Topic 7.2 Factors Affecting Gene Expression Flashcards
(34 cards)
1
Q
RNA splicing
A
- Modifications of pre-mRNA involve the removal of introns and exons.
- The exons are joined together with splicosomes to produce mature, functional mRNA.
- The splicosomes may join the same exons in a variety of ways; producing different phenotypes.
2
Q
Epigenetics
A
- Changes that affect gene activation.
–> Involved in differentiation.
–> Involved in changes in proteins synthesised. - Factors that affect gene control are:
-DNA methylation
-histone modification
-non-coding RNA
3
Q
Regulation of gene expression
A
- Genes can be switched off when they are not needed.
- This prevents cellular resources being wasted.
- Typical human cells express 3-5% of their genes at any given time.
- Cancer results when genes do not turn off properly.
4
Q
DNA methylation
A
- Addition of a methyl group to a base.
- Added by DNA methyltransferase enzyme.
- Can also modify the structure of the histones.
- Changes arrangement of DNA and prevents transcription.
- Switch off genes which cannot be switched on so proteins cannot be transcribed.
5
Q
DNA demethylation
A
- Removal of methyl group.
- Genes become active so can be transcribed.
6
Q
Histone modification
A
- Positively charged proteins.
- DNA helices wind around histones to form chromatin.
- Makes up chromosomes
- When densely supercoiled and condensed genes are not available to be copied (heterochromatin).
- Active chromatin is loose with uncoiled regions opening up more genes for transcription.
7
Q
Histone acetylation
A
- Acetyl group is added to one of the lysines in histone.
- Opens up structure and activates chromatin allowing transcription
- Removing group produces heterochromatin again.
8
Q
Histone methylation
A
- Methyl group is added to a lysine in histone.
- Depending on the position of lysine methylation may cause inactivation of the DNA or activation of a region.
- Methylation is often linked to silencing of a gene.
9
Q
Transcription factors
A
- A protein that controls the transcription of genes so that only certain parts of the DNA are expressed.
-These proteins are which move in from the cytoplasm into the nucleus and bind to specific DNA sites called promoters.
-Promoters are found at the start of their target gene.
10
Q
The transcription factors can be:
A
- Activators: stimulate or increase the rate of the transcription
-Help RNA polymerase to bind to the start of the target gene and activate transcription. - Repressor: inhibit or decrease the rate
-Inhibit or decrease the rate by preventing RNA polymerase from binding to the target gene, therefore stopping transcription.
-They create a loop in the DNA molecule that activates the gene. This allows RNA polymerase to attach to the DNA chain and transcription will start.
11
Q
Gene probes
A
Gene probes identify a particular section of DNA and mRNA.
12
Q
Gene expression in action
A
- Each cell type produces specific proteins that relate to the particular function of the cell.
- This means that different genes must be expressed in different types of cells.
- By comparing the proteins found in different types of cells, scientists can measure the level of differentiation that has taken place and work out which genes have been expressed and which had been suppressed.
13
Q
Controlling gene expression
A
- The Human genome Project found that the human genome has 20,000-25,000 individual genes
- In a differentiated cell, between 10,000 and 20,000 of those genes are actively expressed
- Different combinations are expressed in different cells, creating the variety of structure and function seen in cells of different tissues.
14
Q
Control of gene expression
A
- Gene expression is controlled by switching on and off the transcription of genes.
- Several different transcription factors will be involved in the expression of a gene giving many levels of control.
15
Q
Promoter sequences
A
Are usually found just above the starting point for transcription upstream of the gene
16
Q
Enhancer sequences
A
Regulate the activity of DNA by changing the structure of chromatin, making it open to RNA polymerase.
17
Q
Transcription
A
The genetic code of the DNA is copied to a complimentary strand of RNA before protein synthesis can take place.
18
Q
Transcription factors
A
Protein that bind to the DNA in the nucleus and affect the process of transcribing the genetic material.
19
Q
Stem cells
A
Stem cells are unspecialised cells that divide and develop into other types of cell.
20
Q
Becoming specialised
A
Genes that are expressed get transcribed into mRNA which is then translated. These proteins will then modify the cell (eg. determine structure, cell processes).
21
Q
Totipotent
A
- Can differentiate into any cell type.
- Occur for only a short length of time in mammalian embryos.
–> Zygote.
22
Q
Pluripotent
A
- Can create most cell types.
- Occur in embryo can create most cell types.
–> Blastocyst.
23
Q
Multipotent
A
- Can only produce a limited number of cell types.
- Found in mature mammals.
–> Cells in embryo.
24
Q
Unipotent
A
Found in mature mammals, can only differentiate into one cell type
25
Epigenetic control of stem cells
- The zygote starts as a totipotent and then cells become pluripotent a they divide.
- This occurs due to transcription factors and epigenetic controls switching on and off the transcription of certain genes.
- As development progresses more genes become silenced, and thus become more specialised.
26
Stem cell therapy
Scientists are trying to find ways of using stem cells to treat medical conditions where the patient’s own cells are damaged or faulty.
27
Therapeutic cloning
Experimental technique to produce large quantities of healthy tissue (eg. cells to replace damaged pancreas in someone with type 1 diabetes).
1) Remove the nucleus from a patients normal body cell
2) Transfer it to human ovum which has had its nucleus removed, fuse them with an electric shock which further causes development to take place
3) Pre embryo starts to develop and divide, producing embryonic stem cells
4) The genetics perfectly match the patient. The stem cells can be collected and cultured in a suitable environment to differentiate into the tissue needed.
5) They can then be transferred back into the patient.
28
Induced pluripotent stem cells (iPS cells)
- Adult mouse cells and reprogrammed to become pluripotent again.
- They have introduced certain transcription factors back into the cells which allows them to become pluripotent.
(Removes the ethical issues of stem cells and also removes the risk of rejection).
--> Adult cells made into pluripotent cells.
29
Pros and cons of stem cell therapy
+Revolutionise medicine
+Save lives
+Cure diseases
+Avoid risk of rejection
-Not enough research
-Could cause the development of cancers in the body
(This is evidence that people who have had bone marrow transplants are at higher risk of developing other cancers later)
30
How can histone modification affect gene expression?
- Addition of an acetyl group activates chromatin, allowing transcription.
- Addition of a methyl group can either activate or inactivate chromatin depending on the position of the lysine.
31
How can DNA methylation affect gene expression?
- Involves addition of CH3 group to cytosine bases, which prevents transcription factors from binding.
- Therefore gene expression is suppressed.
32
How are epigenetic involved in cell differentiation?
- Epigenetics control the amount of a cells DNA that is transcribed.
- So ensures only the proteins needed for that specific cells function are produced.
33
How do totipotent cells develop into other types of stem cell?
- Epigenetic modifications result in selective translation of the relevant parts of DNA.
- Totipotent cells develop into pluripotent cells in the early stages of embryonic development.
- Then later into fully differentiated somatic cells.
34
Similarities between iPS and embryonic
- Potential to divide indefinitely.
- Potential to differentiate into a number of different cell types.
