Unit 3 Flashcards
what is a tissue
group of cells working together
how do tissues communicate
direct contact or intercellular junctions
role of actin filaments
determine shape of cell’s surface, necessary for locomotion
role of microtubules
determine positions of organelles and direct intracellular transport
role of intermediate filaments
bear tension and maintain cell shape
how can a plant transfer water and other soil nutrients from its roots, through stems, and to leaves
uses vascular tissues, plasmodesmata, channels that pass between adjacent plant cell walls connect their cytoplasm and enable transport of materials from cell to cell
what are gap junctions
channels between adjacent cells that allow for transporting ions, nutrients, etc
how do gap junctions develop
when set of 6 connexins arrange in elongated donut-like config (connexon)
what is a tight junction
watertight seal between 2 adjacent animal cells, prevents materials from leaking
what is the function of adherens junction
joins actin bundle in one cell to similar bundle in neighboring cell
what type of junction is a desmosome
anchoring
key components of desmosomes
cadherins, intermediate filaments
what do desmosomes provide
tensile strength to epithelial tissues, preserve tissue integrity
what are hemidesmosomes crucial for
anchoring epithelial sheet to underlying basal lamina
which three junctions contribute to maintaining tissue integrity
hemidesmosomes, desmosomes, adherens junctions
what do junctional complex proteins include
tight junctions, adherens junctions, desmosomal junctions
purpose of anchoring junctions
transmit stress, provide structure, maintain tissue integrity
what do tight junctions seal
gaps between cells and separate apical and basolateral surfaces
what do adherens junctions link
epithelial cells to form adhesion belt
what type of receptors in hemidesmosomes anchor cell to extracellular matrix
integrin
gap junctions allow ___ molecules to pass from cell to cell
small
role of extracellular matrix in tissues
ECM is network of proteins and carbohydrates; cells interact with ECM through integrin receptors for migration
true or false: ECM is dynamic and continuously remodels
true
what provides tensile strength in ECM
collagen
how are epithelial cells separated from underlying tissues
by basal lamina
what makes, excretes, and organizes components of the ECM
fibroblasts
what is the most abundant protein in ECM
collagen
what can incorrect collagen assembly cause
skin can be hyper flexible
what molecules in ECM bind to collagen fibrils outside cell
fibronectin
integrin receptors switch from ___ to ____ states
active to inactive
when does an integrin protein switch to an active conformation
when it binds to molecules on either side of the plasma membrane
true or false: integrin establishes a reversible mechanical linkage across plasma membrane
true
what is “outside-in activation”
binding of extracellular ligand causes unfolding of integrin, intracellular domains move apart and reveal binding site for intracellular adaptor proteins which leads to assembly of actin filaments
what is “inside-out activation”
when intracellular adaptor proteins bind to beta subunit, causes alpha and beta subunits to spring apart, driving extracellular portion of integrin into active conformation, process triggered by intracellular regulatory molecules
what do gels of polysaccharides and proteins that fill spaces in ECM do
resist compression
what is proteoglycans
hydrated gel-like substance where collagens and glycoproteins are embedded, resists compressive forces on matrix, permits rapid diffusion of nutrients, etc
what are fibrous proteins
collagen fibers strengthen and help organize matrix, elastin provides resiliency
what are matrix glycoproteins
help cells migrate, settle and differentiate in appropriate locations, components of basal lamina
describe the process of cell signaling (4 stages)
- signal is sent from cell in response to enviro or molecular cue
- signal is received by cell containing specific receptor for signal
- signal is interpreted/transduced by receiving cell
- cell responds in 1+ ways to signal
when does autocrine signaling happen
when cell releases ligand that is received by its own receptor, often occurs during early development of org to ensure that cells develop into correct tissues and take on proper function
what is signaling across gap junctions
transfer of signaling molecules directly next to target cell, allows group of cells to coordinate their response to signal that only one of them may have received
how are gap junctions different in plants
called plasmodesmata, form channels between adjacent cells (create giant communication network)
what is the most common type of cell signaling
paracrine
what is paracrine signaling
cell targets nearby cell
what must happen for paracrine signals to act only locally
ligand molecules are quickly degraded by enzymes or rapidly taken up by neighboring target cells
what is endocrine signaling
long range signaling mech by endocrine cells that secrete hormones as their signaling molecules
what does endocrine signaling rely on to have hormones travel through bloodstream
diffusion and blood flow
why do hormones act at a very low concentration
high specificity of receptor binding
which type of signaling is contact-dependent
juxtacrine
what is juxtacrine signaling
signaling that only influences cells that contact it, important during development and immune responses, direct cell-to-cell contact or interaction between cell-surface receptor and glycoprotein of ECM
how is neuronal signaling a specialized example of paracrine signaling
transfer of signal (neurotransmitter) between nerve cells at synapse
what are neurotransmitters
chemicals released at axon terminals that allow signals to be communicated to target cells
what does the synaptic gap allow for
rapid diffusion of neurotransmitter
what types of molecules function as signals
steroids, amines, peptides
how are hydrophobic signaling molecules transported through extracellular fluids to plasma membrane of target cells
by association with carrier proteins
what are type I intracellular receptors
anchored in cytoplasm by chaperone proteins, conformational change in receptor leads to release of chaperone protein that allows receptor to form homodimer w another receptor (glucocorticoid, androgen, progesterone receptors)
what are type II intracellular receptors
located in nucleus, receptors bound to co-repressor proteins which are released upon ligand binding, allowing receptor to bind to DNA and modulate gene expression
how are signals relayed in the cell
through signaling cascade
what are first messengers
extracellular signals whose binding by receptor proteins in plasma membrane initiates signaling cascade
what are second messengers
intracellular signaling molecules that spread signal to other parts of cell
what are effector proteins
intracellular targets that implement change in cell behavior (gene regulatory proteins, ion channels, etc)
define signal transduction
events that convert one type of signal to another type of signal
what does the speed of a response depend on
nature of target cell’s response
what are protein kinases
enzymes that add 1+ phosphate to signaling protein, may activate or inactivate target protein
where is the energy required to drive phosphorylation cycle from
free energy of ATP hydrolysis
what do phosphate enzymes remove
phosphate group from target proteins and returns them to previous activity state
define amplification
when signal is relayed and activates a molecule, signal molecule can activate many other molecules
what is a scaffold protein
interacts w receptor and holds together other relay molecules in close proximity
