Topic 8.2 - Gene Expression Is Controlled By A Number Of Features Flashcards
What are stem cells? (2)
Undifferentiated / unspecialised cells capable of:
1) Dividing (by mitosis) to replace themselves indefinitely
2) Differentiating into other types of (specialised) cells
Describe how stem cells become specialised during development (3)
1) Stimuli lead to activation of some genes
2) So mRNA is transcribed only from these genes and then translated to form proteins
3) These proteins modify cells permanently and determine cell structure / function
Describe totipotent cells (2)
1) Occur for a limited time in early mammalian embryos
2) Can divide and differentiate into any type of body cell
Describe pluripotent cells (2)
1) Found in mammalian embryos
2) Can divide and differentiate into most cell types
Describe multipotent cells and give an example (2+1)
1) Found in mature mammals
2) Can divide and differentiate into a limited number of cell types
E.g. multipotent cells in bone marrow can divide and differentiate into different types of blood cell
Describe unipotent cells and give an example (2+1)
1) Found in mature mammals
2) Can divide and differentiate into just one type of cell
E.g. unipotent cells in the heart can divide into cardiomyocytes (cardiac muscle cells)
Explain how stem cells can be used in the treatment of human disorders (2)
1) Transplanted into patients to divide in unlimited numbers
2) Then differentiate into required healthy cells (to replace faulty / damaged cells)
Give examples of how stem cells can be used in the treatment of human disorders (2)
1) Potential treatment of Type 1 diabetes by creating healthy islet cells that produce insulin
2) Bone marrow stem cell transplant for SCD / blood cancers
- Destroy patients bone marrow before treatment -> so no faulty cells are produced
- Transplant stem cells from healthy person -> divide and differentiate into healthy cells
Explain how induced pluripotent stem (iPS) cells are produced (3)
1) Obtain adult somatic (body) cells from patient
2) Add specific protein transcription factors associated with pluripotency to cells so they express genes associated with pluripotency
- Transcription factors attach to promoter regions of DNA, stimulating or inhibiting transcription
3) Culture cells to allow them to divide by mitosis
Give some reasons for using stem cells in treating human disorders (4)
1) Can divide and differentiate into required healthy cells, so could relieve human suffering by saving lives and improving quality of life
2) Embryos are often left over from IVF and so would otherwise be destroyed
3) IPS cells unlikely to be rejected by patients immune system as made with patients own cells
4) IPS cells can be made without destruction of embryo and adult can give permission
Give some reasons against using stem cells in treating human disorders (3)
1) Ethical issues with embryonic stem cells as obtaining them requires destruction of an embryo and potential life
2) Immune system could reject cells and immunosuppressant drugs are required
3) Cells could divide out of control, leading to formation of tumours / cancer
What are transcription factors? (2)
1) Proteins which regulate transcription of specific target genes in eukaryotes
2) By binding to a specific DNA base sequence on a promoter region
Describe how transcription can be regulated using transcription factors (3)
1) Transcription factors move from cytoplasm to nucleus
2) Bind to DNA at a specific DNA base sequence on a promoter region
3) This stimulates or inhibits transcription of target genes by helping or preventing RNA polymerase binding
Explain how oestrogen affects transcription (6)
1) Oestrogen is a lipid soluble steroid hormone so diffuses into cell across the phospholipid bilayer
2) In cytoplasm, oestrogen binds to its receptor, an inactive transcription factor, forming an oestrogen receptor complex
3) This changes the shape of the inactive transcription factor, forming an active transcription factor
4) The complex diffuses from cytoplasm into the nucleus
5) Then binds to a specific DNA base sequence on the promoter region of a target gene
6) Stimulating transcription of target genes forming mRNA by helping RNA polymerase to bind
Explain why oestrogen only affects target cells
Other cells do not have oestrogen receptors
Describe what is meant by epigenetics (2)
1) Heritable changes in gene function / expression without changes to the base sequence of DNA
2) Cause by changes in the environment (eg. Diet, stress, toxins)
Describe what is meant by epigenetics
All chemical modification of DNA and histone proteins -> methyl groups on DNA and acetyl groups on histones
Explain how methylation can inhibit transcription (3)
1) Increased methylation of DNA -> methyl groups added to cytosine bases in DNA
2) So nucleosomes pack more tightly together
3) Preventing transcription factors and RNA polymerase binding to promoter
Explain how acetylation can inhibit transcription (3)
1) Decreased acetylation of histones increases positive charge
2) So histones bind DNA more tightly
3) Preventing transcription factors and RNA polymerase binding to promoter
Explain the relevance of epigenetics on disease development and treatment (4)
1) Environmental factors can lead to epigenetics changes
2) These can stimulate / inhibit expression of certain genes that can lead to disease development
- Increased methylation of DNA or decreased acetylation of histones inhibits transcription
- Decreased methylation of DNA or increased acetylation of histones stimulates transcription
3) Diagnostic tests can be developed that detect these epigenetic changes before symptoms present
4) Drugs can be used to reverse these epigenetic changes
What is RNA interference (RNAi) (2)
1) Inhibition of translation of mRNA produced from target genes, by RNA molecules
2) This inhibits expression of a target gene
This happens in eukaryotes and some prokaryotes
Describe the regulation of translation by RNA interference (4)
1) Small interfering RNA (siRNA) or micro RNA (miRNA) is incorporated into / binds to a protein forming an RNA induced silencing complex (RISC)
2) Single stranded miRNA / siRNA within RISC binds to target mRNA with a complementary base sequence
3) This leads to hydrolysis of mRNA into fragments which are then degraded or prevents ribosomes binding
4) Reducing / preventing translation of target mRNA into protein
Describe how tumours and cancers form (2)
1) Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division
2) Tumour formed if this results in mass of abnormal cells
- Malignant tumour = cancerous, can spread by metastasis
- Benign tumour = non cancerous
Describe the main characteristics of a benign tumour (6)
1) Usually grow slowly
2) Cells are well differentiated / specialised
3) Cells have abnormal, regular nuclei
4) Well defined borders and often surrounded by a capsule so do not invade surrounding tissue
5) Do not spread by metastasis
6) Can normally be removed by surgery and they rarely return
