2.1: Cellular form and function

Question 1

what is saccharomyces cerevisiae is common terms

Answer 1

yeast

Question 2

what is the defining feature of a eukaryote

Answer 2

nucleus

Question 3

list the 2 specific parts of an animal cell (that is not found on the plant cell) and its purpose

Answer 3

1. extracellular matrix: specialized material outside the cell
2. lysosome: degradation of cellular components that are no longer needed

Question 4

list the 3 specific parts of an plant cell (that is not found on the animal cell) and its purpose

Answer 4

1. cell wall: cell shape, protection against mechanical stress
2. vacuoles: 2 types: degradation (like lysosome), storage (small molecules and proteins
3. chloroplast: site of photosynthesis

Question 5

differentiate between the cytoplasm, the cytosol and the lumen

Answer 5

cytoplasm: all contents of the cell outside the nucleus
cytosol: aqueous part of the cytoplasm (Water, dissolves ions, soluble, proteins)
lumen: inside of organelles

Question 6

list the 6 cellular functions that occur at membranes

Answer 6

1. compartmentalization/defining boundaries
2. scaffold for biochemical activities
3. selectively permeable barrier
4. transport solutes
5. respond to external signals
6. interactions between cells

Question 7

which scientists found the fluid mosaic model of the membrane (1972)

Answer 7

singer and nicolson

Question 8

what was mosaic mean in the context of the fluid mosaic model of the membrane

Answer 8

mosaic means that there are many proteins and many lipids

Question 9

how can the phospholipids spontaneously assemble into the lipid bilayer

Answer 9

amphipathic and this is more energetically favourable to have heads out and tails in

Question 10

what is the hydrophobic and hydrophilic portions of the phospholipid

Answer 10

hydrophilic or polar head group
hydrophobic tails

Question 11

membranes composed of many different lipids: ______,______,______

Answer 11

phospholipids, sterols, glycolipids

Question 12

if the membrane phospholipids have a glycerol group, what are they called

Answer 12

phosphoglycerides (the groups on the head and the tails are differ)

Question 13

describe a kink in the context of phospholipids

Answer 13

means that the tail is unsat and contains a cis double bond

Question 14

how long is the typical tail of a phospholipid

Answer 14

14-24 carbon atoms

Question 15

in what type of environment do phospholipids spontaneously self-associate into a bilayer

Answer 15

aqueous

Question 16

in the aqueous environment, what does the polar head group of the phospholipid interact with

Answer 16

water

Question 17

describe what are liposomes and its uses

Answer 17

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

Question 18

how does the spherical shape of the phospholipids come about

Answer 18

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

Question 19

what does it mean for cell membranes to be fluid

Answer 19

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)

Question 20

describe the technique for live cell imaging

context of phospholipids, how will we be able manipulate it

Answer 20

laser tweezers are used to manipulate the membrane

Question 21

what is the purpose of the fluidity of the cell membrane

Answer 21

carefully regulated as important for function, eg membrane proteins for transport, enzyme activity, signaling

Question 22

why do phospholipids rarely flip-flip (move from one leaflet to other) on their own

Answer 22

bc it means the hydrophilic heads would have to move through the hydrophobic core

Question 23

describe the factors that affect membrane fluidity

Answer 23

1. temperature: lower temperature = more viscous, less fluid
2. 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

Question 23

describe the role of cholesterol in the membrane (animals have mostly cholesterol, plants have plant sterols and some)

Answer 23

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

Question 23

t/f does scramblase do a rapid flip-flip of random phospholipids

Answer 23

true

Question 23

how many tails does cholesterol have

Answer 23

1 tail

Question 23

what are the two enzymes in the er membrane and golgi that flips lipids from one leaflet to the other

Answer 23

scramblase (phospholipid translocator), flippases (eg phosphatidylserine binds protein kinase c) ^^ er and golgi respective

Question 24

what orientations do membranes always maintain

Answer 24

the cytosolic face (w plasma membrane) faces the cytosol, and the non cytosolic face/leaflet faces the lumen

Question 24

why do we need scramblase

Answer 24

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)

Question 24

what orientations do glycoprotein always maintain

Answer 24

the head is always in the lumen/extracellular space and the membrane glycoprotein crosses the lipid bilayer

Question 24

why does curving of the golgi help

Answer 24

for vesicle trafficking, the curvature helpings the process

Question 24

which leaflet does flippases move phospholipids to

Answer 24

cytosolic leaflet, makes it asymmetric

Question 24

t/f does flippases do a rapid flip-flip of specific phospholipids (eg phosphatidylserine)

Answer 24

true

Question 25

how does the lipid bilayer go asymmetric and why does it do this | honestly this q isn't worded the best

Answer 25

- 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)

Question 25

differentiate between integral and peripheral membrane protein

Answer 25

integral is attached to the lipid, peripheral are associated with diff parts of the membrane

Question 25

sort the following into integral or peripheral membrane proteins: transmembrane monolayer associated lipid linked protein attached

Answer 25

integral: transmembrane, monolayer associated, lipid linked (attached to lipid that is inserted into bilayer) peripheral: protein attached (bound to other proteins, bound to lipids)

Question 25

state the extraction method of integral and for peripheral proteins

Answer 25

integral: use of detergents - destroy the bilayer peripheral: gentle ones used, don't need to destroy bilayer

Question 26

what type of bonding do integral proteins have to the membrane

Answer 26

covalent

Question 27

what type of bonding do peripheral proteins have to the membrane

Answer 27

non covalent

Question 28

describe the 3 membrane spanning domains

Answer 28

1. single alpha helix: hydrophobic aa side chain w hydrophobic tails 2. multiple alpha helices: hydrophilic side chains form an aqueous pore, hydrophobic side chains interact w phospholipid tails 3. beta barrel: eg porin protein in bacteria; rigid, does't undergo conformational change

Question 29

each membrane protein has ____________ - essential for function

Answer 29

specific orientation

Question 30

list the 4 membrane protein functions and examples

Answer 30

1. transporters and channels: Na-K pump, K leak channels (multiple a helices) 2. anchors: integrins (single alpha helix) 3. receptors: receptor kinases (single alpha helix) 4. enzymes: eg adenylyl cyclase (multiple a helices)

Question 31

which membrane protein functions do single and multiple a helices relate to

Answer 31

single: anchors and receptors multiple: transporters and channels, enzymes

Question 31

what techniques can be used to identify protein structures (def refer to slides for an example)

Answer 31

1. x-ray crystallography: determines 3d structure 2. 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)

Question 31

how are monolayer associated membrane proteins anchored into the cytosolic face | looking for a specific protein type

Answer 31

with an amphipathic alpha helix

Question 31

explain the technique of fluorescence recovery after photobleaching (FRAP)

Answer 31

- 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

Question 32

explain the technique of lateral diffusion of membrane proteins (LDMP)

Answer 32

- 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

Question 33

describe the 2 methods of anchoring of the lipid linked membrane proteins

Answer 33

- 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

Question 34

explain the technique of extracting membrane proteins

Answer 34

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