Carbohydrate Metabolism Flashcards
Glucokinase
present in the pancreatic beta-islet cells as part of the glucose sensor and is responsive to insulin in the liver
Hexokinase
traps glucose
Phosphofructokinase-1 (PFK 1)
rate limiting step
Phosphofructokinase-2 (PFK 2)
produces F2,6-BP, which activakes PFK-1
Glyceraldehyde-3-phosphate dehydrogenase
produces NADH
3-phosphoglycerate kinase and Pyruvate Kinase
perform substrate level phosphorylation
Irreversible reactions catalyzed by
Glucokinase, PFK-1, pyruvate Kinase
Aerobic Oxidation of NADH
occurs via electron transport chain
Anaerobic Oxidation of NADH
occurs via cytoplasmic lactate dehydrogenase
Pyruvate Dehydrogensare
converts pyruvate to acetyl-CoA and is stimulated by insulin and inhibited by acetyl-CoA
Citric Acid Cycle Main Substrates
Pyruvate Citrate Isocitrate Ketogluterate Succinyl-CoA Succinate Fumarate Malate Oxaloacetate
Location of CAC
mitochondrial matrix
Main Goal of CAC
to oxidize acetyl-CoA to CO2 and generate NADH, FADH and GTP
Location of ETC
matrix facing surface of the inner mitochondrial membrane
General Steps of ETC
NADH donates electrons to the chain, which are passed from one complex to the next. Reduction potentials increase down the chain until the electrons end up on oxygen, which has the highest reduction potential
How does NADH cross the inner mitochondrial membrane?
2 shuttle mechanisms
glycerol 3-phosphate shuttle
malate-aspartate shuttle
Proton-Motive Force
The electrochemical gradient generated by the ETC across the inner mitochondrial membrane. The intermembrane space has a higher concentration of protons than the matrix; this gradient stores energy, which can be used to form ATP vie chemiosmotic coupling.
ATP Synthase
enzyme responsible for generating ATP from ADP and an inorganic phosphate (Pi)
Summary of the Energy Yield of Metabolic Processes:
Glycolysis:
Pyruvate Dehydrogenase:
CAC:
2 NADH and 2 ATP
1 NADH
3 NADH, 1 FADH2, 1 GTP
NADH Produces:
2.5 ATP
FADH Produces:
1.5 ATP
GTP Produces:
1 ATP
Total Energy Yield from 1 Glucose
30-32
2 ATP from glycolysis + 2 ATP (GTP) from CAC + 25 ATP from NADH + 3 ATP from FADH2
Glycogenesis
the building of glycogen using glycogen synthase and branching enzyme
Glycogen Synthase
Creates alpha-1,4-glycosidic links between glucose molecules.
Activated by insulin in liver and muscles.
Branching Enzyme
Moves a block of oligoglucose from one chain and connects it as a branch using an alpha-1,6-glycosidic link
Glycogenolysis
The breakdown of glycogen using glycogen phosphorylase and debranching enzyme
Glycogen Phosphorylase
removes single glucose 1-phosphate molecules by breaking alpha-1,4 glycosidic links.
In the liver is is activated by glucagon to prevent low blood sugar
In exercising skeletal muscle it is activated by epinephrnie and AMP to provide glucose fo the muscle itself
Debranching Enzyme
moves a block of oligoglucose from one branch and connects it to the chain using an alpha-1,4 glycosidic link
Gluconeogenesis
Occurs in the cytoplasm and the mitochondria, of primarily the liver. Mostly the reverse of glycolysis with the same enzymes but some exceptions.
Three Irreversible Steps of Glycolysis Needed Different Enzymes in Gluconeogenesis
Pyruvate Carboxylase and PEP Carboxykinase bypass Pyruvate Kinase
Fructose-1,6-bisphosphatase bypasses phosphofructokinase-1 (PFK-1)
Glucose-6-phosphatase bypasses hexokinase/glucokinase
Pentose Phosphate Pathway
Occurs in the cytoplasm and generates NADPH and sugars for biosynthesis.
Rate Limiting Enzyme for Pentose Phosphate Pathway
glucose-6-phosphate dehydrogenase
activated by NADP+ and insulin
inhibited by NADPH
Fermentation
occurs in the absence of oxygen, lactate dehydrogenase oxidizes NADH to NAD+ therefore replenishing the oxidized coenzyme for glyceraldehyde-3-phosphate dehydrogenase, reduces pyruvate to lactate
Functions of NADPH
primarily acts as an electron donor, potent reducing agent for many functions
Pathways that form acetyl-CoA
Glycolysis Fatty Acid Oxidation (beta-oxidation) Amino Acid Catabolism Ketones Alcohol
Complex 1 in ETC
NADH donates elections here
Complex 2 in ETC
FADH2 donates electrons here
Complex 3 in ETC
Q-cycle occurs, which is the main contributor to the proton motive force
Complex 4 in ETC
final transfer of electrons to oxygen and water is formed
