Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biochemistry > Fructose & Galactose > Flashcards

Fructose & Galactose Flashcards

1
Q

What are the two ways that fructose exist?

A

As a monosaccharide (free frucose) and disaccharide (sucrose)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are sources of fructose?

A

Honey, fruits, table sugar, high fructose corn syrup

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How is free fructose and sucrose absorbed?

A

Free fructose is absorbed directly by the intestine
Sucrose- digestion occurs entirely in the upper small intestine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What catalyzes the cleavage of sucrose and what does it yield?

A

Sucrase and it yields one glucose unit and one fructose unit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How is fructose absorbed on the mucosal membrane?

A

Via facilitated diffusion by the GLUT5 transport proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How is fructose transported out of the enterocye across the basolateral membrane?

A

By either GLUT2 or GLUT5, although GLUT2 has a greater capacity for transporting glucose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What metabolizes fructose?

A

The liver

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the first step in fructose metabolism?

A

Fructose ————————-> Fructose-1-Phosphate
ATP——-> ADP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What two enzymes can catalyze the first step in fructose metabolism?

A

Fructokinase or alternatively hexokinase
Note: hexokinase has a greater affinity for glucose (20x more)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the second reaction in the metablolism of fructose?

A

F-1-P <——> Glyceraldehyde + Dihydroxyacetone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

F-1-P <——> Glyceraldehyde + Dihydroxyacetone is catalyzed by?

A

Fructose-1-Phosphate aldolase B

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Glyceraldehyde ————>? Enzyme?

A

Glyceraldehyde-3-Phosphate by triose kinase where it interrelates with glucose metabolism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Where is fructokinase found?

A

In the liver, kidneys and small intestine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the km and vmax of fructokinase for fructose?

A

Has a low km and high vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Is glucose or fructose metabolism faster? Why?

A

Fructose metabolism is faster because it bypasses the major rate limiting step (PFK1) in its metabolism.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Where does sorbitol pathway occur?

A

Present in tissue/cells such as seminal vesicles, liver, sperm and ovaries

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Free fructose seen in seminal plasma provides the energy for what?

A

Mobility of spermatozoa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Glucose ———–> Sorbitol. What is the enzyme and what is released?

A

Aldose reductase and NADPH—> NADP+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the second reaction in the sorbitol pathway?

A

Sorbitol——–> Fructose
NAD+—–> NADH by sorbitol dehydrogenase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Sorbitol dehydrogenase is low or absent in lens, nerves, and kidney. Accumulation of sorbitol in these areas leads to what?

A

Diabetes with complications such as cataract, neuropathy, and nephropathies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

A 24-year-old woman reported to the emergency complaining of nausea, abdominal pain, and fainting after ingesting sugar and fructose. She did not enjoy sweet tastes. What is the most likely diagnosis?

A

The patient is most probably suffering from ‘Hereditary fructose Intolerance. The onset of symptoms after ingestion of fructose or fructose containing diet
signify the presence of hereditary fructose Intolerance

22
Q

What is the biochemical defect in fructose heriditary intolerance?

A

aldolase B deficiency

23
Q

What is the inheritance trait of hereditary fructose intolerance?

A

Autosomal recessive trait

24
Q

What are the clinical features of hereditary fructose intolerance?

A

Patients are healthy until fructose or sucrose in ingested. They experience recurring vomitting, abdominal pain, hypoglycemia, fructose in urine, hyperuricemia (Increase in serum uric acid)

25
Q

Long term exposure to fructose leads to:

A

liver failure, renal tubulopathy, hyperuruicemia and growth retardation

26
Q

What is the treatment of hereditary fructose intolerance?

A

Complete elimination of all sources of sucrose, fructose, and sorbitol from the diet.

27
Q

What happens when there is excessive fructose?

A

Inorganic phosphate pool is depleted as a result, the inhibition of AMP deaminase is lost

28
Q

What is the biochemical defect of essential fructosuria?

A

Caused by a deficiency of fructokinase, leading to glucose being excreted in the urine. It is harmless, symptomless, can be mistaken for diabetes mellitus. Autosomal recessive trait

29
Q

What is the major source of galactose?

A

Lactose obtained from milk and milk products

30
Q

When broken down, what also provides galactose?

A

Glycoproteins and galactolipids

31
Q

How is galactose absorbed?

A

It is absorbed by active transport using the sodium dependent co-transporter

32
Q

Where is galactose metabolized?

A

In the liver
Note: galactose is not insulin dependent

33
Q

What reaction does galactokinase catalyze?

A

Galactose to Galactose-1-Phosphate

34
Q

What is the enzyme for galactose-1-phosphate —–> glucose-1-phosphate?

A

Galactose-1-Phosphate uridyltransferase (GALT)

35
Q

UDP glucose —-> UDP galactose is catalyzed by what enzyme and what reaction does this occur in?

A

UDP galactose-4-epimerase (GALE) and occurs in gal-1-p to glu-1-p

36
Q

Excess accumulation of galactose produces what?

A

Galactonic acid and galactiol

37
Q

What are the fates of UDP glucose and UDP galactose?

A

UDP glucose–> can beincoporated into glycogen
UDP glucose can be converted to UDP galactose because it is reversible, so that galactose is not a dietary essential
UDP glucose—> formation of UDP glucuronic acid (conjugated reactions)

38
Q

What does UDP galactose supply?

A

Supplies the galactose for the formation of lactose, glycoproteins, glycolipids, and proteoglycans

39
Q

What is the fate of glucose-1-phosphate?

A

It can be converted to glucose-6-p by phosphoglucomutase to enter the glycolysis pathway or it can be converted to free glucose by g-6-phosphatase

40
Q

A pregnant woman who was extremely lactose intolerant asked her physician if she could still be able to breast feed her baby even though she could not drink milk or dairy products. What advice should be given?

A

The patient should be advised to breast feed the baby after delivery. Lactose is synthesized from UDP galactose and glucose; however, galactose is not required in the diet for lactose synthesis, because galactose can be synthesized from glucose

41
Q

What is the enzyme that synthesizes G-1-P to UDP-glucose?

A

UDP-glucose pyrophorylase

42
Q

The formation of lactase is catalyzed by which enzyme?

A

lactase synthase

43
Q

What is the reaction that catalyzes lactase?

A

G-1-P—-> UDP Glucose
UDP Glucose —-> UDP Galactose
UDP Galactose —–> Lactose

44
Q

What is galactitol?

A

An enzyme made from galactose with a similiar pathway to that of the formation of glucose

45
Q

What is the excess quantities of galactose converted to?

A

Converted to galactitol which builds up in the body and is excessively excreted in the urine

46
Q

What are the effects of high levels of galactitol?

A

It is toxic at high levels and causes tissue damage injuries, especially cataract formation

47
Q

A patient complains of gastric discomfort upon consuming milk. The patient also shows signs of liver, kidney and brain dysfunction. This dysfunction is due to the build up of the toxic compound, galactose-1-P. What is this ?

A

Classical Galactosemia

48
Q
  • What enzyme is the patient lacking in galactosemia?
A

Galactose-1-p uridyl transferase (GALT)

49
Q

What reaction is not being catalyzed in galactosemia?

A

Galactose-1-phosphate uridyl transferase (GALT) catalyzes conversion of galactose-1-p to UDP galactose to form glucose-1-phosphate

50
Q

What are the other enzyme deficiencies associated with Galactosemia?

A

galactokinase and UDP-galactose-4-epimerase

51
Q

Clinical features of galactosemia:

A

failure of neonates to survive, vomitting and diarhhea (after milk ingestion), impaired liver function, hepatomegaly, elevated blood galactose, galactitiol excretion, cataracts, hypoglycemia, mental retardation

Biochemistry (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions