Fructose

Question 1

Fructose rapidly converts to…

Answer 1

glucose, glycogen, lactate, fat

Question 2

Fructose glycemic index is____ but high consumption causes

Answer 2

low, insulin resistance, obesity, type 2 diabetes, dyslipidemia, oxidative stress

Question 3

GLUT 5

Answer 3

transports fructose into the enterocyte, doesn’t require ATP

Question 4

GLUT 2

Answer 4

fructose diffuses into blood vessels at basolaterol pole, and can go into liver

Question 5

How does fructose metabolism in liver differ from glucose?

Answer 5

1. nearly complete hepatic extraction
2. fructokinase and fructose -1-P for initial steps
3. massive uptake and phosphorylation of fructose can lead to degradation of ATP to AMP and uric acid

Question 6

What controls glucose under glycolysis?

Answer 6

• hexokinase, or glucokinase which have a high Km for glucose
• Phosphofructokinase (inhibited by ATP and citrate, feedback regulation based on energy of the cell)
• insulin (stimulates glucokinase gene expression and activates glycolytic enzymes)

Question 7

Fructose metabolism regulation

Answer 7

fructose conversion occurs independent of insulin, is a rapid process because fructokinase has a low Km for fructose, and no feedback system from ATP or citrate

Question 8

What is a problem with lack of fructose regulation?

Answer 8

depletion of free phosphate and a decrease in ATP in liver cells (need ATP for conversion)

Question 9

What happens to the fructose thats converted to glucose?

Answer 9

it’s stored as glycogen or released as plasma glucose

Question 10

What happens to fructose converted to lactate

Answer 10

occurs in liver and enterocyte, leads to lactacidemia

Question 11

What happens to fructose converted to fatty acid?

Answer 11

only a small portion, but could lead to steatosis (fatty liver)

Question 12

Fructose intake increases hepatic glycogen _____ than an equivalent dose of glucose

Answer 12

more

Question 13

Problems with fructose-induced hyperlactatemia

Answer 13

leads to increased adipocytes because it prevents lipolysis from being suppressed

Question 14

Problems with fructose having a low glycemic index

Answer 14

• doesn’t suppress ghrelin (hunger signal) as well as glucose
• hinders leptin increase (satiety signal), causes leptin resistance by increasing cytokine 3 (suppressor of leptin) and decreasing serine/theonine phosphorylation of key proteins which could lead to fatty liver

Question 15

Effect of high-fructose diet compared to same level of glucose

Answer 15

increases VLDL (converts to LDL), increase triglyceride production, decrease TG clearance, very lipogenic (supplied triosephosphate, a fatty acid synthesis precursor), hepatic de novo synthesis is stimulated by providing both the glycerol and the fatty-acyl parts of VLDL-triglycerides

Question 16

How does fructose increase hepatic de novo lipogensis?

Answer 16

trioses-P and acetyl-CoA, increased expression of lipogenic genes
-inhibits insulin signaling by reducing phosphorylation of IRS proteins, activates c-Jun terminal kinase (JNK) and increases oxidative stress