This document includes questions and answers regarding the content of the course. It includes information from turorials, lectures (and practicals). This document helped me pass the course easily.
Case 1
What are the different Autocrine
types of signalling? - Wnt, Th-IL1
+ examples Paracrine
- Wnt, Shh
Endocrine
Juxtacrine
- Notch
Intracrine
Neurocrine/ synaptic
Exocrine
What are the 3 different Anchoring junctions
groups of junctions? Occluding junctions
Channel-forming junctions (communication)
What are the types of Adherens junctions
anchoring junctions? Desmosomes
Hemidesmosomes
Actin-linked cell-matrix junctions/ focal junctions
What are adherens - They connect actin filaments in one cell with that in the neighbour
junctions? cell
- They are composed of classical cadherins (E, P, N), catenins and
actin
- Ca2+ is essential for extracellular cadherin domain interaction
- Actin filaments are smaller than the intermediate filaments and
microtubules and they support the PM and regulate cell movement
and signal transduction.
What are desmosomes? - Connects intermediate filaments in one cell with that in the
neighbour cell
- Composed of non-classical cadherins (desmoglein, desmocolin) as
TM protein
- Adaptor proteins: plakoglobin, plakophilin, desmoplakin.
- The intermediate filaments are relatively large and their function is
mechanical support.
What are - They anchor intermediate filaments in a cell to the extracellular
hemidesmosomes? matrix
- They are composed of integrin alpha6beta4, collagen XVII as TM
proteins
- Adaptor proteins: plectin, dystonin.
What are actin-linked cell - They anchor actin filaments in the cell to extracellular matrix
matrix junctions? - Composed of integrins, Talin, FAK, tensin, vinculin
- This is involved in down-stream signalling events that can result in
migration, adhesion, invasion, proliferation and apoptosis.
What are occluding Tight junctions
junctions? - They are composed of claudins as TM protein
- They are supported by occludins and junction adhesion molecules
(JAMs)
- They are connected by ZO1 proteins (adapter proteins) to actin
filaments
What are the functions of - They hold cells together
tight junctions? - They help to maintain the polarity of cells by preventing lateral
diffusion of integral membrane proteins between apical and
, basolateral surfaces of the cell.
- They prevent passage of molecules and ions through the space
between plasma membranes of adjacent cells.
What are channel- - They are composed of connexons which are composed of connexins
forming junctions? and innexin proteins
- 1 connexon is made up of 6 connexin proteins
- 1 gap junction is composed of 2 attaching connexons
- They can switch between open/ closed states in seconds
- By closing gap junctions, healthy cells can be protected from
damages neighbouring cells
o Damaged cell causes high Ca2+ influx in neighbouring cells
which causes closure of gap junctions, preventing spreading
damage.
What are the functions of - Trafficking/ transport of inorganic ions and small water-soluble
channel-forming molecules between neighbouring cells
junctions? o Ca2+
o Nucleotides
o Amino acids, small peptides
o Vitamins
How does the Notch- 1. The Delta like ligand (dll) has to be activated through ubiquitination
receptor pathway works? 2. Dll binds to the extracellular domain of the notch receptor via their
EGF domains
3. Adam (a protease) cleaves the extracellular domain, dislodging that
component off the receiving cell (=S2 cleavage)
4. Secretase y cleaves NICD off the intracellular domain
5. NICD is free in the cytosol and can bind to a complex of proteins
(like CSL and MAM)
6. This complex will further binds to P3006
7. This complex translocates to the nucleus, where is acts as histone
acetylase
8. Leads to the transcription of notch target genes.
How does the Wnt Inactive
pathway works? 1. In the inactive form, β-catenin is bound to other proteins (like β-
TrCP) that form a complex (=destruction complex)
2. Phosphorylation of β-catenin signals β-TrCP to ubiquitinate the
β-catenin
3. This leads to proteasomal degradation and causes low levels of
β-catenin in the cell
4. Wnt-responsive genes are kept inactive by the Groucho co-
repressor protein bound to the transcription regulator LEF1/TCF
Active
1. Wnt acts to activate its receptor frizzled
2. LRP is phosphorylated by GSK3 and CK12.
3. The translocation of the destruction complex is induced to the
region of the membrane near the frizzled and LRP receptors
4. When Dishevelled binds to LRP, it becomes activated, which
causes inhibition of the destruction complex
5. Axin binds to the phosphorylated LRP and is inactivated,
resulting in disassembly of the degradation complex
6. This prevents β-catenin from being phosphorylated and
prevents β-TrCP from getting into the destruction complex and
, ubiquitinating the β-catenin
7. Levels of β-catenin increases
8. β-catenin translocates into the nucleus
9. β-catenin binds to LEF1/TCF
10. β-catenin bound to LEF1/TCF dislodging Groucho
11. The transcription of Wnt target genes is now stimulated
How does the Shh Inactive:
pathway works? 1. When the pathways is inactivated (no Hedgehog present)
patched inhibits smoothened
2. When smoothened is inhibited it can't enter into the plasma
membrane which means that smoothened resides in the cytosol
(usually within an endosome)
3. Gli proteins like Gli2 and Gli3 are associated with SUFU protein
4. CKI, PKA and GSK3β all phosphorylate GLI2/3
5. When these Gli proteins are phosphorylated, they are
processed by the proteasome and they're cleaved into a their
repressed forms: Gli2R and Gli3R5.
6. These repressor proteins can then translocate into the nucleus
where they can inhibit transcriptional activation of Hedgehog
mediated genes.
Active:
1. This pathway is activated when there are Hedgehog proteins
present, such as sonic hedgehog
2. Shh can bind and inhibit patched
3. The binding of sonic hedgehog to patched is facilitated and
promoted by proteins such as CDO, BOC etc.
4. Once patched is inhibited, patched can no longer inhibit
smoothened
5. Both patched and GPR161 (transmembrane protein) will leave
the membrane of the primary cilium and are degraded within a
proteasome inside the cell
6. Without patched, smoothed is no longer inhibited and will be
phosphorylated by both CKI and GPRK2
7. Smoothened can then enter into the plasma membrane of the
primary cilium next to EVC (protein)
8. KIF7 aids in the movement of both Gli proteins and SUFU
proteins through the primary cilium
9. Gli proteins disassociate from SUFU and are no longer
phosphorylated and degraded
10. Gli2/3 can then translocate and enter into the nucleus where
they can bind to the DNA and induce the expression of Gli
target genes
11. These Glee target genes are responsible for development
patterning and differentiation
How does the JAK-STAT 1. The binding of ligands (cytokines) causes the receptors to
pathway works? dimerize, which brings the receptor-associated JAKs into close
proximity. The JAKs then phosphorylate each other.
2. The activated JAKs then phosphorylate tyrosine residues on the
receptor, creating binding sites for proteins possessing SH2
domains.
3. STATs then bind to the phosphorylated tyrosine’s on the
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