Chapter 18 (Entry of other Sugars)

Question 1

Entry of Fructose via the muscle

Answer 1

Very similar to metabolism of Glucose

Hexokinase is used to convert Fructose into Fructose-6-P

Question 2

Fructokinase

Answer 2

The phosphorylation of Fructose into Fructose-1-P (which is not a metabolite in glycolysis)
Irreversible
Found in the liver

Question 3

Fructose-1-P Aldolase

Answer 3

Catalyzes the cleavage of Fructose-1-P into Glyceraldehyde and DHAP
Reversible
Found in the liver

Question 4

Glyceraldehyde has two pathways

Answer 4

Short: direct to GAP via the enzyme Glyceraldehyde Kinase
Long: to GAP (creating Glycerol-3-P in the process) via several steps

Question 5

Glyceraldehyde (Short Path)

Answer 5

converted to GAP via the enzyme Glyceraldehyde Kinase
Requires 1 ATP (to phosphorylate)
Irreversible

Question 6

Alcohol Dehydrogenase

Answer 6

Changing the aldehyde on Glyceraldehyde into a alcohol to create Glycerol
Consumes a NADH (oxidation)

Question 7

Glycerol Kinase

Answer 7

Adds a phosphate group onto the C#3 of glycerol to create a Glycerol-3-P
Only found in the liver
Requires ATP
Irreversible

Question 8

Glycerol Phosphate Dehydrogenase

Answer 8

Oxidizes the -OH on C#2 of Glycerol-3-P into a ketone to create a DHAP
Consumes NAD+ (reduced)

Question 9

What is the purpose of the longer Glyceraldehyde pathway?

Answer 9

It is used to create Glycerol-3-P which is used as a backbone for triacylglycerols (and other compounds)

Question 10

Entry of Fructose via the liver

Answer 10

Glucokinase has a low affinity for fructose to fructokinase is used

Question 11

Entry of Glycerol

Answer 11

Occurs only in the liver

Same steps used during the long pathway to convert Glycerol to DHAP in the Fructose pathway

Question 12

Entry of Galactose

Answer 12

Galactose is the C4 epimer of Glucose
Only metabolized in the liver
Galactokinase is used

Question 13

Galactokinase

Answer 13

Adds a phosphate group onto the C#1 of Galactose to create Galactose-1-P
Irreversible
Requires ATP

Question 14

Galactose-1-P Uridylyltransferase

Answer 14

Transfers a phosphate group from UDP-Glucose to create a UDP-Galactose
Glucose-1-P continues on down the pathway

Question 15

Phosphoglucomutase

Answer 15

Transfers the phosphate group from C#1 to C#6 to create Glucose-6-P (which continues down glycolysis)

Question 16

What enzyme epimerizes UDP-Galactose back into UDP-Glucose and vice versa

Answer 16

UDP-Galactose-4-epimerase

Question 17

If an infant has a galactose problem

Answer 17

they cannot drink their mothers milk or it will lead to mental retardation

Question 18

Dr. Luis Leloir

Answer 18

won noble prize for galactose metabolism

Question 19

Entry of Mannose

Answer 19

Mannose is C#2 epimer of Glucose
Can use the enzyme hexokinase (muscle)
Adds phosphate group to create Mannose-6-P
Requires ATP
Irreversible

Question 20

Phosphomannose Isomerase

Answer 20

Turns Mannose-6-P into Fructose-6-P

Question 21

Mannose is primarily seen as

Answer 21

Mannose-1-P (via phosphomannose mutase)

Question 22

Aldose Reductase

Answer 22

Reduces aldoses to their corresponding sugar alcohols
Reduces Glucose to Sorbitol
Requires NADPH

Question 23

Aldose Reductase has a (high/low) Km for aldoses which means a lot of substrate is needed

Answer 23

High

High aldolase = increased activity

Question 24

Sorbitol Dehydrogenase

Answer 24

Converts Sorbitol into Fructose
Requires NAD+
Found in sperm (and several tissues)
Low concentrations can lead to damage similar to that of Type 1 Diabetes

Question 25

At which point in the glycolysis pathway does arsenate poisoning become a problem

Answer 25

During the conversion of GAP to 1,3-BPG via GAPDH GAP mistakes arsenate as a phosphate group and creates 1-Arseno-3PG The arsenate is then hydrolized off (no enzyme needed)

Question 26

Why is arsenate poisoning so dangerous

Answer 26

Because this causes the GADPH step to be skipped which leads to a net yield of 0 ATP through glycolysis

Question 27

Bisphosphoglycerate Mutase

Answer 27

Converts 1,3-BPG to 2,3-BPG via the movement of a phosphate group Irreversible

Question 28

Significance of 2,3-BPG

Answer 28

it is a allosteric effector for hemoglobin

Question 29

2,3-BPG Phosphatase

Answer 29

Hydrolyzes the phosphate off of 2,3-BPG to create 3-PG Phosphate group comes off as Pi Irreversible

Question 30

The effect of Hexokinase deficiency on blood oxygen

Answer 30

``` Low Hexokinase = low 1,3-BPG Low 1,3-BPG = low 2,3-BFG Low 2,3-BFG = higher affinity for O2 Blood can carry less O2 than normal Curve shifts to the left ```

Question 31

The effect of Pyruvate Kinase deficiency on blood oxygen

Answer 31

``` Low Pyruvate Kinases = more 1,3-BPG (everything backs up) More 1,3-BPG = more 2,3-BPG More 2,3-BPG = lower affinity for O2 Blood can carry more O2 than normal Curve shifts to the right ```