Oxidation of Glucose

Question 1

What are the 3 stages of glucose oxidation

Answer 1

1. glycolysis + pyruvate dehydrogenase
2. TCA cycle
3. ETC

Question 2

Can glucose enter cells via passive diffusion

Answer 2

no

Question 3

What transporters are required to move glucose across the membrane

Answer 3

GLUTs (glucose transporters)
- reside in the cell membrane

Question 4

What in the body stimulates GLUT mediated glucose uptake in skeletal muscle and adipose tissue

Answer 4

insulin

Question 5

In diabetes, why does the body “starve in the midst of plenty”

Answer 5

because there is glucose to be taken up, but insulin cannot perform that action properly

Question 6

What cell types are entirely dependant on glycolysis for energy provision

Answer 6

red blood cells, renal medulla, brain, and sperm

Question 7

Glycolysis is the only pathway that can provide energy under ______________ conditions

Answer 7

anaerobic

Question 8

Where does glycolysis occur

Answer 8

in the cytosol

Question 9

How many steps are in glycolysis

Answer 9

10

Question 10

What are the first 5 steps of glycolysis called

Answer 10

the preparatory phase

Question 11

What are the last 5 steps of glycolysis called

Answer 11

the pay off phase

Question 12

What is step 1 of glycolysis

Answer 12

phosphorylation of glucose
- ATP is used to phosphorylate glucose (adds a phosphate)

results in glucose-6-phosphate

Question 13

What enzyme is used in step 1 of glycolysis

Answer 13

hexokinase

Question 14

How many isozymes of hexokinase are there

Answer 14

4 (4 different enzymes that can equally effectively catalyze the same reaction)

Question 15

What is step 2 of glycolysis

Answer 15

phosphohexose isomerization
- glucose is changed from a hexose to a pentose ring

results in fructose-6-phosphate

Question 16

What enzyme and cofactor is used in the second step of glycolysis

Answer 16

phosphohexose isomerase
- cofactor is Mg2+

Question 17

What is step 3 of glycolysis

Answer 17

the second phosphorylation
- a phosphate is added to carbon 1 of fructose-6-phosphate

results in fructose 1,6-bisphosphate
(a bisphosphate has 2 phosphates in different locations, whereas a diphosphate has 2 phosphates connected to one another)

Question 18

What enzyme is used in the third step of glycolysis

Answer 18

phosphofructokinase-1 (PFK-1)

Question 19

What is step 4 of glycolysis

Answer 19

the six carbon fructose is split into two 3 carbon units
- fructose 1,6-bisphosphate is split into two separate 3 carbon molecules

results in dihydroxyacetone phosphate and glyceraldehyde 3-phosphate

Question 20

What enzyme is used in step 4 of glycolysis

Answer 20

aldolase

Question 21

What is step 5 of glycolysis

Answer 21

interconversion of the triose phosphates
- dehydroxyacetone phosphate is isomerized into glyceraldehyde 3-phosphate

results in now two glyceraldehyde 3-phosphate molecules

Question 22

What enzyme is required in step 5 of glycolysis

Answer 22

triose phosphate isomerase

Question 23

The mechanism of triose phosphate isomerase is essentially the same as ________________ _____________

Answer 23

phosphohexose isomerase

Question 24

What is step 6 of glycolysis

Answer 24

glyceraldehyde 3-phosphate dehydrogenase
the energy key to glycolysis
- glyceraldehyde 3-phosphate is phosphorylated at carbons 1 and 3

*results in 1,3 bisphosphoglycerate

Question 25

What enzyme is used in step 6 of glycolysis and what cofactor is needed

Answer 25

glyceraldehyde 3-phosphate dehydrogenase - NAD+ is the cofactor

Question 26

What bond is created in step 6 of glycolysis between carbon 1 and the phosphate

Answer 26

a mixed anhydride bond - very high energy *why this step is called the energy key to glycolysis*

Question 27

What is step 7 of glycolysis

Answer 27

phosphoryl transfer from 1,3-BPG to ADP *the first substrate level phosphorylation* - 1,3-bisphosphoglycerate is phosphorylated by ADP *results in 3-phosphoglycerate and ATP formed

Question 28

What enzyme is used in step 7 of glycolysis and what cofactor

Answer 28

phosphoglycerate kinase ADP is the cofactor

Question 29

How many ATP generated per GLUCOSE based on step 7 of glycolysis

Answer 29

1 glucose = 2 moles of 1,3-BPG (remember the double formation of G3P earlier) so that means 2 ATP per 1 glucose

Question 30

What is step 8 of glycolysis

Answer 30

conversion of 3-phosphoglycerate to 2-phosphoglycerate - transfer of phosphate from carbon 3 to carbon 2 via a mutase enzyme (sub-class of isomerase) *results in 2-phosphoglycerate

Question 31

What enzyme is used in step 8 of glycolysis

Answer 31

phosphoglycerate mutase

Question 32

What is step 9 of glycolysis

Answer 32

dehydration of 2-phospoglycerate - water is removed (removal of a hydroxyl) *results in phosphoenolpyruvate*

Question 33

What enzyme is required in step 9 of glycolysis

Answer 33

enolase

Question 34

What is step 10 of glycolysis

Answer 34

transfer of the phosphoryl group from phosphoenolpyruvate to ADP *the second substrate level phosphorylation* - the phosphate on carbon 2 is removed by ADP *results in enolpyruvate which is quickly tautomerized to ketopyruvate*

Question 35

What enzyme is required in step 10 of glycolysis and what cofactor

Answer 35

pyruvate kinase cofactor is ADP

Question 36

How many substrate level phosphorylations are seen in glycolysis

Answer 36

2

Question 37

What is the predominant form of pyruvate

Answer 37

keto form

Question 38

Why is pyruvate found in keto form

Answer 38

lowers the concentration of reaction product and pulls the reaction toward completion, resulting in a large negative delta G