WEEK 3: Gluconeogenesis

Question 1

What tissues require a constant supple of glucose?

Answer 1

tissues that synthesize glucose and tissue that use glucose as their main energy source

Question 2

what tissue use glucose as primary energy source?

Answer 2

brain and nervous tissue
muscle
erythrocytes
testes

Question 3

what tissue synthesize glucose?

Answer 3

liver
kidney

Question 4

when glycogen reserves are depleted, how is glucose made?

Answer 4

from non-carbohydrate resources

Question 5

what are the carbon-containing precursors of gluconeogenesis?

Answer 5

lactate
glycerol
amino acids

Question 6

which steps of glycolysis are irreversible, and need bypass reactions for gluconeogenesis to take place?

Answer 6

pyruvate to PEP
F-1,6 BP to F6P
g^P to glucose

Question 7

how are phosphorylation steps bypassed in glycolysis? Which are those?

Answer 7

G6P to glucose with enzyme glucose 6 phosphatase
F16P to F6P with enzyme fructose 1,6 bisphosphatase

both steps are bypassed by Mg2+ dependent phosphatases

Question 8

Pyruvate kinase is bypassed via a multistep process involving oxaloacetate. Identify the steps.

Answer 8

pyruvate into mitochondria
pyruvate and CO2 form OAA with enz pyruvate carboxylase
OAA to malate
malate exit cell and forms OAA
OAA to PEP with phosphenol pyruvate. Releases CO2
Irreversible steps of glycolysis

Question 9

why must OAA become malate?

Answer 9

malate can exit mitochondria whereas OAA cannot.

Question 10

where does the CO2 come from in the reaction of CO2 and pyruvate forming OAA?

Answer 10

CO2 from bicarbonate (HCO3-) is activated and transferred by pyruvate carboxylate to its biotin prosthetic group.
the enzyme then transfers the CO2 to pyruvate generating oxaloacetate.

Question 11

what happens to odd chain fatty acids?

Answer 11

converted to succinyl CoA via B-oxidation.
krebs cycles converts this to other molecules and then malate, glycolysis reverse reactions and eventually glucose.

Question 12

what is a triglycerol?

Answer 12

glycerol molecules bound to 3 fatty acids

Question 13

how is glycerol channelled in gluconeogenesis?

Answer 13

glycerol is converted into dihydroxyacetone phosphate, then follows the steps to glucose

Question 14

what is protein catabolism?

Answer 14

breakdown of proteins into absorbable monomers for further degradation or reassembly

Question 15

what is the cori cycle?

Answer 15

lactate is produced from glucose in exercising muscles (lack of O2) or erythrocytes (no mitochondria).
lactate goes to liver
liver converts lactate to glucose
glucose is distributed around the body

Question 16

what is the alanine cycle in the muscles?

Answer 16

• Pyruvate is converted to alanine (transamination)
• Prevents toxic levels of ammonia in muscle & in blood

Question 17

what is the alanine cycle in liver?

Answer 17

• Alanine donates NH3 to a-ketoglutarate to form glutamate (transamination) and pyruvate is reformed which can be used for Gluconeogenesis.
• Glutamate is deaminated releasing NH3

Question 18

when is the alanine cycle active?

Answer 18

during starvation - lack of glucose

Question 19

what enzymes are needed for each bypassed step of glycolysis?

Answer 19

pyruvate to PEP - pyruvate carboxylase / PEPCK
F-1,6 BP to F6P - Fructose bisphosphatase-1
g^P to glucose - Glucose-6-phosphatase

Question 20

what enzymes are needed for each bypassed step of glycolysis?

Answer 20

pyruvate to PEP - pyruvate carboxylase / PEPCK
F-1,6 BP to F6P - Fructose bisphosphatase-1
g^P to glucose - Glucose-6-phosphatase