METABOLISM OF MONOSACCHARIDES AND DISACCHARIDES Flashcards
is the process of adding a phosphate group to a molecule. It is a reversible process, meaning that phosphate groups can be removed from molecules.
Phosphorylation
The major source of fructose is ____, which, when cleaved, releases equimolar amounts of fructose and glucose.
sucrose
phosphorylates glucose in most cells of the body and several additional hexoses can serve as substrates for this enzyme.
Hexokinase
provides the primary mechanism for fructose phosphorylation
has a low Km for fructose and a high Vmax
found in the liver, kidney, and the small intestinal mucosa and converts fructose to fructose 1- phosphate, using adenosine triphosphate (ATP) as the phosphate donor.
Fructokinase
fructose1-phosphate is cleaved into dihydroxyacetone phosphate (DHAP) and glyceraldehyde, which are then further metabolized to produce pyruvate
IN GLYCOLYSIS:
pyruvate is converted to DHAP and glyceraldehyde, which are then combined to form fructose 1-phosphate.
IN GLUCONEOGENESIS:
is the metabolic pathway that results in the production of glucose from noncarbohydrate sources, such as pyruvate, lactate, and certain amino acids.
Gluconeogenesis
is the metabolic pathway that results in the breakdown of glucose into pyruvate, yielding energy in the form of ATP.
Glycolysis
Synthesis of Glucose
More energy required
Liver and Kidneys
GLUCONEOGENESIS
Breakdown of Glucose
Less energy required
All cells
GLYCOLYSIS
The rate of fructose metabolism is more rapid than that of glucose because the trioses formed from fructose 1-phosphate bypass ____the major rate-limiting step in glycolysis
phosphofructokinase-1,
a benign condition
Fructokinase deficiency (Essential fructosuria):
:severe disturbance of liver and kidney metabolism
First appear when a baby is weaned from milk and begins to be fed food containing sucrose or fructose.
Aldolase B deficiency (Hereditary Fructose Intolerance)
the C-2 epimer of glucose- is an important component of glycoproteins.
Mannose
phosphorylates mannose to form mannose 6-phosphate.
Hexokinase
isomerizes mannose 6-phosphate to fructose 6-phosphate.
Phosphomannose isomerase
The conversion of glucose to fructose via sorbitol is a two-step process:
Aldose reductase
Sorbitol dehydrogenase
reduces glucose to sorbitol. This enzyme is found in many tissues, including the liver, kidneys, and nerves.
Aldose reductase
oxidizes sorbitol to fructose. This enzyme is found in the liver, ovaries, and seminal vesicles
Sorbitol dehydrogenase
The major dietary source of galactose is ____(galactosyl β-1,4-glucose) obtained from milk and milk products.
lactose
converts galactose to galactose 1-phosphate.
Galactokinase
Galactose 1-phosphate cannot enter the glycolytic pathway until it is first converted to____
uridine diphosphate (UDP)-galactose.
is a nucleotide, which is a type of molecule that is involved in many cellular processes, including metabolism and energy production.
UDP
The enzyme that converts galactose 1-phosphate to UDP-galactose is ____
galactose 1- phosphate uridylyltransferase (GALT)
The enzyme that converts UDP-galactose to UDP-glucose is called ____
UDP-hexose 4- epimerase.
is a sugar molecule that is used to build many important biological molecules. These molecules include lactose, glycoproteins, glycolipids, and glycosaminoglycans.
UDP-galactose
is a genetic disorder that is caused by a deficiency in the enzyme galactose 1-phosphate uridylyltransferase (GALT).
Classic galactosemia
is the enzyme that converts galactose 1- phosphate to UDP-galactose.
GALT
Causes elevation of galactose in blood (galactosemia) and urine (galactosuria)
Causes galactitol accumulation if galactose present in diet
Elevated galactitol can cause cataracts
Treatment is dietary restriction
Galactokinase Deficiency
is a sugar that is found in milk. It is made up of two other sugars: galactose and glucose.
Lactose
The enzyme____ transfers galactose from UDP-galactose to glucose, forming lactose.
lactose synthase
is found in many tissues of the body
Protein A
is only found in milk-producing mammary glands
protein B
is caused by a lack of the enzyme lactase, which is needed to break down lactose into galactose and glucose.
Lactose intolerance
