2.1: Cellular form and function Flashcards
what is saccharomyces cerevisiae is common terms
yeast
what is the defining feature of a eukaryote
nucleus
list the 2 specific parts of an animal cell (that is not found on the plant cell) and its purpose
- extracellular matrix: specialized material outside the cell
- lysosome: degradation of cellular components that are no longer needed
list the 3 specific parts of an plant cell (that is not found on the animal cell) and its purpose
- cell wall: cell shape, protection against mechanical stress
- vacuoles: 2 types: degradation (like lysosome), storage (small molecules and proteins
- chloroplast: site of photosynthesis
differentiate between the cytoplasm, the cytosol and the lumen
cytoplasm: all contents of the cell outside the nucleus
cytosol: aqueous part of the cytoplasm (Water, dissolves ions, soluble, proteins)
lumen: inside of organelles
list the 6 cellular functions that occur at membranes
- compartmentalization/defining boundaries
- scaffold for biochemical activities
- selectively permeable barrier
- transport solutes
- respond to external signals
- interactions between cells
which scientists found the fluid mosaic model of the membrane (1972)
singer and nicolson
what was mosaic mean in the context of the fluid mosaic model of the membrane
mosaic means that there are many proteins and many lipids
how can the phospholipids spontaneously assemble into the lipid bilayer
amphipathic and this is more energetically favourable to have heads out and tails in
what is the hydrophobic and hydrophilic portions of the phospholipid
hydrophilic or polar head group
hydrophobic tails
membranes composed of many different lipids: ______,______,______
phospholipids, sterols, glycolipids
if the membrane phospholipids have a glycerol group, what are they called
phosphoglycerides (the groups on the head and the tails are differ)
describe a kink in the context of phospholipids
means that the tail is unsat and contains a cis double bond
how long is the typical tail of a phospholipid
14-24 carbon atoms
in what type of environment do phospholipids spontaneously self-associate into a bilayer
aqueous
in the aqueous environment, what does the polar head group of the phospholipid interact with
water
describe what are liposomes and its uses
artificial lipid bilayers that are formed by adding phospholipids in an aqueous environment, and is used to study lipid properties (eg adding diff ones tgt), membrane protein properties, drug delivery into cells
how does the spherical shape of the phospholipids come about
because flat (planar) is not favourable bc the tails will encounter water at the edges so it ends up forming a ball to create a sealed compartment
what does it mean for cell membranes to be fluid
a membrane can be deformed without causing damage and can move within each leaflet rapidly: diffuse laterally (left right) rotate (circle) flex (the tails flex)
describe the technique for live cell imaging
context of phospholipids, how will we be able manipulate it
laser tweezers are used to manipulate the membrane
what is the purpose of the fluidity of the cell membrane
carefully regulated as important for function, eg membrane proteins for transport, enzyme activity, signaling
why do phospholipids rarely flip-flip (move from one leaflet to other) on their own
bc it means the hydrophilic heads would have to move through the hydrophobic core
describe the factors that affect membrane fluidity
- temperature: lower temperature = more viscous, less fluid
- composition: (changing comp counters viscosity and low fluidity)
–> phospholipid saturation: cis double bonds increase fluidity at lower temperature (reduce tight packing + more space)
–> phospholipid tail length: shorter hydrocarbon tails increase fluidity at lower temperature (tails interact less)
–> lipid composition: adding cholesterol in animal cell membranes = stiffens, less permeable to water
describe the role of cholesterol in the membrane (animals have mostly cholesterol, plants have plant sterols and some)
there can be up to a 1:1 ratio of cholesterol and phospholipids
- decreases mobility of tails (stiffens membrane like a wedge)
- plasma membrane is less permeable to polar molecules bc cholesterol is so hydrophobic
t/f does scramblase do a rapid flip-flip of random phospholipids
true
how many tails does cholesterol have
1 tail
what are the two enzymes in the er membrane and golgi that flips lipids from one leaflet to the other
scramblase (phospholipid translocator), flippases (eg phosphatidylserine binds protein kinase c)
^^ er and golgi respective
what orientations do membranes always maintain
the cytosolic face (w plasma membrane) faces the cytosol, and the non cytosolic face/leaflet faces the lumen
why do we need scramblase
phospholipids are synthetsized in cytosolic leaflet of er: We get new membranes being synthesized and when they are inserted into a leaflet, you may get imbalance (begins to bend) so the scramblase randomly flips it to balance (more symmetrical growth of the ER membrane)
what orientations do glycoprotein always maintain
the head is always in the lumen/extracellular space and the membrane glycoprotein crosses the lipid bilayer
why does curving of the golgi help
for vesicle trafficking, the curvature helpings the process
which leaflet does flippases move phospholipids to
cytosolic leaflet, makes it asymmetric
t/f does flippases do a rapid flip-flip of specific phospholipids (eg phosphatidylserine)
true
how does the lipid bilayer go asymmetric and why does it do this
honestly this q isn’t worded the best
- glycolipids and glycoproteins
- formed by adding sigar groups to lipids/proteins on luminal face of golgi
- end up on plasma membrane, inside of some organelles (noncytosolic face)
- protects the membrane from harsh environ (Eg lysosome w a very low pH or from outside the plasma membrane)
differentiate between integral and peripheral membrane protein
integral is attached to the lipid, peripheral are associated with diff parts of the membrane
sort the following into integral or peripheral membrane proteins:
transmembrane
monolayer associated
lipid linked
protein attached
integral: transmembrane, monolayer associated, lipid linked (attached to lipid that is inserted into bilayer)
peripheral: protein attached (bound to other proteins, bound to lipids)
state the extraction method of integral and for peripheral proteins
integral: use of detergents - destroy the bilayer
peripheral: gentle ones used, don’t need to destroy bilayer
what type of bonding do integral proteins have to the membrane
covalent
what type of bonding do peripheral proteins have to the membrane
non covalent
describe the 3 membrane spanning domains
- single alpha helix: hydrophobic aa side chain w hydrophobic tails
- multiple alpha helices: hydrophilic side chains form an aqueous pore, hydrophobic side chains interact w phospholipid tails
- beta barrel: eg porin protein in bacteria; rigid, does’t undergo conformational change
each membrane protein has ____________ - essential for function
specific orientation
list the 4 membrane protein functions and examples
- transporters and channels: Na-K pump, K leak channels (multiple a helices)
- anchors: integrins (single alpha helix)
- receptors: receptor kinases (single alpha helix)
- enzymes: eg adenylyl cyclase (multiple a helices)
which membrane protein functions do single and multiple a helices relate to
single: anchors and receptors
multiple: transporters and channels, enzymes
what techniques can be used to identify protein structures (def refer to slides for an example)
- x-ray crystallography: determines 3d structure
- hydrophobicity plots: segments of 20-30 hydrophobic aa can span the lipid bilayer as an alpha helix – predicts whether there is a transmembrane domain (will be the top/hydrophobic peak)
how are monolayer associated membrane proteins anchored into the cytosolic face
looking for a specific protein type
with an amphipathic alpha helix
explain the technique of fluorescence recovery after photobleaching (FRAP)
- protein fused with GFP (green fluorescent protein) or labelled with fluorescent antibody –> bleach fluorescently labelled membrane protein with laser beam –> labelled proteins diffuse randomly throughout membrane –> fluorescence returns to bleached patch
- can show mobile or not mobile bilayer
- recovery rate is high for mobile and not mobile never recovers (bleached patch always there)
- rate of fluorescence recovery: time taken for neighbouring unbleached fluorescent proteins to move to the bleached area
explain the technique of lateral diffusion of membrane proteins (LDMP)
- lateral diffusion within the plane (orientation matters) and NO flip flop
- the study of FRAP
- lateral mobility can also be restricted: tethered to another cell component (in cell, out of cell, between cells), or have diffusion barriers so they can’t go past a point
describe the 2 methods of anchoring of the lipid linked membrane proteins
- protein with a GPI anchor (glycosylphosphatidylinositol): synthesis in ER lumen, end up on cell surface (noncytosolic face)
- protein w another lipid anchor (fatty acid, prenyl): cytosolic enzymes add anchors and directs proteins to this face
explain the technique of extracting membrane proteins
adding detergents – breaks the bilayer and attaches to the phospholipids = micelles
eg tritonX100 surrounds w tail orientation (gets the protein)
it can also surround chunks of the bilayer together
++ aqueous buffer to extract protein
