Cell Bio- Cell Differentiation , Senescence & Apoptosis

Front 1

What is differentiation?

Back 1

A process of generating diverse types of cells (process of cell specialization)

Front 2

How many distinct cell types can a fertilized egg (zygote) differentiate into?

Back 2

More then 200 distinct cell types in vertebrates

Front 3

What is determination?

Back 3

A process in which cell becomes committed to certain fate (committed to certain specialization)

Front 4

When do cells USUALLY become determined?

Back 4

Usually before it starts to differentiate

Front 5

Biological significance of differentiation?

Back 5

a) Development of multicellular organism (ontogenesis)
- Fertilized egg--> mature organism. Development is realized in coordination with cell proliferation. Maintenance is also realized in coordination with cell proliferation

b) Maintenance of tissues and organs:
1. Physiological cell renewal
2. Repair: repair regeneration, wound heeling

Front 6

Basic principles of differentiation:

Back 6

1. Genome remains intact during development. Cells of the organism differ not because they contain different genes but because they express different genes.

2. Cell memory

3.Positive feedback

4. Positional information

Front 7

Cell memory as a basic principle of differentiation:

Back 7

Cells not only become differentiated but they also remain differentiated after the original signal responsible for the differentiation has disappeared. Cells somehow remember the effect of past signals and pass them on to their descendants.

Front 8

Positive feedback as a basic principle of differentiation:

Back 8

Positive feedback such as self- activation provides a mechanism for cell memory (e.g. cytoplasmatic components encoded by set of active genes acts back on the genes to maintain their expression)

Front 9

Positional information:

Back 9

Cells are able to retain an information reflecting their location in the body

Front 10

4 mechanism controlling differentiation:

Back 10

1. Asymmetry
2. Embryonic induction
3. Positional signal
4. Intracellular clock

Front 11

Asymmetry as a control mechanism for differentiation:

Back 11

Chemical and other asymmetries of the egg--> cleavage results in cells with different quantities of determinative molecules

Front 12

Embryonic induction as a control mechanism for differentiation:

Back 12

Interaction of cells or tissues leads to certain fate of one or both participants

Front 13

Positional signal as a control mechanism of differentiation:

Back 13

One cell type producing diffusible substance (hormone, cytokine, morphogen) forms a concentration gradient which provides responding cells with positional signal.

Front 14

Intracellular clock as a control mechanism for differentiation:

Back 14

Cells are spontaneously changing their internal status during the time--> they may respond differently to the same signal according to the time when they receive it. Cells behave as they have some sort of internal clock

Front 15

What are hom coplex/ hox complexes?

Back 15

Evolutionary highly conserved molecular machinery provides positional information along anterior- posterior axis

Front 16

Homeotic genes:
a) Determine what?
b) What are the products of homeotic genes?

Back 16

a) The anterior- posterior character of Drosophila segments

b) Products of homeotic genes, containing highly conserved homeobox sequence which codes for DNA- binding homeodomain (60 AAs), are gene regulatory proteins. These proteins work as molecular labels of body regions.

Front 17

Where are the homeotic genes organized?

Back 17

Homeotic genes are organized within hom complex in one chromosome.
Chromosomal sequence of the genes corresponds to spacial sequence in which the genes are expressed

Front 18

4 homologous complexes in mammals:

Back 18

1. HoxA
2. HoxB
3. HoxC
4. HoxD

Front 19

Where are Hox complexes localized?

Back 19

On different chromosomes

Front 20

What is the function of Hox complexes?

Back 20

Function as specifiers for positional information in vertebrates

Front 21

Maintenance of tissues:

Back 21

1. Tissues with cell renewal
2. Tissues without cell renewal: permanent cells

Front 22

Permanent cells:

Back 22

Nerve cells, heart muscle cells, sensory cells for light and sound, lens fibers (once lost they can not be replaced)

Front 23

Physiological cell renewal:

Back 23

1. Proliferation of differentiated cells (hepatocytes, endothelial cells)
2. Renewal from undifferentiated stem cells (epidermis, blood cells)

Front 24

Renewal from stem cells:

Back 24

1. Unipotent stem cells (epidermis)
2. Pluripotent stem cells (blood cells)

Front 25

Stem cells:

Back 25

Are undifferentiated.
Have the ability to proliferate throughout the lifetime of organism.
Produce some progeny cells that differentiate and other cells that remain stem cells

Front 26

What regulates celle renewal?

Back 26

Cytokines (HGF, interleukines, erythropoietin)

Front 27

Tissue repair:

Back 27

1. Repair regeneration:
Mammals lost ability to regenerate external organs but they have some ability to regenerate internal organs (liver, bone tissue)

2. Wound healing:
Replacement of damaged functional tissue by connective tissue (proliferation of present fibroblasts stimulated by PDGF)

Front 28

Cell senescence:

Back 28

A phenomenon where after certain number of realized cell divisions the cell is losing its ability to proliferate and finally inevitably dies. There is a relationship between cell senescence and organism aging

Front 29

What determines life span of cells?

Back 29

Life span of the cell is not determined by certain time but by certain number of realized cell cycles

Front 30

Hayflick limit:

Back 30

For human embryonic cells about 50 cell cycles (programmed life span)

Front 31

Causes of cell senescence:

Back 31

1. Accumulation of mutations or accumulation of injuries (vs. cells of germ lines, genetic control of senescence)

2. Shortening of telomers at the end of chromosomes (insufficient function of telomerase)
DNA damage-->p53--> p21--> cyclin E/CDK2--> blockage of cell cycle / apoptosis induction

Front 32

Necrosis:

Back 32

Non- physiological (pathological) cell death due to irreversible cell damage resulting from exposure to extreme non- physiological conditions (heat, radioactivity, hypoxia, toxic substances)

Front 33

Apoptosis:

Back 33

Physiological cell death resulting from a need to eliminate the cell where the cell is active participant in self-destruction (the cell commits suicide after receiving signal
Cell has genetic program for self-destruction (programmed cell death)

Front 34

Necrosis characteristics: (7)

Back 34

1. Passive process
2. DNA stays intact
3. Loss of function and integrity of plasma membrane
4. Inflammatory response
5. Cell swelling
6. Chromatin stays intact
7. Desintegration of plasma membrane and cell lysis

Front 35

Apoptosis characteristics: (7)

Back 35

1. Active process (energy supply is acquired)
2. Early DNA degradation
3. Plasma membrane stays intact
4. No inflammatory response
5. Cell shrinking
6. Chromatin condensation
7. Formation of apoptotic bodies

Front 36

Biological significance of apoptosis: (4)

Back 36

1. Regulation of cell number
2. Forming of organism during development
3. Function of immune system
4. Pathological states

Front 37

Regulation of cell number (as a biological significance of apoptosis): 2

Back 37

1. Cell elimination (cells with damaged DNA, virally infected cells)
2. Maintenance of tissue homeostasis: maintenance of steady state number of cells

Front 38

Forming of organism during development (as a biological significance of apoptosis):

Back 38

1. Sculpting of tissues/ organs during development (finger forming, forming of cavities)

2. Tissue/ organ elimination during development (frog tail, male oviduct)

3. Tissue/ organ atrophy

Front 39

Function of immune system (as a biological significance of apoptosis):

Back 39

1. Negative selection of b& t cells

2. Mutual elimination of activated t lymphocytes

Front 40

Pathological states (as a biological significance of apoptosis):

Back 40

1. Tumors (tumor therapy)
2. Diseases associated with apoptosis (alzheimer`s disease, cardiac infarct)

Front 41

Molecular basis of apoptosis (main overview):

Back 41

Activation of cytoplasmic proteases caspases represents key event of initiation of apoptosis. Cleavage of death substrates by caspases leads to initiation of apoptosis execution

Front 42

What are caspases?

Back 42

Caspases are cysteine proteases (they contain active cystein residue which is required for proteolytic activity). They cleave substrates at the place of aspartic acid residue

Front 43

3 functional groups of caspases:

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1. Initiator caspases (caspase-8, caspase-9)
2. Executioner caspases (caspase- 3)
3. Inflammatory caspases (caspase-1)

Front 44

Activation cascade of caspases:

Back 44

Initiator caspases--> executioner caspases--> death substrates

Front 45

Death substrates: (4)

Back 45

1. DNA fragmentation:
Caspase activated DNase (CAD/ inhibitor of CAD (ICAD)

2. DNA repair: Poly (ADP-ribose) polymerasa (PARP)

3. Structural proteins (lamins, cytoskeletal proteins)

4. Regulatory proteins (Rb protein)

Front 46

Induced changes, resulting from proteolytic cleavage of death substrates is realized where?

Back 46

In the nucleus, cytoplasm and plasma membrane more or less independently

Front 47

DNA degradation is usually based on fragmentation:

Back 47

Mono- and oligonukleosomal fragments are generated (--> DNA ladder)

Front 48

Apoptotic signals:

Back 48

1. Endogenous apoptotic signals: Activation of p53

2. Exogenous apoptotic signals: Apoptotic signal molecules

Front 49

Control mechanism of apoptosis induction:

Back 49

1. Proteins of Bcl- 2 family
2. Mitochondria

Front 50

Activation of p53:

Back 50

Results from recognition of DNA damage (breaks) but activation mechanism itself is poorly defined. It is suggested that p53 binds unspecifically to damaged DNA and such interaction leads to activation

Front 51

Activated p53 functions as transcription factor:

Back 51

1. p21 (inhibitor of CDK2)
2. Genes of bcl- 2 family: bax (control mechanism of apoptosis)

Front 52

Apoptotic signal molecules: (5)

Back 52

1. Glucocorticoids

2. Cytokines: viability factors (IL-3, IL-4, IL-6, GM-CSF, IGF-I)

3. Ligands of receptors with death domain: Fas receptor, TNFR1
Interaction of Fas ligand with Fas receptor represents main mechanism of apoptosis induction in immune system

4. Granzyme B: System perforin/ granzyme B is based synergistic action of secreted perforin and granzyme B

5. Proteins of bcl-2 family: Family of related proteins. Proteins are mainly localized in mitochondrial membrane

Front 53

Antiapoptotic proteins:

Back 53

From the family (Bcl-2, Bcl- xL)
Inhibit apoptosis

Front 54

Proapoptotic proteins:

Back 54

Bax family. Induce apoptosis.

Front 55

What decides cell response to apoptotic signal?

Back 55

Ratio between antiapoptotic and proapoptotic proteins of the family decides cell response to apoptotic signal

Front 56

Key step of the main pathway of apoptosis induction is probably represented by changes in:

Back 56

Mitochondria leading to release of proapoptotic factors (AIF, cytochrome c, Apaf-1)

Front 57

Proteins of the family make:

Back 57

Homodimers and heterodimers

Front 58

Change in permeability of mitochondrial membrane:

Back 58

PT (permeability transition) pores, Bax/Bax channels (antiapoptotic proteins of Bcl-2 family via forming heterodimers with bax block channel formation)

Front 59

Release of Apaf- 1 from mitochondrial membrane:

Back 59

Apaf-1 dissociates from complex with antiapoptotic protein of Bcl-2 family localized in mitochondrial membrane (dissociation results from forming heterodimers with proapoptotic member of Bcl-2 family).

Front 60

Cascade of apoptosis induction:

Back 60

Apaf- 1+ cytochrome c+ caspase-9--> apoptosome--> activated caspase- 9---> activated caspase- 3