22. Cell Determination and Cell Senescence Flashcards
Describe cell determination?
Process whereby the cell fate becomes stable. It is followed by cell differentiation. When a cell chooses a particular fate it is said to be determined. Implies a stable change.
Describe cell determination? (4pts)
- Process by which portions of the genome are selected for expression in different embryonic cells.
- Occurs in totipotent, embryonic stem cells.
- A result of asymmetric segregation of cytoplasmic determinants.
- Responsible for assigning the fate of the cells.
Describe cell differentiation? (4pts)
- Process by which a cell becomes specialised in order to perform a specific function.
- Follows cell determination
- A result of differential gene expression
- Responsible for the functional specialisation of the cells.
Describe cell differentiation? (4pts)
- Process by which a cell becomes specialised in order to perform a specific function.
- Follows cell determination
- A result of differential gene expression
- Responsible for the functional specialisation of the cells.
Describe Asymmetrical cell division? (3pts)
- Asymmetrical cell division is due to differential distribution of cytoplasmic molecules (proteins or mRNAs) within a cell before it divides.
- The 2 new daughter cells have different fates therefore have a different gene expression profile.
- Cells with p granules will generate germ cells. Cells with no p granules will give rise by division to other types of cells in the organism.
How is cell determination caused? (2pts)
- Cell determination is caused by inductive signals from neighbouring cells.
- One group of cells influences the development of another group of cells.
Describe Pioneer factors? (4pts)
- Transcription factors that access closed chromatin, remodel it and imitate cell-fate.
- Highly expressed in embryonic stem cells and needed to maintain their pluripotency.
- Can activate or inhibit gene expression via histone modification and DNA methylation.
- Pioneer factors together with co-factors are key in cell-fate decision making.
What is Cell senescene?
Deterioration of the cells due to age
What is Apostosis?
Programmed cell death
Describe Cell senescene? (5pts)
- Cell senescene refers to the deterioration of cells due to age.
- Takes place during the process of ageing.
- Irreversible arrest of cells during cell profileration is the significant feature
- It is caused by oxidative stress, DNA damage and alternation of genetic expression
- It is regulated by genes involved in ageing mechanisms.
Describe Apostosis? (5pts)
- Apostosis is programmed cell death
- Its role is to balance the cell number at a constant rate
- Chromosome condensation is the significant feature
- It is caused by different physiological and pathological conditions.
- Apoptosis is regulated by intracellular proteolytic mechanisms.
Describe the cell lifespan?
- Is the total number of doublings that a cell population goes through before senescence. The length of time for which a cell exists.
- Hayflick and Moorhead found out that normal foetal fibroblasts only reached a maximum of 50 cell populations doublings before becoming senescence. This is the Hayflick limit.
Describe the Hyaflick limit?
The number of times that a normal human cell population will divide before cell division.
Describe normal cells and immortal cells?
Normal cells have a finite lifespan as opposed to immortal cells. The only immortal cells are cancer cells which can divide forever and never reach their hayflick limit.
Describe the effects of cellular senescene? (3pts)
- Morpholoigcal changes I
- Biochemical changes
- Chromatin changes
Describe Morphological changes? (5pts)
- Cells become larger
- Cells display increased granulaity
- Cells flatten out
- Cell borders tend to vanish
- Cytoplasm becomes more vacuole-rich.
Describe Biochemical changes? (2pts)
- Increased perinucleur activity of SA-B-galactosidase.
2. Increases protein levels of senescence markers such as p53.
Describe Biochemical changes? (2pts)
- Increased perinucleur activity of SA-B-galactosidase.
2. Increases protein levels of senescence markers such as p53.
Describe Chromatin changes? (2pts)
- Focal HP1 recruitment
2. Senescene associated heterochromatin foci.
Describe a Telomere?
Regions at the end of chromosome composed of TTAGGG DNA sequences whose function is to preserve chromosome integrity during each DNA replication thus preventing DNA damage (constitutive heterochromatin)
Describe the loss of telomeres?
Loss of telomere by chromosome breakage results in unstable chromosome ends that can fuse with other broken chromosomes or be involved in recombination events or be degraded. It can also involve the damage of telomere flanking genes.
Describe the loss of telomeres?
Loss of telomere by chromosome breakage results in unstable chromosome ends that can fuse with other broken chromosomes or be involved in recombination events or be degraded. It can also involve the damage of telomere flanking genes.
Describe telomeric DNA?
Telomeric DNA is associated with a 6-member protein sheltrin complex that facilitates the formation of loops which cap the chromosome end.
Describe Progressive Telomere shortening?
Progressive telomere shortening occurs in all dividing normal cells mainly due to the incomplete DNA lagging strand. The lagging strand is always shorter than the leading strand. Every time a cell divides telomeres shorten due to this incomplete lagging strand DNA synthesis.
