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SFM > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

1
Q

When ATP needs outpace oxygen delivery, ___ is the primary source of energy.

A

Glycolysis

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2
Q

General reaction of Glycolysis

A

1 glucose —> 2 pyruvate + 2 ATP

*does NOT require oxygen = anaerobic reaction

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3
Q

Glycolysis is a critical source of ATP especially in ___ because __.

A

RBC - they don’t have mitochondria to use aerobic respiration

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4
Q

Glucose is the prefered source of fuel for ___ and ___.

A

RBC (because they lack mitochondria)

Brain (under non-starvation)

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5
Q

The ___ is the distribution center of glucose.

A

Liver

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6
Q

De novo synthesis of glucose is termed ___ and occurs in the ___.

A

Gluconeogenesis

Liver

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7
Q

GLUT Transportors

A

GLUT1 - brain and RBC = high affinity

GLUT2 - liver and kidneys = low affinity

GLUT3 - neurons = high affinity

GLUT4 - skeletal muscle, fat, heart = low affinity
*regulated by INSULIN!

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8
Q

Km is ____ proportional to ___.

A

Inversely

Affinity (of substrate binding)

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9
Q

Glucose transporter ___ is sequestered in vesicles, but inserted into the membrane in response to ____ which induces ___.

A

GLUT4

Insulin binding

Glucose uptake into the cell

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10
Q

Where does each occur?
Glycolysis
Gluconeogenesis

A

Glycolysis - cytoplasm of all cells

Gluconeogenesis - in liver / kidney / small intestine

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11
Q

___ in the liver and pancreas traps glucose within the cell by___.

A

Glucokinase / adding Po on glucose

Hexokinase traps it for all other cells

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12
Q

What enzyme is associated with the rate limiting step in glycolysis?

A

PFK1 (Phosphofructokinase-1)

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13
Q

What reactions require ATP in glycolysis?

A

Trapping of glucose in cell by hexokinase /glucokinase

Conversion of Fructose 6P to Fructose 1,6-BP by Phosphofructokinase-1
*RLS!!

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14
Q

What enzymes are responsible for the generation of ATP in glycolysis?

A

Phosphoglycerate Kinase

Pyruvate Kinase

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15
Q

Explain how PFK-2 affects glycolysis

A

Works as a kinase when dephosphorylated (favored by INSULIN)
=promotes PFK-2 activity —> activates PFK-1

Works as a phosphatase when phosphorylated (favored by GLUCAGON)
=inhibits PFK-2 activity —> deactivates PFK-1

*PFK-1 is the RLS in glycolysis

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16
Q

Tarui Disease is due to a deficiency in ___, which causes ___.

A

PFK-1

Inhibition of ATP production via glycolysis

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17
Q

Pyruvate Kinase (PK) regulation

A

Activated by: Insulin and F1,6BP
- High insulin –> stimulates protein phosphatase, dephosphorylation of PK resulting in active form.

Inhibited by: ATP, alanine, and glucagon
- High glucagon –> cAMP activates protein kinase A (PKA), phosphorylation of PK resulting in inhibited form.

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18
Q

Glycolysis is ___ during exercise to meet energy requirements.

A

Activated

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19
Q

Defective glycolytic enzymes (causing ineffective glycolysis) especially affects ___ resulting in ___.

A

RBCs

Hemolytic anemia

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20
Q

During extreme starvation, the brain “switches” from glucose to ___ as a fuel source.

A

Ketone bodies

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21
Q

Carbohydrate metabolism is orchestrated by ___ and ___ in blood.

A

Insulin / Glucagon

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22
Q

Fanconi-Bickel Syndrome

A

Mutation in GLUT2 transporter inhibits uptake of glucose/fructose/galactose in the liver and pancreas

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23
Q

Direct glucose reserves are sufficient to need glucose needs for ___.

A

About 1 day

*whole body need 160g / brain needs 120 g / glycogen in body stores 190g

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24
Q

Which 4 enzymes of gluconeogenesis bypass glycolysis?

A

Glucose 6 Phosphatase
—>bypasses Hexokinase/Glucokinase

Fructose 1,6 Biphosphatase
—>bypasses PK-1

PEP Carboxykinase + Pyruvate Carboxylase
—>bypass Pyruvate Kinase

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25
Q

Positive regulators of glycolysis

A

Glucose, insulin, AMP, Fru 2,6-BP, Fru 1,6-BP

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26
Q

Positive regulators of gluconeogenesis

A

Glucagon, citrate, cortisol, thyroxine, acetyl CoA

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27
Q

Pyruvate Carboxylase is located where?

A

Mitochondria

28
Q

What enzyme allows for the conversion and reconversion of OAA to Malate?

A

Malate Dehydrogenase

29
Q

What is the rate limiting step of gluconeogenesis?

A

Conversion of Fructose 1,6 Biphosphate to Fructose 6P

—> by Fructose 1,6- Biphosphatase

30
Q

The Cori Cycle

A

Links lactate produced from anaerobic glycolysis in RBC and exercising muscle to gluconeogenesis in the liver.

31
Q

Precursor of gluconeogenesis:

A

Carbs / lipids / proteins

32
Q

Von Gierke Disease (____) is due to a deficiency in ____.

A

GSD1a

Glucose 6-Phosphatase
*causes inefficient release of free glucose into the bloodstream from the liver after gluconeogenesis and glyconeogenesis

33
Q

Monosaccharides of:

  • sucrose
  • galactose
A
  • sucrose = glucose + fructose

- lactose = glucose + galactose

34
Q

Glucose is converted to ___ by ___ and then converted to fructose by___.

A

Sorbitol / Aldose Reductase / Sorbitol Dehydrogenase

35
Q

Fructose can be directly converted to Fructose 6P by ___.

A

Hexokinase

36
Q

Fructose can be converted to Fructose 1P by ___ which feeds into glycolysis/gluconeogenesis as Glyceraldehyde 3P.

A

Fructokinase

37
Q

Fructose can either enter glycolysis or ___.

A

become fats (triacyglycerols)

38
Q

Uptake of fructose, glucose, and galactose is done by…?

A

SGLT1 —> glucose / galactose / Na+

GLUT5 —> fructose

GLUT2 —> glucose / galactose / fructose
*into the bloodstream

39
Q

Fructose metabolism is faster than glucose because it ___.

A

bypasses the RLS of glycolysis

*reason why high fructose corn syrup is NOT healthy; it leads to unregulated generation of Acetyl-CoA which is converted to fatty acids (excess fatty acids lead to obesity and fatty liver)

40
Q

Galactose can be converted to Galactose 1P by ___.

A

Galactokinase

41
Q

What is the rate limiting enzyme in Galactose metabolism?

A

GALT (glucose 1P uridyltransferase)

42
Q

If Galactose is not converted to Glucose, what may occur?

A

It can be converted to Galactitol and accumulate in the eyes, giving rise to cataracts

*usually due to a deficiency in Galactokinase or GALT

43
Q

Galactosemia is a result in a deficiency of ___ or ___.

A

Galactokinase / GALT (glucose 1P uridyltransferase)

44
Q

What is the main products of the Pentose Phosphate Pathway?

A

NADPH / Ribulose 5P

45
Q

In the PPP, conversion of G6P to Ribulose 5P is a ___ reaction.

A

Irreversible oxidative (catabolic)

46
Q

What enzyme is associated with the RLS of the PPP?

A

G6P Dehydrogenase

47
Q

G6P Dehydrogenase deficiency is characterized by…?

A

Hemolytic anemia

*the need for NADPH is high; NADPH can activate glutathione (antioxidant in RBC) during infections

48
Q

NADPH regenerates ___ which is an important antioxidant that detoxifies hydrogen peroxide.

A

Glutathione

49
Q

Rapidly dividing cells (including cancers) favor the production of ___ from the PPP.

A

Ribose 5P

*used in DNA/RNA synthesis

50
Q

Glycogen is formed by ___ and ___ glycosidic bonds.

A

alpha-1,4 (linear) / alpha-1,6 (branching)

  • Glycogen Synthase
  • Glucosyl (4:6) Transferase
51
Q

Glycogen is stored in the form of ___ in ___.

A

granules / liver and muscles

52
Q

Function of glycogen:

Liver vs muscle

A

Liver glycogen = regulates blood glucose

Muscle glycogen = provides glucose/energy for physical activity

53
Q

What is the rate limiting enzyme of glycogenesis? glycogenolysis?

A

Glycogen Synthase
*makes alpha-1,4 glycosidic bonds

Glycogen Phosphorylase

54
Q

Glycogen phosphorylase requires ___ as a cofactor during glycogenolysis.

A

Pyridoxal Phosphate (Vitamin B6)

55
Q

___ is the debranching enzyme in glycogenolysis.

A

Transferase

56
Q

___ removes glucose in the form of ___ during glycogenolysis.

A

Glycogen Phosphorylase / Glucose 1P

57
Q

Once Glucose 1P is converted into Glucose 6P, it will…

A

Be converted to glucose in the liver (by Glucose 6 Phosphatase)

Be used to make energy in muscles

58
Q

____ is an enzyme found only in the liver.

A

Glucose 6 Phosphatase

*reason why muscles cannot reform glucose; gluconeogenesis only occurs in the liver!

59
Q

Regulation of Glycogen Synthase and Glycogen Phosphorylase:

A

Glycogen Synthase:
-Po = ACTIVE (high insulin leads to dephosphorylation)
+Po = inactive

Glycogen Phosphorylase
-Po = inactive
+Po = ACTIVE (high glucagon leads to phosphorylation)

60
Q

Glucagon does not act on ___.

A

Muscle

61
Q

Insulin binds to ____ type receptor, while Glucagon binds to a ____ receptor.

A

GPCR / Tyrosine Kinase

62
Q

Insulin binds receptor and then…

Glycogen synthesis or degradation?how?

A

Activates PkB
—> activates phosphatase
—> dephosphorylates Glycogen Synthase (active) and Glycogen Phosphatase (inactive)
—>Glycogenesis

63
Q

Glucagon binds receptor and then…

Glycogen synthesis or degradation?how?

A

Activates PkA (a kinase)
—>phosphorylates Glycogen Synthase (inactive) and Glycogen Phosphorylase (active)
—>Glycogenolysis

64
Q

Insulin causes ___ while Glucagon causes ___.

A

Dephosphorylation / phosphorylation

65
Q

GSD 0

A

Glycogen Synthase Deficiency - effects chain elongation in glycogenesis.

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