Unit 2 : Bio Membrane

Question 1

Membrane Definition

Answer 1

barriers that define compartments

Question 2

Biological Membrane features

Answer 2

1 ) Bilayer membrane of lipids + proteins
2 ) Membrane is selectively permeable
3 ) Membrane organized but fluid

Question 3

Why do membrane lipids form sheets ?

Answer 3

Amphipathic - head can form H bonds with water , tails cant

Form rough cylindrical shape which stacks together well

Question 4

Liposomes

Answer 4

Lipid bilayers by themselves form into spherical bodies that have water on inside and outside

Question 5

Phospholipid bilayers held together by

Answer 5

hydrophobic interactions

Question 6

Lipid bilayers are stable because

Answer 6

association of hydrophobic groups results in less disruption of H bonded structure of surrounding water

Question 7

Protiens

Answer 7

1 ) long chains of amino acids covalently bonded based on sequence of codon read from mRNA by ribosomes

2 ) fold in specific way that is most stable depending on order of amino acids in primary structure

3 ) secondary structure : backbone interacts non-covalently with itself
Tertiary structure : backbone / R group with other R groups
Quaternary structure : polypep + polypep chain

4 ) Environment affects proteins folding - whether they are soluble or embedded

Question 8

Disulfide bridges

Answer 8

between cysteine residues

Question 9

Chaperones

Answer 9

help with folding - binding parts of protein / complete protein by changing environment of folding

Final fold stable enough - not change when released from chaperone

Question 10

Membrane is selectively permaeble

Answer 10

1 ) Small + non polar = cross easily
2 ) large molecules cannot cross due to size
3 ) Small + Polar molecules (h2o) = slow crossing

Question 11

Water crosses membrane at rate higher than expected for lipid bilayer

Answer 11

proteins in membrane

Question 12

core of lipid bilayer

Answer 12

non-polar environment so water-free zone

Question 13

transporters

Answer 13

transport big / charged molecules across membrane

Question 14

Membrane is organized but fluid

Answer 14

lipid + protein maintain organization of membrane

Question 15

Water on both sides of membrane

Answer 15

lipids cannot escape but move and change places within membrane

Question 16

Membrane is Asymmetric

Answer 16

arrangement of components not same on both sides

Question 17

Key contributors to asymmetry

Answer 17

lipids
proteins
carbohydrates

Question 18

Ectotherm membranes

Answer 18

manipulate environment colder temp = decrease fluidity

Question 19

Endotherm membranes

Answer 19

maintained in strict environment

Question 20

Effect of temp on lipid bilayer

Answer 20

Below the freezing temperature - the mobility of the molecules is substantially restricted and they assume a more ordered, almost crystalline structure

Question 21

Factors affecting fluidity\

Answer 21

1 ) degree of unsaturation - more C=C in HC tail means more fluidity

2 ) shorter C-C chain means more fluidity

3 ) sterol content - cholesterol in animals packs in spaces between fatty acid chain and decreases fluidity
Phytosterol in plants - same purpose

Question 22

Real membranes

Answer 22

regions with varying fluidity

Question 23

FRAP

Answer 23

Fluorescence Recovery After Photobleaching

Question 24

FRAP results

Answer 24

tagged proteins / lipids move into bleached area and bleached area becomes less and less distinct and overtime filled with tagged lipids/proteins

Question 25

Enzymes such as flippases, floppases and scramblases

Answer 25

move lipids from one side of the membrane to the other contribute quite specifically to the asymmetry of the final membrane

Question 26

Integral Membrane Proteins

Answer 26

embedded within the phospholipid bilayer cannot be removed from the membrane without destroying the membrane completely

Question 27

Peripheral Membrane Proteins

Answer 27

more transiently attached to the inner or outer surface of a membrane

Question 28

How proteins are attached to membranes

Answer 28

1 ) Transmembrane proteins 2 ) Lipid-anchored proteins 3 ) Monolayer-associated proteins

Question 29

Transmembrane proteins

Answer 29

extend through the entire membrane have parts that stick out on either side held in place primarily through interactions of the hydrophobic amino acid side chains of the protein with the hydrophobic core of the membrane

Question 30

Lipid-anchored proteins

Answer 30

covalently attached to fatty acids or diacylglycerides

Question 31

Monolayer-associated proteins

Answer 31

protein is held in place by an alpha-helix that is amphipathic (i.e. non-polar on one side only)

Question 32

Transmembrane proteins use secondary structure to pass through the membrane

Answer 32

backbone of the the polypeptide chain is always polar so always capable of forming H-bonds They often push the R-groups towards the outside of the structure, where they are available to interact with the environment

Question 33

Alpha-helices in pores and channels

Answer 33

general arrangement will be a circular cluster of alpha-helical 'rods' extending through the membrane must have both hydrophobic and hydrophilic components in the appropriate areas to interact with the different parts of the bilayer Centre of the pore (in red) must have the correct properties for whatever is going to pass through this pore amphipathic- can both interact with the environment and for a channel with specific properties in the center

Question 34

Beta-barrels in transmembrane proteins

Answer 34

require a specific arrangement of their R-groups outside of the beta-barrel must be able to interact with the environment -help to hold the protein in the environment inside of the barrel - create space that will allow water and other small molecules to pass through the membrane without hindrance

Question 35

Membrane Protein Function

Answer 35

1 ) Structural - anchors, helping to attach the membrane to organelles - linkers, which help connect several proteins in the membrane and can help to provide shape 2 ) Transport proteins - mediate the transport of different types of molecules across the membrane in either direction 3 ) Enzymes - enzymatic activity, for a whole variety or cellular functions 4 ) Receptors - key for the cell to be able to sense and respond to its environment

Question 36

Hydropathy plot

Answer 36

looks for alpha-helical transmembrane domains looks for a linear stretch of amino acids that are 'hydrophobic enough' to allow them to exist stably within the confines of the hydrophobic core of the lipid bilayer

Question 37

Reading hydropathy plot output

Answer 37

X-axis is the linear sequence of the protein, listed from N-terminus to C-terminus Y-axis is a number known as the hydropathy index

Question 38

Protein Separation via SDS-PAGE

Answer 38

gel electrophoresis used for protein separation - Charged macromolecules move towards anode (+ charged electrode) Smaller molecules move farther because larger molecules travel more slowly because they spend more time impeded in the strands of the gel than the small molecules

Question 39

biological membranes are 2-dimensional fluids

Answer 39

all components of the membrane are able to diffuse in the plane of the membrane, unless they are anchored to the cytoskeleton or to extracellular material

Question 40

Hybrid Cell Experiments

Answer 40

examine how mobile a particular protein is within its membrane https://canvas.ubc.ca/courses/90472/files/15885111/preview

Question 41

Spectrin

Answer 41

provides a flexible meshwork below the membrane used for anchoring, and maintenance of cellular shape

Question 42

Glycocalyx

Answer 42

Glycolipids + Glycoproteins

Question 43

Glycolipids

Answer 43

integral parts of the membrane

Question 44

Glycoproteins

Answer 44

proteins that carry attached polysaccharides

Question 45

cell identity markers

Answer 45

Glycoproteins and glycolipids are very important in establishment of membrane cell identity markers

Question 46

ECM in animals

Answer 46

SEM of fibroblasts in connective tissue Hyaluronan, a relatively simple type of polysaccharide Proteoglycans form large aggregates

Question 47

ECM in plants

Answer 47

Plant cell wall