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NEET MDS Shorts

19023
Biochemistry

The eye change include an increase in blood vessels and inflammation of the conjunctivae, cornea is invaded by capillaries, producing opaque areas and even ulceration. Dermatitis characterized by a greasy and scaly reddened lesion develops on the skin around the nasolabial folds and may extend to a butterfly shape on the cheeks. There many also be lesions at the corners (canthi) of the eyes and lobes of the mouth.

53785
Biochemistry

The principal role of Vitamin E in the prevention of oxidative damage is to potentiate the action of superoxide dismutase

18233
Biochemistry

Methionine is sulphur containing AminoAcid

17726
Biochemistry

The correct sulfur-containing amino acid among the options provided is:

1. Cystine

Explanation:

Amino acids are the building blocks of proteins, and they are characterized by the presence of an amino group (-NH2) and a carboxyl group (-COOH). Some amino acids also contain a side chain that is unique to each amino acid and determines its chemical properties. Sulfur is an important element in the structure and function of certain amino acids.

Cystine is a sulfur-containing amino acid, which is formed by the oxidation of two cysteine molecules. Cysteine is the amino acid that contains a sulfur atom in its side chain as a thiol group (-SH). When two cysteine residues are adjacent in a polypeptide chain and the thiol groups react with each other, they form a disulfide bond (-S-S-), resulting in the formation of cystine. This disulfide bond is crucial for the tertiary structure of proteins, contributing to their stability and function, particularly in the context of protein folding and maintaining the integrity of protein domains.

The other options listed are not sulfur-containing amino acids:

2. Proline is an imino acid, meaning it contains an -NH group instead of an -NH2 group. Its side chain is a cyclic secondary amine and does not contain sulfur.
3. Arginine is a basic amino acid with a guanidino group in its side chain, which is composed of nitrogen, carbon, and hydrogen atoms but no sulfur.
4. Isoleucine is a branched-chain amino acid, with a methyl group and an isobutyl group on its side chain. It is a hydrophobic amino acid and does not contain sulfur.

36542
Biochemistry

Uric acid is a purine derivative, increased by purine salvage reactions that convert purines, purine ribonucleosides, and purine deoxyribonucleoside to mononucleotides (incorrect answer 4).
 
Such salvage reactions require much less energy than de novo synthesis (incorrect answers 1, 2). The liver is the major site of purine nucleotide biosynthesis and provides excess purines for other tissues that cannot synthesize purines. 

A defect in hypoxanthine-guanine phosphoribosyl transferase, one of the enzymes of purine salvage, is responsible for purine overproduction and subsequent hyperuricemia observed in Lesch-Nyhan syndrome.

38738
Biochemistry

Glutamate-pyruvate trans-aminase is predominantly present In Liver

40041
Biochemistry

The reaction used for estimating free amino, groups in proteins is Deamination with HNO2

82127
Biochemistry

Following digestion, the products of digestion enter the bloodstream.
These include glucose, amino acids, triacylglycerides packaged into chylomicrons from the intestine, and very low density lipoproteins from the liver.
The hormone of anabolism, insulin, is also elevated because of the signaling of the glucose and amino acids in the blood, which allows release of insulin from the β-cells of the pancreas. Insulin aids the movement of glucose and amino acids into cells. In contrast, all the hormones and energy sources associated with catabolism are decreased in the blood during this time. Long-chain fatty acids and glycerol released by lipolysis from adipocytes are not elevated. Glucagon and epinephrine are not released. The only time glucose levels rise significantly above approximately 80 mM is following a well-balanced meal when glucose is obtained from the diet. The concentration of glucose reaches a peak 30 to 45 minutes after a meal and returns to normal within 2 hours after eating. This response of blood glucose after eating (mimicked by giving 50 g of oral glucose) is the basis for the glucose tolerance test. In the event of insulin deficiency (diabetes mellitus), the peak glucose concentration is abnormally high and its return to normal is delayed.

30496
Biochemistry

Glycine is a Glycogenic amino acid, only

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.

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