Lectures 11-12 - Regulation of glucose/glycogen Flashcards
1
Q
how is the activity of enzymes regulated? (2)
A
- number of molecules
- effective activity/activity of existing molecules
2
Q
common regulatory mechanisms at organism level (5)
A
- pathways in opposite directions are not favored simultaneously
- maximizes product utilization
- ability to partition metabolites between alternate pathways (glycolysis vs pentose-phosphate pathway)
- draw on fuel best suited for need
- slow down synthetic pathways when products accumulate
3
Q
glycolysis, gluceoneogenesis and pentose phosphate pathway are connected through several shared ________ and __________
- ex: 3 fates of glyceraldehyde 3P?
A
intermediates and enzymes
- converted to dihydroxyacetone phosphate in gluconeogenesis
- oxidized to pyruvate in glycolysis
- converted to fructose 6P in pentose phosphate pathway
4
Q
glycolysis is regulated to maintain constant ____ levels
A
ATP
5
Q
glycolysis if AMP is (high/low) and ATP is (high/low)
A
- high AMP
- low ATP
6
Q
gluconeogenesis if AMP is (high/low)
A
low
7
Q
regulation of _____/_____ levels along with regulation of (3 enzymes) to regulate glycolysis
A
- ATP/NADH levels
- hexokinase, PFK-1 and pyruvate kinase
8
Q
(3 hormones) regulate expression/function of glycolytic enzymes
A
- glucagon
- epinephrine
- insulin
9
Q
hexokinase 1 and 2
- predominant in ?
- affinity for glucose?
- allosterically inhibited by ?
A
- predominant in muscle
- high affinity for glucose (activity reaches max quickly –> rapidly saturated)
- G 6phosphate
10
Q
hexokinase 4:
- predominant in ?
- affinity for glucose?
- inhibited by ?
- activity increases when?
- Glu escapes glycolysis at (high/low) concentration
A
- liver
- lower affinity for glucose
- by regulatory protein: glucokinase regulatory protein (GKRP)
- at high glucose concentration (around 10mmol)
- low concentration
11
Q
how does glucokinase regulatory protein inhibit hexokinase 4?
- high concentration of (?) inhibits hexokinase 4 vs high what activates it?
A
- by drawing it into the nucleus
- high fructose 6P will make hexokinase 4 be attached to GKRP
- high glucose activates hexokinase
12
Q
hexokinase and glucose 6 phosphatase are _____________ regulated
A
transcriptionally regulated
13
Q
in liver:
- high blood glucose will increase transcription for ?
- low blood glucose will increase transcription for ?
A
- high blood glucose –> hexokinase 4
- low blood glucose –> glu-6-phosphatase
14
Q
what is the only “substrate” for PFK-1?
A
ATP
15
Q
how to inhibit/increase PFK-1 activity? (3)
A
- high ATP allosterically inhibits PFK1 (lowers affinity to F6P)
- high citrate increases ATP-inhibition (= inhibits PFK1)
- high AMP or ADP relieves ATP-inhibition (increase PFK1 activity)
16
Q
(high/low) AMP allosterically inhibits Fructose 1-6 bisphosphatase
A
high
17
Q
- if AMP is high and ATP is low –> to ___________
- if AMP is low –> to __________
A
- glycolysis
- low AMP = gluconeogenesis
18
Q
fructose 2,6 bisphosphate –> increases or decreases PFK1 and FBPase-1 activity, which stimulates what pathway?
A
- F26BP increases PFK1 activity –> stimulates glycolysis
- F26BP inhibits FBPase-1 activity –> NO gluconeogenesis
19
Q
which 2 enzymes synthesizes/degrades Fructose 2,6 bisphosphate?
A
- PFK-2 converts fructose 6P to fructose 2,6 bisphosphate
- FBPase-2 convers F 2,6 BP to Fructose 6P
20
Q
is fructose 2,6 bisphosphate a glycolytic intermediate?
A
no!
21
Q
fructose 2,6-bisphosphate acts as allosteric ________ of PFK1 and _________ of FBPase-1
A
- activator of PFK1
- inhibitor of FBPase-1
22
Q
why is PFK-2/FBPase-2 enzyme unusual? (2)
A
- because it’s a bifunctional enzyme (2 separate enzymatic activities)
- expressed from a single gene: PFKFB1
23
Q
are PFK-1 and FBPase-1 encoded by the same gene?
A
no, by 2 genes: PFKM and FBP1
24
Q
how is PFK-2/FBPase-2 regulated?
A
phosphorylation!
25
PFK-2/FBPase-2 active or inactive when phosphorylated? increase or decrease glycolysis/gluconeogenesis?
- OH: PFK-2 active + FBPase-2 inactive --> stimulates glycolysis + inhibits gluconeogenesis
- PO4: PFK-2 inactive + FBPase-2 active --> inhibits glycolysis + stimulates gluconeogenesis
26
what does insulin stimulate for PFK-2/FBPase-2?
vs glucagon?
insulin: stimulates phospho-protein phosphatase --> dephosphorylation --> active PFK-2 and inactive FBPase-2
- glucagon: stimulates adenylcyclase-cAMP-PKA (cAMP dependent protein kinase) --> phosphorylation --> inactive PFK2 and active FBPase-2
27
what mediates increase in glycolysis following a high carb meal?
- this rises as the glucose enters _________ and _____ pathways
xyulose 5-phosphate
- rises when glucose enters glycolytic and PPP pathways
28
what does an increase in xyulose 5-P do to glycolysis and gluconeogenesis?
activates phosphoprotein phosphatase --> dephosphorylates PFK2 and FBPase2 --> increase F26BP --> stimulates glycolysis and inhibits gluconeogenesis
29
how is pyruvate kinase regulated in liver? (2)
hint: phosphorylation vs dephosphorylation
- glucagon stimulates PKA --> PKA phosphorylates pyruvate kinase which makes it inactive (in liver)
- PP will dephosphorylate pyruvate kinase, which makes it active (in muscle and liver)
30
Phospho enol pyruvate to pyruvate by pyruvate kinase--> 1 thing increases activity vs 2 things decrease activity
- F16BP (which eventually becomes PEP) stimulates pyruvate kinase
- ATP, acetyl-CoA, long chain FA allosterically inhibit pyruvate kinase
- alanine (from transamination of pyruvate) slows down/inhibits pyruvate kinase --> slows down formation of pyruvate
31
muscle isoform of pyruvate kinase is not regulated by ?
PKA phosphorylation
32
2 fates of pyruvate in liver?
- to oxaloacetate --> gluconeogenesis --> glucose in mitochondria
- to acetyl-coa --> citric acid cycle --> energy!
33
when liver has sufficient FA for beta-oxidation --> _____A______ concentration is high
- ____A_____ stimulates glucose synthesis via gluconeogenesis by activating _________ __________ (converts pyruvate to oxaloacetate) and by inhibiting _______ _______ _________ (blocking pyruvate transformation to acetyl-coa)
A = acetyl-CoA
- activating pyruvate carboxylase
- inhibiting pyruvate dehydrogenase complex
34
what is ChREBP? and ChoRE?
ChREBP: carbohydrate response element binding protein --> a transcription factor
ChoRE: carbohydrate response element
35
Is phosphorylated ChREBP activated/deactivated?
deactivated!
36
how does ChREBP transcriptionally regulate enzymes? 5 steps
1. glucose enters, becomes xylulose 5P through PPP
2. xylulose 5P activates PP2A which dephosphorylates serine residue on ChREBP
3. ChREBP that has a dephosphorylated serine enters nucleus
4. xylulose 5P will again activate PP2A which dephosphorylates threonine on ChREBP --> ChREBP now fully dephosphorylated
5. fulle dephosphorylated ChREBP binds to ChoRE and turns on expression of genes to increase FA synthesis and increase glycolysis
37
xyulose 5P controls activity of _______ in which way? for ChREBP
- PP2A (dephosphorylates ChREBP)
- allosterically
38
transcriptional regulation of enzymes for gluconeogenesis. 3 steps
1. insulin binds to receptor --> stimulates PKB
2. PKB phosphorylates FOXO1, which inactivates it
3. FOXO1 is tagged by ubiquitin + degraded by proteasome
39
what is FOXO1? active when what? what does it suppress/activate?
FOXO1 = nuclear transcription factor
- active when unphosphorylated
- FOXO1 suppresses transcription of enzymes of glycolysis, pentose phosphate pathway and FA synthesis + stimulates gluconeogenesis (glucose 6 phosphatase + PEP carboxykinase)
40
what prevents phosphorylation of FOXO1?
glucagon
41
transcriptional regulation is VERY __________
- multiple _______ ________ can bind to same __________
- complex
- transcription factors can bind to same promoters
42
mutation of 1 transcription factor can have an impact on __________ formation
disease
43
how is glucose stored in animals and plants?
animals: glycogen
plants: starch
44
where is glycogen primarily found? + how many % weight
- liver: 10% of weight
- muscle: 1-2% weight
45
where is glycogen stored? + in what particles (2)?
- in cytosolic granules
- elemental particles of glycogen = beta particles --> contain 55k glucose with 2k non-reducing ends
- alpha rosettes contain 20-40 beta particles
46
glycogen depleated after (2)
- 12-24h fasting in liver
- 1h strenuous exercise in muscle
47
liver _________ serves as reservoir of glucose for other tissues when _________ ___________ is not available
- glycogen
- dietary glucose
48
total amount of energy stored as glycogen is far (more/less) compared to stored fat
far less
49
what (3) can store glycogen? (apart from muscle and liver)
- astrocytes (brain)
- heart
- adipose tissues
50
what is glycogenolysis:
breakdown of glycogen into formation of glu-1-phosphate
51
3 enzymes responsible for glycogenolysis
1. glycogen phosphorylase
2. glycogen debranching enzyme
3. phosphoglucomutase
52
glycogen phosphorylase acts on the ____-_________ end --> adds what to what? forming what?
- non-reducing end
- adds inorganic phosphate (Pi = cofactor) to non-reducing end of glycogen --> forms glucose 1-P and a shortened glycogen
53
glycogen phosphorylase depends on _________ _________ cofactor
pyridoxal phosphate
54
glycogen phosphorylase continues working on the ____-_________ end until it reaches a _________ (what linkage?)
- non-reducing
- branch (alpha 1-6 linkage)
55
how does debranching enzyme function? (2 steps)
1. transferase activity of debranching enzyme shifts a block of 3 glu to a nearby non-reducing end --> reattaches with alpha 1-4 linkage
2. glucosidase activity of debranching enzyme releases the free glucose without a phosphate group at C1
56
does the debranching enzyme require Pi?
no
57
in glycogen degradation, glucose 1-P is converted to ?
glucose 6P
58
which enzyme converts glu-1P to glu-6P? how? (3 steps)
- phosphoglucomutase
1. phosphoglucomutase has an active site with serine residues that is phosphorylated
2. phosphate from serine transferred to C6 of glucose --> forming g-1-6biphosphate
3. PO4 from glucose's C1 will rephosphorylate the serine residue
59
Is glucose-6P dephosphorylated? if so, why and how? (4 steps)
- yes! in the liver for transport out of liver
1. G6P transported into endoplasmic reticulum through T1
2. glucose 6-phosphatase removes Pi --> G6P to glucose
3. glucose leaves endoplasmic reticulum through T2 to cytosol
4. glucose leaves cytosol through GLUT2 to bloodstream
60
in muscle:
1. muscle contributes to blood glucose concentration?
2. glucose 6 phosphotase expression is (high/low)
3. hexokinase __ and ___ have high/low affinity for glucose
4. GLUT4 is __________ dependent
1. Nope
2. low
3. hexokinase 1 and 2 have high affinity
4. insulin dependent
61
4 general steps of glycogenesis
1. formation of UDP-glucose (by NDP-sugar-pyrophosphorylase)
2. initial short chain synthesis (by glycogenin)
3. elongation (by glycogen synthase)
4. branching (by glucogen-branching enzyme)
62
where does glycogenesis take place? (2)
- can take place in any cells
- predominantly in liver
63
what is the precursor for glycogenesis? structure?
sugar nucleotide (UDP-glucose)
- glucosyl group + 2 phosphates + uridine
64
step 1 of glycogenesis
- what into what?
- enzyme?
- name of reaction?
- what attacks what?
- sugar phosphate (ie glucose 1P) + NTP --> pyrophosphate (PPi) (that's degraded to 2 Pi) + sugar nucleotide (NDP-sugar)
- NDP-sugar pyrophosphorylase
- condensation reaction between sugar phosphate and NTP
- O- of sugar phosphate acts as nucleophile + attacks alpha phosphate of NTP (that has 3 P)
65
which enzyme degrades pyrophosphate (PPi) into 2 Pi?
inorganic pyrophosphatase
66
step 2 of glycogenesis
(3 steps)
1. OH of Tyr residue of glycogenin attacks C1 of glucose moiety on UDP-glucose = transfer of glucose to OH of glycogenin + release of UDP
- using glucosyltransferase activity of glycogenin
2. OH of glucose that is now attached to glycogenin attacks C1 of glucose moiety on another UDP-glucose --> release of UDP
- using chain extending activity of glycogenin
3. repeated 6 more times so that 8 glucose are attached to glycogenin
- then, glycogenin not needed anymore --> glycogen synthase takes over
67
glycogenin
- acts as ?
- forms glycogen by ?
- primer protein
- catalyzing its assembly
68
Step 3 of glycogenesis
(3 steps ish)
1. glycogen synthase allows removal of phosphate of C1 of glucose moiety on UDP-glucose --> attaches glucose on non-reducing end of glycogen chain that has at least 4 residues
2. release of UDP
3. glycogen synthase continues with alpha 1-4 linkage
69
glycogenesis:
- G_P --> G_P
- G_P --> ?
- G6P --> G1P
- G1P --> UDP-glucose
70
can glycogen synthase do alpha 1-6 linkages?
no
71
why do we need branching/what are the biological effects of branching? (2)
- increases water solubility
- increases number of nonreducing ends = increase number of sites for glycogen synthase
72
which enzyme does the branching in glycogenesis? how?
- glycogen-branching enzyme
- takes 7 (from image) glucose and makes an alpha 1-6 linkage at the branch point --> forming a new non-reducing end
73
each chain/branch of glycogen has __ to ____ glucose residues
12-14
74
2 regulatory points of glycogen metabolism that we focus on?
- glycogen --> glycose-1P through glycogen phosphorylase
- UDP-glycose --> glycogen through glycogen synthase
75
glycogen phosphorylase --> active or less active when phosphorylated?
- which form is a and which is b?
- phosphorylated on which residues?
- what enzymes phosphorylates it?
- using what?
- where?
- active when phosphorylated (a form) vs less active when unphosphorylated (b form)
- phosphorylated on Ser side chains
- phosphorylase b kinase (converts phosphorylase b to phosphorylase a)
- using 2 ATP
- in contracting muscle
76
what will increase phosphorylase b kinase activity?
- glucagon (liver)
- epinephrine
- increase in Ca2+ concentration
- increase in AMP concentration in muscle (from increase in exercise)
77
what dephosphorylates phosphorylase a to phosphorylase b?
- using what?
phospho-protein phosphotase (PP1)
- using 2 H2O
78
2 hormones activate _______ receptor respectively in 2 types of cells --> kinase cascade for glycogenolysis (6 steps) --> final product can be used in (2)
- epinephrine in myocyte/muscle + glucagon in hepatocyte/liver
- activate G-protein receptor
- activate adenylyl cyclase --> cyclic AMP --> activates PKA --> activates phosphorylase b kinase --> activates glycogen phosphorylase a --> converts Glycogen to glucose 1P
- glucose 1P can be used in glycolysis for muscle contraction and converted to glucose and enter blood glucose
79
how is glycogen synthase activated/deactivated?
- when GSK3 is unphosphorylated --> adds 3 PO4 to Ser residues on glycogen synthase a, which makes it inactive (b form)
- glycogen synthase b is dephosphorylated by PP1 to make glycogen synthase a (active)
80
hormonal regulation: stimulation of glycogenesis by insulin (7 steps)
- think of receptor tyrosine kinase activity with PIP3
1. insulin binds to receptor
2. autophosphorylation of receptor tyrosine kinase + phosphorylation of insulin receptor substrate 1 (IRS1)
3. IRS1 activates PI3K --> which converts PIP2 to PIP3
4. PIP3 activates PDK1, which phosphorylates and activates PKB
5. PKB phosphorylates GSK3 on Ser residue--> GSK3 becomes inactive
6. glycogen synthase stays active (because GSK3 can't convert it to inactive form) and can make glycogen out of glucose residues
7. PKB also stimulates movement of glucose transporter GLUT4 from internal membrane vesicles to plasma membrane, increasing uptake of glucose
81
2 ways that insulin increases glycogenesis
1. deactivates GSK3 --> so no phosphorylation of glycogen synthase
2. activates PP1 so glycogen synthase b is converted to glycogen synthase a
82
what inhibits glycogenesis in insulin pathway?
glucagon and epinephrine! they block the dephosphorylation of glycogen synthase b
83
PP1 acts on which 3 enzymes?
- phosphorylase kinase
- glycogen phosphorylase
- glycogen synthase
84
regulation of glucose metabolism in muscle:
- muscle lacks _________ receptor
- muscle isoform pyruvate kinase is not phosphorylated by ______
- muscle does not produce ________
- lacks glucagon receptor
- not phosphorylated by PKA
- does not produce F26BP
