Metabolism of Hexoses Other than Glucose Flashcards
list 4 sources of fuel
Together with glucose, the hexoses fructose, galactose, and mannose are prominent metabolic fuels.
How many pathways are there for fructose
Two pathways for the metabolism of fructose; one occurs in muscle and the other occurs in liver
what is a Major fuel source in diets that contain large amounts of fruit or sucrose
fructose
where do the 2 pathways for fructose metabolism occur?
in the liver and the muscle
is fructose metobolism shorter in the muscle or the liver
Fructose metabolism in muscle differs little from that of glucose. Hexokinase phosphorylates fructose, yielding F6P. The entry of fructose into glycolysis therefore involves only one reaction step.
does glucokinase have a high or low affinity for hexoses
Liver contains a hexokinase known as glucokinase, which has a low affinity for hexoses, including fructose
how many enzymes are involved in the fructose metabolism in the liver
Liver converts fructose to glycolytic intermediates through a pathway that involves seven enzymes
can hexokinase or PFK phosphorylate fructose 1 phosphate?
Neither hexokinase nor PFK can phosphorylate fructose-1-phosphate at C6 to form the glycolytic intermediate FBP.
what kind of aldolase is in muscle ?
Muscle contains Type A aldolase, which is specific for FBP.
which fate of pyruvate process has coupling?
alcohol fermintation. The decarboxylase taking off the co2 makes it go forward so much that the conversion of acetyaldehyde to ethanol is no longer reversible.
what does it mean to say that we have a decarboxylation reaction?
we pop off a co2.
what is Tpp a co enzyme for?
Pyruvate decarboxylase contains the coenzyme thiamine pyrophosphate (TPP; also called thiamine diphosphate; ThDP)
what is the function of Yeast alcohol dehydrogenase (YADH)
Enzyme that converts acetaldehyde to ethanol
which enzyme does zinc bind to ?
Zn2+ polarizes the carbonyl group of acetaldehyde to stabilize the developing negative charge in the transition state of the reaction
if we have excess mannose will it convert to glucose eventually?
NO. It will be stopped by the single arrow due to hexokinase
if we have an excess amount of fructose in the liver , are we able to convert this mannon up the pathway towards glucose?
no. the fructose is unable to go up the pathway due to pfk creating a single arrow.
is F1P a substrate of glycolysis?
no
where is type B aldolase found?
its found in the liver
what does type B aldolase do?
it breaks up F1P
name the 2 enzymes that we can use to add a phosphate onto glyceraldehyde when breaking down fructose in the liver
we can use a glyceraldehyde kinase to add a phosphate . or we can use a dehydrogenase
Fructose intolerance results from a deficiency in Type ___ aldolase.
Fructose intolerance results from a deficiency in Type B aldolase.
how is galactose obtained?
Obtained from the hydrolysis of lactose
what sugar does hexokinase not work on
Hexokinase phosphorylates glucose, fructose, and mannose, it does not recognize galactose
why does an Epimerization reaction must occur before galactose enters glycolysis.
because hekokinase does not recognize galacose
what is the relationship between glucose and galactose
it is an epimer of carbon 4
what is vitamin B3
niacin
what kind of enzymes move functional groups
mutase
what is galactosemia caused by?
Most cases of galactosemia involve a deficiency in the enzyme catalyzing Reaction 2 of the interconversion, galactose and galactose.
what is the relationship between mannose and glucose
it is an epimer at carbon 2
what 2 enzymes are required to convert mannose into glycolysis?
hexokinase and phosphomannose isomerase
