NEET MDS Shorts
74255
Dental Materials
Epoxy resins
· Abrasion resistance is many times greater than gypsum
· More expensive
· Undergoes 0.1 – 0.2% shrinkage, thus their shrinkage is approximately equal to gypsum. This is less of problem with newer formulations & polyurethane resin.
· Their detail reproduction is better.
· Hydrocolloids, polysulfides are not compatible with them.
85647
PeriodonticsBone graft procedures are most successful in treating narrow three-wall defects.
62442
Oral SurgeryPerform Caldwell-Luc to remove the tip: The Caldwell-Luc procedure (or a modified, less invasive version) has long been considered the standard surgical method for retrieving a displaced root or foreign body from the maxillary sinus, especially when it is mobile within the sinus cavity or the condition has become chronic. It involves creating a small bone window in the anterior wall of the maxillary sinus to access and remove the fragment.
61767
General MicrobiologyDiphtheria bacilli that ferment glycogen and starch are classified as Mitis.
33215
Oral Medicine
Nephrotic syndrome is associated with hyperlipidemia, particularly increased levels of LDL and cholesterol. The underlying mechanism involves the loss of albumin in the urine, which leads to hypoalbuminemia. This causes an increased synthesis of very low-density lipoproteins (VLDL) by the liver to compensate for the loss of oncotic pressure. Additionally, the loss of proteins that normally bind to cholesterol in the blood, such as lipoproteins, results in decreased clearance of LDL.
56692
RadiologyExplanation: In a Coolidge tube, the cathode is typically made of molybdenum, which has a high melting point and is effective for electron emission. The anode is usually made of copper, which has excellent thermal conductivity, allowing it to dissipate heat generated during x-ray production effectively.
72029
Oral SurgeryThe scalpel blade most commonly used for oral surgical procedures is No. 15.
57914
PharmacologyDoxapram and nikethamide are both known as analeptic agents, which are central nervous system stimulants. Propylbutamide is a less common or potentially misspelled term, but doxacurium is a non-depolarizing neuromuscular blocking agent, not a stimulant. Therefore, doxacurium is the agent that is not an analeptic.
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.
28686
Oral PathologyTic douloureux, also known as trigeminal neuralgia, is a condition characterized by severe facial pain. It is associated with the trigeminal nerve (cranial nerve V), which is responsible for sensation in the face and motor functions such as biting and chewing.