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Biochemistry > Cell Signaling Pathways: Insulin > Flashcards

Cell Signaling Pathways: Insulin Flashcards

1
Q

What is a major metabolic fuel?

A

glucose

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2
Q

Circulating levels of glucose are tightly regulated through the opposing actions of principally:

A

insulin

glucagon

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3
Q

Insulin ___ glucose levels

A

reduces

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4
Q

Glucagon ____ glucose levels

A

raises

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5
Q

What does the mammalian brain depend upon as its primary/major source of energy?

A

glucose

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6
Q

Glucose is derived from what materials?

A

those ingested in the diet

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7
Q

Carbs exist as : (3)

A

polysaccharides
disaccharides
monosaccharides

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8
Q

starch and glycogen are:

A

polysaccharrides

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9
Q

sucrose, maltose, and lactose are:

A

disaccharides

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10
Q

galactose, glucose, and fructose are:

A

monosaccharides

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11
Q

What represents about 60% of the carb intake for Westerners?

A

starch

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12
Q

Carbs are broken down into what in the gut?

A

hexoses

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13
Q

Can hexoses pass freely through the cell membrane?

A

no

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14
Q

How are hexoses absorbed since they can’t pass freely though the CM?

A

absorbed via glucose transporters like GLUT4

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15
Q

Insulin released by Beta Islet cells when blood glucose is (low/high).

A

high

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16
Q

How is blood glucose regulated when it’s high?

A

high blood glucose –> insulin released by Beta Islet cells in pancreas (also inhibits glucagon release by Alpha Islet cells) –> increased uptake of glucose –> glucose converted into glycogen (muscle and liver) or triglycerides (adipocytes)–> normal blood glucose levels

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17
Q

Which organ releases insulin?

A

pancreas

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18
Q

How is blood glucose regulated when it’s low?

A

low blood glucose –> glucagon released by Alpha Islet cells in pancreas (also inhibits insulin release by Beta Islet cells) –> glycogen and triglycerides converted into glucose and fatty acids –> normal blood glucose levels

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19
Q

Type of post-translational modification that effects protein function:

A

phosphorylation

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20
Q

Is phosphorylation reversible?

A

yes

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21
Q

What can REVERSIBLY turn an enzyme or receptor on or off altering its function?

A

phosphorylation

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22
Q

What does reversible phosphorylation result in?

A

conformational change in structure of enzymes and receptors causing them to become activated or deactivated

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23
Q

The protein-phosphate bond is a (low/high) energy bond.

A

high

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24
Q

Where does phosphorylation occur?

A

specific side chains of enzymes or receptors: serine, threonine, tyrosine, histidine

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25
Q

enzyme catalyzing a phosphorylation reaction:

A

kinase

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26
Q

enzyme that uses a high energy source of phosphate; most commonly ATP

A

kinase

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27
Q

enzyme that removes phosphate residues (dephosphorylation):

A

phosphatase

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28
Q

Insulin can decrease blood glucose in 2 ways:

A
  1. dephosphorylates via protein phosphatase which activates glycogen synthase
  2. dephosphorylates via protein phosphatase which deactivates glycogen phosphorylase
    * * both preventing conversion to glucose 1-phosphate but allowing conversion from glucose to glycogen and storage of glycogen
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29
Q

Glucagon/epinephrine can increase blood glucose in 2 ways:

A
  1. Activates cAMP which activates protein kinase A which phosphorylates and inhibits glycogen synthase
  2. Activates cAMP which activates phosphorylase kinase which phosphorylates and activates glycogen phosphorylase
    * *both lead to conversion of glycogen to glucose 1-phosphate
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30
Q

What is the first molecule in insulin biosynthesis?

A

Proinsulin

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31
Q

Which molecules cleave proinsulin at specific sites?

A

prohormone convertase 2 and 3

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32
Q

The cleavage of proinsulin leads to the production of:

A

active insulin and C-peptide

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33
Q

Where is insulin stored?

A

granules in B-cells of pancreas

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34
Q

Which molecule activates insulin gene expression?

A

Ca2+

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35
Q

Ca2+ activates insulin gene expression via which protein?

A

Calcium Responsive Element Binding (CREB) Protein

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36
Q

Is the activation of insulin gene expression a slow or fast process?

A

slow

37
Q

What causes K+ATP channels to close causing depolarization in the pancreas?

A

increased ATP:ADP ratio

38
Q

The closing of K+ATP channels causing depolarization in the pancreas causes which channels to open and which molecule is released into the cell?

A

voltage-gated Ca2+ channels

Ca2+

39
Q

The release of Ca2+ from voltage-gated Ca2+ channels

causes rapid:

A

exocytosis of stored insulin

40
Q

What is the normal fast blood glucose:

A

70-130 mg/dL

41
Q

Describe the overall kinetics of insulin release:

A

initial fast response followed by more prolonged phase

42
Q

Is the first phase of insulin release kinetics fast or slow and why?

A

fast

rapid exocytosis of stored insulin granules

43
Q

Is the second phase of insulin release kinetics fast or slow and why?

A

slow

insulin production via gene expression

44
Q

Insulin is what type of hormone?

A

Protein/peptide hormone that has PM-bound receptor system

45
Q

What is the insulin receptor composed of?

A

alpha and beta chains

46
Q

What are the alpha and beta chains of the insulin receptor activated by?

A

insulin
IGF-I (insulin-like growth factor-1)
IGF-II (insulin-like growth factor-2)

47
Q

The insulin receptor belong to what class of receptors?

A

tyrosine kinase receptors

Transmembrane receptor

48
Q

Binding of ligand (insulin or IGF-II) to the alpha chains of the ectodomain induces what?

A

structural change (conformational change) in the receptor leading to autophosphorylation of tyrosine residues within the intracellular TK domain of the beta chain.

49
Q

Insulin binding to ___ activates a _____ of ______ signaling.

A

IR-beta
cascade
intracellular

50
Q

How many different glucose transporters?

A

13

51
Q

What are the main glucose transporters?

A

GLUT1-5

52
Q

What are 2 ways glucose uptake in cells can occur?

A
  • facilitated (passive) diffusion = transport down concentration gradient via carrier protein
  • active transport = energy requiring transport against concentration gradient
53
Q

process of passive transport with transport aided by integral membrane channels or carrier proteins and causes a conformational change

A

facilitated diffusion

54
Q

Describe the process of Na+ coupled sugar transport:

A

extracellular Na+ binds to protein channel in membrane causing conformational change which allows glucose to bind and get transported, along with Na+, into the intracellular side and when Na+ leaves, the protein returns to its normal state

55
Q

Insulin increases the translocation of which GLUT receptor to the CM?

A

GLUT4

56
Q

Which transporter mediates intestinal absorption of glucose from the diet on the luminal side of the intestinal enterocyte?

A

Sodium-Glucose co-Transporter 1 (SGLT1)

57
Q

Which transporter is important in the basolateral efflux of glucose into the blood stream?

A

GLUT2

58
Q

Which transporter is important in the glucose-mediated secretion of incretin hormones, GIP and GLP-1?

A

SGLT1

59
Q

Gut hormones released after eating that stimulate the secretion of insulin by the beta-cells of the pancreas:

A

incretin hormones

60
Q

Major incretin hormones:

A

glucagon-like peptide-1 (GLP-1)

gastric inhibitory peptide (GIP)

61
Q

Both GLP-1 and GIP are inactivated by the enzyme ____________.

A

dipeptidyl peptidase-4 (DPP-4)

62
Q

Where is dipeptidyl peptidase-4 (DPP-4) released from?

A

endothelial cells of blood vessels

63
Q

Lead to increased insulin secretion and decreased glucagon levels and consequently improvement in hyperglycemia:

A

DPP-4 inhibitors

64
Q

Ex. of DPP-4 inhibitor

A

serine protease

65
Q

First DPP-4 inhibitor agent approved by FDA in 2006:

A

Sitagliptin

66
Q

hormone lowers blood glucose by stimulating cellular uptake and glycogen synthesis:

A

insulin

67
Q

example of insulin

A

Humalin R (T1 diabetes)

68
Q

Insulin action on rat adipocytes shows as insulin increases, glucose uptake ____ and lipolysis _____.

A

increases

decreases

69
Q

What is the storage form of glucose?

A

Glycogen

69
Q

What are the 2 fates of glucose once it’s converted in glucose-6-phosphate?

A
  • stored as glycogen

- enters glycolysis to form pyruvate which has multiple fates

70
Q

Where is glucagon produced?

A

Alpha cells of pancreas

71
Q

Where is insulin produced?

A

Beta cells of pancreas

72
Q

Insulin regulates changes in metabolic pathways regulating fatty acid synthesis and glycogen synthesis primarily by altering the ________ statues of key enzymes on these pathways.

A

Phosphorylation

73
Q

What type of process is insulin release by the pancreas?

A

Biphasic: slow and fast

74
Q

In the rapid release of insulin by the pancreas, what is contained in the stored vesicles that get exocytosed?

A

Active insulin and C-peptide

75
Q

During insulin release by the pancreas, the _____ transporter transports glucose into the cell where it is converted into ___ via _____ and _____. This causes the ________ ratio to increase and consequently closes __ channel causing _________. This causes _______ channels to open which releases _____ into the cell causing rapid _____ of stored insulin and activates insulin ____ _______ via _____ which is a slow process.

A 
GLUT2
ATP
Glycolysis and Krebs 
ATP:ADP ratio
Katp
Depolarization 
Voltage-gated Ca2+ channels 
Ca2+
Exocytosis
Gene expression
CREB
76
Q

The affinity (Kd) of the insulin receptors (IRA & IRB) for insulin is ____ and ____ for IGFs, so in order to get IGF binding to insulin receptor, they need to be at (lower/higher) concentrations.

A

High
Low
Higher

77
Q

IGF1 & IGF2 bind to their receptors in addition to which insulin HOMOdimer?

A

IRA (insulin receptor alpha)

78
Q

Signaling via the insulin receptor involves a series of adaptor proteins (___ & ___) which transduce the signal via ___ and ___ kinases to effect changes in key metabolic activities and gene expression within the nucleus.

A

IRS1 & IRS2
AKT
MAP

79
Q

How does insulin. Increase the translocation of GLUT4 to the cm?

A

Insulin binds to a receptor on the CM —> causes signaling transduction cascade -> GLUT4 secretory vesicles in the cytoplasm move to the CM via exocytosis -> exocytosis leaves the GLUT4 behind on the cell which increases the number of receptors on the membrane —> increases glucose uptake in the cell

80
Q

What occurs during the transport of glucose in the gut?

A

Gathered is a high concentration of glucose in the intestinal lumen (gut). The SGLT1 protein transporter on the micro Billie of the lumen transports glucose and Na+ from the gut into the enterocyte (epithelial cell) which starts to raise the glucose concentration in the enterocyte. GLUT2 on the basolateral membrane can move glucose down its concentration gradient into the bloodstream. At the same time, Na+ concentration is high so Na+ need to be moved out on the basolateral membrane through Na+/K+ ATPase

81
Q

What do GLP1 receptor agonists do?

A

Stimulate incretin receptor in absence of GLP1

82
Q

Ex of GLP1 receptor agonist

A

Trulicity

83
Q

Inhibitor that increases incretin levels

A

DPP4 inhibitors

84
Q

Blocks reabsorption of glucose by the kidney

A

SGLT2 (Farxiga)

85
Q

How does insulin affect lipolysis?

A

Insulin binds to insulin receptor on adipocyte which activates tyrosine kinase cascade and leads to phosphorylation of PDE3B which converts cAMP to AMP (cAMP leads to release of FFA) (inhibits cAMP). When cAMP is inhibited by the phosphorylation cascade, it converts to AMP and doesn’t allow free fatty acid release since we don’t want FFA dumped into blood when there are high levels of circulating glucose.

86
Q

Insulin activates ______ via dephosphorylation which converts acetyl-CoA into ______ which promotes synthesis of fatty acids in the cytoplasm.

A

ACC

Malonyl-CoA

87
Q

Glucagon deactivates ACC via __________ which does not produce malonyl-CoA.

A

Phosphorylation

88
Q

Insulin is a characteristic of the “___ state”

A

Fed

Biochemistry (9 decks)

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