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BIO 200 > Unit 2 : Bio Membrane > Flashcards

Unit 2 : Bio Membrane Flashcards

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1
Q

Membrane Definition

A

barriers that define compartments

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2
Q

Biological Membrane features

A

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

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3
Q

Why do membrane lipids form sheets ?

A

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

Form rough cylindrical shape which stacks together well

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4
Q

Liposomes

A

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

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5
Q

Phospholipid bilayers held together by

A

hydrophobic interactions

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6
Q

Lipid bilayers are stable because

A

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

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7
Q

Protiens

A

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

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8
Q

Disulfide bridges

A

between cysteine residues

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9
Q

Chaperones

A

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

Final fold stable enough - not change when released from chaperone

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10
Q

Membrane is selectively permaeble

A

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

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11
Q

Water crosses membrane at rate higher than expected for lipid bilayer

A

proteins in membrane

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12
Q

core of lipid bilayer

A

non-polar environment so water-free zone

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13
Q

transporters

A

transport big / charged molecules across membrane

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14
Q

Membrane is organized but fluid

A

lipid + protein maintain organization of membrane

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15
Q

Water on both sides of membrane

A

lipids cannot escape but move and change places within membrane

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16
Q

Membrane is Asymmetric

A

arrangement of components not same on both sides

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17
Q

Key contributors to asymmetry

A

lipids
proteins
carbohydrates

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18
Q

Ectotherm membranes

A

manipulate environment colder temp = decrease fluidity

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19
Q

Endotherm membranes

A

maintained in strict environment

20
Q

Effect of temp on lipid bilayer

A

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

21
Q

Factors affecting fluidity\

A

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

22
Q

Real membranes

A

regions with varying fluidity

23
Q

FRAP

A

Fluorescence Recovery After Photobleaching

24
Q

FRAP results

A

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

25
Q

Enzymes such as flippases, floppases and scramblases

A

move lipids from one side of the membrane to the other

contribute quite specifically to the asymmetry of the final membrane

26
Q

Integral Membrane Proteins

A

embedded within the phospholipid bilayer

cannot be removed from the membrane without destroying the membrane completely

27
Q

Peripheral Membrane Proteins

A

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

28
Q

How proteins are attached to membranes

A

1 ) Transmembrane proteins

2 ) Lipid-anchored proteins

3 ) Monolayer-associated proteins

29
Q

Transmembrane proteins

A

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

30
Q

Lipid-anchored proteins

A

covalently attached to fatty acids or diacylglycerides

31
Q

Monolayer-associated proteins

A

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

32
Q

Transmembrane proteins use secondary structure to pass through the membrane

A

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

33
Q

Alpha-helices in pores and channels

A

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

34
Q

Beta-barrels in transmembrane proteins

A

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

35
Q

Membrane Protein Function

A

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

36
Q

Hydropathy plot

A

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

37
Q

Reading hydropathy plot output

A

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

38
Q

Protein Separation via SDS-PAGE

A

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

39
Q

biological membranes are 2-dimensional fluids

A

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

40
Q

Hybrid Cell Experiments

A

examine how mobile a particular protein is within its membrane

https://canvas.ubc.ca/courses/90472/files/15885111/preview

41
Q

Spectrin

A

provides a flexible meshwork below the membrane

used for anchoring, and maintenance of cellular shape

42
Q

Glycocalyx

A

Glycolipids + Glycoproteins

43
Q

Glycolipids

A

integral parts of the membrane

44
Q

Glycoproteins

A

proteins that carry attached polysaccharides

45
Q

cell identity markers

A

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

46
Q

ECM in animals

A

SEM of fibroblasts in connective tissue

Hyaluronan, a relatively simple type of polysaccharide

Proteoglycans form large aggregates

47
Q

ECM in plants

A

Plant cell wall

BIO 200 (2 decks)

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