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Carbohydrate Metabolism 2
Terms in this set (48)
What is gluconeogenesis?
The formation of glucose from several different kinds of starting materials
What are the starting materials for gluconeogenesis?
Can start with pyruvate, TCA cycle compounds, or amino acids
How many reactions in the gluconeogenesis pathway are not shared between it and glycolysis?
Where in the body does gluconeogenesis occur?
Liver, sometimes kidney
What is the first irreversible reaction in gluconeogenesis? (hint: think of the last reaction in glycolysis)
Pyruvate -> PEP
Pyruvate -> PEP reaction - what happens, why it works, list the intermediate compound
1 ATP and 1 GTP are consumed because energy is needed to form a high energy compound (PEP)
Transport involved in pyruvate -> PEP reaction
Pyruvate carboxylase is in the mitochondria, and PEP carboxylase is in the cytoplasm
Oxaloacetate needs to be converted to malate for transport out of the mitochondria
Malate aspartate shuttle - connects with TCA cycle
Net movement of NADH to the cytoplasm, where it is needed later on
What is the second unique step in gluconeogenesis?
Fructose-1,6-bisP to G6P
What type of reaction is occurring in the fructose-1,6-bisP conversion to G6P in gluconeogenesis?
Dephosphorylation by a phosphatase
Isomerization to G6P
What is the third unique reaction in gluconeogenesis? (hint: think of the first reaction in glycolysis)
G6P to glucose
What type of reaction is occurring in the G6P conversion to glucose in gluconeogenesis?
Dephosphorylation by a phosphatase
Where in the cell can glucose be formed?
Mitochondria, cytoplasm, ER
Where is glucose exported from in order to enter the blood stream?
Glucose needs to be exported from the liver so it can reach the body tissues via the blood stream.
At what locations in the cell does gluconeogenesis occur?
Starts in the mitochondria, then moves to the cytoplasm
What is reduced and what is oxidized in gluconeogenesis? Is it catabolic or anabolic?
Pyruvate is reduced
NADH is oxidized
How much ATP is required to create 1 glucose molecule from 2 pyruvates?
What by-product is formed as a result of the irreversible reactions of gluconeogenesis?
Allosteric regulation of gluconeogenesis
Activated by high energy
Inhibited by low energy
Role of fructose-2,6-bisP, and what makes it
Determines how much glycolysis vs gluconeogenesis is occurring at any given time
Made by a kinase, destroyed by a phosphatase - both are part of the same enzyme
F-2,6-bisP PFK-2/FBPase-2 enzyme complex...how does it work?
Not phosphorylated: PFK-2 (kinase) is active
Stimulates glycolysis, activated by insulin
Phosphorylated: FBPase-2 (phosphatase) is active
Stimulates gluconeogenesis, activated by glucagon
Glycolysis vs. Gluconeogenesis: location within the cell
Gluconeogenesis: mitochondria, then cytoplasm
Glycolysis vs. Gluconeogenesis: starting point/product
Glycolysis: starts with glucose/other sugars, ends with pyruvate
Gluconeogenesis: starts with pyruvate/TCA compounds, ends with glucose/G6P
Glycolysis vs. Gluconeogenesis: intermediates
Glycolysis: intermediates are all used in gluconeogenesis
Gluconeogenesis: certain intermediates (oxaloacetate, malate) are not used in glycolysis
Glycolysis vs. Gluconeogenesis: reactions
Glycolysis: reactions shared except for 3
Gluconeogenesis: reactions shared except for 4 (5-6 if you count transport)
Glycolysis vs. Gluconeogenesis: ATP
Glycolysis: 2 ATP consumed per glucose
Gluconeogenesis: 6 ATP consumed per glucose
Glycolysis vs. Gluconeogenesis: NAD+/NADH
Glycolysis: NAD -> NADH
Gluconeogenesis: NADH -> NAD
Glycolysis vs. Gluconeogenesis: enzymes
Glycolysis: all shared except 3
Gluconeogenesis: all shared except 4 (5-6 if you count transport)
Glycolysis vs. Gluconeogenesis: regulation
Glycolysis: Activated by AMP, F-2,6-bisP, insulin
Inhibited by ATP, citrate, glucagon
Gluconeogenesis: Activated by acetyl CoA, citrate, glucagon
Inhibited by AMP, ADP, F-2,6-bisP, insulin
In what pathways is G6P involved in (made or broken down)?
Pentose phosphate shunt
1 branch every 10 glucose
Glycogenin acts as anchor for future addition of glucose to the polymer
What are the 2 types of glycosidic bonds found in glycogen?
alpha 1,4 glycosidic
alpha 1,6 glycosidic (branch points)
Why is glycogen branched?
Allows for quick mobilization of energy (can be broken down quickly if needed)
Generates little to no osmotic pressure compared to individual glucose molecules
Steps of glycogenesis
1. Isomerization of G6P to G1P
2. G1p + UTP = UDP-glucose, PPi released
3. Glucose breaks off from UDP, binds to glycogen
Enzymes of glycogenesis
1,4 bonds: glycogen synthase
1,6 bonds: branching enzyme
Formation of branching points in glycogenesis
Branching enzyme creates a branch point by transfering 7 glucoses to the alpha 1,6 glycosidic bond.
Regulation of glycogen synthase
Activated by G6P
Glucagon -> phosphorylation -> inactive
Insulin -> dephosphorylation -> active
What basic reaction is happening in glycogenolysis? How are individual glucoses protected? Why?
Phosphorylase breaks alpha 1,4 glycosidic bonds, joins free ends of each individual glucose to a phosphate group.
Leaving the phosphate on helps link G1P to other pathways through isomerization of G6P
Enzymes of glycogenolysis
Glycogen phosphorlyase breaks 1,4 bonds
Transferase moves 3 glucoses from the branch to the main chain, can break/form 1,4 bonds
Alpha 1,6 glucosidase breaks 1,6 branch point
Regulation of glycogenolysis
Activated by AMP
Inhibited by ATP, G6P
Glucagon -> phosphorylated -> active
Insulin -> dephosphorylated -> inactive
Overall effect of insulin on glycogen metabolism
When insulin levels are high...
Turns ON glycogen FORMATION
Turns OFF glycogen BREAKDOWN
Overall effect of glucagon on glycogen metabolism
When glucagon levels are high...
Turns ON glycogen BREAKDOWN
Turns OFF glycogen FORMATION
Glycogenesis vs. Glycogenolysis: intermediates
Glycogenesis: G6P, G1P, UDP-glucose
Glycogenolysis: G1P, G6P, glucose
Glycogenesis vs. Glycogenolysis: phosphate compound
Glycogenesis vs. Glycogenolysis: enzymes
Glycogenesis: glycogenin, glycogen synthase, branching enzymes
Glyogenolysis: glycogen phosphatase, transferase, alpha-1,6-glucosidase
Glycogenesis vs. Glycogenolysis: regulation
Glycogenesis: Activated by G6P, insulin
Inhibited by Pi, glucagon
Glycogenolysis: Activated by AMP, Pi, glucagon
Inhibited by ATP, G6P, insulin
Can galactose and fructose enter glycolysis?
Yes, they both can. Galactose can be converted to G6P and fructose can be converted to F6P, both of which are glycolysis intermediates.
Effect of low blood glucose on carbohydrate metabolism
Low blood glucose
Effect of high blood glucose on carbohydrate metabolism
High blood glucose
THIS SET IS OFTEN IN FOLDERS WITH...
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