2024年9月26日 星期四

憋屎冠軍:艾氏樹蛙蝌蚪的超凡脫俗

 

圖片來源:維基百科

生活在樹洞或竹筒中的艾氏/台灣樹蛙,因為環境極小,竟然練就了一身「憋屎」的本事!憋多久呢?來看看

2024年9月24日 星期二

灰雁的擇偶指南:尋找你的『膽』中注定

 

灰雁。圖片來源:維基百科

擇偶的標準是什麼呢?過去的研究,有些說要身強體壯,有些說要個性相投。

我們來看看最近這個灰雁的研究!

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2024年9月18日 星期三

我們的「魔法子彈」是否成了水槍?

 

抗生素耐受性測試。圖片取自維基百科

三十多年前我在醫院實習時,時不時的就會看到上圖右那樣的細菌測試結果。

那意味著,那隻細菌是抗藥菌。

通常,我們就會盡量挑選可用的抗生素來用,而醫師有時甚至得開立多種抗生素給被這樣的細菌感染的病患。

最近發表在《柳葉刀》的研究報告發現,我們跟細菌的戰爭,似乎,正在節節敗退。

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2024年9月13日 星期五

Selenocysteine

 

Source: Wikipedia

Selenocysteine is a structure formed when the sulfur in cysteine is replaced by selenium. As a result of this substitution, selenocysteine has a lower reduction potential than cysteine and is more suitable as an antioxidant. Selenocysteine is a crucial amino acid in the composition of selenoproteins, which are found in both prokaryotes and eukaryotes. Consequently, selenocysteine is now considered one of the basic amino acids that make up proteins. In other words, proteins are no longer composed of just 20 amino acids, but 21!

A well-known selenoprotein is glutathione peroxidase, which is responsible for reducing hydrogen peroxide (H2O2) to water. Although selenocysteine is a basic amino acid in protein composition, unlike the other twenty amino acids, it doesn't have its own genetic codon. Instead, it uses UGA (a stop codon) along with a roughly sixty-base "selenocysteine insertion sequence" (SECIS element) as a signal for inserting selenocysteine. In prokaryotes, the SECIS element is located close to the UGA codon. In archaea and eukaryotes, the SECIS element is often found in the 3' untranslated region (3'-UTR) of the messenger RNA (mRNA).

Source: Wikipedia


When selenium is absent, the translation of selenoproteins stops at the UGA codon, resulting in incomplete, non-functional proteins. Only when selenium is present can complete proteins be produced. Selenocysteine was discovered in 1976 by Thressa Stadtman of the National Institutes of Health (NIH). She and her husband were the first married couple at NIH, each with their own laboratory, and the two labs also collaborated.

For the origin of cysteine, please refer to "Cysteine and Bladder." The "seleno-" in selenocysteine obviously comes from selenium, though "seleno-" is not a prefix. However, due to its association with selenoproteins, it seems to have been widely adopted.

References:

pyrrolysine: the 22nd standard amino acid???

 

Source: Wikipedia

The world is constantly changing, altering our understanding from past textbooks. The nine planets became eight, twelve pairs of cranial nerves are now thirteen, and the discovery of selenocysteine increased the standard protein amino acids from twenty to twenty-one. However, the discovery of pyrrolysine in archaea and some bacteria in 2002 once again challenged the composition of standard protein amino acids. Some scientists argue that pyrrolysine should be considered the twenty-second amino acid, while others disagree; after all, only methane-producing archaea and some bacteria (including E. coli) use pyrrolysine.

In 2002, scientists discovered pyrrolysine at the active site of methyltransferase in Methanosarcina barkeri. Later, pyrrolysine was found in many methyltransferases; its function in enzymes may be to help adjust the position of methyl groups for reaction with cofactors. Unlike hydroxyproline, pyrrolysine has a genetic code, UAG. Readers might exclaim: Wait! Isn't UAG one of the stop codons? Yes, it is. However, like selenocysteine using UGA, pyrrolysine's use of UAG requires special equipment.

Microorganisms capable of using pyrrolysine carry a special transfer RNA (tRNA) that bears pyrrolysine and has an anticodon to recognize UAG. Moreover, this unique tRNA has its own dedicated aminoacyl-tRNA synthetase (aaRS) responsible for attaching pyrrolysine. Pyrrolysine is synthesized from two lysines and, due to its pyrrolidine structure (see proline), it has the prefix "pyrro-" in its name.

The microbial world is fascinating, and the microorganisms we can cultivate in laboratories likely represent only a small fraction of all microbes. Perhaps in the future, with a better understanding of microorganisms and deep-sea life, we might discover more unique amino acids, and the list of standard protein amino acids may grow even longer!

References:

Wikipedia. Pyrrolysine.

Srinivasan, G; James, C. M.; Krzycki, J. A. 2002. Pyrrolysine encoded by UAG in Archaea: charging of a UAG-decoding specialized tRNA. Science. 296 (5572): 1459–1462. doi:10.1126/science.1069588

停經大騷動:科學家發現讓卵巢「提早下班」的基因密碼

 

卵巢。圖片來源:維基百科

我不知道大家有沒有聽過一種說法:晚停經會比較長壽。

我第一次聽到這個說法,是一位中醫師告訴我的。當時我覺得:真的嗎?

最近的研究發現,提早停經會不會長壽不知道,但是可能會有一些其他的影響喔!

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2024年9月3日 星期二

菌從口入:我們的食物微生物體

 

圖片來源:Cell

如果你看過「我們只有10%是人類」這本書,你可能會想到,其他的生物呢?

事實上,可能所有的生物都有一部分是微生物。所以,當我們吃東西時,我們也會吃下一些食物本身的微生物,尤其是發酵食品,更是微生物滿滿!

這些微生物,會不會影響我們?最近的一個大型研究,帶著我們去看這些現象!

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