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Biology 2B03 > Week 9 + Module 8 > Flashcards

Week 9 + Module 8 Flashcards

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1
Q

what is Embryogenesis

A

Formation of inner cell mass of embryonic cells

As number of cells in the embryo increases, they separate into one of three developmental germ layers

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2
Q

what is Multicellularity

A

stable interactions between cells

requires cells to associate/interact and maintain connections

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3
Q

Three developmental germ layers

A

Ectoderm (outside)
Endoderm (inside)
Mesoderm (middle)

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4
Q

Sponge adhesion experiment

A

Demonstrated in 1907 by H.V. Wilson in experiment using cells of 2 species of sponges:

  • Individual cells of these multicellular organisms were separated apart using fine mesh
  • Cells were then mixed together and over time, cells from the same species were able to recognize and associate back together, but cells from different species didn’t
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5
Q

Frog embryo cell adhesion experiment

A

1950’s Johannes Holtfreter

  • Took cells from 2 different developmental germ layers and separated apart individual cells
  • Cells from similar tissues recognized each other and ended up associated, mimicking organization seen in the original embryo (tissue-specific lineages)
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6
Q

How do cells stay together and communicate once agregated

A
  • Cells stay together through a collection of transmembrane proteins called cell adhesion molecules (CAMs)
  • After aggregation, cells form specialized cell junctions that stabilize cell to cell interactions and facilitate communication between adjacent cells
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7
Q

Epithelial cell structure - 5 components

A
  • connect on lateral surfaces to form epithelial sheets
  • sheets form inner lining of digestive system and outer skin layer
  1. Tight junctions (s)
  2. Adherens junctions (s)
    - in the adhesion belt
  3. Desmosomes (s)
    - look like hemi, visible structures
  4. Hemidesmosomes (b)
  5. Gap junctions (s)

s = sides
b = basal surface
a = apical

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8
Q

What are tight junctions

A

aka zonula occludens

  • connect adjacent cells just below apical surface
  • completely seal off space

Prevents fluid from moving across the layer of cells, restricting the diffusion of small molecules
= no leaking of digestive enzymes

looks like those boards made of pool noodles

0/
0/
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/ = Linear arrays of proteins called occludin and claudin are closely arranged between neighboring cells

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9
Q

Is the tight junction a single junction

A

not a single junction, but an accumulation of structures that form a complete junctional band between cells

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10
Q

Junctional band

A
  • Prevents diffusion of membrane proteins from apical to basolateral regions of plasma membrane
  • Completely prevents diffusion of molecules in the extracellular space between cells

like a belt

ADHERENS junction

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11
Q

Gap junctions - location, function, size

A

on the sides of the cells
- directly link their cytosols

allow for:
- integration of metabolic activities
- ion and small molecule exchange
(including cAMP and calcium)
- holding cells together (pinching membrane)

1.5-2 nm in diameter
free diffusion of molecules up to 1kDa in size in channels

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12
Q

Connexon hemichannel composition - relationship to gap junction

A

hexagonal
- 6 individual connexin protein subunits

2 lined up hemichannels make a gap junction

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13
Q

Gap junctions and contractions

A

Coordination of cardiac muscle contraction and uterine muscle contractions

  • Stimulation of one cell can lead to a response shared by many cells through diffusion of secondary messengers directly through the flow of cytosol between cells
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14
Q

Plasmodesmata

A
  • structure in plant cells
  • Important to structure and function of phloem in flowering plants
  • forms the sieve tube plate that connects phloem cells
  • connect companion cells to phloem cells

Communication through plasmodesmata involves trafficking of informational macromolecules (transcription factors, gene transcripts, small RNAs)

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15
Q

Phloem

A

system of elongated tubes formed from linear arrays of connected cells

Carrying nutrients (products of photosynthesis - sucrose) from leaves to the rest of the plant

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16
Q

Companion cells

A

When sieve-tube elements are metabolically inactive:

Specialized cells (companion cells) provide cells with ATP, proteins and other substance for sieve-tube development and functions

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17
Q

Adherens junctions

A
  • indirectly connection actin cytoskeleton between neighbouring cells
  • can connect the same (homo) or different (hetero) cells
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18
Q

4 families of adherens junctions

A
  1. Cadherins - homo
  2. Members of the Ig-superfamily - homo
  3. Integrins - hetero
  4. Selectins - hetero
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19
Q

What are cadherins + what other molecule do they need to cause aggregation

A

Critical cell adhesion molecules

  • Calcium-dependent CAMs that mediate homophilic interactions
  • Includes E-cadherin (epithelial), N-cadherin (neural) and P-cadherin (placental)
  • Mediate epithelial cell-cell adhesion near the spiral surface of cells, below the tight junctions
  • Only connect to cells expressing the same cadherin
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20
Q

What is in the multiprotein adhesion complexes? What do they do?

A

Adhesion is mediated by multiprotein complexes which anchor cadherin to the actin cytoskeleton
- Transmembrane cadherins
- Cytosolic cofactors
- Catenins

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21
Q

Desmosomes vs. hemidesmosomes

A

Desmosomes - link 2 cells together

Hemidesmosomes - attach cells to extracellular matrix

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22
Q

Benefit of WBCs + example

A

help with immune response

ex. neutrophils

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23
Q

Cell adhesion is important for…

A
  • Establishing and maintaining cell connections
  • Cell function requires transient/temporary associations that are broken and established

ex.
- Migration of cells during embryogenesis
- Movement of leukocytes/WBCs in the blood through adhesion of endothelial cells or blood vessels and leukocytes

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24
Q

3 families of WBCs

A
  1. Granulocytes
  2. Monocytes
  3. Lymphocytes
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25
Granulocytes
- target pathogens - includes neutrophils, eosinophils, and basophils e/b no extravasation
26
Neutrophils
- most numerous granulocytes - Primarily target bacterial infections and are one of the first cells to respond to trauma - Undergo process of extravasation
27
Monocytes (macrophages)
- Type of leukocyte that differentiates into macrophages - Macrophages engulf invading bacteria of dead/damaged cells through phagocytosis - Do extravasation
28
Lymphocytes
- Lyse or destroy virally infected cells and tumour cells - NK (natural killer cells), T and B cells (immune response) - Do extravision
29
5 steps of extravasation
1. Capture 2. Rolling 3. Slow rolling 4. Firm adhesion 5. Transmigration
30
Extravasation step 1: neutrophil capture
- Transient/temporary association between neutrophil and apical surface of an endothelial cell (of blood vessel) - Neutrophils are still pushed by the flow of blood through the vessels, but movement is slower - Mediated through cytokines; change the behaviour of the endothelial vessel wall cells
31
Extravasation capture example
Example of cytokine: TNF-alpha - A receptor on the basal surface of the endothelial cell receives the signal and triggers the release of selectins that then appear on the apical surface of endothelial cells
32
When cytokine signal received
- Secretory vesicles transport P-selectin to surface of endothelial cells - P-selectin interacts with the selectin-specific glycoprotein on surface of the leukocyte
33
Extravasation step 2: rolling
- Cells roll along surface of the endothelial cells in blood vessels - Establish and lose transient connections - P-selectin associations can involve PSGl1
34
Extravasation step 3: slow rolling
- Rolling eventually slows over time as the number of associations between neutrophil and endothelial cells increase - Density of selectins increases as neutrophil gets closer to the site of infection - Many endothelial cells at site of infection display P-selectin and E-selectin
35
Extravasation step 4: firm adhesion
- With stronger attachment of neutrophil with the endothelial cells - A membrane-anchored signal/cytokine on the endothelial cell called (PAF) - Platelet activating factor, interacts with the transmembrane receptor on the neutrophil called the PAF-receptor (ex. CXCR1 And CXCR2 (members of GPCR family)) - Activation of PAF receptor by ligand-binding initiates signal pathway inside the neutrophil - Changes in gene expression and activation of another cell adhesion molecule (integrin adhesion) - The integrin interacts with the ligand ICAMS to further slow movement and firmly adheres
36
Integrin composition and states
In inactive form: - Propeller and beta-A domains are pointed down and form the ligand-binding domain - While folded down, the integrin cannot recognize it In active form: - Integrin can bind to its ligand on the endothelial cells - Increases activity of association between integrins and ligands - Activation of integrins signals more changes in neutrophil behaviour
37
Extravasation step 5: transmigration
Neutrophil no longer moves within bloodflow and has stopped at the site of infection: - Migrates by crawling between endothelial cells - Connections between endothelial cells are broken by enzymes produced by the transmigrating neutrophil
38
7 stages of mitosis
1. interphase 2. prophase 3. prometaphase 4. metaphase 5. anaphase 6. telophase 7. cytokinesis
39
Interphase
- chromosome duplication and cohesion - centrosome duplication
40
Prophase
- break down microtubule array - replace with mitotic asters - aster separation - chromosome condensation - kinetochore assembly
41
Prometaphase
- nuclear envelope breakdown - chromosomes captured, bi-oriented, and brought to spindle equator
42
Metaphase
- chromos aligned at metaphase plate
43
Anaphase
- APC/C activated and cohesins degraded Ana A: chromosome mvmt to poles Ana B: spindle pole separation
44
Telophase
- nuclear envelope reassembly - contractile ring assembly
45
Cytokinesis
- reformation of interphase microtubule array - contractile ring forms cleavage furrow
46
Motor proteins in mitosis (3 uses)
1. establishing a bipolar mitotic spindle in pro 2. attaching chromosomes in prometa/meta 3. orchestrating chromatic separation in ana
47
Microtubule polarity and subunit addition
- made of a/b tubulin dimers a = GTP = (-) end b = GDP = (+) end
48
Motor protein transport direction
Kinesin to plus end Dynein to minus end
49
Kinesin-1-catalyzed vesicle transport
vesicle kinesin receptor kinesin heads (2) move towards plus end
50
Other types of kinesin and their functions
Kinesin-2 - heterotrimeric - transports organelles Kinesin-5 - bipolar - slides between two microtubules Kinesin-13 - super small, basically just heads - disassembles ends of the microtubules
51
Centrosome structure
- pericentriolar material (surrounding the mother centriole) contains Y-TuRC microtubule nucleating structures
52
Y-TuRC
Y-Tubulin ring complex - nucleates the (-) end of the microtubule
53
G1/S phase centrosome duplication
- duplication of each centriole to create two pairs - initiated by CDKs and Plk4 - centrioles separate and a daughter crows from each daughter growth complete by G2
54
Centrosome separation in mitosis
- M phase CDKs activation initiates centrosome splitting - each new MTOC nucleates assembly of microtubules and is pushed to opposite sides of the nucleus - MPF indirectly leads to activation of Nek2 kinase that enables separation of centrosomes
55
Role of Kinesin-5 in centrosome separation (meetaphase)
- bipolar - attaches to a microtubule on each centrosome - travels in opposite directions (both to + end) - pushes centrosomes apart
56
3 types of MTs in the bipolar spindle
1. Astral - project towards cell cortex 2. Kinetochore - connected to chromosomes 3. Polar - project to the cell center where distal (+) ends overlap
57
Bipolar vs. monopolar chromosome attachment in prometaphase
Bipolar - both centrosomes attach to the chromosome (one from each side) Monopolar - one centrosome attaches to the chromosome
58
Kinetochore attachment
- attaches to the (+) end of a KT MT - dynamic attachment
59
Bipolar vs. monopolar chromosome attachment in metaphase
All chromosomes must have bipolar attachment for the cell to enter anaphase
60
MTs in Anaphase A
Microtubule shortening - centrosomes pulled poleward shorten both at the... a) centrioles (poleward MT flux) b) chromosomes (pacman kinetochores)
61
MTs in Anaphase B
Kinesin and dynein - sliding force btwn polar microtubules - also growth at (+) end of polar MTs due to kinesin 5 - dynein shortens astral MTs
62
Chemo - why lose hair?
- targets fast dividing cells so affects hair and intestinal cells
63
Taxol as a cancer treatment
- from yew trees - prevents microtubule depolmerization - stabilizes, prevents mitosis, prevents cell division / mitosis
64
Issues with multipolar spindles
- usually lead to aneuploidy and cell death - cancer cells usually have this
65
How do cancer cells with multipolar spindles survive
healthy cells - inhibit clustering - form multipolar spindles - those with too many centrosomes die or become aneuploid cancer cells - no inhibition of clustering = centrosomal clustering - produces identical daughter cells
66
Cancer solution
- prevent centrosomal clustering (not needed by healthy cells) - MT poisons result in cancer cell death (yay) and multipolarity (boo)

Biology 2B03 (12 decks)

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