Stem Cells/Differentiation/Cell Cycle Flashcards
What is the hierarchy of stem cell potency?
Totipotent
Pluripotent
Multipotent
Unipotent
Name a type of adult tissue stem cell
Multipotent Haematopoietic Stem Cell
Mesenchymal Stem Cell
Induced Stem Cell
Neural Stem Cell
What are some examples of unipotent cells?
Epithelial Stem Cells, Neural Cells
Summarize advantages of using different stem cells in medicine?
Adult: harder to culture, easier for transfusing
Embryonic: Ethical problems, rejection, pluritpotent
Give examples of pluripotent cells
Embryonic stem cells
Pluripotent Primordial Germ Cells (endoderm, mesoderm, ectoderm)
Multipotent
Adult Stem cells
Haematopoietic Stem Cell
Mesenchymal Stem Cells,
Summarise the advantages and disadvantages of using different stem cells in medicine
Adult Stem Cells: Less controversial, Rejection isn’t an issue, multipotent
Embryonic: Controversial, chance of rejection, pluripotent,
Summarise the advantages and disadvantages of using different stem cells in medicine
Adult Stem Cells: Less controversial, Rejection isn’t an issue, multipotent
Embryonic: Controversial, chance of rejection, pluripotent,
Summarise current knowledge of the role of stem cells in cancer
Looking at cancer therapy that addresses cancers beginning in progenitor stem cells vs somatic cell that moves backwards to acquire stem-cell-like traits
Targeting cancer stem cells (Anti-CD47 treatment)
Describe the potential medical applications of stem cells
Inducing pluripotent stem cells to differentiate into RBCs
Limbal Stem Cell from eye used in eye to treat injured cornea (Holoclar)
Injections of Colony Stimulating Factor to mobilize stem cells in blood (instead of drawing from bone marrow)
What components are needed for the production of erythrocytes to occur?
Iron- (reduced from Fe3+ to Fe2+) needed for haem synthesis,
B12- needed for DNA maturation & condensation of RBC
Folic Acid- needed for DNA maturation & condensation of RBC
Carbohydrates- to make haemoglobin
Fats- to make haeme
Erythropoietin- initiates Myeloid Stem Cell differentiation into erythrocyte
What events stimulate Erythropoiesis?
Hypoxia
Hypoxia allows for release of Hypoxia Inducible Factor, which then stimulates production of Erythropoietin production in Kidneys
Where does Erythropoiesis occur?
In the red bone marrow at the epiphysis of long bones
Describe the process of Erythropoiesis?
Haematopoietic Stem Cell -> Myeloid Stem Cell (induced to make erythrocytes when erythropoietin present) -> Pro-erythroblast -> basophilic erythroblast (lots of RNA present make it basophilic- loves blue) -> polychromatic erythroblast (haemoglobin synthesis turns cell red, red/blue (poly colours)) -> orthochromatic erythroblast (loss of nucleus-acid loving, turns it solely red) -> reticulocyte -> erythrocyte (matured reticulocyte)
What initiates the development of platelets?
Kidneys/liver release thrombopoietin -> stimulates Myeloid Stem Cell differentiation into Megakaryocytes -> thrombopoietin also stimulates megakaryocyte maturation into platelets -> megakaryocyte produces ~1000-3000 platelets.
Where are excess platelets stored?
Spleen
What is another name for platelets?
Thrombocytes
What is the name of the division a stem cell undergoes?, and what type of daughter cells are produced? (RK)
Asymmetric division. Two daughter cells are produced, one is identical to the mother stem cell + the other is a slightly specialised cell (progenitor/precursor) which has a reduced proliferative capacity
When and where are totipotent cells found? (RK)
Early stages of development in the embryo, examples include zygote (fertilized cell) and morula (early stage embryo consisting of 16 cells called blastomeres)
What are induced pluripotent stem cells (iPSCs)? (RK)
Pluripotent stem cells generated directly from adult somatic cells (e.g. skin fibroblasts) by genetic reprogramming
What are cancer stem cells and what are 2 hypotheses in which they arise? (RK)
Sub-population of stem-like cells that exist within tumour cells that exhibit both characteristics of cancer cells and stem cells. They are thought to arise from normal stem cells or progenitor cells that acquire cancerous characteristics, or from normal adult somatic cells that acquire both stem cell and cancer cell characteristics
Do all cells undergo life cycles?
No, i.e. Granulosome cells of the epidermis do not replicate and divide, red blood cells & neutrophils dont divide
Leukocytes only sometimes divide
What is G nought, ir quiesence?
When cells are not replicating,
How long does the cell cycle typically take in a human?
About 1 day G1- 11 hours S- 8 hours G2- 4 hours M`-1 hour
What happens in G1?
Cells grow back to their organelle size
Monitor external environment for optimal time to replicate, and looking for growth factors
What happens in G2?
Cells prepare for cell division
Duplication of cell organelles
What happens in M phase?
Mitosis and Cytokinesis
What are the stages of mitosis?
Prophase- chromosome strands shorten and thicken, nuclear envelope disappears, centrioles move to poles
Prometaphase- spindle extends into nucleus to attach to the chromosome
Metaphase- all chromosomes consist of sister chromatids attach to spindles
Anaphase- sister chromatids are moved to either end of cell
Telophase- Chromatids arrive at either end of pole, spindles disappear
In what stage of the cell cycle is DNA Polymerase most active?
S Phase
What is a cyclin?
Short lived protein that regulate CDK activity
Vital in regulating
Why is the cell cycle regulated?
We would have uncontrollable growth without it (tumours)
Necessary to ensure DNA replication is done correctly and at the right time
What are Cyclin-Dependent Kinases?
A protein that functions at different stages of cycle to allow progression once forming a complex with cyclin
What are some pairings of CDKs and Cyclins and the stages of the cell cycle they regulate?
CDK 4/6 and Cyclin D- regulates G1 progression
CDK 2 and Cyclin E- Regulates movement into S phase
CDK 2 and Cyclin A- Regulates movement into G2 and Mitosis
CDK 1 and Cyclin B- Regulate movement past Metaphase
What is a Cyclin-Dependent Kinase Inhibitor?
Regulates CDK and Cyclin activity in response to environmental factors or damaged DNA by forming inactive complex or acting as competitive ligand
What is Maturation Promoting Factor?
Another name for CDK 1/ Cyclin B
How do Cyclins regulate CDK?
A CDK isn’t active unless cyclin is bound to it.
Cyclin is produced when cell cycle progression is needed, and automatically binds CDKs
cyclin is destroyed afterwards
What determines if a cell moves forward in the cell cycle?
Cyclins
What are the types of Cyclin-Dependent Kinase Inhibitors?
p21 CIP- offer extra level of control (can inhibit all CDKs, but primarily associated with CDK2)
p27 KIP- Directly inhibits Cyclin D/CDK4 & E/CDK 2
p16 INK- Encodes inhibitor of Cd/ CDK 6 & 4
How does CDK 1/ Cyclin B work to encourage cell cycle progression?
Cyclin B, synthesized during G2, associates with CDK1- now active- known as Maturation Promoting Factor (MPF)
CDK1 now phosphorylates lamins (lamins are intermediate filaments that are part of nuclear lamina) to aid in break down of nuclear envelope
Also phosphorylates histones and condensins which aids in condensation of chromosomes
Phosphorylates Microtubules Associates Proteins (MAPs) that are needed for microtubule assembly
When is the restriction Checkpoint of the cell cycle?
During G1 phase, a point of commitment to replication, or not
When is the DNA Damage Checkpoint in the cell cycle?
During the G1 transition and G2 phases
What is the last checkpoint in the cell cycle and what is it checking for?
The Metaphase checkpoint
Ensures chromatids are secured to mitotic spindles
What are growth factors?
Secreted signalling molecules that act on cells, impacting their growth and behaviour
What are some common growth factors?
EGF, VEGF, PDGF
What is the retinoblastoma protein?
The gate-keeper to the cell cycle
How does the RB protein typically work?
Found bound to E2F
This binding of RB to E2F disallows E2F from allowing transcription of DNA and initiating the production of proteins needed for the cell cycle
Phosphorylation of RB causes dissociation of RB from E2F
What is E2F?
A transcription factor that allows the initiation of transcription of proteins (i.e. DNA Polymerase) needed for the cell cycle
What is an example of a tumour suppressor gene?
Retinoblastoma, P53, BRCA1
What do tumour suppressor genes do?
They halt the cell cycle until appropriate conditions are met by initiating production of proteins that will stop the progression of the cycle
How does p53 respond when it detects damaged DNA?
Damaged DNA is detected by P53 causing
CKI P21 production -> binds to CDK 2 Cyclin E/A and/or CDK 1 Cyclin B, halting progression
How does the p53 gene respond to extensive DNA damage?
Transcribe genes that cause cell apoptosis
What is done at the metaphase checkpoint?
Spindle Assembly Checkpoint
Delays onset to anaphase until all chromosomes are correctly attached to spindle fibres, inhibition is removed once all chromosomes are correctly bound to spindles.
What does p53 do for cell regulation/transcription?
It increases in quantity in response to cell damage, acts as transcription factor to regulate cells that regulate cell growth
i.e. regulates transcription of p21cip that halts the cell cycle, will initiate transcription of apoptotic factors if cell DNA is too damaged
Describe the receptors, transduction, and response of the Ras pathway.
Growth Factor stimulates tyrosine kinase receptor -> dimerization -> autophosphorylation of intracellular component of receptor -> GRB2 can now bind intracellular receptor-> SOS binds GRB2 -> SOS catalyses RAS phosphorylation -> Ras phosphorylates B-RAF -> B-RAF phosphorylates MEK 1/2 -> MEK 1/2 phosphorylates ERK 1/2 -> activation of transcription factors of AP1 family (Fos, Jun) -> transcription of cyclin D -> complex CD / CDK4 &6 formation -> progression past G1 phase
What is an example of an enzyme linked receptors and what is the typical ligand?
Tyrosine kinase and Growth Factors
What is a G-protein linked coupled receptors and its typical ligand?
Large, trimeric, transmembrane receptor that is activated by hormones, chemicals, (i.e. serotonin, adrenalin) to stimulate an intracellular secondary messenger
What is an ion-channel linked receptor and its typical ligand?
A transmembrane receptor which, when activated by ions, will allow ions into cells to alter electrical properties.
I.e. glutamate neurotransmitter
What are the categories of receptors, and their types?
Intracellular receptors- Hydrophobic or Gases
Extracellular receptors- Ion-Channel Linked, G-Protein Linked Couple Receptor, Enzyme Linked
What is an example of a hydrophobic receptor ligand?
Oestrogen, testosterone
Bind hormone receptor intracellularly, and travel and complex into the nucleus
What is an example of a gaseous receptor ligand?
Nitric Oxide diffuses through the plasma membrane of smooth endothelial muscle cells in blood vessels of the corpus cavernosum of the penis to bind Guanylate Cyclase.
What are the types of intracellular transduction pathways as well as an example?
Kinase Cascades- involves amplification, and kinases and phosphotases
i.e. Mitogen Activated Protein Kinases (MAPKKK activates MAPKK which activates MAPK which acts on effector molecule).
Secondary Messengers- involves transmission and amplification of signal. Production of many secondary messengers
i.e. • Cyclic AMP (cAMP) - produced by the enzyme adenylyl cyclase
• Inositol triphosphate (IP3)and Diacylglycerol (DAG) - produced by the enzymephospholipase C
• Calcium ions - released from intracellular stores by IP3, or flow into cell upon ion channel activation
What responses can signal transduction cause?
- Altered targetprotein activity
e. g. phosphorylation alters the activity of many metabolic enzymes - Altered targetprotein binding
e. g. blocks, or causes, binding of a target protein to an inhibitor or activator protein - Alteredprotein localization
e. g. movement of a transcription factor from nucleus to cytoplasm stops it acting on DNA
e. g. causes co-localisation of an enzyme with its substrates, allowing the enzyme to function
What are two exceptions to the central dogma of molecular biology?
Reverse transcriptase
Non-coding RNAs (tRNA, rRNA, miR)
How do transcription factors affect transcription?
Bind to very small sequences of DNA Can increase (activator) or decrease (repressor) rate of transcription
What are some examples of transcription factors?
Nuclear Hormone Receptors- Ligand-dependent transcription factors
-glucocorticoid, oestrogen, testosterone, and retinoic acid receptors
p53 and E2Y
What is an example of a drug impacting transcription factors?
Steroid act on transcription factor to impact gene expression
What form the transcription initiation complex?
6 primary transcription factors (TF) involved, RNA Polymerase II, TATA Box.
RNA polymerase binds to TFIIB which is bound to TATA box sitting on DNA
TATA binds to promoter
What is the CCAAT Box?
CAT Box is used to stabilize the other transcription factors
What are gene enhancers or silencers?
Aid or deplete the transcription of genes.
They therefore can alter the expression of genes over time
How does p53 act as a promoter and repressor of cell survival?
Activator- p53 activates transcription of p21 leading to cell cycle arrest, allowing for DNA repair
Repressor- inhibits transcription of survivin gene, leading to apoptosis
How does Oct-1 act as a transcription promoter or repressor?
Oct1 represses transcription of thyroid stimulating hormones in all cells apart from thyrotrophs in the pituitary
How does E2F work to either promote/repress transcription?
Promotes transcription of genes for S phase
How does Snail work as a transcription repressor or promoter?
Promotes the repression of E-cadherin in epithelial cell cancers (allows for epithelial to mesenchymal transition during embryological development)
No E-cadherin means less rolling adhesion, but better invasive capabilities
What is a super-enhancer locus control region?
Locus control region areas that when a transcription factor binds, will open tightly wound chromatin, allowing for transcription factors bind
i.e. locus control region ahead of globin gene in erythrocytes.
What is constitutive gene expression?
Expressed in all cells at all time, maintain cell function
i.e. beta-actin (microfilaments of cells), or ribosomal proteins, or GAPDH (needed in 6th stage of glycolysis), and general transcription factors needed for gene transcription
What is are inducible gene expression?
Only expressed in certain tissues or at certain times.
i.e. Almost all protein, CD4, CD8, collagen 1 by fibroblasts needing to make fibroblasts, globin only in erythrocytes, myelin in myelin producing cells.
Time: Cyclins are present in any cell but only during cell replication, inflammatory cytokines, foetal development ones. Foetal-globin expression during development, which declines after birth. Beta-globin then begins to be more highly expressed in cells expressing haemoglobin after birth.
