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 is the citric acid cycle controlled?
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 steps of the citric acid cycle are regulated?
The TCA cycle is regulated allosterically at the 3 irreversible steps:
citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase
.
Why is the citric acid cycle regulated?
Regulation of the citric acid cycle is important as
reactions that are unchecked will lead to large amounts of wasted metabolic energy
. The ability to regulate the cycle keeps the cell in a stable state, and this function is maintained by three mechanisms: The availability of substrates.
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.
What activates the citric acid cycle?
The citric acid cycle begins with the
transfer of a two-carbon acetyl group from acetyl-CoA to the four-carbon acceptor compound (oxaloacetate) to form a six-carbon compound (citrate)
. The citrate then goes through a series of chemical transformations, losing two carboxyl groups as CO
2
.
What is regulation of gluconeogenesis?
Insulin and glucagon are the most important hormones regulating hepatic gluconeogenesis
. They demonstrated antagonistic effects on blood glucose levels. Under fasting or feeding, the blood circulating levels of the two hormones will change, subsequently affecting the expression of gluconeogenetic genes.
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 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 are the three key regulatory enzymes in 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.
What hormones inhibit the citric acid cycle?
- insulin activates TCA cycle.
- glucagon inactivates TCA cycle.
Why citric acid cycle is called TCA cycle?
Citric acid is a so-called tricarboxylic acid, containing three carboxyl groups (COOH)
. Hence the Krebs cycle is sometimes referred to as the tricarboxylic acid (TCA) cycle.
What are the key features of the citric acid cycle?
Key Points
The eight steps of the citric acid cycle are
a series of redox, dehydration, hydration, and decarboxylation reactions
. Each turn of the cycle forms one GTP or ATP as well as three NADH molecules and one FADH2 molecule, which will be used in further steps of cellular respiration to produce ATP for the cell.
What is the role of citric acid cycle Class 11?
(i)
It explains the process of breaking of pyruvate into CO
2
and water
. It is major pathway of generation of ATP. (ii) More energy is released (24 ATP) in this process, as compared to glycolysis.
What are the key control points within the citric acid cycle quizlet?
- citrate synthase. ATP and NADH (products) function as allosteric inhibitors; citrate and succinyl-CoA are allosteric inhibitors too.
- isocitrate dehydrogenase. …
- α-ketoglutarate dehydrogenase complex. …
- What enzyme catalyzes the rate-limiting step of the citric acid cycle. …
- products of the Citric Acid Cycle.
How does citrate become isocitrate?
Citrate is then converted into isocitrate
by the enzyme aconitase
. This is accomplished by the removal and addition of water to yield an isomer. Isocitrate is converted into alpha-ketogluterate by isocitrate dehydrogenase. The byproducts of which are NADH and CO
2
.
Why does the citric acid cycle operate under aerobic conditions?
This is considered an aerobic pathway because
the NADH and FADH2 produced must transfer their electrons to the next pathway in the system, which will use oxygen
. If this transfer does not occur, the oxidation steps of the citric acid cycle also do not occur.
How does glucagon regulate gluconeogenesis?
It is known that glucagon reduces lipogenesis by multiple mechanisms. For instance,
by increasing gluconeogenesis and decreasing glycolysis, glucagon inhibits lipogenesis by decreasing 3-carbon substrates available for fatty acid synthesis
(85).
How is glycogenolysis regulated?
Glycogenolysis is regulated
hormonally in response to blood sugar levels by glucagon and insulin, and stimulated by epinephrine during the fight-or-flight response
. Insulin potently inhibits glycogenolysis. In myocytes, glycogen degradation may also be stimulated by neural signals.
How does insulin regulate gluconeogenesis?
Insulin exerts direct control of gluconeogenesis
by acting on the liver
, but also indirectly affects gluconeogenesis by acting on other tissues. The direct effect of insulin was demonstrated in fasted dogs, where portal plasma insulin suppressed hepatic glucose production.
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.
Why must glycolysis be regulated?
Because glycolytic intermediates feed into several other pathways, the regulation of glycolysis occurs at more than one point. This
allows the regulation of several pathways to be coordinated
. For example, dihydroxyacetone phosphate is the precursor to the glycerol component of lipids.
How is cellular respiration regulated?
Cellular respiration is controlled by a variety of means. The entry of glucose into a cell is controlled by the transport proteins that aid glucose passage through the cell membrane. Most of the control of the respiration processes is accomplished
through the control of specific enzymes in the pathways
.
