Proteinogenic amino acids are amino acids that are incorporated biosynthetically into proteins during translation. The word "proteinogenic" means "protein creating". Throughout known life, there are 22 genetically encoded (proteinogenic) amino acids, 20 in the standard genetic code and an additional 2 (selenocysteine and pyrrolysine) that can be incorporated by special translation mechanisms.In contrast, non-proteinogenic amino acids are amino acids that are either not incorporated into proteins (like GABA, L-DOPA, or triiodothyronine), misincorporated in place of a genetically encoded amino acid, or not produced directly and in isolation by standard cellular machinery (like hydroxyproline). The latter often results from post-translational modification of proteins. Some non-proteinogenic amino acids are incorporated into nonribosomal peptides which are synthesized by non-ribosomal peptide synthetases. Both eukaryotes and prokaryotes can incorporate selenocysteine into their proteins via a nucleotide sequence known as a SECIS element, which directs the cell to translate a nearby UGA codon as selenocysteine (UGA is normally a stop codon). In some...

Methods for alignment of protein sequences typically measure similarity by using a substitution matrix with scores for all possible exchanges of one amino acid with another. The most widely used matrices are based on the Dayhoff model of evolutionary rates. Using a different approach, we have derived substitution matrices from about 2000 blocks of aligned sequence segments characterizing more than 500 groups of related proteins. This led to marked improvements in alignments and in searches using queries from each of the groups.

A nutrient is either a chemical element or compound used in an organism's metabolism or physiology. A nutrient is essential to an organism if it cannot be produced by the organism and must be obtained from a food source. This article deals with nutrition in animals, especially humans. Nutrition in plants, fungi, bacteria and archaea is not discussed here. Substances that provide energy Carbohydrates are compounds made of sugars. Carbohydrates are named by the number of sugar units they have. Monosaccharides (such as glucose and fructose) have one. Disaccharides (such as sucrose and lactose) have two. Oligosaccharides, and polysaccharides (such as starch, glycogen, and cellulose) have more. Proteins are organic compounds that are amino acids joined by peptide bonds. The body cannot make some of these; so they must come from food. In the body, proteins are broken down through digestion back into free amino acids. Fats are a glycerin molecule with three fatty acids attached. Fats are needed to keep cell membranes functioning...

Ang pag-ikot ng asido sitriko (na tinatawag ding gulong asido tricarboksiliko, ang TCA cycle, o gulong Krebs, citric acid cycle) ay isang serye ng pagsasanib kimika ng may napakahalagang papel sa lahat ng selulang may buhay na gumagamit ng oksihena bilang bahagi ng respirasyong selular. Sa mga organismong aerobiko, ang gulong ng asido sitriko ay bahagi ng landasing metaboliko na kasangkot sa kimikang paggawa ng tubig at carbon dioxide mula carbohydrates, lipidos at protina, at makagawa ng isang porma ng materyang magagamit na lakas. Ito ang ikalawa sa tatlong landasing metaboliko sa loob ng katabolismong molekula panglakas at sa paggawa ng ATP. Ang ibang pang landasin ay ang glikolisis at posporilasyong oksidatibo (oxidative phosphorylation). Ang pag-ikot ng asido sitriko ay nagdudulot rin ng simuno sa maraming mga kompuwesto tulad ng mga asido amino at ang ilang pagsasanib nito ay mahalaga rin sa mga selulang gumaganap sa pangangasim (permentasyon). Mga panlabas na link The chemical logic behind the Krebs cycle Naka-arkibo 2006-09-25 sa Wayback Machine.

Virutubishi (kutoka neno "rutuba") ni sehemu ya vyakula ambavyo viumbehai huishi na kukua. Virutubishi hutoa nishati kwa wingi kwa viumbe hai wanaohitaji kwa kufanya kazi. Virutubisho huwapa ufadhili muhimu wa kimetaboli. Aina zote za virutubisho zinaweza kupatikana kutoka kwenye mazingira. Virutubisho hutumiwa kujenga na kutengeneza tishu na kudhibiti michakato ya mwili wakati virutubisho vinabadilika, na kutumika kwa nishati. Mbinu za ulaji wa virutubisho ni tofauti kwa mimea na wanyama. Mimea hupata virutubisho moja kwa moja kutoka kwenye udongo kupitia mizizi na majani yake. Wanyama wana mifumo maalum ya kupungua ambayo hufanya kazi ya kuvunja virutubisho kwa nishati na kwa kutumia virutubisho kwa umetaboli na anabolizimu (awali ya kujenga) katika mwili. Vidonge vya kimwili vinajumuisha, mafuta, protini (au vitalu vya ujenzi, amino asidi), na vitamini. Mchanganyiko wa kemikali kama vile madini ya chakula, maji (H2O), na oksijeni pia inaweza kuchukuliwa kuwa virutubisho. Virutubisho inachukuliwa kuwa muhimu kama inapaswa kupatikana kutokana na chanzo cha nje au kwa sababu viumbe hawawezi kuifanya au kwa sababu hakuna...