Exam 4 Lesson 41

Question 1

How is plant cell wall deposited?

Answer 1

in layers

Question 2

what do successive layers of cellulose microfibrils reflect?

Answer 2

adjustments of microtubule orientation

Question 3

layers of plant cell wall/membrane

Answer 3

plasma membrane, primary cell wall, middle lamella

Question 4

components of primary cell wall

Answer 4

cross-linking glycan, cellulose microfibril, pectin

Question 5

How are cellulose microfibrils aligned?

Answer 5

parallel to one another and perpendicular to the axis of cell elongation

Question 6

how does expansion happen?

Answer 6

perpendicular to the orientation of the microfibrils, allowing cell to orient growth

Question 7

In connective tissue in animals, when does orientation of secreted structural fibers like collage occur?

Answer 7

after secretion

Question 8

What does orientation of cell fibers affect?

Answer 8

cell migration

Question 9

what are fibroblasts?

Answer 9

the cells mainly responsible for secreting the ECM found in connective tissue

Question 10

how can fibroblasts align collagen fibrils?

Answer 10

they can attach to and pull on a field of randomly oriented collagen fibrils to align them. Cells then move out along the collagen array. Tendons form by this mechanism in connective tissue.

Question 11

Functions of the basal lamina

Answer 11

a. tissue stabilization
b. isolation of cells from other cells (bbb)
c. filtering of small molecules
d. signaling for cell proliferation, survival
e. determination of cell polarity

Question 12

How is basal lamina structured?

Answer 12

it is a two-dimensional sheet of ECM made from specialized collagens and other glycoproteins and proteoglycans.

Question 13

what are laminins?

Answer 13

they key organizing components of the basal lamina

Question 14

how do cells bind to basal lamina?

Answer 14

via laminin receptors (integrins)

Question 15

what does basal lamina mediate?

Answer 15

specialized interactions between cells, such as the neuromuscular junction

Question 16

what controls how cells perceive and respond to signals?

Answer 16

the cell wall/ECM

Question 17

what does the hydrated matrix control?

Answer 17

the “porosity” and physiochemical conditions in the ECM (controlling pore size, pH, ion concentrations, etc.)

Question 18

What does controlling pore size do?

Answer 18

the matrix controls the ability of certain chemicals or growth factors to move through ECM.

Question 19

What happens if a particular signal molecule can’t pass through ECM?

Answer 19

the cell will not perceive the signal

Question 20

How do signal molecules approach cell surface receptors?

Answer 20

Some signal molecules first bind to ECM components (like GAGs) and are then moved laterally to cell surface receptors. Others are only recognized by surface receptors if they are bound to one of the ECM components. In this case, the ECM component is a co-ligand or co-receptor.

Question 21

What are integrins?

Answer 21

Type I membrane proteins with an N-terminal ectodomain domain and a C-terminal cytosolic domain.

Question 22

What do integrins bind to?

Answer 22

an ECM component with their ectodomain and to anchor proteins with their cytosolic domain. The anchor protein s then link the integrins to the actin filaments.

Question 23

how does fibronectin glycoprotein in ECM bind to certain integrins?

Answer 23

via an “RGD” motif

Question 24

what is “integrin switching”?

Answer 24

an important part of EMT process and has major effects on properties like cell adhesion to the ECM and cell motility.

Question 25

what is fibronectin?

Answer 25

a key organizer of the ECM
soluble proteins that form insoluble fibers on the cell surface when under tension (interactions with integrant). This is how cell controls organization of ECM supporting fibers.

Question 26

what allows fibronectin to organize the ECM and bind to cells?

Answer 26

numerous protein-protein interaction domains

Question 27

integrins can be “active” or “inactive” depending on

Answer 27

1. whether the ectodomains are bound to the ECM

2. whether the cytosolic domains are bound to the anchor proteins

Question 28

How can integrins be activated to bind ECM and actin filaments?

Answer 28

by “outside-in” or “inside-out” signals

Question 29

Outside-in activation

Answer 29

RGD peptide mimics the integrin binding site on fibronectin. In response to RGD, the conformation of the integrin ectodomain changes. The change is transmitted to the cytosolic domain, exposing a strong binding site for the anchor proteins and leading to an associating with actin filaments.

Question 30

Inside-out activation of integrins

Answer 30

different signal transduction cascades can recruit talon (an anchor protein) to bind to beta integrin, leading to a conformational change in the ectodomain (activation) and binding to ECM components

Question 31

what does actin cytoskeleton promote?

Answer 31

cell shape change, cell spreading, secretion of materials from storage granules

Question 32

what can active integrins recruit?

Answer 32

protein kinases to assemble signaling scaffolds

Question 33

Focal Adhesion Kinase (FAK)

Answer 33

tyrosine kinase phosphorylates itself and other target proteins at the anchor site, leading to inhibition/disassembly of focal adhesions

Question 34

what can loss of FAK lead to?

Answer 34

too many focal adhesions, preventing cell spreading and inhibiting migration

Question 35

what does elevated FAK contribute to?

Answer 35

overactive cell migration

Question 36

what does integrin signaling depend on?

Answer 36

the types of integrins expressed by cell

Question 37

What does integrin signaling cooperate with?

Answer 37

growth factor receptors

Question 38

How does integrin signaling work?

Answer 38

through FAK kinase and Src family kinases (SFKs) to affect numerous signaling pathways

Question 39

what does integrin signaling affect?

Answer 39

cell proliferation survival, migration

Question 40

What kind of attachment do many cells require for survival? what can failure to attach lead to?

Answer 40

attachment to ECM/lamina
failure to attach can lead to
a. in early mouse embryo, endoderm cells send an apoptotic signal to ectoderm cells
b. ectoderm cells attached to basal lamina survive

Question 41

what is “anchorage dependence”?

Answer 41

some cells require attachment to ECM molecules to survive/proliferate.

Question 42

Do transformed cells/tumor cells have anchorage dependence?

Answer 42

no

Question 43

How does FAK regulate cell proliferation?

Answer 43

it interacts with growth factor receptors to control the ERK/MAPK pathway

Question 44

do animal stem cells need to be attached to lamina to survive?

Answer 44

yes

Question 45

what do some cells do in order to migrate?

Answer 45

they secrete specific proteases that degrade proteins in the ECM. Examples are matrix metalloproteases or serene proteases.

Question 46

How do cells secrete degrading proteases?

Answer 46

some cells secrete inactive proteases into the ECM and activate them with a second secreted activator in a local region.
other cells secrete inactive proteases into the ECM, then bind them to surface receptors at particular points on the cell surface.