Chapter 20 - Gene expression Flashcards
What are totipotent stem cells?
Stem cells which can differentiate into any type of cell they have total potential
What are two key features of stem cells?
- Ability to differentiate into other cells and become specialised
- Self renewal
Can you explain how cells lose their totipotency and become specialised?
Certain genes are turned on or off which causes the totipotent cells to differentiate and become specialised then cannot un differentiate the process is reversible
Can you describe cell differentiation and cell specialisation?
Cell differentiation is the process in which cells become specialised for a particular function by particular genes being expressed or not
Can you describe the origins of stem cells?
Stem cells originate in the fetus as embryonic stem cells then become fetal and adult stem cells
Can you describe the different types of stem cells?
Totipotent - found in the embryo and can differentiate into any type of cell
Pluripotent - can differentiate into almost all types of cell but not the placenta
Multipotent - Can differentiate into a limited number of cells
Unipotent - can only differentiate into one type of cell
What are some sources of stem cells in mammals?
Embryonic stem cells, fetal stem cells in umbilical cord, cortex, retina and cortex and adult stem cells om bone marrow, skin, blood, eyes and brain
What are the two ways to control gene expression?
- Regulating transcription
2. Regulating translation
What controls transcription?
Transcription factors
How does oestrogen affect transcription?
- Oestrogen is a steroid hormone lipid soluble which enters the cells membrane through simple diffusion across the phospholipid bilayer
- Oestrogen binds to the oestrogen receptor on the transcription factor and causes a change in shape of the DNA binding site on the transcription factor
- The DNA binding site can then bind to the promotor region of DNA and allows RNA polymerase to bind and transcription occurs so gene is switched on
What is epigenetics?
The study of an organisms genetics caused by modification of gene expression rather than alteration of the genetic code itself
What is a nucleosome made up of?
A 8 histone protein core with DNA wrapped round it
What is the type of DNA called that is more condensed, less accessible to transcription factors so inactive?
Heterochromatin
What is the type of DNA called that is less condensed, more accessible to transcription factors and so active?
Euchromatin
What are two processes that affect the shape of the DNA - histone complex?
- Acetylation of histone proteins
2. Methylation of DNA
What is the epigenome?
The epigenome is the chemical changes to the DNA and histone proteins of an organism which can be passed down to an organisms offspring with the DNA. It is flexible unlike the DNA sequence and alters due to the environment
What is acetylation and what effect does it have on the epigenome?
Acetylation is where an acetyl group is added to the histone protein this causes the DNA to pack more loosely so transcription factor can more easily bind to the promoter region so gene is switched on
Decreased acetylation causes he negatively charged phosphate groups to attract more strongly to DNA causing tighter more condensed DNA histone complex
What is methylation and what effect does it have on the epigenome?
Methylation is the addition of a methyl group onto the cytosine base in DNA
Methylation attracts proteins that cause deacetylation of histone and block promotor transcription factors from binding
Switches off the genes
What causes methylation and acetylation?
Aging, environmental influences, lifestyle e.g. smoking or diet
How can gene expression be controlled by translation?
- Double strand of RNA is broken up by an enzyme into small interfering RNA (siRNA)
- One of the two strands of siRNA combines with an enzyme
- siRNA strand pairs with complementary bases on a mRNA strand
- The enzyme cuts the mRNA into smaller sections so it can longer be translated
What is cancer?
Cancer is a group of diseases caused by mutations to genes that regulate and control the cell cycle and mitosis resulting in uncontrolled growth of cells
What are the two types of tumour?
- Benign - non cancerous
2. Malignant - cancerous
What are some features of a benign tumours?
- Can grow to a large size but grow slowly
- Cells produce adhesion molecules on their cell surface membranes causing them to stick to each other so they don’t spread
- Surrounded by a dense capsule so remain in a compact structure
- Usually only have a localised effect
- Can usually be removed by surgery and rarely recur
What are some features of malignant tumours?
- Can grow to a large size and grow rapidly
- Cells usually have a large nucleus that appears dark due to large amount of DNA caused by uncontrolled cell division
- Cells often unspecialised unlike in benign where they are usually specialised
- Cells do not produce adhesion molecules on their surface so tend to spread to other areas called metastasis
- Tumours are not surrounded by a capsule so grow finger like projections into surrounding tissues
- More likely to be life threatening and effects whole body
- Removal usually involves surgery as well as chemotherapy and radiotherapy and usually recurs
What is metastasis?
The process by which primary tumours spread and result in secondary tumours in other parts of the body
What are the two main genes involved in control of cell division?
- Proto-oncogenes (accelerator for cell division)
2. Tumour suppressor genes ( breaks for cell division)
What two things can lead to cancer?
- Activation of oncogenes
2. Inactivation of tumour suppressor genes
What may cause activation of oncogenes?
Hypomethylation (reduced methylation)
What many cause inactivation of tumour suppressor genes?
Hypermethylation (increased methylation)
What is the link between oestrogen and breast cancer?
After menopause oestrogen not needed so it is more likely to to regulate menstrual cycle instead it is found in breast tissues and promotes transcription so will be activated to continually divide and positive feedback occurs as the tumour increases in size more oestrogen is produced and increases size even further
Can you explain how pluripotent stem cells can be used to treat human disorders?
Induced pluripotent cells are produced from unipotent stem cells which are genetically modified by inducing genes and transcriptional factors to turn on genes and acquire characteristics of embryonic stem cells a type of pluripotent stem cell.
Can be used to regrow tissues as they can self replicate so can be used to regrow tissue that has been damaged in an accident or due to disease
