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MCM - Rusheil > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

1
Q

GLUT1 , 2 , 3 , 4

A

Glucose transporters to get glucose past the cell membrane into cell.

GLUT1: Ubiquitious but high in RBCs and brain. High affinity for glucose.

GLUT 2: Main transporter in liver (low affinity)

GLUT 3: Main transporter in neurons (high affinity)

GLUT4: In skeletal muscle, heart and adipose tissue (insulin dependent)

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2
Q

Glycolysis yield

A

1 mol glucose —> 2 mol Pyruvate

-Generate NET 2 ATP and 2 NADH

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3
Q

Anaerobic respiration critical for which cells?

A

RBCs (no mitochondria) and overworked muscles (lacking O2)

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4
Q

Hexokinase and Glucokinase

A

Isozymes for G —> G6P (step 1 glycolysis). Traps glucose in cells via phosphorylation.

Hexokinase - all cells. High affinity, even at low [G]. Inhibited by G6P.

Glucokinase - liver, pancreatic Beta-cells. Low affinity. Sequestered in nucleus during fasting state, active during fed state. Not inhibited by G6P.

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5
Q

Phosphofructokinase-1 (PFK1)

A

Step 3 glycolysis: F6P —> F1,6bisP

  • RATE-LIMITING ENZYME OF GLYCOLYSIS
  • Requires ATP (investment)
  • Dephosphorylated = Active

Stimulated by AMP and F2,6bisP
Inhibited by ATP and Citrate

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6
Q

Glyceraldehyde 3P Dehydrogenase

Phosphoglycerate Kinase

Pyruvate Kinase

A

3 Payoff enzymes in glycolysis

G-3P-Dehydrogenase: G3P —> 1,3Bisphosphoglycerate - 2 NADH

Phosphoglycerate Kinase: 1,3BPG —> 3-phosphoglycerate - 2ATP

Pyruvate Kinase: Phosphoenolpyruvate —> Pyruvate - 2 ATP

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7
Q

Pyruvate Kinase regulation in glycolysis

A

Catalyze irreversible reaction:
Phosphoenolpyruvate (PEP) —> Pyruvate

  • Stimulated by Insulin and F1,6BP
  • Inhibited by Alanine, ATP and Glucagon (PEP would then enter gluconeogenesis)
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8
Q

G6P pathways

A

G6P could:

  • continue the process of glycolysis —> F6P
  • G6P —> G1P: Galactose metabolism or Glycogen synthesis
  • Pentose Phosphate Pathway precursor
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9
Q

Defective Glycolysis Enzyme Consequences

A

Hemolytic anemia (resulting mostly from Pyruvate kinase defect)

Neurological problems (from a couple other enzymes)

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10
Q

RBC and Glycolysis

A

Glycolysis is RBCs only mechanism to make energy.

  • Glycolysis failure in RBC = ATP deficiency
  • Ion gradients powered by ATP disrupted (Na+/K+, etc.)
  • Leads to REDUCED CELL VIABILITY ==> RBC death (HEMOLYTIC ANEMIA).
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11
Q

Diabetes Type 1

A

Hyperglycemia caused by severe insulin deficiency due to loss of Pancreatic beta-cells (possibly from immune destruction).

No insulin to trigger glucose uptake via GLUT4. Blood sugar level = HIGH

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12
Q

Diabetes Type 2

A

Insulin resistance which progresses to loss of beta-cell function

-possibly from mutations in glucokinase, aberrant conversion of pro insulting to insulin, defective insulin receptor, infection, etc.

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13
Q

Hemolytic Anemia

A

Premature destruction of RBCs.

Cause(s):

  • Nutritional deficiencies (iron, folate, vit B12)
  • Defects in glycolytic enzymes (e.g. Pyruvate kinase)
  • Elevated cholesterol

Marker: Elevated LDH (Less RBCs carrying oxygen = Less cellular respiration = increased anaerobic respiration?)

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14
Q

Tarui Disease

A

Deficiency in PFK-1

  • Exercise-induced muscle weakness/cramps (muscles cannot metabolize glycogen stores)
  • Hemolytic anemia (RBC’s only mech for energy compromised)
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15
Q

Gluconeogenesis (location, job and precursors)

A

Used to increase blood glucose levels converting Pyruvate —> Glucose
-3 irreversible steps of glycolysis are bypassed in gluconeogenesis

Occurs in the kidney, liver and SI

Major precursors: lactate, AAs and glycerol

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16
Q

Gluconeogenesis Regulation

A

Stimulated by: Glucagon, citrate, cortisol, thyroxine, acetyl-CoA

Inhibited by: ADP, AMP, F26BisP

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17
Q

Gluconeogenesis Bypass enzymes

A

Pyruvate —> Phosphoenol Pyruvate

 (1) Pyruvate Carboxylase and
 (2) Phosphoenolpyruvate carboxykinase

Fructose 1,6 Bisphosphatase —> F6P
(3) Fructose 1,6 Bisphosphatase

G6P —> G
(4) Glucose-6-Phosphatase

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18
Q

Pyruvate Carboxylase

A

Pyruvate —> oxaloacetate

First step in converting Pyruvate to Phosphoenolpyruvate in MITOCHONDRIA.
A mitchondrial enzyme, requires biotin.

Activated by: Acetyl-CoA, cortisol

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19
Q

Phosphoenolpyruvate Carboxykinase

A

Oxaloacetate —> PEP

Last step in converting Pyruvate to PEP, occurs in CYTOSOL. Bypasses Pyruvate Kinase reaction

Activated by: Cortisol, glucagon, thyroxin

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20
Q

Fructose 1,6 BisPhosphatase

A

Converting F1,6bisP —>F6P

RATE-LIMITING ENZYME, bypasses PFK-1 reaction.

Activated by: Cortisol and citrate
Inhibited by: AMP and F26BP

21
Q

Glucose-6-Phosphatase

A

Converting G6P —> G

Occurs only in liver, kidney, SI and pancreas, bypasses the hexokinase/glucokinase reaction.

Muscle cells LACK this enzyme, thus cannot convert G6P to free glucose after glycogenolysis. G6P instead enters glycolysis/TCA for energy needs

Activated by: Cortisol

22
Q

Cori Cycle

A

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

  • Prevents lactate accumulation
  • Regenerates glucose
23
Q

F1,6bisPhosphatase Deficiency

A

Hypoglycemia, lactic acidosis, Ketosis

24
Q

Von Gierke Disease

A

Deficiency in Glucose-6-Phosphatase

Inefficient release of glucose into blood by liver in gluconeogenesis

Hypoglycemia, lactic acidosis, hepatomegaly due to buildup of glycogen.

Diet management is therapy

25
Q

Fanconi-Bickel syndrome

A

Autosomal Recessive disorder - mutation in GLUT2 transporter (which takes up fructose, glucose and galactose).

Failure to thrive, hepatomegaly, abdominal bloating. Fasting hypoglycemia and post-meal hyperglycemia.

Treatment: Vitamin D and uncooked cornstarch (prevents spikes in blood sugar and provides sustained release of glucose)

26
Q

Hereditary Fructose Intolerance

A

Inability to metabolize fructose from F1P to Glyceraldehyde and DHAP

27
Q

Galactosemia

A

Galactose metabolism disorder, deficiency in either two enzymes: GALT or Galactokinase

GALT deficiency:

  • Accumulation of galactitol
  • CLASSIC galactosemia: failure to thrive, liver failure, sepsis

Galactokinase deficiency:
-Accumulation of galactose and galatitol in blood/urine. Accumulation of galactitol in lens of eye = cataracts in infancy

28
Q

Pentose Phosphate Pathway

A

Glucose-6-P from glycolysis enters PPP. Phagocytic cells have VERY high PPP activity, high in lung and liver tissue.

Oxidative phase:

  • Produce sugar for DNA and RNA formation: ribulose-5P
  • Produce 2 NADPH via oxidation of Glucose-6-P and 1 CO2

Non-oxidative phase produces nucleotide precursors and glycolysis intermediates that cycle back to glycolysis or gluconeogenesis (F6P and Glyceraldehyde-3-P)

Oxidative steps = Irreversible

Non-oxidative steps = reversible

29
Q

G6P Dehdrogenase (G6PD)

A

RATE LIMITING ENZYME of PPP oxidative phase

NADP+ reduced —> NADPH
G6P oxidized
NADPH inhibits G6P (Feedback inhibition from product)

G6PD Deficiency: Hemolytic Anemia due to elevated NADPH need
-Requires oxidizing medication

30
Q

Glutathione

A

An important antioxidant (G—SH) that detoxifies hydrogen peroxide with glutathione reductive

Regenerated by NADPH from PPP

31
Q

6-Phosphogluconate Dehydrogenase

A

Last enzyme in oxidative phase of PPP—> ribulose-5P formation

Produces NADPH and CO2

32
Q

Reducing/non-reducing ends of Glycogen

A

Non-reducing ends each contain terminal glucose with C4 hydroxyl group. Glycogen degraded/extended from non-reducing end

Reducing ends consist of glucose monomer connected to GLYCOGENIN protein.
-glycogenin creates short glycogen polymer on itself—> primer for glycogen synthesis

33
Q

Glycogen storage

A

In liver, muscle and other tissue.

Stored as granules, which contain glycogen and other enzymes required for glycogen metabolism.

34
Q

Glucokinase/hexokinase regarding glycogen

A

First enzyme of Glycogenesis:

Traps Glucose in hepatocyte or muscle cells BYU phosphorylation to G6P.

35
Q

Phosphoglycomutase

A

Glycogenesis enzyme, step 2

G6P —> G1P

(Moves the phosphate group)

36
Q

UDP-glucose pyrophosphorylase

A

Enzyme in Glycogenesis

G1P —> UDP-glucose

Transfers UTP on to G1P releasing a phosphate

37
Q

Glycogen Synthase

A

RATE-LIMITING ENZYME in Glycogenesis

Catalyzes glucose from UDP-glucose onto non-reducing end of glycogen
(Alpha-1,4 glycosidic bond)

Dephosphorylated = ACTIVE

38
Q

Glucosamine (4:6) transferase

A

Glycogen gets to 11 residues, stops, breaks off last 7 residues from alpha-1,4-glycosidic linkage and reattached somewhere with alpha-1,6 linkage.

BRANCHING ENZYME of Glycogenesis
-branching increases solubility of glycogen

39
Q

Glycogen Phosphorylase (GP)

A

RATE LIMITING ENZYME of Glycogenolysis

Cleaves G1P residue from non-reducing end of glycogen.
Utilizes Vitamin B6 (Pyridoxal) as CO-FACTOR

Takes glucose residues off until about 4 residues of next branch (alpha-1,6 linkage)

Phosphorylated = INACTIVE

40
Q

Debranching enzyme

A

Glycogenolysis debranching enzyme uses transferase (4:4) activity, taking 3 glucose residues close to a branch site and attaching them to non-reducing end with alpha-1,4 linkage

Debranching enzyme cleaves the last residue with the alpha-1,6 link producing a free glucose residue

41
Q

Pompe Disease

A

Defect in lysosomal alpha-1,6-glucosidase (acid maltase)

Lysosomes contain small amount of branched glycogen

42
Q

Why muscle cells cannot hydrolyzed G6P to glucose

A

Livers take G1P and convert to G6P after glycogenolysis. Then they use GLUCOSE-6-PHOSPHATASE to confer G6P to free glucose to enter blood.

Muscle cells LACK glucose-6-phosphatase thus cannot convert it to free glucose. Instead G6P in muscles enter glycolysis and TCA.

43
Q

Blood Glucose Criteria

A

Normal: 70-100 ml/dL (fasting) , = 140 mg/dL (fed)

Prediabetic (at risk): 100-125 mg/dL (fasting) , >140 mg/dL (fed)

Diabetes mellitus: > 125 mg/dL (fasting) , > 199 mg/dL (fed)

44
Q

GSD 0

A

Deficiency in glycogen synthase

  • cannot synthesize glycogen
  • muscle cramps (lack of glycogen in muscle)
  • vulnerable to hypoglycemia when fasting
  • must eat frequently
45
Q

Cori Disease

A

Deficiency in alpha-1,6-Glucosidase (DEBRANCHING enzyme)

  • Many short branches in glycogen
  • light hypoglycemia and hepatomegaly
46
Q

Anderson Disease

A

Deficiency in glucosyl (4:6) transferase (BRANCHING enzyme)

  • long chain glycogen, few branches
  • enlarged liver and spleen, scarring of liver tissue
    - death
47
Q

McArdle Disease

A

Deficiency in muscle glycogen phosphorylase

  • Patient unable to supply muscle with enough glucose
  • weakness, muscle cramps
48
Q

Hers Disease

A

Deficiency in liver glycogen phosphorylase. Prevents glycogen breakdown in liver —> accumulates in liver —> hepatomegaly

-low blood glucose levels

MCM - Rusheil (6 decks)

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