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Biochem > G Proteins > Flashcards

G Proteins Flashcards

1
Q

G Protein Definition

A

Guanosine nucleotide binding proteins

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2
Q

GPCR details

A

G Protein coupled receptors

  1. Plasma membrane receptor = 7 transmembrane helical segments
  2. G protein active with GTP
  3. Effector enzyme in plasma membrane activated by G protein
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3
Q

Generic pathway for G proteins

A

1st messenger - Allosteric transition for GPCR - G protein activated - G protein binds to effector protein - causes change in concentration for second messenger - binds to target

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4
Q

Two big functions of GPCRs

A

Detect hormones/growth factors

Aid in smell/ taste

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5
Q

Beta adrenergic receptor

A

Base form for GPCRs

Mediates epinephrine effects = adrenaline

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6
Q

Where are beta adrenergic receptors located?

A

Muscle, liver, adipose tissue

On membrane

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7
Q

G Protein structure

A

3 subunits:

alpha = binding site for GTP or gdp = GTPase functionality

GPCR is transmembrane component not G protein

Beta

Gamma

When gdp bound = heterotrimeric

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8
Q

When is Gs accurate?

A

Stimulated G protein = activated = GTP

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9
Q

AC Enzyme function

A

Adenylyl Cyclase = integral plasma membrane protein

Synthesizes cAMP from ATP = removes PPi

Stimulated by Galpha protein

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10
Q

ATP structure reminders

A

Two aromatic rings with 2 N each, one has nh2 offshoot,
Glucose ring with oh x2
3 po4 groups

Nitrogen
Glucose
Phosphorous

= NGP = nasty gal pal = energizes me the whole night !!!

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11
Q

cAMP structure reminders

A

Same as atp but has lost PPi

P interacting w glucose rings = comrades

= nitrogens, glucose, phosphorous

Nasty gal pal with piss taken out of her by AC = air conditioning has ruined her amazing hair that she spent a lot of time on and she has to put a jacket on

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12
Q

AMP structure reminders

A

Like cAMP but p is not interacting with glucose ring

Nitrogen, glucose, phosphorus

cAMP minus the c = comrades

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13
Q

Cyclic nucleotide phosphodiesterase

A

cAMP -> AMP via hydrolysis

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14
Q

What does cAMP activate?

A

Protein kinase A
= PKA

Memory: the camp at peak A = best mountain camp around = fight or flight

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15
Q

Why is PKA important?

A

Key to phosphorylation of important ser or thr residues of proteins for fight or flight response

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16
Q

How many cAMPs to activate PKA?

A

4

2 per regulatory subunit

17
Q

PKA structure details

A

Bound to AKAP = a kinase anchoring protein

Dimer of two R subunits = regulatory subunits = dimerization domain is amino terminal attached to AKAP

Each r subunit has 1 catalytic subunit
When inactive = atp binding site blocked by R subunits

Conformational change caused by cAMP = C subunits available for ATP binding = transfer of P to side chain of a ser or thr in residue of target protein

18
Q

PKA consensus sequence

A

X-r-r/k-x-s/t-b

X=any, r=arg, k=lys, s/t= ser or thr, b= basic

Ex in rage at rack
Ex stabs

19
Q

FRET

A

Fluorescence resonance energy transfer

Fret proportional to (1/d^6) between fluorescent proteins

Lower fluorescence if close enough

20
Q

FRET for detecting cAMP in cells

A

BFP gene with R unit of PKA

GFP gene with C unit of PKA

More cAMP = more blue bc units further apart

Less cAMP = more green bc units close together

21
Q

FRET for PKA activity in cells

A

Cyan gene fused with top half of hybrid protein to be phosphorylated by PKA = consensus sequence in middle

Yellow gene fused with bottom half of same protein

When protein phosphorylated = two halves close together = yellow color = PKA activity

When protein not phosphorylated = far apart = cyan color

22
Q

Epinephrine pathway
In hepatocyte

A

Epinephrine binds to cell membrane via GPCR = beta adrenergic receptor

G protein is activated

Activates AC to produce more cAMP from ATP

cAMP activates PKA

PKA phosphorylates phosphorylase b kinase

Which phosphorylates glycogen phosphorylase a

Which activates glycogen breakdown to glucose 1 phosphate to glucose

= amplification occurs at each step
= very rapid

23
Q

1 molecule epinephrine is how many molecules of glucose released?

A

100,000

24
Q

Mechanisms for terminating b adrenergic receptor response

A

-epinephrine concentration less than Kd = dissociation

-GTP hydrolysis within G alpha
= gtpase

-removal of second messenger
= hydrolysis of cAMp via cyclic nucleotide phosphodiesterase to AMP

-Effects of pathways reversed by phosphoprotein phosphatases
= PP1 for beta adrenergic receptor pathway

25
Q

Desensitization mechanism for beta adrenergic receptor

A

-beta gamma subunit recruits beta ARK = kinase that phosphorylates ser resides at Carboxyl end of receptor

-phosphorylated receptor binds to arrestin = arrests continued activation of incoming G proteins
= also recruits clathrin for endocytosis of receptor

-arrestin dissociates and receptor loses Ps = returns to surface

26
Q

Desensitization mechanism memory

A

Beta ARK = bark kinase = fucks with bark of cell = membrane = epinephrine receptor = kinase so phosphorylates = barks like dog listening to sers

Barking puts P in ears = barking calls over master = Beta-arrestin = beta boy arresting beta receptor = frat boy doesn’t like things that suck up his drugs = jailed up in clathrin = powerful father helps him
= MAPK cascade = same as insulin = cell proliferation = jails are for growing

27
Q

What cascade is triggered by Barr and receptor binding?

A

MAPK

28
Q

How does G protein interact with atp?

A

P loop interacts with gamma P of ATP

Switching off of G protein relates to hydrogen bonds
When Pi cleaved - hydrogen bonds of switches break = Galpha protein inactive

29
Q

Cholera toxin

A

Secreted by bacteria into intestine

Breaks into subunits

One subunit interacts with small G protein ARF6 and turns off GTPase activity by pairing NAD+ to P loop = permanently active

= super high cAMP and PKA activity
= efflux of NaCl is constant = water loss = dehydration

30
Q

Different G proteins

A

Gs and Gq are stimulatory

Gi is inhibitory

31
Q

What does Gq alpha activate?

A

PLC in Membrane

32
Q

What does PLC stand for? What does it do?

A

Phospholipase C

Converts PIP2 to IP3 + DAG

IP3 = ca2+ into Cytosol from ER lumen

Ca2+ activates PKC = MAPK/ PI3K pathways = cell proliferation/ glycogen synthesis/ glucose uptake

Ca2+ activates insulin release in pancreas = but not beta adrenergic receptors on pancreas

33
Q

What does Gi alpha do?

A

Inhibits AC

= lessens conversion of ATP to cAMP = not so much glycogen breakdown

34
Q

Protein kinases in cell

A

Receptor thyrosine Kinase ==> PKB = PI3K pathway

GPCR (Gs) ==> PKA = beta adrenergic pathway

GPCR (Gq) ==> PKC = ca2+ Release = Mapck = PI3K pathway

35
Q

Gs with PKA vs Gq with PKC Memory

A

Gs = beta adrenergic = cAMP
= camp on peak A = PKA

Gq = Gq Magazine = men’s magazine = pretty little cumberbatch = PLC activated = IP3 = ingenious person 3 times
==> genius = separate from heart = calcifer = or secret to genius is Bones and Milk = ca2+

Heart is moved by performance of cumberbstch = calcifer moves = kinase C
Protein kinase C = peak calcium = calcium up = PKC

36
Q

PIP2 structure reminders

A

2 esters
P group
Carbon ring with 3x OH, 2x PO3 groups

Two p groups on ring = P^2

Esters = good smells = perfume = P at front

37
Q

PIP3 structure reminders

A

Phospholipid

2 esters - FA chains
P group
Carbon ring = 2x OH either end of OC connecting to p group, 3x Po4 groups

3 po4 coming off of ring = p^3

Esters = perfume = P at start

38
Q

IP3 structure reminders

A

P group
Carbon ring = 3x OH, 2x P groups

3 p groups total = IP^3

Biochem (23 decks)

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