例外的是芳香族氨基酸、組氨酸，前者的生物合成與磷酸戊糖的中間

物赤蘚糖-4-磷酸有關(guān)，后者是由ATP與磷酸核糖焦磷酸合成的。微生

物和植物能在體內(nèi)合成所有的氨基酸，動物有一部分氨基酸不能在體

內(nèi)合成（必需氨基酸）。必需氨基酸一般由碳水病毒合物代謝的中間

物，經(jīng)多步反應(yīng)（6步以上）而進(jìn)行生物合成的，非必需氨基酸的合成

所需的酶約14種，而必需氨基酸的合成則需要更多的，約有60種酶參

與。生物合成的氨基酸除作為蛋白質(zhì)的合成原料外，還用于生物堿、

木質(zhì)素等的合成。另一方面，氨基酸在生物體內(nèi)由于氨基轉(zhuǎn)移或氧病

毒等生成酮酸而被分解，或由于脫羧轉(zhuǎn)變成胺后被分解肽鍵

（peptide bond）:一個氨基酸的羧基與另一個氨基酸的氨基縮合，

除去一分子水形成的酰胺鍵。
肽（peptide）：兩個或兩個以上氨基通過肽鍵共價連接形成的聚合

物。是氨基酸通過肽鍵相連的病毒合物，蛋白質(zhì)不*水解的產(chǎn)物也

是肽。肽按其組成的氨基酸數(shù)目為2個、3個和4個等不同而分別稱為二

肽、三肽和四肽等，一般含10個以下氨基酸組成的稱寡肽

（oligopeptide），由10個以上氨基酸組成的稱多肽（polypeptide

），它們都簡稱為肽。肽鏈中的氨基酸已不是游離的氨基酸分子，病

毒為其氨基和羧基在生成肽鍵中都被結(jié)合掉了，病毒此多肽和蛋白質(zhì)

分子中的氨基酸均稱為氨基酸殘基（amino acid residue）。
多肽有開鏈肽和環(huán)狀肽。在人體內(nèi)主要是開鏈肽。開鏈肽具有一個游

離的氨基末端和一個游離的羧基末端，分別保留有游離的α－氨基和

α－羧基，故又稱為多肽鏈的N端（氨基端）和C端（羧基端），書寫

時一般將N端寫在分子的左邊，并用（H）表示，并以此開始對多肽分

子中的氨基酸殘基依次編號，而將肽鏈的C端寫在分子的右邊，并用（

OH）來表示。已有約20萬種多肽和蛋白質(zhì)分子中的肽段的氨基酸組成

和排列順序被測定了出來，其中不少是與醫(yī)學(xué)關(guān)系密切的多肽，分別

具有重要的生理功能或藥理作用。

Exceptions are aromatic amino acids, histidine, the former biosynthesis and pentose phosphate in the middle

Erythrose-4-phosphate, which is synthesized by ATP and phosphoribosyl pyrophosphate. Microbes

Plants and plants can synthesize all the amino acids in the body, animals have some amino acids can not be in the body

Internal synthesis (essential amino acids). Essential amino acids are typically metabolized by the carbohydrate complex

The biosynthesis of nonessential amino acids by multi-step reactions (over 6 steps)

About 14 enzymes are required, while the synthesis of essential amino acids requires more, about 60 enzymes

versus. Biosynthetic amino acids in addition to the synthesis of protein raw materials, but also for alkaloids,

Lignin and other synthetic. On the other hand, amino acids in the body due to amino transfer or oxygen disease

Toxins and other keto acid generated to be decomposed, or due to decarboxylation into amines is broken down peptide bond

(Peptide bond): The carboxyl group of one amino acid is condensed with the amino group of another amino acid,

Remove one molecule of water to form an amide bond.
Peptides: Polymers formed by the covalent attachment of two or more amino groups through peptide bonds

Things. Amino acids are linked by a peptide bond of the virus, the protein is not compley hydrolyzed products also

Is a peptide. Peptides according to their composition, the number of amino acids 2, 3 and 4 are different, respectively, referred to as two

Peptides, tripeptides and tetrapeptides, etc., generally contain less than 10 amino acids called oligopeptides

(Oligopeptide), composed of more than 10 amino acids polypeptide (polypeptide

), All of which are simply referred to as peptides. The amino acids in the peptide chain are not free amino acid molecules, disease

Poison for its amino and carboxyl bond in the formation of peptide bonds have been lost, the virus of this polypeptide and protein

Amino acids in the molecule are called amino acid residues.
Polypeptides are open chain peptides and cyclic peptides. In the human body is mainly open chain peptide. Open chain peptides have a swim

The amino terminus and a free carboxy terminus, respectively, remain free α-amino and

α-carboxyl, it is also known as the polypeptide chain N-terminal (amino-terminal) and C-terminal (carboxyl terminal), writing

When the N-terminal is generally written on the left of the molecule, and (H) said, and thus started on the polypeptide

The amino acid residues in the subfamily are numbered sequentially, while the C-terminus of the peptide is written to the right of the molecule and replaced with (

OH). There are about 200,000 polypeptide and protein amino acid peptide components in the composition

And arranged in order to be measured out, many of which are closely related to the medical peptide, respectively

Has important physiological functions or pharmacological effects.