The Krebs cycle is controlled and regulated
by the availability of the NAD+ and FAD substrates
, while high concentrations of NADH inhibit it.
What are the regulatory steps of the citric acid cycle?
Explanation: The regulated steps of the citric acid cycle are
citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase
. These steps are inhibited and stimulated by various products and reactants within the citric acid cycle.
Where is citric acid cycle regulated?
The citric acid cycle is controlled
through the enzymes that break down the reactions that make the first two molecules of NADH
. The enzyme isocitrate dehydrogenase and α-ketoglutarate dehydrogenase helps to regulate the citric acid cycle. The regulation of the cycle depends on the ATP and NADH levels.
What activates the regulatory enzymes of the Krebs cycle?
Regulation by calcium.
Calcium is also used as a regulator in the citric acid cycle. Calcium levels in the mitochondrial matrix can reach up to the tens of micromolar levels during cellular activation. It activates
pyruvate dehydrogenase phosphatase
which in turn activates the pyruvate dehydrogenase complex.
How is citrate synthase regulated?
Furthermore, citrate synthase is
inhibited by NADH, citrate (which competes with oxaloacetate), and succinyl-CoA
(an example of competitive feedback inhibition). In many plants, bacteria and fungi, such as the peroxisomes of baker’s yeast, citrate synthase plays a role in the glyoxylate cycle.
What hormones inhibit the citric acid cycle?
- insulin activates TCA cycle.
- glucagon inactivates TCA cycle.
What steps in the citric acid cycle are regulated Why are they regulated?
TCA cycle is regulated by
allosteric regulation
. The metabolites regulate the cycle by feedback inhibition. The enzyme isocitrate dehydrogenase and ⍺-ketoglutarate dehydrogenase are the main controlling point. ATP and NADH inhibit the enzymes isocitrate dehydrogenase and ⍺-ketoglutarate dehydrogenase.
How are glycolysis and TCA cycle regulated?
Regulation of the TCA Cycle
Citrate: Inhibits phosphofructokinase, a key enzyme in glycolysis
. This reduces the rate of production of pyruvate and therefore of acetyl-coA. Calcium: Accelerates the TCA cycle by stimulating the link reaction.
How is citrate synthase activated?
In the citric acid cycle, these remaining carbon atoms are fully oxidized to form carbon dioxide. Citrate synthase starts this process by
taking the molecules of acetate and attaching them to oxaloacetate
, which acts as a convenient handle as the carbon atoms are passed from enzyme to enzyme in the citric acid cycle.
What enzymes regulate the TCA cycle?
The three regulatory enzymes of the TCA cycle are
citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase
. These enzymes are allosterically regulated and catalyse the irreversible steps of the TCA cycle, which are the main point of regulation.
How does the citric acid cycle act as a catalyst?
The citric acid cycle utilizes mitochondrial enzymes. The first step is fusion of the acetyl group of acetyl-CoA with oxaloacetate,
catalyzed by citrate synthase
. CoA-SH and heat are released and citrate is produced. Citrate is isomerized by dehydration and rehydration to isocitrate.
Which steps of glycolysis are regulated?
Glycolysis can be regulated by enzymes such as
hexokinase, phosphofructokinase and pyruvate kinase
. Gluconeogenesis can be regulated by fructose 1,6-bisphosphatase. The control of glycolysis begins with the first enzyme in the pathway, hexokinase.
