8.2 Gene expression Flashcards
What are differentiated cells
Cells that are specialised for a particular function
What is an example of a gene that is permanently switched on
Genes for respiratory enzymes
What is an example of a gene that can be switched on and off
Lac operon, which is a digests lactose in bacteria
What are stem cells
Undifferentiated cells
What can all stem cells do
Continually divide
What can totipotent stem cells do
Divide and produce any type of body cell
What can pluripotent stem cells do
Divide and differentiate into almost any type of cells
What is the only mammalian cell that is totipotent
Zygote
What plant cells are totipotent
All
What are multipotent stem cells
Divide and differentiate into limited number of cells
Where might you find multipotent stem cells in humans
Bone marrow
What mammalian cells are pluripotent
Embryonic
What can unipotent stem cells do
Divide and differentiate into 1 type of cell
What type of mammal would you find multipotent and unipotent stem cells
Mature mammals
What does iPS cells stand for
Induced pluripotent stem cells
What type of cell becomes an iPS cell
Unipotentn stem cell
What happens to the unipotent stem cell to become iPS cells
Inducing genes and transciption factors to express themselves
Why are iPS cells more valuable than embryonic stem cells
iPS cells can limitlessly divide whereas embryonic stem cells can limitly divide
What risk arises when using iPS
Cancer
Why is there a risk of cancer when using iPS cells
As the cells can divide limitlessly
What type of clone is used to specific produce embryonic stem cells
Therapeutic
How effective are iPS cells
Not that effective and therefore don’t always work
What triggers transciption to start
The binding of a protein to the DNA
What is the name of the site on DNA where the transcription factor binds
Promoter region
If the transcription factor didn’t bind to the DNA at the promoter region, what happens to the gene
The gene is switched off and is not expressed as a protein
What does steroid hormone mean in terms of transport across membranes
Lipid soluble so simply diffuse
What is the example of the steroid hormone on AQA spec
Oestrogen
What is the role of the steroid hormone oestrogen in initiating transcription
- Oestrogen simple diffuse into the cytoplasm of the cell.
- Oestrogen then binds to the transcription factor that is already in the cytoplasm.
- The transcription factor changes shape so is now complementary in shape to the promoter region on DNA
- The binding of the transcription factor stimulates RNA polymerase
After oestrogen diffuses into the cell, what happens
Oestrogen binds to the transcription factor
What is the effect of oestrogen binding to the transcription factor
The transcription factor changes shape to become complementary to the promoter region
What does the shape change in the transcription factor, make the transcription factor complementary to
The promoter region on DNA
What does the binding of the transcription factor to the promoter region of DNA stimulate
RNA polymerase
Define epigenetics
Ability to control gene expression by factors other than change in DNA base sequence
What does epigenetics do the genes
Switches them on and off
What are the 2 types of epigenetic modifications
- DNA methylation
- Histone modification
What DNA bases usually is methylated
Cytosine
What happens to the base when DNA methylation occurs
A methyl group (-CH3) is added to a base
What is the effect of DNA methylation
Reduces the ability of the the methylated base to be recognised in transcription so reduces ability of gene to be expressed
Why are heavily methylated DNA bases less likely to be transcribed
As transcription factors are less likely to bind
What are the 2 types of histone modification
- Histone methylation
- Histone Acetylation
With histone methylation, what happens to the affinity between DNA and histones
Increase in affinity
What is the effect on the chromatin when the affinity between DNA and histones is high, histone methylation
Chromatin is more condensed
When chromatin is more condensed, what does this mean for the genes
The genes are less accessible to transcription factors
When genes are less accessible to transcription factors what does this mean
Less likely to be expressed, the gene is essentially switched off
What is the name of the marker associated with histone methylation
Silencing
What is the affinity like between DNA and histones in histone acetylation
Lower affinity
What does low affinity between DNA and histones mean for chromatin
Less condensed
When chromatin is less condensed, what does this do to the accessiblity of the gene
More accessible to transcription factors
When genes are more accessible to transcription factors, what does this mean in terms of expression
More likely to be expressed, switched on
What does amino acids being methylated or acetylated determine
How tightly packed the nucleosome is
What does siRNA stand for
Small interfering RNA
What is siRNA made from
Formed from dsRNA (double stranded RNA)
What does dsRNA stand for
Double stranded RNA
What happens to dsRNA to form siRNA
dsRNA is broken into smaller siRNA by an enzyme
What bonds does the enzyme the cuts dsRNA, catalyse the hydrolysis of
Phosphodiester bonds
Once the siRNA strands are formed, what happens to the strands
The hydrogen bonds between the 2 strands are hydrolysed so a single strand is produced
What does the single strand of siRNA do
Combines with an enzyme
What is the name of the enzyme the siRNA combines with
RISC
What does RISC stand for (not on spec)
RNA induced silencing complex
What happens to the siRNA and enzyme
The siRNA guides the enzymes to mRNA where there is complementary base pairs between siRNA and mRNA
Once the siRNA and mRNA have formed complementary base pairs, what does the enzyme then do
Enzyme then cuts the mRNA into smaller pieces, hydrolysing the phosphodiester bonds
What is the effect of cutting the mRNA into smaller pieces
The mRNA cannot be translated at the ribosome
If the mRNA cannot be translated, what is the gene said to be
Silenced as the gene protein is not formed
What happens to the smaller pieces of mRNA that cannot be translated
Hydrolysed into individual nucleotides that can be reused
What is a tumour
A group of abnormal cells that form a growth
What are the 2 types of tumours
- Beign
- Malignant
What type of tumours cause harm to the body
All types
How may a tumour cause harm
- Blockages, obstructions
- Damage the organs by pressure
What is the growth rate of a beign tumour like
Slow
What type of molecules do beign tumours make
Adhesion molecules
What do the adhesion molecules of a beign tumour result in the formation of
A capsule around the abnormal cells
What does the capsule around a beign tumour mean the tumour cannot do
Metastasise, spread out
Do the cells or beign tumour tend to be differentiated or undifferentiated
Differentiated
Why are beign tumours relatively easy to cut out
Because all the abnormal cells are contained within a capsule
Is the impact of a beign tumour localised
Yes
What may lead to the formation of a beign tumour
- Inflammation
- Injury
- Diet
- Genetics
- Toxins
- Radiation
What is the growth rate of a malignant tumour like
Fast
Are tumour cells in a malignant tumour differentiated or undifferentiated
Undifferentiated
With the cells being undifferentiated in a malignant tumour, what does this mean they can form
Can generate own blood supply
What does the undifferentiated malignant tumour cells secrete
Chemicals which can form the tumours own blood vessels
Why does the formation of the tumours own blood vessels mean the malignant tumour cells can metastasise (move)
Can break out from the group of tumour cells and enter the blood supply
Why are malignant tumours hard to cut out
As no capsule and the cells can metastasise
What might cause a malignant tumour
- UV or x-ray exposure
- Tobacco smoke
- Aspestos
- Processed food
In the majority of cases, what is the main reason as to why cancer cells arise
The gene that regulate mitosis mutates
What is the name of transcription factors that stimulate gene expression
Activators
What is the name of transcription factors that inhibit gene expression
Repressors
What is the role of the protoncogenes
Express protein that involves in the initiation of DNA replication and mitosis
What are oncogenes
Mutated protoncogenes
What do oncogenes cause
Permanent activation of the protein that is involved in the initiation of DNA replication and mitosis
What are tumour-suppressors role
Express proteins that slow down cell division and cause apotosis which DNA replication errors are detected
What happens when a tumour suppressor gene is mutated
The gene that codes for the protein that slows down cell division is permanently switched off
When the protein that slows down cell division is switched off, what is the result
Cell division is uncontrolled
When a tumour suppressor gene is mutated apotasis is inhibitied, what is the effect of this
Mutated cells are not identified and therefore programmed cell death does not occur so mutated cells divide and lead to tumour formation
Are oncogenes hypomethylated or hypermethylated
Hypomethylated
When oncogenes are hypomethylated, what happens to the chromatin
Less condensed chromatin
How does hypomethylation of oncogenes lead to permanently switching on the protein that initiates DNA replication and mitosis
- Chromatin is less condensed
- Gene is more accessible to transcription factors
- Increased expression of gene/ the gene is permanently switched on
Are tumour suppressor genes hypomethylated or hypermethylated
Hypermethylated
How does hypermethylation of a tumour suppressor gene inactivate the gene
- More condensed chromatin
- So gene is less accessible to transcription factors
- Gene is less expressed
- So gene is switched off
What do tumour cells in breast tissue do
Produce oestrogen
What does the production of oestrogen from the tumour cells in breast tissues do to the size of the tumour, and what is this an example of
- Increase the size of the tumour
- Example of positive feedback
How does oestrogen increase the number of tumour cells
- Oestrogen binds to transcription factors
- Transcription factors the bind to the protoncogene
- This then permanently turns on the protonogene
- So DNA replication and mitosis occur uncontrollably
What can be used to slow down the tumour growth
Use siRNA which leads to mRNA being cut up so the proteins are no translated
BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins.
Mutations in BRCA1 and BRCA2 can cause cancer (lines 1–2). Explain how (3 marks)
- Change in DNA base sequence/triplet;
- Change in (sequence of) amino acids
OR
Change in primary/tertiary/3
0 structure; - (Results in) rapid/uncontrollable cell division;
Effective treatment of ER-positive breast cancers often involves the use of drugs
which have a similar structure to oestrogen (lines 9–10).
Suggest and explain how these drugs are an effective treatment of ER-positive breast
cancers. (3 marks)
- (Drug) binds to (oestrogen/ER)
receptor; - Prevents binding of
oestrogen/hormone; - No/fewer transcription factor(s)
bind to promoter
OR
RNA polymerase not
stimulated/activated;
Treatment with drugs might be able to reverse the epigenetic changes that cause
cancers (lines 16–17). Suggest and explain how. (3 marks)
- (Drugs could) increase methylation of
oncogene(s); - (Drugs could) decrease methylation of tumour
suppressor gene(s); - (Increased) methylation of DNA/gene(s)
inhibits transcription/expression (of genes)
OR
Decreased methylation of DNA/gene(s)
stimulates transcription/expression (of genes); - Decreased acetylation of histones inhibits
transcription/expression (of genes)
OR
(Increased) acetylation of histones stimulates
transcription/expression (of genes);
