ability to do once differentiated?
loose the ability to divide
How are cells able to control their division?
loosing its ability to divide by differentiating
apoptosis = controlled cell death
What is a tumour?
a large mass of abnormal cells that form a growth and can be found in any tissue
How do all tumours cause damage to the body?
by restricting blood flow by causing blockages or obstruction
exerting pressure on organs and taking up space from organs
Wha are the 2 types of tumours?
benign and malignant
Which type of tumour grows more rapidly?
malignant
Which type of tumour is cancerous?
maligant
Which type of tumour cannot spread?
benign
What does metastasise mean?
spread
Why cant benign tumours spread?
they produce adhesion molecules which stick cells together and stick to the tissue to form a capsule surrounding the tumourous cells so preventing metastisis
Are benign tumour cells differentiaed or not?
remain differentiated = abnormal specialised cells
How can benign tumours be treated?
can be easily cut out as they are contained in a capsule
How are benign tumours developed?
inflammation and infection
injury
diet
genetics
toxins and radiation
Are malignant tumour cells differentiated or not?
cells become undifferentiated back to stem-like cells
How are malignant cells able to spread and metastisise?
they have the ability to secrete chemicals to generate their own blood supply for resp and nutrients
they are able to spread through the bloodstream and lymphatic system
How are maligant tumours treated?
surgery to remove but alongside chemotherapy or radiation therapy
What are the causes of malignant tumours?
UV or x-ray exposure
tabbacco smoke
(mutagenic agents)
processed food
aesbestos
What is the cause of uncontrolled mitosis therefore tumour development majority of the time?
there is a mutation in genes regulating mitosis
What are the 3 ways tumours can develop?
gene mutation in a tumour suppressor gene or proto-oncogenes
abnormal methylation of tumous supressor genes or oncogenes
increase in oestrogen concentration
What is the role of tumour supressor genes?
expresses a protein that slows cell division and causes apoptosis where a mutation is detected in DNA replication
What happens when a tumour suppressor gene is mutated?
mutation causes the gene to permenantly switch off = uncontrolled cell division, mutated cells are not detected and divide rapidly, apoptosis is inhibited
What is the role of proto-oncogenes?
expresses a protein involved in the initiation of DNA replication and mitosis
What is an oncogene?
a mutated proto-oncogene
What does a oncogene do?
permenantly activated proto-oncogene causes continuous cell division
How does abnormal methylation affect tumour suppressor genes?
hypermethylated = increased number of methyl groups
chromatin is more condensed
reduced gene expression
gene it switched off = inhibited apoptosis
How does abnormal methylation affect oncogenes?
hypomethylated = less methylation
chromatin is less condensed
gene is more likely to be expressed
gene is permenantly switched on = continuous cell division
How does a tumour develop in breat tissue?
oestrogen starts to be produced by fat cells in breast tissue after menopause
How does an increases oestrogen concentration lead to tumour development?
more oestrogen binds to transcription factors that bind to proto-oncogenes, permenantly switching those genes on = increased cell division
How do tumours in breast tissue grow as a result of increased oestrogen conc?
cells in the tumour continue to produce oestrogen which increases the size of the tumour
it is an example of positive feedback
How can tumour growth caused by an increased oestrogen conc be limited?
introduction of siRNA to cut mRNA before it is translated to proto-oncogenes
