Cell Differentiation, Aging, Death and Regeneration. Flashcards
What happens when a cell differentiates?
It undertakes major changes in shape, size, metabolic activity, and overall function.
What does the exact role of a tissue in an organism depend on?
what type of cells it contains.
What are stem cells?
Cells with the potential to develop into many different types of cells inn the body.
What are the two major types of stem cells?
1) embryonic stem cells
2) adult stem cells
What are the three key features of stem cells?
1) divide and renew (themselves over a long time)
2) unspecialized, (so cannot do specific functions in the body)
3) have the potential to become specialized cells (eg. muscle, blood and brain cells)
What do stemcells typically have?
The capacity to mature into many different cell types.
What are transcription factors?
Proteins one of a class of proteins that bind to specific genes on the DNA molecule and regulate which genes are transcribed in a cell (either promoted or inhibited).
Why are transcription factors vital for stem cells?
They regulate which genes are transcribed in a cell, therefore cause cells to differentiate.
How do transcription factors function?
they turn themselves on and off at different types during differentiation.
Explain the mechanism of differentiation.
Genes are turned on or off through transcription factors.
What do transcription factors regulate?
Gene expression.
What is “cell potency”?
The varying ability of stem cells to differentiate into specialized cell types.
Which cells differentiate more? the ones with high or low potency?
high potency
What are the three types of stem cells?
1) Totipotent: give rise to all cells found in an embryo and extraembryonic cells.
2) Pluripotent: give rise to all cells within the body, but not the placenta.
3) Multipotent: develop into a limited number of cell types in a specific lineage.
What cells have proliferative capacity?
- Labile cells
- Stabile cells
- Permanent non-dividing cells
Explain “labile cells”. State examples.
- continuously divide
- eg. surface epithelial cells of the skin and gastrointestinal tract
Explain “stabile cells”. State examples.
- nondividing under normal circumstances
- induced to reenter the cell cycle by exposure to growth factors
- eg. parenchyma cells of the liver, kidney, pancrease, mesenchymal cells.
Explain “permanent non-dividing cells”. State examples.
- lost all capacity for proliferation
- eg. nerve cells, cardiac muscle
What are the two main categories of cell aging?
- programmed
- damage or error theories
What are programmed theories? What does regulation depend on?
aging follows a biological timetable (a continuation of the one that regulates childhood growth and development).
- regulation depends on changes in gene expression that affect the systems responsible for maintenance, repair and defence responses.
What are damage or error theories?
Emphasize environmental assaults to living organisms that induce cumulative damage at various levels of aging.
What are the three subcategories of the programmed theories?
1) PROGRAMMED LONGEVITY (aging results of a sequential switching on and off of certain genes
2) ENDOCRINE THEORY (biological clocks through hormones control the pace of aging)
3) IMMUNOLOGICAL THEORY (immune system is programmed to decline over time, leading to an increase in vulnerability to infectious disease)
What are the five subcategories of the damage or error theories?
1) WEAR AND TEAR THEORY (vital parts of cells wear out)
2) RATE OF LIVING THEORY (the greater an organism’s oxygen basal metabolism, the shorter its lifespan)
3) CROSS-LINKING THEORY (accumulation of cross-linked proteins damages cells and tissues).
4) FREE RADICALS THEORY (free radicals cause damage to the macromolecular cmponents of the cells)
5) SOMATIC DNA DAMAGE THEORY (with an increase of age, genetic mutations occur, causing cells to deteriorate and malfunction).
What is the biological name for “cell death”?
apoptosis
Explain a live example of apoptosis.
the tail of a frog is lost (stimulated by an increase in thyroid hormone in the blood).
What does cell death help with?
regulation of cell numbers.
What are the 4 main apoptosis pathways?
1) activation of receptors
2) direct mitochondrial injury
3) irreparable injury to DNA
4)injury of the cell membrane
What are the two major pathways through which a cell can elicit apoptosis?
- the intrinsic (mitochondrial) pathway
- the extrinsic (death receptor) pathway
How is the extrinsic pathway activated?
through signals from other cells.
How is the intrinsic pathway activated?
by internal surveillance mechanisms.
What is one common pathway of bringing about apoptosis?
the activation of CASPASESES.
What are CASPASASES?
- a group of cysteine proteases.
- they exist in cells as inactive proenzymes until activated by the cellular machinery.
What do caspasases result in?
DNA fragmentation, cytoplasmic and chromatin condensation, membrane bleb formation, cell breakup and removal of the debris of phagocytes.
How many stages are there of apoptosis? Name them.
4 stages.
1) induction/signalling
2) effector phase
3) degradation phase
4) phagocytic phase
What happens during the induction phase?
- molecular systems are activated
- cell survival mechanisms are activated
- absence of morphological changes
Is the induction phase reversible?
yes
What happens during the effector phase?
- determined by the loss of mitochondrial transmembrane potential
(causes an opening of a large ionic channel called “permeability transition pore complex” or “megachannel” through which mitochondrial substances are released into the cytosol.)
Is the effector phase reversible?
it is the “no return” point
What happens during the degredation phase?
- several enzymatic mechanisms are activated (DNA degredation, crosslinks amongst proteins are broken)
- morphological changes appear (cell surface specialixzations and cell-to-cell junctions are broken, chromatin is condensed, nucleus is fragmented, organelles are undamaged)
What happens during the phagocytic phase?
- recognition by macrophage phagocytosis (because of the junction over the cellular surface)
- absence of inflammatory response
Explain shortly the process of apoptosis.
1) break of intracellular junctions, cell shrinkage, chromatin begins to condensate.
2) chromatin condenstations continues, cellular blebbing, apoptotic bodies are enclosed by fragmented membrane.
3) apoptotic bodies are phagocited by neighbouring cells and macrophages, without an inflammatory response.
4) reparative response results from the proliferation of the neighbouring cells.
What are the major steps of apoptosis?
- cell shrinks
- cell frangments
- cytoskeleton collapses
- nuclear envelope dissasembles
- cells release apoptotic bodies
What is a “bleb”?
A bleb is an irregular bulge in the plasma membrane of a cell caused by localized decoupling of the cytoskeleton from the plasma membrane.
State examples of apoptosis inducers.
- withdrawal of growth factors
- loss of matrix attachments
- viruses
- free radicals
- ionising radiation
- DNA damage
- ligand binding at “death receptors”
State examples of apoptosis inhibitors.
- presence of growth factors
- extracellular cell matrix
- sex steroids
- viral proteins
What is “necrosis”?
An inflammatory response. Necrosis is the death of body tissue. It occurs when too little blood flows to the tissue. This can be from injury, radiation, or chemicals. Necrosis cannot be reversed.
Explain the process of necrosis.
- small blebs form, the structure of the nucleus changes
- cell and mitochondrial swelling. blebs become larger; no organelles are located in the blebs.
- plasma (cell) membrane ruptures and releases the cell’s contents. the organelles are no longer functional.
What is regeneration?
the process by which the remaining cells of an injured organ regrow to offset the missed cells.
Explain the cycle of the stem cell.
The STEM CELLS proliferate, giving rise to PROGENITORS that thereafter receive signals to DIFFERENTIATE. Aged cells recieve signals to dye.
STEM CELLS -(proliferation)-> PROGENITORS –> DIFFERENCIATED CELLS
What is “proliferation”?
Rapid increase in the number or amount of something. (Rapid reproduction of a cell).
