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.
38424
EndodonticsThe most common consequence of vital tooth bleaching is apical periodontitis. This occurs due to: 1) Penetration of bleaching agents through enamel and dentin tubules to the pulp, 2) Chemical irritation of pulp tissue leading to inflammation, 3) Potential pulp necrosis in severe cases, 4) Subsequent periapical inflammation. This risk is higher with stronger concentrations and longer exposure times. Proper isolation and controlled application help minimize this risk.
89184
Oral SurgeryLongest acting local anaesthetic is Bupivacaine.
19090
Physiology
The primary mechanism of H+ secretion by parietal cells is through the action of the H+-K+ ATPase pump, also known as the proton pump. This enzyme is responsible for actively transporting H+ ions into the gastric lumen while moving K+ ions into the cells, thereby acidifying the gastric content.
66346
Orthodontics
SOLUTION Elgiloy (Cobalt-Chromium) alloy is supplied in a softer state and can be heat hardened.
After hardening heat treatment, the softest elgiloy becomes equivalent to regular stainless steel.
25695
NEETMDS
Subgingival plaque attached to the epithelium is particularly harmful because it is in direct contact with the junctional epithelium, allowing the release of bacterial toxins and enzymes that directly trigger the host/s immune response, leading to significant inflammation, connective tissue destruction, and ultimately bone loss.
48452
RadiologyThe technique employed in radiotherapy to counteract the effect of tumour motion due to breathing is known as gating.
39685
NEETMDS
N-butyl cyanoacrylate is a type of medical adhesive (surgical glue) used to close wounds and incisions by holding the edges of the skin together (skin apposition) without the need for stitches.
77265
Oral Medicine
The aortic valve is located between the left ventricle and the aorta and is responsible for preventing the backflow of blood into the left ventricle during systole, ensuring that blood is efficiently pumped out of the heart into the systemic circulation.
87121
General Microbiology
The typical clinical features of typhoid fever can be listed as follows:
1. High fever, bradycardia, and a palpable spleen: Typhoid fever is
characterized by a sustained high fever, often reaching 103°F to 104°F (39°C to
40°C). Bradycardia, or a slower than normal heart rate, occurs in some cases.
The spleen may also become enlarged and palpable due to the infection.
2. Rash, joint pain, and respiratory symptoms: Some patients may develop a rash
known as "Rose spots," which are small, red spots on the abdomen and chest.
Joint pain can occur, and respiratory symptoms may include a dry cough.
3. Diarrhea, abdominal cramps, and vomiting: Diarrhea and severe abdominal
cramps are common in the early stages of typhoid fever, which can lead to
significant dehydration and discomfort for the patient.
4. Headache, photophobia, and neck stiffness: Headaches and sensitivity to light
(photophobia) are often present, and in severe cases, neck stiffness can occur
due to inflammation of the meninges, known as meningitis.