Gene Expression Flashcards
What is a stem cell?
Undifferentiatied cells that can divide indefinitely and turn into other specific cell types
Name the three types of stem cell
- totipotent
- pluripotent
- multipotent
What is a totipotent stem cell?
Can develop into any cell type including the placenta and embryo
What is a pluripotent stem cell?
Can develop into any cell type excluding the placenta and embryo
What is a multipotent stem cell?
Can only develop into a few different types of cell
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
What is a unique feature of pluripotent cells?
Can divide in unlimited numbers and can therefore be used to repair or replace damaged tissue
What is a unipotent cell?
- cell that can only develop into one type of cell
- happens at the end of specialisation when the cell can only propagate its own type
- e.g cardiomyocytes (heart cells)
Which types of stem cell are found in embryos?
Totipotent and pluripotent
Give some uses of stem cells
- medical therapies
- drug testing on artificially grown tissues
- research
How are induced pluripotent stem cells produced?
From mature somatic cells
Cell regains capacity to differentiate through the use of proteins in particular transcription factors
What is a transcription factor?
A protein that controls the transcription of genes so that only certain parts of the DNA are expressed
How do transcription factors work?
- Move from cytoplasm to nucleus
- Bind to promoter region upstream of target gene
- Makes it easier or more difficult for RNA polymerase to bind to gene which either 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 the 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 the base sequence of DNA
How does increased methylation of DNA affect gene 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 histones affect gene transcription?
- charged histones bind to - charged DNA
- decreasing acetylation increases positive charge of histones
- binding becomes too tight and prevents transciption 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 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 prokaryotes
What are some characteristics of benign tumours?
- slow growth
- clear boundary due to cell adhesion molecules
- cells retain function and normal shape
- don’t spread easily
- easy to treat
What are some characteristics of malignant tumours?
- rapid uncontrollable growth
- ill-defined boundary
- cells do not retain function and often die
- spreads quickly and easily (metastasis)
- difficult to treat
Describe the role of tumour-suppressor genes
- code for proteins that control cell division/stopping the cell cycle when damage is detected
- also involved in programming apoptosis
Explain how tumour-suppressor genes can be involved in developing cancer
- 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
- code for proteins that stimulate cell division
Explain how proto-oncogenes can be involved in developing cancer
- mutation in the gene could turn it into a permanently activated oncogene
- decreased methylation or increased acetylation can cause excess transcription
- 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 the cell to divide uncontrollably
Explain how oestrogen can be involved in developing breast cancer
- oestrogen is an activator of RNA polymerase
- so in areas of high oestrogen concentration like in the breast, cell division can become uncontrolled
