NEET MDS Shorts
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.
34849
BiochemistryIodine is a characteristic component of Thyroxine
87780
BiochemistryThe concentration of ketones is increased in body due to: 1. Starvation 2. High fat diet 3. Diabetes mellitus
83114
Biochemistry
Saturated fatty acids are a type of fat that has a chemical structure with a
single bond between each carbon atom in the fatty acid chain and no double
bonds. These types of fats are typically solid at room temperature. Out of the
given options, stearic acid (C18:0) is the only saturated fatty acid. The others
are:
1. Oleic acid (C18:1) is a monounsaturated fatty acid, which means it has one
double bond. It is commonly found in olive oil, canola oil, and avocados.
2. Linolenic acid (C18:3) is a polyunsaturated fatty acid, specifically an
omega-3 fatty acid, with three double bonds. It is found in plant sources like
flaxseeds, chia seeds, and walnuts.
3. Arachidonic acid (C20:4) is also a polyunsaturated fatty acid, an omega-6
fatty acid with four double bonds. It is found in animal fats, such as meat, and
in smaller amounts in some plant oils like sunflower oil and peanut oil.
Stearic acid, on the other hand, is a common saturated fatty acid found in
various animal fats and certain vegetable oils like coconut oil, palm kernel
oil, and cocoa butter. It is known for its role in the structure of cell
membranes and as a precursor for the biosynthesis of cholesterol in the body.
While it is important to consume fatty acids for good health, excessive
consumption of saturated fatty acids has been associated with higher levels of
LDL (low-density lipoprotein) cholesterol, which is often referred to as "bad"
cholesterol, and an increased risk of heart disease. However, it is important to
maintain a balanced diet that includes both saturated and unsaturated fatty
acids in moderation.
46890
Biochemistryâ-oxidation of fatty acid occursin Mitochondria
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BiochemistryGlycine is a Glycogenic amino acid, only
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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
64826
BiochemistryProthrombin production in the liver is dependent upon Vitamin K intake
17077
BiochemistryEnamel most likely effected by deficiency of vitamin A
32382
BiochemistryThe rate limiting step in glycolysis is catalyzed by Phosphofructokinase