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Sugar conversion and ethanol metabolism PBC
Terms in this set (58)
what monosaccharides make up sucrose?
glucose and fructose
what monosaccharides make up lactose?
glucose and galactose
what monosaccharides make up maltose?
glucose and glucose
what makes up starch?
starch is a polymer of glucose
where in the body are complex carbohydrates converted into simple sugars?
intestines and the stomach
what glucose based intermediate bridges glycogen and glycolysis?
glucose 1-phosphate <-----> glucose 6-phosphate
name the three enzymes in the LIVER which help link fructose to glycolysis. What do they each do?
fructokinase- uses ATP to convert fructose to fructose 1-phosphate
aldolase B- splits fructose 1-phosphate into dihydroxyacetone-phosphate and glyceraldehyde
triose kinase- uses ATP to convert glyceraldehyde into glyceraldehyde 3-phosphate
what are the two intermediate products from the metabolism of fructose IN THE LIVER that enter glycolysis?
what enzyme converts fructose into a glycolytic intermediate OUTSIDE OF THE LIVER? What is that intermediate?
hexokinase converts fructose into fructose 6-phosphate which participates in the 3rd reaction of glycolysis (substrate for phosphofructokinase-1)
what symptoms result from a deficiency in fructokinase?
benign fructosuria- high fructose levels will be present in the urine. This may present as an indicator for diabetes but that is only because the test cannot distinguish between high glucose (diabetic) and fructose
what two enzymes participate in the conversion of glucose to fructose?
aldose reductase: glucose -> sorbitol
sorbitol dehydrogenase: sorbitol -> fructose
In this rxn NADPH reduces glucose while NAD+ oxidizes sorbitol
what three enzymes participate in the synthesis of glucose and galactose into glycoproteins, glycolipids, proteoglycans, and lactose?
UDP -glucose 4-epimerase
galactose 1-phosphate uridyl transferase
what common intermediate is the branching point for the placement of galactose into glycoproteins, glycolipids, proteoglycans, and the synthesis of lactose?
which two 6C sugar molecules are actually epimers? What is the significance of this considering their presence in the body?
UDP-glucose and UDP-galactose differ only by the orientation of a hydroxyl group on their 4th carbon. Because UDP 4-epimerase can convert between the two, it is not necessary to consume galactose because it can be made from glucose.
name two uses of galactose
construction of components within the cellular membrane such as glycoproteins, glycolipids, and proteoglycans as well as the production of lactose
what is the only location within the body that lactose is produced?
in the mammary gland of the adult female
what is the name of the enzyme which helps make lactose? What two subunits exist within it?
galactosyltransferase and alpha-lactalbumin
in what cellular organelle is lactose sythase found
endoplasmic reticulum lumen
what does the alpha-lactalbumin subunit of lactose sythase do to help in the production of lactose?
it lowers the Km of its partner subunit galactosyl transferase more than 1000x
describe the pathway for galactose to enter glycolysis
step 1.) galactose is phosphorylated by galactokinase into galactose 1-phosphate
step 2.) galactose 1-phosphate uridylyltransferase transfers a uridylyl group from UDP-glucose onto galactose and trades its phosphate group onto glucose making glucose 1-phosphate
step 3.) glucose 1-phosphate can be converted into glucose 6-phosphate via phosphoglucomutase which enters glycolysis at step 2
how can galactose provide energy for a cell?
when it is converted into glucose 1-phosphate and metabolized via glycolysis
what condition results from an inability to metabolize galactose? An error in which two enzymes are responsible for this condition? Which of these errors is more common?
galactosemia is an inability to metabolize galactose. This is due to an error in either galactokinase or galactose 1-phosphate uridylyltransferase which prevent the conversion of galactose into glucose 1-phosphate which can enter glycolysis. The more common mutation is found in galactose 1-phosphate uridylyltransferase
a genetic mutation in which galactose pathway enzyme results in the less serious form of galactosemia? Which is the more serious version?
galactose kinase = mild galactosemia
galactose 1-phosphate uridylyltransferase = serious galactosemia
a mutation in which galactose pathway enzyme would result in galactosemic symptoms such as: liver failure, cataracts, mental retardation, and jaundice (build up of bilirubin)
a mutation in:
galactose 1-phosphate uridylyltransferase
list the four main monosaccharides from which all other sugars are derived
glucose, fructose, galactose, mannose
list 5 important functions of UDP-glucuronate
1.) bilirubin diglucuronide
2.) glucuronides (negatively charged foreign compounds destined for excretion)
what substance plays a role in helping to remove foreign compounds such as drugs, sterioids, xenobiotics and bilirubin from the body?
what is a single word that describes this action? How does it do this?
UDP- glucuronate participates in detoxification by additing negative charges to these substances making them more soluble in water
what enzyme converts UDP-glucose into UDP-glucuronate?
what enzyme attaches foreign substances to UDP-glucuronate?
bilirubin is a breakdown product of what compound?
why do newborns present with jaundice? What is a common form of therapy to help eliminate high bilirubin levels?
the liver is newly activated and must adjust to the removal of bilirubin which is a byproduct found in the blood as a result of heme breakdown. Expose the baby to sunlight to help eliminate it.
where is UDP-glucuronate typically conjugated with contaminants targeted for elimination?
the liver and kidneys
what compounds are conjugated to sugars so as to facilitate their interconversion from one type to another?
the nucleotide UDP
what two components make up lactose (careful one is conjugated to something)
glucose + UDP-galactose
what is the precursor to UDP-glucuronate?
what is the precursor to UDP-glucose in the glucuronate pathway?
in what organ is the majority of ethanol metabolized?
within the liver
describe the first two steps of ethanol metabolism. What are the enzymes involved? What carriers are involved? what are the products?
1.) ethanol is oxidized by NAD+ using the enzyme alcohol dehydrogenase (ADH) to produce acetaldehyde
2.) acetaldehyde is further oxidized by NAD+ using the enzyme aldehyde dehydrogenase (ALDH) to produce acetic acid (acetate)
what does acetaldehyde do when released into the blood?
it can cross link proteins causing damage
how is acetic acid used within the body if in excess
it is converted to acetyl-coA within the muscles and used by the TCA cycle
in what organelle is aldehyde dehydrogenase found?
in what organ is alcohol dehydrogenase found?
How many isozyme classes of alcohol dehydrogenase enzyme (ADH) are there? Where are the class I enzymes found?
Which class is thought to contribute to cancer?
class I is found in the liver and does the lionshare of metabolism
class II and IV are thought to induce cancer
What enzyme catalyzes the synthesis of fatty acids using acetate? Where is it found?
acetyl CoA synthetase I
found in the liver
where is acetyl CoA Synthetase II found? What is its main contribution to the metabolism of ethanol
found in the mitochondria of heart and skeletal muscle, this enzyme converts acetate (a by product of aldehyde dehydrogenase in ethanol catabolism) to acetyl-coA to be used for energy in the TCA cycle
what does MEOS stand for?
microsomal ethanol oxidizing system
name an alternate metabolic pathway for ethanol. What % of ethanol undergoes this pathway? Where does it take place?
microsomal ethanol oxidizing system (MEOS)- uses NADPH to reduce ethanol to acetaldehyde
how does the MEOS pathway enable a drinker to build up tolerance to ethanol?
consumption induces the production of more enzyme thus increasing metabolic capacity
which enzyme is the key player in the MEOS metabolic pathway?
cytochrome P450 (CYP2E1)- this enzyme can be induced to increase its number which results in ethanol tolerance
why is it bad to drink a lot of ethanol on an empty stomach?
This lack of fuel but excess of ethanol causes a drain on the readily available NAD+ levels causing a buildup in NADH. To compensate, NADH reduces pyruvate to make lactate which can be toxic at high levels
what behavior contributes to a fatty liver?
excessive consumption of ethanol
what two pH affecting conditions can result from excessive ethanol consumption?
lactic acidosis- both are actually results of high NADH levels
what is the intermediate byproduct of alcohol dehydrogenase (ADH) and microsomal ethanol oxidizing system (MEOS)?
What produces free radicals in the ethanol metabolic pathway? What damage do they cause?
cytochrome P450 (CYP2E1)
damage includes lipid peroxidation, inflammation and necrosis
describe how ethanol can lead to hepatitis
ethanol is converted to acetaldehyde via alcohol dehydrogenase enzyme. This toxin causes cellular damage including entering the mitochondria and causing damage
what are the four degrees of liver destruction thanks to alcoholism
steatosis = good
fibrosis = some damage
cirrhosis = ruined liver, must be transplanted
name two cell types which participate in fibrosis of the liver
shrinking liver, fatty deposits (steatosis), drop in clotting proteins and albumin, high ammonia levels, and jaundice are all symptoms of what liver condition?
cirrhosis of the liver
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