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ANAT 212 > Lecture 8 > Flashcards

Lecture 8 Flashcards

1
Q

what can proteins be modified by

A

lipids - covalently bound to lipids = like another ex of ptms

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2
Q

describe phospholipid synthesis - generally

A

synthesis on cytosolic side of er membrane
fatty acids (acyls) are attached to coenzyme A in chemically reactive states
glycerol-phosphate, head group added in sequence by enzymes

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3
Q

describe phospholipid synthesis - specifics

A

oh faces environment
protects hydrophobic fatty acid tail and brings to cytosolic part of er membrane and insert into membrane
CoA transferase = intermediate facilitates addition of glycerol group
hydroxyl removed and acetyl coa added
fatty acid brought by carrier into membrane and then sequential steps = to add polar head
choline attached as head into fatty acids

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4
Q

where are phospholipids and cholesterol synthesizedc

A

Phospholipids and cholesterol are synthesized on the cytosolic side of the
ER membrane
makes membranes unbalanced since has less phospholipids and more fatty acids

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5
Q

what does scramblase do

A

protein in ER membrane = flips lipids randomly
atp independent function
helps balance amount of phospholipids in outer and inner membrane
non specific = recognizes any phospholipids

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6
Q

how are lipids transported

A

secretory pathway by vesicles

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7
Q

what is flippase

A

at pm
more specific
maintains membrane asymmtry
ex = phosphatidyl serine always facing cytosol
atp depent
direcional
lipid specific

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8
Q

how are new lipids brought to pm

A

by vesicles and flipped to correct orientation

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9
Q

what maintains lateral organization and membrane asymmetry

A

mechanisms

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10
Q

how are lipids transported

A

vesicles between organelles of secretory pathway
carrier proteins through cytosol
contact sites between organelles = er and mito

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11
Q

how to control traffic of proteins

A

adding other proteins into bilayer
localization of proteins in membrane depend on other proteins that allow protein to be inserted into membrane

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12
Q

what does sequence of protein determine

A

structure
function
localization

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13
Q

what does structure of membrane proteins involve

A

added contacts with lipids

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14
Q

what does localization of membrane proteins require

A

protein based targeting mechanism

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15
Q

what are not associated with membranes

A

soluble proteins

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16
Q

which interactions important to be inserted into membrane

A

hydrophobic interactions with phospholipids

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17
Q

describe integral membrane proteins

A

tightly anchored by hydrophobic interactions with interior of bilayer

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18
Q

describe parts of integral membrane proteins

A

1 or more trans membrane alpha helices = must have
transmembrane beta barrel = depends on formation of beta strands
amphipathic alpha helix in one face of membrane - hydrophobic on one side and polar on other

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19
Q

describe alpha helix for integral membrane proteins

A

amphipathic
hydrophobic aas interaction with membrane and another part = hydrophobic or polar aas that will interact with cytosol
so alpha helix part of membrane

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20
Q

describe lipid anchored or peripheral membrane proteins

A

not integral part or transversing it

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21
Q

describe lipid anchored proteins

A

proteins covalently linked to one or more lipids or fatty acid groups
strength of anchor depends on number and type of lipid
specific aas around them to be attached

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22
Q

describe peripheral membrane proteins and name 2 types

A

attached by non covalent interactions
with integral membrane proteins
with lipid head groups

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23
Q

describe peripheral membrane proteins with integral membrane proteins

A

strong interactions

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24
Q

describe peripheral membrane proteins with lipid heads

A

weak interactions
residues that can form non covalent interactions with polar head of phospholipids = not v strong but allows proteins to localize into membrane

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25
compare transmembrane proteins and lipid anchored proteins
tm = function in both cellular compartments, cell surface receptors, transporters lipid anchored proteins = function in one side of membrane intracellular signalling
26
describe trans membrane helices
Transmembrane α-helix is the most common form of attachment
27
describe structure of transmembrane helices
Like all α-helices, amino acid side chains point outwards in transmembrane helices, side chains are hydrophobic to interact with lipids internal hydrogen bonds maintain structure of helix some hydrophilic aas tho
28
can proteins have more than one helical domain
can have one or more helical tm domain single and multipass proteins
29
describe single and multiple TM helices
tm helices longer, more hydrophobic than interior of soluble protein usually 18-24 aas long hydrophobic aa = means that alpha helix inserted into membrane can often be predicted from hydrophobicity of primary sequence can see regions inserted into membrane
30
describe hydrophobicity index
experimentally aas can be characterizes diff diff indices use various methods and scales side chains still have local proteins
31
what does length of tm helices match
width of membrane
32
describe longer tm helices
may partition into thicker microdomains or insert at angle in thinner membranes sixe of alpha helix must fit thickness of membrane
33
which proteins can rotate easily
proteins with single TM helix
34
describe function of some polar aa's in tm helix
could be in contact with aq environment a bit and sometimes alpha helices get together and make a pore = transmembrane transporter need polar on interior so wont repel substrate
35
describe TM helical structures
Multiple TM helices can fold together into functional structures embedded in the membrane Interior between helices can be free of lipid Many transporter proteins have multiple TM helix structure, although are not otherwise related (not homologous)
36
describe transmembrane b barrels
in some tm domains = b strands form tm barrel = b sheets wrapped into cylinder number of tm strands can vary side chains point out into lipid bilayer and inside = h bonds hold strands together
37
what does more beta sheets do for a b barrel
more = determines how big substrate they transport from one end of cell is
38
when is tm protein orientation determined
during insertion into membrane cannot flip - have order and direction
39
are ptms the same in the cytosol
noo since er is bound to sugars
40
describe secretory pathway modifications
domains modified differently from cytosolic domains disulfide bonds between cysteines oligosaccharides (glycosylation) stabilize protein structure
41
describe protein modifications in the cytosol
phosphorylation acetylation methylation ubquitination
42
can membrane proteins flip
never but lipids can
43
how is movement of ions and polar molecules across membranes controlled
by proteins mechanism depends on concentration gradient of solute
44
name 2 proteins that control ions and polar molecules
channel pump/transporter
45
describe channel
allows movement along gradient does not require energy - atp independent regulated by opening and closing
46
describe pump/transporter
causes movement against gradient required energy - atp regulated by turning atpase on and off
47
describe channel proteins
allow regulated flow of ions or other molecules across membranes from one compartment to other
48
what can tm helices form
water filled channel
49
describe water filled channel
opening controlled by cytosolic domains or subunits some tm helices must be on polar side selective for ions = depends on how much channel opens how much ions get in or out
50
describe voltage gated k+ channel
fundamental for neurons, heart, brain, cell function Rat Brain K+ channel homotetramer = neuron signaling, homologs: heart rhythm Pore controlled by voltage sensor, other domains
51
describe ion selectivity of channel proteins
Channel pore contains Selectivity Filter for specific ion, eg. K+ Carbonyls from peptide backbone line the pore Ions normally bind water Ions with the right size can exchange water for carbonyls – partial dipoles Wrong size cannot bind carbonyls completely and is rejected
52
give ex of ion selectivity
potassium and sodium = both pos but diff sizes sodium too small to fir into channel well = only engages in a couple of interactions
53
describe atp dependent transporters
transport of some substrates across membrane is unfavourable = against gradient some proteins use atp hydrolysis to transport substrates sodium potassium pump = maintains ion gradient across pm atp binding casette - abc = transporters for small molecules = cholesterol, toxins, phospholipid flippases
54
describe multidrug resistance transporter - gen
abc transporter with 2 symmetric atpase domains pumps toxins out of cancer cells = resistance to chemotherapy
55
describe lipid anchored proteins- modifications
cytosolic proteins can be covalently linked to acyl - fatty acid or prenyl chains specific enzymes attach lipid to n terminus or cys side chain N END RULEEE
56
describe single lipid chain
provides transient interaction with membrane protein bound to membrane = covalently linked to lipid = ptm
57
describe 2 or more lipid chain
needed for strong membrane anchor
58
describe acylation
N-Gly/N-cys = remove met and 2nd aa= cys or gly = similar to n end rule produces amide linkage or just with cys = thioester linkage - can be anywhere
59
describe prenylation
depends on cysteine = has be last 4 aa away from cooh terminus = cys-a-a-x-cooh forms thioester linkage
60
which lipid modification is reversible
Cys S-acylation is reversible (thioester) and can be used to regulate interactions with membranes thioester to cys = reversible - kinases, since they have many of these proteins = participates in signalling
61
which lipid modification is irreversible
N-terminal acylations (amide) are permanent Prenylation: special branched lipids permanently attached to Cys (thioether)
62
describe cysteine
Sulfhydryl side chain is chemically reactive disulfide bond formation lipid modification = thioester, thioether --> acylation ub e1 activating and e2 conjugating enzymes - thioester
63
describe cysteine prenylation motif
Prenylation motif: Caax-COO- (a=alkyl side chain; x=any) aax sequence cleaved off, Cys is prenylated
64
describe gpi anchored proteins
Some proteins have a special TM helix removed and become covalently linked to glycosyl-phosphatidyl-inositol (GPI) anchor Strong membrane attachment Only on lumenal/extracellular side; attached at ER, function at exterior of PM (Extracellular matrix, neuronal receptors.........) More rotational freedom than proteins with TM helices
65
what are gpi anchored proteins used for
folded in er lumen provides flexibility = can more more in er lumen = more mobility protein bound to membrane by gpi anchor = transferred for mobility
66
describe multidrug resistance transporter - 3 steps
1 - no nucleotide = inward open, high affinity for substrate 2 - atp bound = closed, conformational change 3 - atp hydrolysis = outward open (conformational change), low affinity for substrate = release toxin if have v high concentration of transporters

ANAT 212 (34 decks)

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