Gluconeogenesis (Carbohydrate Anabolism)

Question 1

The brain requires how many grams of glucose

Answer 1

120 grams/day out of the entire bodies 160g

Question 2

What provides the glucose supply needed

Answer 2

1. Glycogen reserves (190g)
2. Bodily fluids (20 g)

Question 3

T or F: When glucose is depleted (fasting or prolonged exercise), glucose must be synthesized from other sources

Answer 3

True (gluconeogenesis)

Question 4

Gluconeogenesis

Answer 4

Gluconeogenesis is the biosynthesis of glucose from non-carbohydrate precursors (Like a reverse glycolysis , but the three “irreversible” reactions must be bypassed)

Question 5

Gluconeogenesis takes place in the

Answer 5

1. LIVER
2. Kidney (kidney uses up a lot of glucose so not so much here)

Question 6

T or F: Glucose levels in the blood are not relatively constant

Answer 6

False, Concentration of glucose levels maintains relatively stable all the time due to glycolysis and gluconeogenesis

Question 7

Glycolysis and gluconeogenesis mainly occurs in

Answer 7

Glycolysis: Mainly muscles and brain
Gluconeogenesis: Mainly liver

Question 8

Name the 5 gluconeogensis precursors and their origin

Answer 8

Question 9

Gluconeogenesis substrates photo

Answer 9

Anything form the Kreb Cycle (TCA cycle) can become glucose

Question 10

Problem with gluconeogenesis

Answer 10

Must bypass the irreversible steps of glycolysis, so needs high energy investment

Question 11

Compare and contrast reaction 1,3, 10 of glycolysis with gluconegensis (enzymes involved)

Answer 11

Question 12

2 reactions of gluconeogenesis reaction 1 are necessary to bypass glycolysis reaction 10

Answer 12

Reaction 1: Carboxylation of pyruvate into oxaloacetate

Reaction 2: Phosphorylation and decarboxylation of oxaloacetate in phosphoenolpyruvate

Question 13

Reaction 1 of gluconeogenesis

Answer 13

Carboxylation of pyruvate into oxaloacetate (catalyzed by pyruvate carboxylase)

**Pyruvate carboxylase is also used to convert pyruvate into oxaloacetate to replenish the intermediates of the TCA cycle, this cycle take places in the mitochondrial matrix (anaploresis)

**Biotin ( not a cofactor) = prosthetic arm and adds COO group to molecule

Question 14

Reaction 1 of gluconeogenesis is catalyzed by [ blank] and occurs in the [blank]

Answer 14

pyruvate carboxylase (can only be found in the mitochondrial matrix) and the mitochondrial matirx

Question 15

Mitochondria has 2 purposes

Answer 15

1. Send pyruvate to TC cycle (Krebs cycle)
2. Convert pyruvate to oxaloacetate (move away from TC/Krebs cycle

Question 16

Pyruvate enters the mitochondria by

Answer 16

Mitochondrial Pyruvate Carrier (MPC).

Question 17

Mitochondrial pyruvate carrier is made of

Answer 17

Heterodimer of MPC1 and MPC2

Question 18

What is another function of the mitochondrail pyruvate carrier transporter

Answer 18

This transport mechanism is also used for the conversion of pyruvate into Acetyl-CoA (TCA cycle substrate).

Question 19

Reaction 1 gluconeogenesis (malate shuffle) 2 steps:

Answer 19

1. To exit the mitochondria, oxaloacetate must be reduced to malate by the mitochondrial malate dehydrogenase (MDH2)
2. Once in the cytosol, malate is reoxidized to oxaloacetate by the cytosolic malate dehydrogenenase (MDH1)

Question 20

Malate shuffle step 1

Answer 20

To exit the mitochondria, oxaloacetate is reduced to malate using NADH (provides electron (oxidation) to convert to L-malate) by MDH2 (mitochondrial malate dehydrogenase)

Question 21

Malate Shuttle step 1 transporter

Answer 21

Use the Malate-Aspartate shuttle to export malate to the cytoplasm
**Mainly, the malate α-ketoglutarate transporter located in the mitochondrial membrane

Question 22

Reaction 1 gluconeogenesis (malate shuffle) step 2

Answer 22

In the cytosol, malate is reoxidized into oxaloacetate and NADH

Question 23

4 Characteristics of gluconeogenesis reaction 1

Answer 23

1. reducing equivalents (stored on NAD+) are transported from the mitochondria to the cytosol
2. These reducing equivalents (NADH) will be used later by the glyceraldehyde-3-phosphate dehydrogenase (GAPDH).
3. More NADH in the mitochondria than in the cytosol
4. Need NADH for further reactions, so you take electrons by storing it on malate in mitochondria and then using malate to form oxaloacetate and NADH to produce more NADH in the cytosol (since there is so little)

Question 23

4 Characteristics of gluconeogenesis reaction 1

Answer 23

1. reducing equivalents (stored on NAD+) are transported from the mitochondria to the cytosol
2. These reducing equivalents (NADH) will be used later by the glyceraldehyde-3-phosphate dehydrogenase (GAPDH).
3. More NADH in the mitochondria than in the cytosol
4. Need NADH for further reactions, so you take electrons by storing it on malate in mitochondria and then using malate to form oxaloacetate and NADH to produce more NADH in the cytosol (since there is so little)

Question 24

Reaction 2 gluconeogenesis

Answer 24

Phosphorylation and decarboxylation of oxaloacetate in phosphoenolpyruvate catalyzed by phosphoenolpyruvate carboxykinase (PEPCK).

Question 25

Where does reaction 2 of gluconeogenesis take place

Answer 25

cytsol

Question 26

Gluconeogensis reaction 2 characteristics

Answer 26

1. The CO2 that was attached by the pyruvate carboxylase in reaction 1 will be released during this reaction which will provide the electrons necessary for the P-O bond 2. PEP becomes a better substrate for future/following reactions (formed by removing the CO2 from a previous molecules (in this case oxaloacetate) to provide necessary electrons to form phosphate-oxygen bonds -GTP = high energy (treat it like an ATP) = needs investment of 1 GTP

Question 27

Energy profile of the first bypass 4 characteristics

Answer 27

1. Under intracellular conditions: ΔG = - 25kJ/mol 2. Two high energy phosphates must be invested for the synthesis of one phosphoenolpyruvate. 3. Remember that we need 2 molecules of phospho-enolpyruvate to produce one molecule of glucose. 4. 2 ATP and 2 GTP needed/molecule of glucose.

Question 28

Name and describe the alternative path for the first bypass

Answer 28

This alternative path is mainly used when lactate is the substrate. The main reason being that cytosolic NADH is generated by the lactate dehydrogenase. **No need to carry reducing equivalents (NADH) outside of the mitochondria. In image: Left side is what we just covered, so right image is the new alternative path = uses lactate to convert to pyruvate and produces PEP in the mitochondria that is transported out through a PEP transporter into the cytosol to continue the pathway -Malate transporter is regulated which determines which of the 2 pathways is used (if malate transporter is turned off then we will use lactate)

Question 29

Reactions 3-8 gluconeogenesis

Answer 29

Same as glycolysis just backwards

Question 30

Gluconeogensis reaction 9

Answer 30

Hydrolysis (use of water) of fructose-1,6-bisphosphate into fructose-6-phosphate catalyzed by fructose-1,6-bisphosphatase (FBPase). **Bypass glycolysis reaction 3 (Phosphofructokinase)

Question 31

fructose-1,6-bisphosphatase (FBPase) converting fructose-1,6-bisphosphate into fructose-6-phosphate

Answer 31

Removes 1 phosphate on carbon number 1 -Error in structure (image) should have another oxygen (OH) on C2 of both structures (LOOK UP STRUCUTRE TO CONFIRM) **Fun fact: The fructose 1,6 bisphosphatase was shown to be a key enzyme in regulating the metabolic rate of hibernating animals, the enzyme activity is temperature sensitive (less active when it is cold and therefore, inhibiting gluconeogenesis).

Question 32

Gluconeogensis Reaction 10

Answer 32

Question 33

Gluconeogenesi reaction 11

Answer 33

Bypass glycolysis reaction 1 (Hexokinase) Reaction 11: Hydrolysis of glucose-6-phosphate into glucose catalyzed by the glucose-6-phosphatase.

Question 34

Energy balance sheet for gluconeogenesis

Answer 34

Table only shows standard delta G = doesn’t actually represent at cellular level, but standard delta G = favourable to move in forward direction for gluconeogenesis -The actual delta G is are -25 kJ/mol

Question 35

Why cant glycolysis operate in reverse

Answer 35

Costs 4 ATP, 2 GTP, and 2 NADH because without it its +79.9kJ/mol and the reaction will not proceed in the forward direction for gluconeogenesis

Question 36

Why is gluconeogenesis necessary?

Answer 36

1) Brain, nervous system and red blood cells generate ATP mostly from glucose 2) When glycogen stores are depleted we need to get glucose from somewhere: -In between meals but mostly during the night. -In more extreme conditions like starvation or a vigorous exercise **He likes to use examples such as starvation in the woods on exams to determine pathways to use**

Question 37

Explain when gluconeogensis is needed (graph-wise)

Answer 37

1) After a few hours after breakfast, glycogenolysis will kick in which is our storage of glucose to release more glucose because all our energy from breakfast has been used 2) Then after we used our glucose stores, gluconeogenesis will kick in to start breaking down non-carbohydrates to produce glucose for activities until we eat again -Eg. If we only have 2 meals a day (eg. Ramadan) then you will have a greater peak of gluconeogenesis during the day because less glucose intake from meals

Question 38

Gluconeogeneis from lactate

Answer 38

1) muscle and erythrocytes produce lactate. 2) This lactate from the muscles cells and erythrocytes travel to the liver. 3) In the liver lactate is converted back into glucose (Lactate is re-oxidized to pyruvate by the liver lactate dehydrogenase (LDH)) and return to the blood where it is available for the muscle cells/erythrocytes (Cori Cycle) **Note there is a PEP alternative pathway

Question 39

Gluconeogensis from glycerol

Answer 39

1) When our stock of carbohydrates is depleted (glucose and glycogen), fatty acids will become the principal metabolic fuel to fulfill the energy demand. 2) Catabolism (through hydrolysis)of triacylglycerides leads to the production of glycerol and free fatty acids: ->These fatty acids will be used as fuel for the TCA cycle. ->Glycerol will be converted to dihydroxyacetone phosphate. This molecule will further be converted to glyceraldehyde-3-phosphate (Reaction 7 of gluconeogenesis).

Question 40

Gluconeogenesis from amino acids

Answer 40

1. When stocks of carbohydrates and fatty acids are low, glucose molecules can be generated from catabolism intermediates of muscle proteins (proteins from any tissues can be metabolized). 2. High rate of amino acid catabolism in the muscles is rare and occurs only in certain nutritional or pathological states: -Hyperproteic diets (High protein diets) -Fasting -Type 1 diabetes (lose wight and muscle mass = tons of glucose but body does not get insulin signal, so it does gluconeogenesis and cant detect glucose = protein catabolism) **All amino acids, except leucine and lysine (ketogenic), are glucogenic.

Question 41

Glucogenic

Answer 41

Glucogenic: able to be converted into glucose

Question 42

T or F: All amino acids are glucogenic

Answer 42

F: Leucine and lysine are not

Question 43

Anaploresis

Answer 43

Replenishing TCA cycle intermediates (eg. pyruvate is converted to oxaloacetate by pyruvate carboxylase. Oxaloacetate then binds with Acetyl-CoA to produce citrate via citrate synthase (TCA cycle)

Question 44

What reaction step in gluconeogenesis is involved in hibernation and why

Answer 44

Reaction 9 (Fructose-1,6-bisphosphate to fructose-6 phosphate by fructose-1,6-bisphosphatase) because it prevents gluconeogenesis from happening (burns energy instead of making glucose because they arent intaking any food) = enzyme is less active when cold because it is temperature sensitive