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BioChemistry > Carbohydrate Metabolism - NYIT > Flashcards

Carbohydrate Metabolism - NYIT Flashcards

1
Q

How does arsenic poison/harm?

A

Arsenic in the form of arsenate looks like phosphate in structure, it adds to glyceraldehyde-3-P in step 6. It causes instability and spontaneous hydrolysis of G3P -> 3-phosphoglycerate bypassing the substrate level phosphorylation and preventing the net 2 ATP from forming.

particularly damaging to RBC because glycolysis is their one form of energy production

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2
Q

how does flouride work?

A

inhibits enolase at step 9 and the production of phosphoenolpyruvate

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3
Q

pyruvate kinase deficiency

A

recessive mutation causes RBC to express markedly lower levels of pyruvate kinase and because RBC lack mitochondria this effects their source of energyand the produce 50% ATP leading to hemolytic anemia

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4
Q

what tissues produce lactate normally? what causes lactate production over Acetyl-CoA?

A

RBCs, Skin, Brain, Skeletal muscles and renal medulla

In times lacking of mitochondria and in times of low oxygen

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5
Q

What’s the cori cycle? What tissues use it?

A

cori cycle is the generation of lactate in either skeletal muscle during extreme exercise or RBC. Lactate is produces for the reoxidizing of NADH to NAD+. When at rest the lactic acid travels by blood to the liver where it’s converted to glucose by gluconeogensis.

RBCs only use this cycle because of no mito

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6
Q

lactic acidosis

A

caused by elevated plasma concentration of lactate which decreases pH

can be caused by failure to re-oxidize NADH (maybe by a blocked ETC), ethanol intoxication (excess NADH), pyruvate carboxylate deficiency, impaired PDH, respiration or oxygen delivery (like CO poisoning) or excessive exercise

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7
Q

glucogon causes what metabolism changes?

A

inc glycogenolysis
inc gluconeogenesis
inc lipolysis
dec liver glycolysis

activates protein kinase A

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8
Q

insulin causes what metabolism changes?

A

inc glycogen synthesis
inc fatty acid synthesis
inc triglyceride synthesis
inc liver glycolysis

activates phophatase

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9
Q

Pyruvate Dehydrogenase Complex

A

alpha-keto acid dehydrogenase family of enzymes
Contains 3 subunits: E1, E2, E3
E1 - thiamine/TPP coenzyme
E2- lipoic acid and Coenzyme A
E3 - FAD+ and NAD+
converts pyruvate to acetyl-coa with release of CO2 and NADH per pyruvate

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10
Q

How is PDH regulated?

A

turned on by PDH phosphatase and off by PDH kinase

Kinase in inhibited by pyruvate and ADP and activated by acetyl-coa and NADH

phosphatase is activated by Ca2+

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11
Q

What are the irreversible steps of that CAC?

A

Step 1 - citrate synthase formation of citrate from acetyl-coa and oxaloacetate.

step 3 - isocitrate dehydrogenase (Rate Limiting) and forms alpha-ketogluterate. Produces CO2 and NADH and H+

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12
Q

What inhibits citrate synthase?

A

citrate, NADH, succinyl-CoA

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13
Q

what step of CAC is inhibited by flouroacetate? (rat poison)

A

aconitase - enzyme for isomerization of citrate - step 2

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14
Q

what regulates the rate limiting step of the Krebs cycle?

A

isocitrate dehydrogenase is inhibited by ATP and NADH and activated by Ca2+ and ADP

isocitrate -> alpha-ketogluterate

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15
Q

whats the second step of CAC that releases CO2?

A

step 4 that is catalyzed by alpha-ketogluterate dehydrogenase and produces succinyl CoA

Release CO2, NADH and H+

product has a high-energy bond

inhibited by high energy products and activated by Ca+

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16
Q

what step of the TCA Cycle produces ATP?

A

Indirectly by way of GTP, the high energy bond from succyinl CoA gets transferred to succinate by succinyl-coa synthetase making a GTP which transfers to make a ATP - step 5

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17
Q

what’s unique about succinate dehydrogenase?

A

It also serves as complex II of the ETC, ONLY ENZYME OF THE CAC EMBEDDED IN THE INNER MITO MEMBRANE

In step 6 of the CAC is catalyzes the rxn succinate -> fumerate releasing FADH2

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18
Q

what is the purpose of malate dehydrogenase?

A

malate dehydrogenase is step 8 of the CAC and it regenerates oxolaacetate and releases the final NADH

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19
Q

whats the total amount of ATP that can be produced out of glycolysis, PDH, CAC and ETC?

A

36 to 38 ATPs

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20
Q

what are the 3 most important regulated enzymes of the CAC?

A 
citrate synthase (-) citrate
isocitrate dehydrogenase  (+) ADP, Ca2+. (-) NADH
alpha-ketogluterate dehydrogenase  (+) Ca2+. (-) NADH
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21
Q

what is a way that oxaloacetate can be replinished in the CAC cycle?

A

pyruvate carboxylase converts pyruvate to oxaloacetate
cofactor - biotin and requires ATP/Mg2+
(+) Acetyl-CoA
Also, first enxzyme of gluconeogenesis

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22
Q

what is an anaplerotic reaction?

A

rxns that replinish intermediates of the TCA cycle (anaplerotic means filling up)

done form amino acid degradation

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23
Q

what are Leigh syndromes?

A

subacute necrotizing encephalomyelopathy

caused by one of many mutations, PDH complex deficiency and pyruvate carboxylase deficiency are two of them

causes lactic acidemia, which leads neurologic damage, and u

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24
Q

Beriberi disease or Wernicke-korsakoff syndrome

A

thiamine Vit B1 def, a cofactor of PDH and alpha-ketogluterate dehydrogenase

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25
Q

how does insulin effect Fructose 2,6- Bisphosphate levels?

A

Insulin activates the phosphatase which will in turn de-phosphorylate PFK-2 (activating it’s kinase abilities) the PFK-2 kinase phosphorylates Fructose-6-Phosphate to F-2,6-BisP, which in turn activates PFK1 at step 3 of glycolysis

opposite happens for glucogon which activates the phosphatase ability of PFK2 and dephos F2,6BP to F6P

PFK2 is active with dephos

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26
Q

what is the activator of glycolysis?

A

Fructose-2,6-BisPhosphate

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27
Q

what is the purpose of gluconeogenesis and where does it happen?

A

it’s purpose is for glucose homeostasis as tissues like RBC can only use glucose and the brain who perfers use of glucose

happens in the liver, somewhat kidney

28
Q

what are the precursors that can feed into gluconeogensis?>

A

lactate
pyruvate

alanine by removal of amino group (alpha-ketoacid),
-> pyruvate from muscle gets converted to alanine which transports to liver, alanine will drop off the amino to the urea cycle in the liver and then provide pyruvate for gluconeogenesis (glucose-alanine cycle)

glycerol (from fatty acid breakdown) - enters as DHAP with Glycerol 3 phos intermediate

29
Q

what enxyme reverses step 10 of glycolysis and serves as step 1 of gluconeogenesis?

A

pyruvate -> oxaloacetate by pyruvate carboxylase (biotin cofactor)

irreversible, activated by Acetyl-CoA

in mitohondria

30
Q

what is the significance of step 2 of gluconeogenesis?

A

by PEP carboxykinase the reversing of step 10 of glycolysis is complete and oxaloacetate is converted to PEP, this requires GTP

irreversible

starts in mitochondria and moves to cytosol

31
Q

3rd reaction of gluconeogenesis that reverses a step of glycolysis?

A

reversal of step 3 of glycolysis, dephosphorylation of Fructose 1,6-BisP to F-6-P by Fructose I,6-BisPhosphatase

irreversible and inhibited by F-2,6-BP and AMP

32
Q

what’s the final step of gluconeogenesis that reverses the first step of glycolysis?

A

Glucose-6-Phosphate to Glucose by Glucose-6-Phosphatase, irreversible, enzyme found in ER membrane and only in the liver and kidney

33
Q

how much energy is consumed by gluconeogenesis?

where does this energy come from?

A

6 ATP and 2 NADH

fatty acid breakdown

34
Q

regulation of gluconeogenesis

A

signal for activation: during fasting or prolonged exercise, with a high protein diet or during stress or injury

when it’s subtrates are available and NAD+

alcohol -> impairs gluconeogenesis causing low blood sugar and high lactose (acidosis)

glucogon - activates

35
Q

pentose phosphate pathway, what goes in and what goes out?

A

Glucose-6-phosphate goes in the oxidative path releasing a C02 and producing NADPH and/or 5C-sugar - irreversible

Fructose-6-phosphate enters non-oxidatively producing ribose-5-phosphate and bypassing NADPH production - reversible

enzymes are G6PDH - oxidation. transketolase and transaldolase are non-oxidative

36
Q

Uses of NADPH?

A

biosynthesis
reduction of glutathione for dealing with ROS
reduction of oxygen to produce ROS

37
Q

what combinations of products are available from the pentose phosphate pathway?

A 
NADPH x2
NADPH and Ribose-5-phosphate
^oxidative and irreversible
ribose-5-phosphate only 
ribose-5-phosphate and ATP
^non-oxidative and reversible
38
Q

Glucose-6-phosphate dehydrogenase def

A

G6PD or G6PDH deficiency - mutation that causes a decrease in activity

without NADPH for RBC the concentration of ROS rises and damages Hb, Hb forms crosslinked aggregates called Heinz bodies on the cell membrane which compromises its integrity causing hemolysis as the RBC tries to travel into small capillaries

NADPH makes reduced glutathione which removes H2O2 and lipid peroxides

39
Q

what color does glycogen stain with what type of stain?

A

magenta with PAS stain

40
Q

where in the body and where in the cell is glycogen stored?

A

in liver, skeletal muscle and kidney

in cytosol as granules

41
Q

at what point of glycogen are free glucose added?

A

the non-reducing end - the end without a free aldehyde

42
Q

what type of linkages do you find in glycogen?

A

alpha-1,4 linkages

alpha-1,6 linkages - branching (branching occurs every 8 to 12 residues)

43
Q

Glucose-6-Phosphate enters glycogenesis as what form?

A

glucose-1-phosphate

44
Q

how does glucose get added to the non-reducing end of glycogen?

A

it’s carried by UDP-Glucose, glycogen synthase catalyzed the transfer from UDP to the chain

45
Q

what step of glycogenesis is irreversible?

A

the activation of G1P to UDP-glucose giving a PPi, by UDP-glucose pyrophosphorylase

glycogen synthase addition to non-reducing end with 1,4 linkages is also irreversible

46
Q

what’s a requirement of glycogen synthase thats similar to DNA replication?

A

requires a primer, oligosaccharide primer

primer is made by glycogenin (both a enzyme and scaffold) builds a oligomer using UDP-glucose as donors (8)

First glucose is added to tyrosine residue

the only reducing end is found on the glucose linked to glycogenin

47
Q

branching in glycogenesis

A

branching enzyme - 1,4 to 1,6 transferase removes 6 to 8 residues from the non-reducing end of glycogen and attaches it about 4 residues away from the last branch as a 1,6-glycosidic linkage

48
Q

glycogenolysis

A

done by glycogen phosphorylase which is irreversible and regulated. Removes alpha-1,4-linkages using P (traveling on pyridoxyl phosphate with Vit B)

49
Q

debranching enzyme

A

bifunctional protein
4:4 glucan transferase removes 3 glucose to the nonreducing end. leaving single alpha-1,6-linkage which is removed by alpha-1,6-glucosidase releasing a free glucose at the branching point as G-1-P

50
Q

exact location of glucose-6-phosphatase

A

ER of liver cells

51
Q

pompe disease

A

type II glycogen storage disease

deficiency of lysomal alpha-1,4-glucosidase causing accumulation of glycogen

inborn

excessive glycogen in lysosomes

enlarged heart

infantile onset -> early death from heart failure

52
Q

effect of phosphorylation on glycogen synthase and phosphorylase

A

phosphorylation turns off glycogen synthase and turns on glycogen phosphorylase (through phosphorylase kinase) glucogon stimulates phosphorylation

insulin causes dephosphorylation which turns on glycogen synthase and off GP

53
Q

allosteric regulators of glycogenesis and glycogenelysis

A

allosteric inhibitors of glycogonolysis - G-6-P, ATP and Glucose in liver,
AMP is a positive regulator in muscle

glucose-6-phosphate positively regulates both tissues in glycogenesis

54
Q

what tissue does glucogon not effect? What tissue is AMP effective in?

A

glucogon has no effect in muscle

AMP is in the muscle, has no effect in liver

55
Q

von gierke disease type Ia and type Ib

A

Type Ia - glucose-6-phosphatae
Type Ib - glucose-6-phosphate translocase - neutropenia and recurrent infections

fasting hypoglycemia, liver and kidney, fatty liver and hepato- and renomegaly, growth retardation and delayed puberty, increased glycogen storage, progressive renal disease

treatment - nocturnal infusions of glucose

56
Q

cori disease

A

4:4 transferase or 1:6 glucosidase def

causes fasting hyprglycemia and glycogen has an abnormal structure

57
Q

McArdle syndrome

A

skeletal muscle glycogen phosphorylase def

liver enzyme is normal, temporary weakness and cramping of skeletal muscle after exercise, no rise in lactate during strenuous exercise, myoglobinemia and myoglobinuria, benign but chronic, lots of glycogen in muscle

def in liver enzyme causes Type VI hers disease

58
Q

Fructose metabolism

A

main source is sucrose and fruits/veggies

transporter is GLUT5

enzymes are fructokinase and aldolase B

59
Q

fructokinase def

A

essential fructosuria is autosomal recessive, benign and causes fructose accumulation in the blood

60
Q

hereditary fructose intolerance

A

aldolase B def
autosomal recessive
causes severe hypoglycemia, vomiting, jaundice, hemorrhage, hepatomegaly, renal dysfunction, hyperuricemia and lacticacidemia

61
Q

sorbital metabolism

A

alcohol of glucose

enzymes are aldose reductase and sorbital dehydrogenase

hyperglycemia causing sorbital accumulation cataract formation, peripheral nephropathy or retinopathy

62
Q

galactose metabolism

A

from lactose

galactokinase phosphorylated galactose, galactose-1-phosphaste UT activates galactose-P and, UDP-hexose 4-epimerase converts it to UDP-Glucose which leaves as G-1-P

63
Q

galactokinase def

A

rare, autosomal recessive

elevation of galactose in blood and urine

galactitol accumulation -> cataracts

treatment is dietary restriction

64
Q

classic galactosemia

A

galactose 1-phosphate uridylytransferase def

autosomal recessive

galactosemia and galactosuria, vomiting, diarrhea and jaundice

accumulation of galactose-1-phosphate and galacititol in nerve, lens, liver and kidney

developmental delay

early ovarian failure in women

65
Q

aldose reductase

A

unimportant unless galactose levels are high

elevated galactitol -> cataracts

66
Q

what two enzymes release free glucose?

A

glucose-6-phosphatase

alpha-1,6-glucosidase (debranching)

BioChemistry (16 decks)

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