Biochemistry- Glycogen

Question 1

What happens when glucose enters a cell?

Answer 1

converted to glucose-6-phosphate via hexokinase/glucokinase (note that G6P can be converted back via glucose-6-photphatase)

Question 2

What else can happen to G6P?

Answer 2

conversion to glucose-1- phopshate or

conversion to 6-phosphogluconolactone via G6PD (glucose-6-phosphate dehydrogenase) (HMP shunt) or

conversion to fructose-6-phosphate

Question 3

How else can glucose-1-phosphate be made?

Answer 3

galactose conversion to galactose-1-phosphate via galactokinase (mild galactosemia from deficiency)

and then to glucose-1-phosphate via galactose-1-phosphate uridultransferase (severe galactosemia from deficiency)

Question 4

What is the final part of the HMP shunt?

Answer 4

conversion of ribulose-5-phosphate to fructose-6-phosphate via transketolase

Question 5

What happens to fructose-6-phosphate?

Answer 5

conversion to fructose-1,6-bisphosphate via phosphofructokinase-1 (PFK-1)

reverse process via fructose-1,6-bisphosphatase

Question 6

What happens to fructose-1,6-bisphosphate?

Answer 6

conversion to DHAP and glyceraldehyde-3-P via aldolase B (liver) and A (muscle)

DHAP and glyceraldehyde-3-P can convert to one another spontaneously

Question 7

How else can DHAP and glyceraldehyde-3-P be made

Answer 7

fructose conversion to fructose-1-phosphate via fructokinase (essential fructosuria with deficiency)

and then to DHAP and glyceraldehyde via aldolase B (fructose intolerance with deficiency)

Question 8

What happens to glyceraldehyde-3-P?

Question 9

What happens to PEP?

Answer 9

conversion to pyruvate via pyruvate kinase (pyruvate can convert to lactate)

Question 10

What happens to pyruvate?

Answer 10

conversion to acetyl-CoA via pyruvate dehydrogenase requiring thiamine (TPP)

Question 11

What happens to acetyl-CoA?

Answer 11

entrance into the TCA or

conversion to acetoacyl-CoA and malonyl-CoA (made into fatty acids; requires biotin cofactor)

Question 12

What happens to acetoacyl-CoA?

Answer 12

conversion to HMG-CoA

and then to mevalonate (via HMG-CoA reductase) for production of cholesterol or

to acetoacetate for ketone body production

Question 13

Describe the early steps of the TCA cycle

Answer 13

acetyl-CoA converts oxaloacetate to citrate using citrate synthase

citrate to isocitrate to a-ketoglutarate (via isocitrate dehydrogenase)

Question 14

What happens to a-ketoglutarate?

Answer 14

conversion to succinyl-CoA via a-ketoglutarate dehydrogenase (requires thiamine cofactor)

Question 15

How else can succinyl-CoA be made?

Answer 15

odd-chain fatty acids, branched-brain fatty acids, methionine, and threonine can be converted to propionyl-CoA

propionyl CoA can be converted to methylmalonyl CoA via propionyl-CoA carboxylase (requires biotin)

methylmalonyl CoA is then converted to succinyl CoA using vitB12

Question 16

What happens to succinyl-CoA?

Answer 16

conversion to succinate to malate to oxaloacetate (cycle complete)

Question 17

How else can oxaloacetate be made?

Answer 17

directly from pyruvate via pyruvate carboxylase using biotin as a cofactor

Question 18

What else can happen to oxaloacetate?

Answer 18

conversion back to phosphoemolpyruvate (PEP) to make glucose

Question 19

Describe the initial steps of the urea cycle

Answer 19

NH₃+CO₂ and carbamoyl phosphate convert ornithine to citrulline

Question 20

What happens to citrulline in the urea cycle?

Answer 20

conversion to argininosuccinate and then to arginine (using asparate; fumarate is given off)

arginine is converted to ornithine