Metabolic Pathways Flashcards
What is the rate limiting enzyme for glycolysis?
Phosphofructokinase
PFK
What is the rate limiting enzyme for gluconeogenesis?
fructose bisphosphatase-2
What is the rate limiting enzyme for TCA cycle
isocitrate dehydrogenase
What is the rate limiting enzyme for glycogen synthesis
glycogen synthase
What is the rate limiting enzyme for glycogenolysis
glycogen phosphorylase
What is the rate limiting enzyme for HMP shunt
glucose 6 phosphate dehydrogenase (G6PD)
What is the rate limiting enzyme for urea cycle
carbamoyl phosphate synthetase
What is the rate limiting enzyme for Fatty acid synthesis
Acetyl Co-A carboxylase
ACC
What is the rate limiting enzyme for fatty acid oxidation (Beta oxidation)
carnitine acetyltransferase
What is the rate limiting enzyme for ketogenesis
HMG Co-A synthase
What is the rate limiting enzyme for cholesterol synthesis
HMG CoA reductase
What is the embden meyerhof pathway?
glycolysis
Glycolysis
Location
Net ATP
cystol
2
TCA cycle
Location
Net ATP
mitochondrial matrix
2 GTP
ETC
Location
Net ATP
inner mitochondrial membrane
32 (G3P shuttle)
34 (malate aspartae shuttle)
What is the fate of pyruvate during oxidation
Enzyme
Product
Function
Enzyme: pyruvate dehydrogenase
Product: acetyl coa
Function: ATP production and FA synthesis
What is the fate of pyruvate during reduction
Enzyme
Product
Function
Enzyme: lactate dehydrogenase
Product: lactate
Function: anaerobic glycolysis
What is the fate of pyruvate during carboxylation
Enzyme
Product
Function
What is the fate of pyruvate during
Enzyme: pyruvate carboxylase
Product: oxaloacetate
Function: gluconeogenesis; replenishes TCA
What is the fate of pyruvate during transamination
Enzyme
Product
Function
What is the fate of pyruvate during
Enzyme: alanine transaminase
Product: alanine
Function: amino acid synthesis
What are the four different steps of gulconeogenesis from glycolysis?
- Pyruvate –> oxaloacetate
E: pyruvate carboxylase; uses 2 ATP –> 2 ADP
- Oxaloacetate –> PEP
E: PEP carboxykinase; uses 2 GTP –> ADP
- Fructose 1,6 bisphosphate –> Fructose 6 phosphate
E: (FBPase) Fructose Bisphophatase-1; uses H2O –> Pi
- G6P –> glucose
E: (G6Pase) Glucose-6-Phosphatase-1; uses H2O –> Pi
What are the 2 places for gluconeogenesis?
Liver (90%)
Kidney (10%)
Why does gluconeogenesis not occur in the muscle?
The muscle lacks the glucose 6 phosphotase enzyme, the last step to convert G6P to glucose.
When does gluconeogenesis occur?
Occurs when there is low blood glucose.
What inhibits the PEP carboxykinase enzyme?
Insulin
remember that carboxykinase is used in glycogenolysis and the whole point of the cycle is to increase blood glucose levels.
What is an allosteric inhibitor of PFK?
High [ATP]
High [Citrate] - krebs cycle
What is an inhibitor of the enolase enzyme? Signficance in oral bacteria?
Fluoride
Fluoride inhibits glycolysis in oral bacteria thus kills bacteria no production of acid –> no caries!
During the glycogenesis reaction, where do the reactions occur?
There are two locations:
Mitochondria: conversion of pyruvate to oxaloacetate
Cytoplasma: everything else (oxaloacetate –> glucose)
What is the structure of glycogen?
a polysaccharide of glucose; storage form of glucose
made alpha 1,4 straight bond and alpha 1.6 branched bonds
alpha 1,4 (most common)
alpha 1,6 bonds (faster mobilization)
Where are most carbs stored in the body?
What is the role of glycogen stored in liver? muscle?
Liver and muscle
Liver maintains blood glucose levels
Muscle provides quick energy, glucose during exerise
What is the enzyme of glycogenolysis? Function? What intermediates activate the enzyme?
Glycogen phsophorylase
Phosphorylation to cut off end of glycogen branch to turn into active form
Intermediates: cAMP, epinephrine, glucagon
Does glucagon activate the glycogen phosphrylase enzyme in both the liver and muscle?
No, glucagon cannot act on the muscle because it doesnt have a role in blood glucose regulation.
Glucagon acts on the liver to start glycogenolysis, what other system does it work on?
It activates the adenyly cyclase in adipocyte plasma membrane to raise cAMP which turns other enzymes on to breakdown triglycerols to FAs to be used as fuel.
What are the differnet numbers of carbons involved in CAC?
Oxaloacetate (4 C)
Citrate (6C)
isocitrate (6C)
alpha ketoglutarate (5C)
Succinyl CoA (4C) –> Oxaloacetate (4C)
what is the most immediate available source of oxaloacetate?
aspartic acid
note: OOA is interconvertable with aspartic acid
What is the only enzyme that is in both CAC and ETC?
succinate dehydrogenase
What inhibits the TCA and ETC cycle?
malonate
the competitve inhibitor of succinate dehydrogenase.
During ETC, NADH is fed to which enzyme? FADH2?
NADH- Cytochrome Complex 1- NADH dehydrogenase complex
FADH2- Cytochrome Complex 2 - succinate dehydrogenase complex
What is another name for the pentose phosphate pathway?
hexose monophosphate shunt (HM-shunt)
what is the stoichiochemistry of the pentose phosphate pathway?
glucose 6 phosphate + 2 NADP + H2O –> Ribose 5 phosphate + 2 NADPH + 2H + CO2
What is the ultimate goal of PPP? Is ATP produced?
To produce ribose for nucleotide synthesis and NADPH for fatty acid and steroid synthesis.
NO
NADPH produced from PPP can also help with what?
Helps rid of free radicals of erythrocytes and H2O2 (hydrogen peroxide).
What is the rate limiting step of PPP? What does this enzyme catalyze?
Glucose 6 phosphate dehydrogenase
What occurs when there’s a deficiency of glucose 6 phosphate dehydrogenase?
hemolytic anemia due to a decrease in NADPH production thus increase in oxidizing agents in RBCs
What is the pathway of glycogenolysis? What is the pathway of glycogenolysis?
Gylocgenolysis
Glycogen —(glycogen phosphorylase)—-> glucose 1 phosphate –(phosphoglucomutase)—> glucose 6 phosphate –(glucose 6 phosphatase)—–> glucose
What is the pathway of glycogenesis? What is the pathway of glycogenesis?
Glucose –(hexokinase)—-> glucose 6 phosphate —-(phosphoglucomutase)—-> glucose 1 phosphate –(glycogen synthase)—> glycogen
