BIO230 UofT Final Exam

What domains are polar in multicellular organisims

Apical domain
basolateral domain

Polarized cells can...

have different functions at different cell regions
define inside v outside
transmit signals from one end to the other

Exocytosis

directly to the target domain
-out

endocytosis

process by which a cell takes material into the cell by infolding of the cell membrane
in

Trafficking routes

polarized
proteins are organized at sorting station
balanced by retrieval pathways

ER-> Golgi-> plasma membrane

some trafficking routes are polarized

Transmembrane ->Golgi network

proteins are organized at sorting stations

ER retrieval from Golgi

different routes are balanced by retrieval pathways

Most cargo moves through

Constitutive sectretion

What is not required for constitutive secretion

specific signals

returns membrane back to the golgi

clathrin-coated vesicles

Clathrin-coated vesicles

shrink vesicle
makes cargo more concentrated

Regualted secretion

releases material in response to a signal
do not fuse with the plasma membrane until signal is received

Cytokinesis

division of the cytoplasm to form two separate daughter cells

Phagocytosis

A type of endocytosis in which a cell engulfs large particles or whole cells

Plasma membrane repair

fixes a wound in the cell by exocytosis

Plasma membrane - early endosome- lysosome

polarized

endosomes

sorting stations

re-secretion to plasma membrane

retrieval pathways

3 options for endocytosed proteins

recyclying, transcytosis, degradation

Vesicle trafficking types

donor membrane into cytoplasm
vesicle fusion
donor membrane away from the cytoplasm

what does LDL bind to?

LDL receptors coated with clathrin triskelion

COPII

ER to cis-Golgi

COPI

Golgi to ER

Clathrin

Trans Golgi-->Lysosomes; Plasma membrane-->Endosomes

Retromer

multiprotein coat that forms on an endosomal vesicle only

SNARE proteins

help mediate vesicle fusion
t-SNARES and v-SNARES required
-must be on opposite membranes

ESCRT proteins

can form vesicles away from the cytoplasm
into lumen or extracellular space
vesicle formation machinery in cytoplasm

ESCRT-0

binds PI(3)P and collects mono-ubiquitinated cargo proteins, provides binding site for ESCRT-I
- initiation and cluster cargo selection step

ESCRT-1, 2, and 3

help push vesicle away from cytosol

How many of the following are examples of vesicle formation into the cytoplasm?
COPII-mediated secretory vesicle formation at the ER
ESCRT-Mediated vesicle formation
clathrin-mediated endocytic vesicle formation
any process mediated by SNARE proteins

2

Phosphoinositides

label different membrane domains
diff membrane domains and compartments contain diff lipids
diff PIPS are found at diff subcellular locations
Phosphorylation site positions are numbers in brackets
total number of phosphorylation sites subscript number

PI(3)P

phagocytosis
-endosomes
-can phosphorylate PI(3,4)P2 and PI(3,5)P2
-can dephosphorylate PI

PI(4)P

endocytosis
-golgi
-can dephosphorylate PI
-can phosphorylate PI(3,4)P2 and PI(4,5)P2

PI(4,5)P2

Golgi and PLasma membrane
can dephosphorylate Pi(5)P and PI(4)P
can phosphorylate PI(3,4,5)P3
bind to adaptor proteins for clathrin mediated enodocytosis

PI(3,5)P2

Endocytosis
-late endosomes
-can dephosphorylate PI(5)P

PI(3,4,5)P3

phagocytosis
-plasma membrane
-can dephosphorylate PI(4,5)P2 and PI(3,4)P2

Structure of Phosphoinositides

inositol sugar-blue
phosphate group-yellow
glycerol-grey
lipids-orange

Rab GTPase

molecular switches that can direct vesicles
off when bound to GDP
on when bound GTP
GEF turns on this exchange from GDP to GTP

Rabs and PIPS combination in early endosome

Rab5-GTP recruits PI 3-Kinase
PI(3)P can recruit Rab5-GEF
More Rab5-GEF makes more active Rab5-GDP

Rabs and SNARES

work together in vesicle targeting & fusion
interact with tethering protein

Polar cytoskeleton organization

Microtubules
actin
intermediate filaments

Microtubules

transport vesicles and proteins to diff ends of the cell

actin

defines cell shape and behaviour

Intermediate filaments

contribute to cell polarity

Interphase crawling/ migrating cell

microtubules radiate from cell centre
actin enriched at cell cortex

Mitosis

microtubules form the mitotic spindle
actin at cell cortex dissembles

cytokinesis

microtubules keep cell components separate
actin forms the contractile ring

Polar tublin dimers for polar microtubules

monomeric proteins
-alpha tubulin
-beta tubulin
-both form dimers
tubulins bind and hydrolyze GTP
tubulin heterodimers assemble head-to-tail to make polarized protofilaments

alpha tubulin

found at minus end
d-form heterodimer
-less stable
-GDP-bound
-is hydrolized t-form subunits
-if found at tip of microtubule will fall (depolymerization)

Beta tubulin

found at plus end
t-form heterodimer adds to plus end
-stable associations
-GTP-bound

Dynamic instability

The rapid switching between growth and shrinkage shown by microtubules.

gamma tubulin

interacts w/ alpha tubulin at minus end
nucleates or stabilized the (-)end
protects microtubules from depolymerization at (-) end
(+) end grows away from nucleation site
in animals, found near centrioles
in plants, found on other microtubules

Microtubule-associated proteins (MAPs)

a class of proteins that participate in the regulation of microtubule assembly and function
some kinesis can "walk" towards (+) end
some dyneins can move towards (-) end
hold onto vesicles or organelles w/ other domain
both use ATP hydrolysis for energy

Transported along microtubules

vesicles and organelles

Which of these statements about microtubules is true?
a) when a centrosome is present each microtubule contains a variable number of protofilaments
b)long, growing microtubules will contain GTP and GDP
c) A cell with many microtubules will not have any actin filaments
d) gamma-tubulin stabilizes microtubules minus ends by anchoring them onto a cylindrical centriole core

B

Actin Monomers

asymmetric
polar
bind and hydrolize ATP
assemble polarized actin filaments

Actin Filaments

t form (ATP bound)-more stable
D form (ADP bound)-less stable
T form polymerize and then hydrolyze into a d form in the (-) end... T form more likely in (+) end

treadmilling

Hydrolysis will catch up with the (-) end because it is slow
Hydrolysis lags behind the (+) end

pushes cell leading edge forward
-(+) end grows towards edge
-allows cells to crawl
-must be anchored tho

ARP2/3 complex

A protein complex that binds actin filaments and initiates the formation of branches.
nucleates the (-) end and protects them from depolymerization
(+) end grows away from complex
nucleate actin filaments on pre-existing filaments
whole network can go through treadmilling
proteins sever (-) end to release complex
-will depolymerize
-capped
proteins cap the (+) ends
-will stop additional subunits
-will go towards edge of cell

Integrins

anchor actin filaments to the extracellular matrix

directly bind extracellular matrix proteins

indirectly acts w/ actin filaments

prove adhesion necessary for cell migration

Mysosin

motor domains use ATP hydrolysis for energy
hold onto vesicles or organelles w/ their other domain
can help cells contract
"walk" towards (+) end
actin and myosin work together to generate force

A graduate student adds actin monomers and ATP into a test tube with a buffer that resembles the cell cytosol. What else must be added to the tube to produce ADP?
a) severing protein cofilin
b) nucleating protein ARP2/3
c) cofilin and ARP2/3
d) nothing

D

RHO family GTPases

influence actin organization (Rho, Rac, and Cdc42)
molecular switches
affects cell shape, cell polarity and cell behaviour
on when bound to GTP
off when bound to GDP

activation of Rho family GTPases

can have a dramatic effect on the organization of actin filaments in fibroblasts

Rac-- thick wall
Rho-- lines across one end to the other (a lot)
Cdc42-- lines spreading away from the wall

Rac-GTP activation

dominates the leading tip to explore and to push the cell forward

Rho-GTP activation

dominates at the back to pull the back of the cell

Cytoskeletal organization

defines cell polarity
symmetry breaking
cytockeleton polarization is triggered

symmetry breaking

anterior v posterior

Which of the following would most directly increase the amount of constitutive protein secretion?
a) a chemical that increases the formation of COPI-coated vesicles
b) a chemical that increases the formation of COPII-coated vesicles
c) a chemical that increases the formation of clathrin-coated vesicles
d) a chemical that increases the formation of ESCRT-0

B

epithelial tissue

cells directly connected to each other with minimal extracellular matrix
polarized

connective tissue

cells dispersed through extracellular matrix

basal lamina

separates the connective tissue and the epithelial tissue

epithelial cells

skin, disgestive tract, surrounding organs
polar
different functions
inside v outside
basal domain adheres to basal lamina
lateral domain adheres to each other
apical domain is exposed

tight junction

seals gap between epithelial cells
apical domain
basal domain
basolateral domain
domains are defined and maintained
formed by occludins & claudins
limit diffusion into extracellular space
limit diffusion of membrane proteins
regulates what enters organism

adherens junctions

connects actin filament bundle in one cell with that in the next cell
form first
provide polarity cues to define apical from basolateral domains

desmosome

connects intermediate filaments in one cell to those in the next cell

gap junction

allows the passage of small water-soluble molecules from cell to cell

Cadherins

cell-cell junctions
transmembrane proteins expressed by both cells
interact homophilic interactions of their extracellular domains
require Ca2+
directly link adjacent cells
indirectly interact w/ actin filaments
indirectly link the actin cytoskeleton btwn adjacent cells in epithelial tissues
interact in patches to form a strong adhesion belt

integrins

cell-extracellular matrix junctions
heterodimers directly bind to extracellular matrix(EXCM) proteins
transmembrane domain
indirectly interact w/ actin filaments
alpha and beta subunit act together to bind to an EXCM protein

Homophilic interactions

btwn E-cadherins
btwn N-cadherins
none btwn E and N cadherins
sort into 2 seperate groups

Adhesion belts

mediate morphogenisis
-pulls cells to form a tube
-diff cadherins establish new interactions and ensure neural tube closure

Which of the following most closely resembles adherins junctions mutation in the outer epithelium of Drosophila embryos?
a) Hemidesmosome mutation in the outer epithelium
b) calcium removal at the outer epithelium
c) intermediate filament depolymerization in the outer epithelium
d) occludin mutation in the outer epithelium

B

Basal domain

faces the inside of the body

apical domain

faces the surface, cavity or organ

basolateral domain

basal & lateral domains often grouped

Occludins & Claudins

form homophilic interactions
directly link adjacent cells
many rows of them will form tight junction

Active transporters

move glucose into the epithelial cell on the apical domain

passive carriers

basolateral domain allow glucose to diffuse out of the epithelial cell into the connective tissue/blood

Cell polarity

the cell has a "front" and "back"
extracellular or internal signals can polarize cell behaviour
initial polarity signal is external

Intracellular trafficking + cytoskeleton organization + cell adhesion = functional epithelium

An occludin mutation in ________ cells will directly affect _____.

a) intesitnal epithelial; glucose transport
b) drosophila embryonic; movement of the outer epithelium
c) drosophila embryonic; segmentation of the outer epithelium
epithelial; adherens junction formation

A

Multicellular development

ongoing process that occurs in adults from stem cells

Embryogenesis

fertilized egg --cleavage--> blastula--gastrulation--> grastula

Cleavage

cell proliferation

Gastrulation

cell differentiation
cell morphogenisis

change from ball of cells to an embryo with a guy & 3 germ layer

Grastula

Ectoderm- outer layer
Mesoderm- hanging around in the middle
Endoderm- middle but still slightly connected

ectoderm

epidermis and nervous system

Mesoderm

muscles, skeleton, gonads, kidneys, circulatory system

Endoderm

gut, liver, lungs

Morphogenesis

generation of shape
1. cell internalization
2. elongation
3. fine repositioning of cells