Lecture 17

Question 1

What is gluconeogenesis?

Answer 1

• • indirect synthesis of glucose

- - not exactly the reverse of glycolysis

Question 2

Which of the following is NOT a reason as to why our bodies spend energy to make glucose?
A) we can only store 190g of glucose at any time
B) stores of glucose only last for little over a day.
C) we need to make sure enough glucose is present for the brain
D) We don’t actually make glucose and its all a hoax

Answer 2

D

Question 3

True or false.

The organs that are capable of gluconeogenesis are the liver and the kidney

Answer 3

true

Question 4

True or false

non-carbohydrate precursors that can enter gluconeogenesis include glycerol, amino acids, and lactate

Answer 4

true

Question 5

T or F, major tissue for gluconeogenesis is the LIVER and occurs mainly in cytosol, though some precursors come from the mitochondria

Answer 5

True

Question 6

Why isn’t glucose synthesis simply the reverse of glucose metabolism?

Answer 6

– Energetics

– also there are 3 key reactions in glycolysis are energetically very favorable – i.e. deltaG is negative:

glucose –> glucose 6-P

fructose 6-P –> fructose 1,6-BP

PEP –> pyruvate

– this means the reactions are, essentially, irreversible and thus evolution needed a way around this to synthesize glucose

Question 7

What are the different enzymes involved in gluconeogenesis?

Answer 7

• • pyruvate carboxylase, – phosphophenol –pyruvate carboxykinase
• • fructose 1 6 bisphosphatase and

– glucose 6 phosphatase

Question 8

Where does gluconeogesis occur?

Answer 8

– cytosol except for the initial step that occurs in the matrix

Question 9

Which enzyme is involved in the conversion of pyruvate to oxaloacetate?

Answer 9

– pyruvate carboxylase

– carboxylation of pyruvate occurs in mitochondria – oxaloacetate must then be sent to the cytoplasm for conversion to PEP

– occurs through a malate intermedediate and uses a malate transporter

Question 10

What is the net input/output during the formation of oxaloacetate from pyruvate?

Answer 10

will input 1ATP, 1 HCO3 (bicarbonate). will release and ADP and Pi

Question 11

Which cofactor is necessary for the first reaction of gluconeogesis?

Answer 11

biotin

Question 12

True or false

There is a transfer of NADH from inside the matrix to outside the matrix during gluconeogenesis

Answer 12

True

Question 13

Which enzyme is involved in the use and reformation of NADH/NAD+ during the first step of gluconeogesis

Answer 13

malate dehydrogenase

– because remember oxaloacetate is converted to malate intermediate

Question 14

True or false

Lactate can be used as precursor to pyruvate and amino acids can be formed into oxaloacetate

Answer 14

True

Question 15

Which enzyme is responsible for the formation of phosphophenol pyruvate (PEP) from oxaloacetate

Answer 15

PEP carboxykinase

– a decarboxylation and phosphorylation reaction converts oxaloacetate to PEP while burning a GTP

Question 16

What is the next in/output of conversion of oxaloacetate to PEP?

Answer 16

– 1 GTP input and an output of one GDP and CO2

Question 17

True or false
a carboxylation followed by a decarboxylation is a coupling event that occurs in gluconeogenesis in order to overcome the positive free energy of converting to PEP

Answer 17

True

Question 18

How is gluconeogenesis different from glycolysis?

Answer 18

• • energetics
• • deltaGknot prime for reverse glycolysis = + 31 kJ/mol – Not going to happen

– gluconeogenesis uses a carboxylation/decarboxylation cycle to get PEP from pyruvate, and this is much more energetically favorable deltaG = -25 kJ/mol

– however, it has to utilize an ATP and a GTP, energetically expensive

Question 19

T or F, after formation of PEP, gluconeogenesis proceeds as reverse glycolysis

Answer 19

True; reaction direction is determined by the concentrations of reactants, until we hit the fructose 1,6-BP step

Question 20

What is the net output/input between PEP to FBP?

Answer 20

-1ATP -1NADH -1H20 and + 1 ADP + 1Pi

Question 21

Which enzyme is responsible for the conversion of FBP to F6P

Answer 21

– FBPase –> allosteric enzyme under

– Fructose 1,6 - BP is converted to fructose 6-P by dephosphorylation

Question 22

what are the products of the reaction of FPasE?

Answer 22

– one Pi

Question 23

What enzyme is responsible for the formation of glucose from G6p?

Answer 23

– glucose 6-phosphatase

– Fructose 6-P readily converts to glucose 6-P

– this enzyme allows liver and kidney want to send glucose into the bloodstream

– this enzyme is also expressed primarily in those tissues

Question 24

true or false GPase is present only in the liver and kidney

Answer 24

true

Question 25

true or false | FPase is an allosteric enzyme

Answer 25

true

Question 26

What is the next product of gluconeogenesis when 2 pyruvate are used?

Answer 26

- - 1 glucose - - 4ADP - - 2GDP - - 6Pi - - 2NAD+ - - 2H+

Question 27

How many NTPS are burned per glucose regenerated from pyruvate?

Answer 27

- - 6 - - 4ATP - - 2GTP

Question 28

T or F, lactate can serve as a precursor for gluconeogenesis via the Cori Cycle

Answer 28

True

Question 29

T or F, under heavy exertion, lactate produced by muscles isn't wasted, as it can be regenerated into glucose by the liver

Answer 29

True

Question 30

Which two amino acids are mainly involved in the gluconeogenic pathway?

Answer 30

-- Alanine and Glutamine

Question 31

When would amino acid metabolism occur?

Answer 31

-- when fasting or starving, muscle protein will breakdown -- main source of pyruvate

Question 32

What are major control mechanisms?

Answer 32

-- substrate-level control, concentration of reactants or products of the reaction activating/inhibiting the reaction -- feedback control, products of Citric Acid Cycle influencing enzymatic reactions. At high ATP concentrations, flux through Citric Acid cycle slows and intermediates accumulate

Question 33

Describe phosphofructokinase regulation

Answer 33

-- PFK an allosteric enzyme that is activated (R state) by low energy charge (low ATP) and inhibited by high energy -- ATP is also a substrate for the reaction, so binds in the active site -- it binds at the allosteric site with lower affinity so only inhibits at HIGH ATP concentrations

Question 34

True or false | PFK is a homotetramer

Answer 34

true

Question 35

What are the pathways that F6P can take in the context of glucose breakdown?

Answer 35

it can turn into F16BP or turn into F26BP

Question 36

True or false | The non phosphorylated PFK2 enzyme stimulates glycolysis

Answer 36

True -- regulation by phosphorylation, activating one activity versus the other -- kinase activity versus phosphatase activity is controlled by hormone regulation in liver

Question 37

How does the conformation of PFK change when phosphorylated vs not?

Answer 37

-- when phosphorylated the FBpase site is connected and the kinase site is separated, resulting in breakdown of fructose 26 bisphosphate. -- When not, the kinase site is together and the phosphatase site is not, resulting in increase kinase activity and formation of F26BP

Question 38

True or false | insulin stimulates FBP2 by increasing protein phosphatase activity

Answer 38

True

Question 39

True or false | glucagon exerts its influence on F2BP levels by increasing activity of cAMP-dependent protein kinase

Answer 39

True

Question 40

True or false | pyruvate kinase is allosterically activated by F16BP

Answer 40

true

Question 41

Which of the following is pyruvate kinase not inhibited by? A) acetyl coa B) ATP/alanine C) F16BP D) cAmp dependent phosphorylation in the liver

Answer 41

C

Question 42

true or false | PC and PEPCK are activated by acetyl goa

Answer 42

true

Question 43

True or false | glucagon stimulates PEPCK and insulin inhibits it

Answer 43

true

Question 44

true or false | hexokinase is inhibited by G6P in non-liver cells

Answer 44

true; however liver isozyme (hexokinase IV/glucokinase) is NOT subject to feedback inhibition

Question 45

``` Which of the following stimulate PFK activity? A) Citrate B) ATP C) AMP/ADP D) G6P ```

Answer 45

C; AMP, ADP and also F2, 6 BP

Question 46

True or false | citrate and ATP stimulate FBPASE

Answer 46

false. inhibit pfk

Question 47

true or false | FBpase is inhibited by F26P and amp

Answer 47

true

Question 48

true or false | the reactions between G69 and glucose and vice versa are regulated by substrate level control except in the liver

Answer 48

true

Question 49

Describe the regulation of Hexokinase

Answer 49

-- inhibited by product G-6-P; however, the liver isozyme (hexokinase IV/glucokinase) is NOT subject to feedback inhibition

Question 50

Explain how insulin and glucagon activate glycolysis and gluconeogenesis.

Answer 50

-- insulin activates kinase activity (high glucose, F2, 6B activates Glycolysis inhibits gluconeogenesis) -- glucagon activates phosphatase activity (low glucose, no activation of Glycoloysis)

Question 51

T or F, pyruvate kinase is allosterically inhibited by: Acetyl- CoA

Answer 51

True, also ATP, amino acids and hormonal regulation in liver isoforms

Question 52

T or F, PC and PEPCK are activated by Acetyl-CoA

Answer 52

True

Question 53

T or F, glucagon tells us about low blood sugar

Answer 53

True, this activates the synthesis of phosphoenol-pyruvate carboxykinase