NEET MDS Shorts
46890
Biochemistryâ-oxidation of fatty acid occursin Mitochondria
62959
BiochemistryTyrosine is Aromatic amino acid
18233
BiochemistryMethionine is sulphur containing AminoAcid
41039
Biochemistry
The rate limiting step in cholesterol synthesis is HMG CoA reductase. Here's
a detailed explanation:
Cholesterol synthesis is a complex process that involves multiple enzymatic
steps. This process begins with the condensation of acetyl-CoA molecules to form
acetoacetyl-CoA, which is then converted into HMG CoA
(3-hydroxy-3-methylglutaryl-CoA) by the enzyme HMG CoA synthetase. HMG CoA is
further converted to mevalonate by the action of HMG CoA reductase. This
reaction is the rate limiting step of the cholesterol synthesis pathway. The
rate limiting step is the slowest step in a metabolic pathway and is responsible
for controlling the overall rate of the process.
HMG CoA reductase is a critical regulatory enzyme that is tightly controlled
because it is the first committed step in the synthesis of cholesterol from
acetate. This enzyme is responsible for reducing HMG CoA to mevalonate, which is
the precursor of all isoprenoids, including cholesterol, steroids, and other
important biological molecules. The rate limiting nature of this step is due to
the fact that HMG CoA reductase is subject to both allosteric regulation and
feedback inhibition.
Allosteric regulation involves the binding of regulatory molecules, such as ATP,
citrate, and NADH, which can either activate or inhibit the enzyme. For example,
when cellular ATP levels are high, the enzyme is inhibited, which reduces
cholesterol synthesis. Conversely, when ATP levels are low, the enzyme is
activated, leading to increased cholesterol production. Citrate, a molecule
derived from the citric acid cycle, inhibits HMG CoA reductase when it builds up
in the cytosol, indicating that the cell has enough energy and does not need to
synthesize additional cholesterol.
Feedback inhibition occurs when the end product of the pathway, cholesterol,
binds to the enzyme and reduces its activity. This is a form of negative
feedback regulation that helps to maintain homeostasis of cholesterol levels
within the cell. When cellular cholesterol levels are high, the enzyme is
inhibited, which slows down the synthesis of new cholesterol molecules.
Conversely, when cholesterol levels are low, the enzyme is less inhibited, and
the synthesis rate increases.
The other enzymes listed, HMG CoA synthetase and mevalonate synthetase, are
involved in the synthesis of HMG CoA and the subsequent transformation of
mevalonate, but they are not the rate limiting steps. HMG CoA lyase, on the
other hand, is part of an alternative pathway that breaks down HMG CoA into
acetyl-CoA and acetoacetate. This enzyme is not directly involved in the rate
limiting step of cholesterol synthesis.
57919
BiochemistryThe formation of oxyhemoglobin is influenced by 1. pH 2. CO2 concentration 3. Temperature
41719
BiochemistryVitamin C deficiency is due to defect of Lysyl hydroxylase
32382
BiochemistryThe rate limiting step in glycolysis is catalyzed by Phosphofructokinase
93915
Biochemistry
The enzyme phosphatidate phosphatase converts phosphatidic acid to diacylglycerol during synthesis of triacylglycerides. The function of adipose tissue is the storage of fatty acids as triacylglycerols in times of plenty and the release of fatty acids during times of fasting or starvation. Fatty acids taken in by adipocytes are stored by esterification to glycerol-3-phosphate. Glycerol-3-phosphate is derived almost entirely from the glycolytic intermediate dihydroxyacetone phosphate through the action of glycerol-3-phosphate dehydrogenase. Glycolytic enzymes are active in adipocytes during triglyceride synthesis, but those of glycogen degradation (low levels in adipocytes) and gluconeogenesis (ie, glucose-6-phosphatase) are not. Glycerol kinase is not present to any great extent in adipocytes, so that glycerol freed during lipolysis is not used to reesterify the fatty acids being released. The enzyme triacylglyceride lipase is turned on by phosphorylation by a cyclic AMP-dependent protein kinase following epinephrine stimulation.
30496
BiochemistryGlycine is a Glycogenic amino acid, only
67413
BiochemistryEpinephrine causes increased blood glucose level due to: 1. Increased glycogenolysis in liver and muscle 2. Activation of phosphorylase 3. Inhibition of glycogen synthesis in liver