8.2.2 Regulation of transcription and translation Flashcards
What is a transcription factor?
A protein that controls the transcription of genes so that only certain parts of the DNA are expressed, e.g., in order to allow a cell to specialise.
proteins that bind to base sequences on DNA’s promoter region to initiate transcription
in eukaryotes, transcription of target genes can be stimulated or inhibited when
specific transcriptional factors move from the cytoplasm into the nucleus.
This can turn on/off genes, so only certain proteins are produced in a particular cell.
what causes specialization of cells
transcription factors cause particular genes in cells to turn on and off which is what causes specialisation
How do transcription factors work?
1- Move from the cytoplasm into the nucleus.
2- Bind to the promoter region upstream of the target gene.
3- Make it easier or more difficult for RNA polymerase to bind to the gene.
This increases or decreases the rate of transcription.
what is upstream and promoter region
Upstream’ - refers to the DNA before the start of the coding region
The promoter is a section of DNA upstream of the coding region that is the binding site for proteins that control the expression of the gene, including:
RNA polymerase
Transcription factors
what direction is DNA transcribed
5’ to 3’ direction to produce messenger RNA (mRNA)
Without the binding of a transcription factor,
the gene is inactive, and the protein won’t be made.
how does oestrogen lead to transcription
- it binds to receptor sit on transcription factor
- this causes the shape of the TF to change slightly
- the TF becomes complimentary to DNA and it binds to dna, leading to transcription
Give an example of a hormone that affects transcription and explain how it works.
The steroid hormone oestrogen diffuses through the cell membrane.
Forms a hormone-receptor complex with the ER-α receptor in the cytoplasm.
The complex enters the nucleus & acts as a transcription factor to facilitate the binding of RNA polymerase.
what can oestrogen do
initiate transcription - is a steroid hormone
Epigenetics
Epigenetics is the heritable change in gene function, without changing the DNA base sequence.
these changes are caused by changes in the environment and can inhibit transcription.
In eukaryotic organisms, gene expression (protein synthesis) can be controlled by
epigenetic
what are the 2 things that inhibit transcription
increased methylation and decreased acetylation
Increased methylation
methyl group attaches to DNA specifically cytosine
the DNA histone complex is more tightly packed
transcriptional factor can’t bind
No transcription
switched off
decrease acylation
Positively charged histones bind to negatively charged DNA. Decreasing acetylation increases the positive charge of histones. Binding becomes too tight and prevents transcription factors from accessing the DNA. Therefore, gene transcription is suppressed.
what are factors that add chemical tags
diet, stress toxins
an add epigenetic chemical tags to the DNA and this can control gene expression in eukaryotes.
what is an epigenome
A single layer of chemical tags on the DNA .
how does the epigenome affect whether or no genes are expressed
- it impacts the dna histone complex’s shape to make it tightly wound or unwound
- if it is tightly wound, the gene is not expressed
- if it is unwound, the gene is expressed
How might epigenetic changes affect humans?
They can cause disease, either by over-activating a gene’s function (such as in cancer) or by suppressing it.
Give an application of epigenetics.
Treatments of various diseases.
Development of ways to reverse epigenetic changes.
Describe the process of RNA interference, including the organisms in which it occurs.
RNA molecules act to inhibit gene expression, usually by destroying mRNA so that it cannot be translated. Occurs in eukaryotes and some prokaryote
How does RNA interference work?
Double-stranded RNA (dsRNA) is cut into small interfering RNA (siRNA) by an enzyme.
One strand of siRNA combines with a protein to form the RNA-induced silencing complex (RISC).
The siRNA strand binds to complementary mRNA in the cytoplasm.
The mRNA is cut into small pieces by RNA hydrolase, preventing translation.
This ensures gene silencing by blocking protein production
The relevance of epigenetics on the development and treatment of disease, Tumour suppressor genes
Tumour suppressor genes produce proteins to slow down cell division and cause cell death if DNA
copying errors are detected.
Tumour suppressor genes could become hypermethylated, meaning an increased number of methyl
groups attached to it. This abnormal methylation results in the gene being deactivated (turned off).
The relevance of epigenetics on the development and treatment of disease,- oncogenes
oncogenes, as they may be hypomethylated, reducing the number of
methyl groups attached. This results in the gene being permanently turned on.
This abnormal methylation can result in the growth of tumours due to uncontrolled cell division.
Describe the role of tumour-suppressor genes.
Code for proteins that control cell division; in particular, stopping the cell cycle when damage is detected. They are also involved in programming apoptosis (i.e., ‘self-destruction’ of the cell).
Explain how tumour-suppressor genes can be involved in developing cancer.
A mutation in the gene could code for a nonfunctional protein. Increased methylation or decreased acetylation could prevent transcription.
Cells will divide uncontrollably, resulting in a tumour.
Describe the role of proto-oncogenes.
Control cell division; in particular, code for proteins that stimulate cell division.
Explain how proto-oncogenes can be involved in developing cancer.
A mutation in the gene could turn it into a permanently activated oncogene. Decreased methylation or increased acetylation can cause excess transcription.
This results in uncontrolled cell division and the formation of a tumour.
Explain how abnormal methylation of genes can cause cancer.
Hyper-methylation of tumour-suppressor genes or oncogenes can impair their function and cause the cell to divide uncontrollably.
Explain how oestrogen can be involved in developing breast cancer.
We already know oestrogen is an activator of RNA polymerase. Therefore, in areas of high oestrogen concentration, such as adipose tissue in the breasts, cell division can become uncontrolled.
