Cell bio- membrane Flashcards
7 organelles with a membrane
plasma nuclear (inner and outer) ER Golgi Mitochondria (inner and outer) Peroxisomes lysosomes
What are the three main lipids in a membrane?
phospholipids
sphingolipids
cholesterol
What are the 6 components of a membrane?
lipids (phospholipids, glycolipids) proteins (integral, peripheral) carbs water divalent cations cholesterol
What is the difference between prokaryotic and eukaryotic lipid bilayer?
bacteria are composed of one main type of phospholipid and contain no cholesterol
Eukaryotes are varied and contain a large amount of cholesterol and a mixture of different phospholipids
amphipathic
have hydrophobic polar end and one hydrophobic nonpolar end
what are the four parts of a phospholipid molecule?
choline
phosphate
glycerol
hydrocarbon chain
what are the two ways lipid molecules assemble?
spherical micelles
bimolecular sheets- bilayers
is the open formation or the closed formation of a phospholipid bilayer more energetically favorable?
closes structure
what are the four major phospholipids in the plasma membrane of mammalian cells?
phosphatidylcholine
phosphatidylethanoalmine
phosphatidylserine
sphingomyelin
which major phospholipid has a net negative charge?
phosphatidylserine
movement of phospholipids in bilayer- transversal diffusion
flip-flop
moves to a different layer (lipid on bottom layer switches with one on top layer
rare
movement of phospholipids in bilayer- lateral diffusion
happens readily and rabidly
lipids of same layer switch with one another
What does the fluidity of a lipid bilayer depend on?
composition (lipid composition and cholesterol content) and temperature
phase transition
change of a lipid bilayer from a liquid state to a rigid crystalline state (gel)
How do cis-double bonds in the hydrocarbon chains affect the membrane structure?
make it more difficult to pack the chains together (and to freeze)
more spread apart= thinner membrane
how does a shorter chain affect the fluidity of the membrane?
reduces the tendency of hydrocarbon tails to interact with one another
membrane remains fluid at lower temps
how does cholesterol affect the membrane?
improve permeability-barrier properties
stabilize the hydrocarbon chains by orienting their hydroxyl groups with polar heads of phospholipid molecules
inhibits phase transitions
what type of structures do saturated fatty acids form?
parachrystaline structures
less space between tails
what type of structures do unsaturated fatty acids form?
formation of kinks
more space between tails
what is the extracellular matrix?
a collection of extracellular molecules secreted by cells
what is the function of ECM? (4)
structural and bichemical support to surrounding cells
cell adhesion
cell-cell communicaon
differentiation
What do animal ECM include? (2)
intersitial matrix
basement membrane
intersitial matrix
present between different animal cells in intercellular space
gels of polysaccharides and fibrous proteins fill intercellular spaces= act as compression buffer
basement membranes
sheet-like depositions of ECM with epithelial cells
Three types of connective tissue in animals and their type of ECM
- bone tissue= collagen fibers and bone mineral
- loose connective tissue= reticular fibers and ground substance
- blood= ECM is blood plasma
how are macromolecules in the ECM produced?
locally by cells in the matrix and secreted via exocytosis
What are the three major classes of macromolecules in the ECM?
glycosaminoglycans (GAGs)
fibrous proteins
non-collagen fibrous proteins
Glycosaminoglycans
eg) cartilage
large and highly charged polysaccharides
proteoglycans when linked to proteins
fibrous proteins
collagen
eg) skin and bone
non-collagen fibrous proteins
glycoprotiens
eg) elastin, fibronectin, laminin
collagen
fibrous, long, stiff
triple-stranded helical proteins
rich in proline, glycine and glycosylated
Two types of fibril-forming collagen and what tissues they are found in
type 1= bone, skin, tendon, ligaments, cornea, internal organs
type 3- skin, blood, internal organs
elastin
gives tissues elasticity
hydrophobic protein rich in proline and glycine (not glycosylated)
skin, blood vessels, lungs
glycoproteins
have multiple domains with specific binding sites for other matrix macromolecules and for receptors of the cell surface
Basal lamina (basement membrane)
specialized form of ECM
thin, flexible, touch
essential component of all epithelia
laminin
primary organizer of the sheet structure of the basal lamina
composed of three long polypeptide chains held together by disulfide bonds
intigrins
link the cytoskeleton wiht the ECM
transmembrane cell adhesion proteins= matrix receptors
Cell junction
multiprotein complexes that provide contact between neighboring cells or between a cell and the extracellular matrix
functions of a cell junction (5)
- bind cells to one another
- reduce stress places upon cells
- build up the paracellular barrier of epithelia
- control of paracellular transport
- enable communication between neighboring cells
What two type of tissues are cell junctions more abundant?
epithelial tissues (lining of gut or skin) connective tissues (bone or tendon)
what do cell-cell junctions attach?
direct attachments between cells
what do cell-matrix junctions attach?
cytoskeletal filaments are anchored and linked to the basal lamina
what are the three types of cell-cell junctions?
- tight junctions (occluding junctions)
- cell-cell anchoring junctions
- gap junctions (communicating junctions)
what are the two types of cell-cell anchoring junctions?
adherens
desmosomes
what is the type of cell-matrix junction?
cell-matrix anchoring junction
what are the two types of cell-matrix anchoring junction?
actin linked
hemidesmosomes
What makes up the junctional complex?
tight junction
cell-cell anchoring junctions” adherens and desmosomes
tight junction
seal gap between apithelial cells
impermeable to macromolecules
permeable to ions and small molecules
where are tight junctions located?
most apical location of epithelial cells (lining of intestinal mucosa, bladder)
What are the two proteins that make up tight junctions and what to they make?
cloudin and occuldin
make sealing strands to hold adjacent plasma membranes tocether
what two diseases are associated with tight junctions malfunctioning?
Celiac disease
Crohn’s disease
cell-cell anchoring junctions
form strong, membrane-spanning structures that are tethered inside the cell to filaments of the cytoskeleton
Where are cell-cell anchoring junctions located?
widely distributed. mostly in tissues that are subject to severe mechanical stress
(heart, muscle, epidermis)
what is a protein used in cell-cell anchoring junctions?
cadherins- calcium-dependent adhesion
adherens junction: cell-cell anchorinig junction
“adhesion belt”
connects actin filament bundle in once cell with another= provides anchorage site for cytockeleton
helps model shape of multicellular structures
where are asherens junctions located?
more basal than tight junction
guides organization of developing tissues (construction of vertebrae nervous system)
found in epithelial cells, cardiac muscle, fibroblasts
Desmosome: cell-cell anchoring juncitons
connects intermediate filaments in one cell to another
provide anchorage site for cytoskeleton
links with intermediate filaments
provides mechanical strength
where are desmosome junctions located?
in tissues that suffer a lot of stress/stretch
skin, intestines, stomach, bladder
Gap junctions
allows passage of small water-soluble molecules from cell to cell without having to pass through pl (ions, glucose)
narrow gap
where are gap junctions located?
tissues containing electrically excitable cells (cardiac muscle, connective tissue, intestines, epithelial tissue, neurons)
cell-matrix anchoring junctions
depend on integrins
activated by extracellular matrix ligands or intracellular activator proteins
what are the 2 functions of cell-matrix anchoring junctions?
produces intracellular signals that can influence cell behavior (proliferation, survival, polarity and migration)
sense and respond to mechanical forces acting across the junction
actin-linked cell matrix junction
“focal adhesion”
anchors actin filaments in cell to extracellular matrix
can be small and transient or large and durable
hemidesmosome: cell-matrix junction
anchor intermediate filaments in a cell to the extracellular matrix
use integrins
where are hemidesmosomes located?
epithelial cells connecting the basal face of the cell to basal lamina
