Read More
Date: 11-12-2019
6776
Date: 16-12-2019
1814
Date: 11-4-2017
1684
|
The Amino Acid Residues in Proteins Are L Stereoisomers
Nearly all biological compounds with a chiral center occur naturally in only one stereoisomeric form, either D or L. The amino acid residues in protein molecules are exclusively L stereoisomers. D-Amino acid residues have been found only in a few, generally small peptides, including some peptides of bacterial cell walls and certain peptide antibiotics. It is remarkable that virtually all amino acid residues in proteins are L stereoisomers. When chiral compounds are formed by ordinary chemical reactions, the result is a racemic mixture of D and L isomers, which are difficult for a chemist to distinguish and separate. But to a living system, D and L isomers are as different as the right hand and the left. The formation of stable, repeating substructures in proteins generally requires that their constituent amino acids be of one stereochemical series. Cells are able to specifically synthesize the L isomers of amino acids because the active sites of enzymes are asymmetric, causing the reactions they catalyze to be stereospecific.
|
|
إجراء أول اختبار لدواء "ثوري" يتصدى لعدة أنواع من السرطان
|
|
|
|
|
دراسة تكشف "سببا غريبا" يعيق نمو الطيور
|
|
|
|
قسم الشؤون الفكرية يقيم برنامج (صنّاع المحتوى الهادف) لوفدٍ من محافظة ذي قار
|
|
الهيأة العليا لإحياء التراث تنظّم ورشة عن تحقيق المخطوطات الناقصة
|
|
قسم شؤون المعارف يقيم ندوة علمية حول دور الجنوب في حركة الجهاد ضد الإنكليز
|
|
وفد جامعة الكفيل يزور دار المسنين في النجف الأشرف
|