Valencik: Carbohydrate metabolism III

Question 1

What two sugars make up lactose?

Answer 1

galactose and glucose

Question 2

What two sugars make up sucrose?

Answer 2

fructose and glucose

Question 3

What sugars make up trehalose?

Answer 3

glucose and glucose

Question 4

How does fructose enter glycolysis?

Answer 4

Converted to DHAP or G3P

Question 5

How does galactose enter glycolysis?

Answer 5

Converted to G6P

Question 6

How does mannose enter glycolysis?

Answer 6

Converted to F6P

Question 7

Most common form of fructose is (blank). Fructose tastes sweeter than (blank). It is less rapidly absorbed in the intestine, but more rapidly (blank).

Answer 7

sucrose; glucose; metabolized

Question 8

What two steps convert Fructose to glycolytic intermediates in the liver?

Answer 8

Fructose —> Fructose-1-phosphate via Fructokinase

F1p —> Glyceraldehyde + DHAP
Aldolase B

Question 9

Which of the following is the slow step in fructose metabolism in the liver?

Fructose —> Fructose-1-phosphate via Fructokinase

F1p —> Glyceraldehyde + DHAP
Aldolase B

Answer 9

The first step, so F1P accumulates

Question 10

Where does F1P enter glycolysis in the LIVER?

Answer 10

Bypasses two regulated steps (glucokinase and PFK1) and is converted to DHAP

Question 11

What steps in glycolysis does F1P stimulate?

What steps does it inhibit?

Answer 11

Stimulates glucokinase and pyruvate kinase

Inhibits phosphohexose isomerase and aldolase

Question 12

Fructose is metabolized faster than glucose, so (blank) directs dietary glucose into glycogen synthesis.

Answer 12

fructose-1-phosphate

Question 13

A mutation in fructokinase leads to this condition

Answer 13

essential fructosuria

Question 14

A mutation in aldolase B leads to this condition and these symptoms

Answer 14

fructose intolerance, neusea, vomiting, hypoglycemia, liver damage

Question 15

Where does fructose enter glycolysis in the MUSCLE?

Answer 15

Fructose is converted directly to F6P, so it does not bypass the regulated step of glycolysis (PFK1)

Question 16

What converts fructose to F6P in muscle? What is required for this reaction?

Answer 16

hexokinase; ATP

Question 17

What is one reason why fructose can be bad for you?

Answer 17

Fructose will be converted to F1P in great concentrations, which requires a lot of Pi, which impairs oxidative phosphorylation

Question 18

3 steps of galactose metabolism

Answer 18

Galactose –> Galactose-1-phosphate via galactokinase

Gal1P –> UDP galactose via galactose-1-phosphate uridyl transferase

UDP galactose –> UDP glucose via UDP galactose 4-epimerase

Question 19

If there is a mutation in the enzyme that takes Galactose 1 phosphate to UDP galactose, what condition does this cause?

Answer 19

Classic galactosemia, TYPE 1 GALT

Will cause liver damage, vomiting after eating, must avoid milk.

Question 20

If there is a mutation in the enzyme that takes UDP galactose to UDP glucose, what condition does this cause?

Answer 20

GALE deficiency TYPE 3

Can be mild or severe

Question 21

Why is early diagnosis essential when there are defects in the metabolism of galactose

Answer 21

Galactose-1-phosphate can accumulate and cause vomiting, liver damage, mental deficiency, and cataracts.

Question 22

Why can defects in the galactose pathway lead to cataracts?

Answer 22

Deficiency in the Polvol pathway

Question 23

Why is fructose metabolized faster in the liver than in the muscle?

Answer 23

In the liver, it enters after the committed step of glycolysis

Question 24

What do nucleated cells use the pentose phosphate pathway for?

Answer 24

To generate NADPH

To generate precurosors of nucelotide biosynthesis

Question 25

NADPH is used for reductive biosynthesis of (blank) and cholesterol and for defense against (blank).

Answer 25

fatty acids | oxidative

Question 26

Two products of the pentose phosphate pathway

Answer 26

Ribose-5-phosphate | NADPH

Question 27

NADPH and R5P can be used in the biosynthesis of these four things

Answer 27

fatty acids cholesterol neurotransmitter nucleotides

Question 28

Two branches of the pentose phosphate pathway

Answer 28

oxidative | non-oxidative

Question 29

What is the committed step of the pentose phosphate pathway? What is this step dependent on?

Answer 29

Glucose-6-phosphate ---> 6 phosphogluconate via G6P dehydrogenase NADP+

Question 30

Availability of (blank) regulates G6PDH

Answer 30

NADP+

Question 31

If NADPH is forming faster than it is being used, what happens?

Answer 31

NADP+ is decreased and the committed step of the PPP does not proceed

Question 32

What are the most important enzymes in the non-oxidative phase of the pentose phosphate pathway?

Answer 32

transketolase and transaldolase

Question 33

What are the products of the non-oxidative phase of the PPP? What is the purpose of the non-oxidative phase?

Answer 33

2 F6P and G3P; to generate pentoses that can feed into glycolysis

Question 34

1st rxn of non-oxidative phase: The transketolase reaction coverts two pentose phosphates to a (blank) and a (blank)-sugar phosphate. How many carbons are transferred? What is this reaction dependent on?

Answer 34

triose; seven; two carbons; TPP

Question 35

2nd rxn of non-oxidative phase: How many carbons does transaldolase transfer? What is it dependent on?

Answer 35

3 carbons; energy and vitamins

Question 36

3rd rxn of non-oxidative phase: How many carbons does transketolase transfer? What are the products of this reaction? What is this reaction dependent on?

Answer 36

two carbons; G-3-P and F6P; TPP

Question 37

You can use the pentose phosphate pathway in four different ways.

Answer 37

``` To generate: NADPH and R5P NADPH only Ribose only NADPH and C2 units for Fatty acids ```

Question 38

Uses nucleotide-activated sugars derived from glucose in the biosynthesis of glycolipids, glycoproteins and proteoglycans

Answer 38

uronic acid pathway

Question 39

The products of the uronic acid pathway can feed into this pathway

Answer 39

PPP

Question 40

Why run the PPP in RBCs?

Answer 40

To provide the reducing power necessary to protect RBCs from oxidative damage

Question 41

In RBCs, NADPH is used to keep (blank) reduced.

Answer 41

Glutathione

Question 42

What protects RBCs from highly reactive oxygen derivatives?

Answer 42

Glutathione

Question 43

Why are RBCs affected most by G6PDH deficiency?

Answer 43

RBCs cannot synthesize new G6PDH proteins to replace defective ones. Therefore they must protect their proteins from oxidative damage by maintaining a reducing environment in the cell

Question 44

What is one advantage of G6PDH deficiency?

Answer 44

malaria resistance