Gene expression Flashcards
Define Stem cells
Undifferentiated cells that can continually divide and become specialised.
Define Totipotent Stem cells
Stem cells that can produce any type of body cell.
They are found in the very early stages in the embryo.
Define Pluripotent Stem Cells
Stem cells that can produce any type of cell, except the placenta. Can be taken from an embryo from day 4 - 16.
What are some of the issues associated with using Pluripotent Stem cells to make other cells?
- The stem cells may continually divide, possibly creating a tumor.
- Ethical issues - an embryo must be created and destroyed (potential for life).
Define Multipotent stem cells
Stem cells which can differentiate into a limited amount of cells and are found in the bone marrow.
Define Unipotent stem cells.
Stem cells which can only differentiate into one type of cell.
How are induced pluripotent cells made?
Unipotent cells from a consenting adult can give their unipotent cells and in a laboratory, the cell’s genes that were previously turned off to specialise it, are turned back on to make it pluripotent. (Transcriptional factors).These can divide indefinitely.
What are transcriptional factors and how do they work?
The transcriptional factor is a tertiary protein which is made of the DNA binding site and receptor.
It moves from the cytoplasm to the nucleus and attaches onto the DNA, causing RNA polymerase to attach onto the DNA and begin transcription.
RNA polymerase’s active site is only complementary to the transcriptional factor and the DNA together.
What is the role of oestrogen in transcription?
Oestrogen is a lipid soluble steroid hormone which binds to the receptor on the transcriptional factor, as it is complementary.
This changes the shape of the DNA binding site, which makes it complementary to the DNA.
The transcriptional factor is now activated.
Define epigenetics
Epigenetics is the heritable change in the gene function without the change to the DNA base sequence.
Define epigenome
Epigenome refers to all the chemical modifications to all the DNA and histones, that do not affect the base sequence.
What causes changes to the epigenome?
Changes in the environment such as smoking, stress, exercise and diet.
Describe acetylation of histones.
Acetyl groups can bind to the lysine amino acid groups on the histones.
This causes a bond to form between the histone and the acetyl group, causing a removal of the bond between the histone and the DNA.
The DNA is less tightly wrapped, therefore more transcriptional factors can bind to the DNA strand, therefore, gene expression is stimulated.
Describe methylation of DNA.
The addition of a methyl group to the DNA (cytosine base) which
- causes the inhibition of transcriptional factors
- attracts protiens which condense the DNA-histone complex by inducing the de-acetylation of the histones. This causes the DNA-histone complex to be more tightly wrapped.
How does the inhibition of translation work?
- The double stranded RNA (from excess mRNA) (dsRNA) is broken down into small strands using enzymes (Dicer), and one of the small sections is called small interfering RNA
- Then the siRNA associates itself with proteins. A RISC complex, then one of the strands is degraded.
- The single stranded siRNA then attaches onto the target complementary mRNA strand and the associated proteins break it down into smaller chunks, therefore inhibiting translation.
