8.2: Gene Expression Flashcards
Describe totipotent cell type
Can differentiate into any type of cell e.g. cells in a zygote/ all plant tissue
Describe pluripotent cell types
Can differentiate into almost any type of cell e.g. embryonic/ fetal stem cells
Describe multipotent cell type
Can differentiate into a limited number of specialised cells. Found in adult tissue which usually produce same type of cell e.g. bone marrow producing any type of blood cell
Describe unipotent cell type
Can only differentiate into a single type of cell e.g. cardiomyocyte (cardiac muscle cell)
What is a stem cell?
Undifferentiated cells, which can divide indefinitely and turn into other specific cell types
What happens to totipotent cells during embryonic development?
Certain parts of the DNA are selectively translated so that only some genes are ‘switched on’, in order to differentiate the cell into a specific type and form the tissues that make up the foetus.
Give a unique feature of pluripotent cells and the use of this feature
They can divide in unlimited numbers and therefore can be used to repair or replace damaged tissues
What is a unipotent cell? Give an example
A cell that can only develop into one type of cell. This happens at the end of specialisation when the cell can only propagate its own type. An example is cardiomyocytes (heart cells)
Which types of stem cells are found in embryos?
Totipotent and pluripotent
Multipotent and unipotent cells are only found in mature mammals
Give some uses of stem cells
Medical therapies e.g. bone marrow transplants, treating blood disorders.
Drug testing on artificially grown tissues
Research e.g. on formation of organs and embryos
How are induced pluripotent stem cells produced?
From mature, fully specialised (somatic) cells. The cell regains capacity to differentiate through use of proteins in particular transcription factors
What is a transcription factor?
A protein that controls the transcription genes so that only certain parts of the DNA are expressed e.g. in order to allow a cell to specialse
How do transcription factors work?
- Move from cytoplasm into nucleus
- Bind to promoter region upstream of target gene
- Makes it easier of more difficult for RNA polymerase to bind to gene. This increases or decreases rate of transcription
Give an example of a hormone that affects transcription and explain how it works.
- Steroid hormone oestrogen diffuses through cell membrane
- Forms hormone-receptor complex with ER alpha receptor in cytoplasm
- Complex enters the nucleus & acts as transcription factor to facilitate binding of RNA polymerase
What is meant by epigenetics?
A heritable change in gene function without change to base sequence of DNA
How does increased methylation of DNA affect transcription?
Involves addition of a CH3 group to cytosine bases which are next to guanine.
Prevents transcription factors from binding
Therefore gene transcription is suppressed
How does decreased acetylation of DNA affect transcription?
Positively charged histones are positively charged bind to negatively charged DNA. Decreasing acetylation increases positive charge of histones. Binding becomes too tight and prevents transcription factors from accessing the DNA. Therefore gene transcription is suppressed.
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 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 prokaryotes
Give some characteristics of benign tumours.
- slow growth
- defined by a clear boundary due to cell adhesion molecules
- cells retain function and normal shape
- dont spread easily
- easy to treat
Give some characteristics of malignant tumours
- rapid, uncontrollable growth
- ill-defined boundary (finger like projections)
- cells do not retain function and often die
- spreads easily and quickly (metastasis)
- difficult to treat
Describe role of tumour- suppressor genes
Code for proteins that control cell division; in particular, stopping cell cycle when damage is detected. They are also involved in programming apoptis i.e. self destruction of cell
Explain how tumour-suppressor genes can be involved in developing cancer
A mutation in gene could code for a nonfunctional protein. Increased methylation or decreased acetylation could prevent transcription.
Cells will divide uncontrollably resulting in a tumour
Describe role of proto-oncogenes
Controls cell division; in particular, codes for proteins that stimulate cell division
Explain how proto-oncogenes can be involved in developing cancer
Mutation in 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 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 cells to divide uncontrollably.
Explain how oestrogen can be involved in developing breast cancer
Oestrogen is an activator of RNA polymerase. Therefore, in areas of high oestrogen concentration, such as adipose tissue in breasts, cell division can become uncontrollable.
