Lecture 9. Other Sugars, Gluconeogenesis and Pentose Phosphate Pathway

Question 1

How does lactose intolerance occur?

Answer 1

When the enzyme that breaks down lactose is not present

Question 2

What is the name of the rare condition where galactose cannot be broken down?

Answer 2

Galactosemia

Question 3

What other dietary sugars fit into glycolysis?

Answer 3

Galactose and fructose

Question 4

What stage of glycolysis does fructose enter?

Answer 4

Stage 2

Question 5

How long can naked mole-rats survive in a totally oxygen deprived environment (anoxia)?

Answer 5

18 minutes

Question 6

What is gluconeogenesis?

Answer 6

The sequence of reactions that converts pyruvate to glucose

Question 7

Where does gluconeogenesis mostly take place?

Answer 7

The liver and kidneys

Question 8

What is the main purpose of gluconeogenesis?

Answer 8

To maintain adequate glucose levels in the blood

Question 9

What does gluconeogenesis use?

Answer 9

ATP and GTP

Question 10

What occurs in the futile cycles?

Answer 10

Net loss of ATP by hydrolysis

Question 11

How are futile cycles avoided?

Answer 11

Tight regulation of metabolic pathways
PFK and Fructose-1,6-bisphosphatase both tightly and oppositely regulated

Question 12

What enzyme converts pyruvate to oxaloacetate?

Answer 12

Pyruvate carboxylase

Question 13

What enzyme converts oxaloacetate to PEP?

Answer 13

PEP carboxykinase

Question 14

What is the starting material for gluconeogenesis in lactate and some amino acids?

Answer 14

Pyruvate

Question 15

What is the starting material for gluconeogenesis in some amino acids?

Answer 15

Oxaloacetate

Question 16

What is the starting material for gluconeogenesis in glycerol?

Answer 16

Dihydroxyacetone

Question 17

Where does gluconeogenesis take place?

Answer 17

Cytosol

Question 18

How is gluconeogenesis regulated?

Answer 18

Oppositely to glycolysis

Question 19

What is the pentose phosphate pathway?

Answer 19

The sequence of reactions that converts glucose to pentoses (then to hexoses and trioses) with the production of NADPH

Question 20

Why are pentoses needed?

Answer 20

Ribose-5-P needed for DNA and RNA (and ATP, NAD⁺, FAD, CoA) synthesis

Question 21

What happens in the oxidative stage of the pentose phosphate pathway?

Answer 21

G-6-P to ribulose-5-P giving 2 NAPDH

Question 22

What happens in the non-oxidative stage of the pentose phosphate pathway?

Answer 22

Ribulose-5-P to ribose-5-P and glycolytic intermediates

Question 23

Oxidative step 1 in PPP

Answer 23

Glucose 6-P Dehydrogenase oxidises to an intramolecular ester forms NADPH (control step)

Question 24

What controls glucose-6-P entry into the PPP?

Answer 24

Glucose-6-P-DH

Question 25

What controls glucose-6-P-DH activity?

Answer 25

The level of NADP⁺

Question 26

Oxidative step 2 in PPP

Answer 26

Gluconolactonase hydrolyses intramolecular ester

Question 27

Oxidative step 3 in PPP

Answer 27

6-P gluconate DH oxidatively decarboxylates - forms NADPH, releases CO₂

Question 28

Non-oxidative stage in PPP

Answer 28

Ribulose 5-P → Ribose 5-P through aldose isomerisation

Question 29

What is transketolase?

Answer 29

C₂ transfer

Question 30

What is transaldolase?

Answer 30

C₃ transfer

Question 31

How many modes does the PPP have?

Answer 31

4

Question 32

What is mode 1 of PPP?

Answer 32

No NADPH production, G-6-P completely converted to ribose-5-P

Question 33

What is mode 2 of PPP?

Answer 33

Production of both NADPH and ribose-5-P

Question 34

What is mode 3 of PPP?

Answer 34

NADPH needed but not ribose-5-P

Question 35

What is mode 4 of PPP?

Answer 35

Cells need NADPH and ATP

Question 36

What is favism?

Answer 36

Recessive X-linked disorder
Hemolytic anemia when eating fava beans and sometimes other legumes
Glucose-6-P dehydrogenase deficiency