{"id":2338,"date":"2026-09-01T18:34:14","date_gmt":"2026-09-01T18:34:14","guid":{"rendered":"https:\/\/www.jrebsen.dk\/?post_type=aktivitet&#038;p=2338"},"modified":"2026-09-01T18:35:09","modified_gmt":"2026-09-01T18:35:09","slug":"hvor-kommer-vitaminerne-oprindeligt-fra","status":"publish","type":"aktivitet","link":"https:\/\/www.jrebsen.dk\/?aktivitet=hvor-kommer-vitaminerne-oprindeligt-fra","title":{"rendered":"Hvor kommer vitaminerne oprindeligt fra?"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">I naturen dannes <strong>vitaminer ikke for at v\u00e6re vitaminer for os<\/strong>. De er molekyler, som planter, svampe og mikroorganismer producerer til deres eget stofskifte. For os bliver de til <em>vitaminer<\/em>, fordi vi under evolutionen har mistet evnen til at fremstille nogle af dem, men stadig har brug for dem.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">De fleste vitaminer dannes biologisk af:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>planter<\/strong><\/li>\n\n\n\n<li><strong>bakterier<\/strong><\/li>\n\n\n\n<li><strong>svampe<\/strong><\/li>\n\n\n\n<li>i nogle tilf\u00e6lde dyr<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">De bygges ud fra almindelige metaboliske mellemprodukter fra fx:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>glucose \u2192 glykolyse \u2192 pyruvat \u2192 acetyl-CoA \u2192 forskellige biosynteseveje<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">samt fra aminosyrer og andre sm\u00e5 organiske molekyler.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Der findes alts\u00e5 ikke \u00e9n f\u00e6lles &#8220;vitaminsyntese&#8221;. Hvert vitamin har sin egen biosyntesevej.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">2. Hvorfor laver organismer vitaminer?<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Hos den organisme, der producerer vitaminet, har stoffet typisk en helt almindelig funktion i stofskiftet.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Mange vitaminer eller deres aktive former fungerer som <strong>coenzymer<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det vil sige:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>enzym + coenzym \u2192 funktionelt enzymsystem<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Et enzym kan eksempelvis ikke flytte bestemte elektroner eller kemiske grupper alene. Vitamin-afledte molekyler fungerer som sm\u00e5 kemiske &#8220;v\u00e6rkt\u00f8jer&#8221;, der g\u00f8r dette muligt.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Derfor er vitaminer fundamentalt knyttet til cellernes stofskifte.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">3. B-vitaminerne \u2013 is\u00e6r produkter af mikroorganismer og planter<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">B-vitaminerne er gode eksempler.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">B1 \u2013 thiamin<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Thiamin fremstilles af:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>planter<\/li>\n\n\n\n<li>bakterier<\/li>\n\n\n\n<li>svampe<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">De producerende organismer bruger det selv til at danne <strong>thiaminpyrofosfat, TPP<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">TPP bruges af enzymer i oms\u00e6tningen af kulhydrater.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Eksempel:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>pyruvat \u2192 acetyl-CoA<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">kr\u00e6ver et enzymkompleks, hvor TPP spiller en central rolle.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">S\u00e5 planten laver ikke B1 &#8220;til os&#8221;. Den laver TPP for at kunne drive sit eget stofskifte.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">4. B2 \u2013 riboflavin<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Riboflavin produceres af blandt andet:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>planter<\/li>\n\n\n\n<li>svampe<\/li>\n\n\n\n<li>bakterier<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Det dannes gennem en r\u00e6kke reaktioner fra forbindelser fra det centrale stofskifte.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Riboflavin bruges til at danne:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>FMN og FAD<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Disse kan:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>modtage elektroner \u21c4 afgive elektroner<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">FAD er fx centralt i citronsyrecyklus og elektrontransport.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Derfor har B2 sin oprindelige funktion som en del af cellens <strong>redox- og energistofskifte<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">5. B3 \u2013 niacin<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Niacin kan dannes af mange organismer og kan blandt andet fremstilles ud fra aminosyren:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>tryptophan<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det bruges til dannelse af:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>NAD\u207a og NADP\u207a<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Disse er nogle af cellens vigtigste elektrontransport\u00f8rer:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>NAD\u207a + elektroner \u2192 NADH<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">De findes i n\u00e6sten alt levende stofskifte.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Mennesket kan faktisk selv danne noget niacin fra tryptophan, men ikke n\u00f8dvendigvis nok til hele behovet.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">6. B5 \u2013 pantothensyre<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Pantothensyre dannes is\u00e6r af:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>planter<\/li>\n\n\n\n<li>bakterier<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Det bliver en del af:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>coenzym A<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Coenzym A bruges til transport af kulstofgrupper.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det mest kendte eksempel er:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>acetyl-CoA<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Dermed befinder B5 sig lige i centrum af oms\u00e6tningen af:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>kulhydrat<\/li>\n\n\n\n<li>fedt<\/li>\n\n\n\n<li>aminosyrer<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">7. B6<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Vitamin B6 produceres af planter og mange mikroorganismer.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Den aktive form, <strong>pyridoxalfosfat<\/strong>, bruges is\u00e6r ved reaktioner med aminosyrer.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Fx:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>aminosyre A + ketosyre B \u21c4 ketosyre A + aminosyre B<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det g\u00f8r B6 vigtigt for organismens egen produktion og omdannelse af aminosyrer.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">8. B7 \u2013 biotin<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Biotin fremstilles af:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>planter<\/li>\n\n\n\n<li>bakterier<\/li>\n\n\n\n<li>visse svampe<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Biotin fungerer som en slags <strong>CO\u2082-b\u00e6rer<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Enzymer kan binde CO\u2082 til biotin og derefter overf\u00f8re den til et andet molekyle.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det bruges blandt andet ved:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>acetyl-CoA \u2192 fedtsyresyntese<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">S\u00e5 ogs\u00e5 her er vitaminets oprindelige funktion almindelig grundl\u00e6ggende biokemi.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">9. B9 \u2013 folat<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Planter og mikroorganismer kan selv fremstille folat.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Mennesket kan ikke.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Folat fungerer som transport\u00f8r af <strong>\u00e9n-kulstofgrupper<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det er blandt andet n\u00f8dvendigt for dannelsen af:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>puriner<\/li>\n\n\n\n<li>thymidin<\/li>\n\n\n\n<li>DNA<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Alle organismer, der deler celler, har derfor brug for dette kemiske system.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">10. B12 er det s\u00e6rligt interessante tilf\u00e6lde<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Vitamin B12 produceres i naturen kun af bestemte bakterier og ark\u00e6er.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Hverken:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>planter<\/li>\n\n\n\n<li>dyr<\/li>\n\n\n\n<li>svampe<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">kan bygge B12 fra bunden.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">B12 er et meget komplekst molekyle omkring et centralt:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Co\u00b2\u207a\/Co\u00b3\u207a \u2013 koboltatom<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Dets biosyntese kr\u00e6ver et stort antal enzymatiske trin.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Bakterierne bruger selv B12 som coenzym til forskellige kemiske omlejringer og stofskifteprocesser.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Hvorfor findes B12 s\u00e5 i k\u00f8d?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Ikke fordi koen fremstiller B12.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Mikroorganismer fremstiller det.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Hos dr\u00f8vtyggere lever B12-producerende mikroorganismer fx i ford\u00f8jelsessystemet. B12 kommer dermed ind i dyrets stofskifte og v\u00e6v.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Man kan meget forenklet se f\u00f8dek\u00e6den:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>bakterier \u2192 dyr \u2192 menneske<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det er derfor mere korrekt at sige, at B12 grundl\u00e6ggende er et <strong>mikrobielt produkt<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">11. Vitamin C \u2013 planter fremstiller selv ascorbat<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Planter fremstiller vitamin C, <strong>ascorbat<\/strong>, fra sukkerstoffer.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Meget forenklet:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>glucose \u2192 flere mellemprodukter \u2192 ascorbat<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For planten er ascorbat blandt andet en vigtig:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>antioxidant<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Fotosyntese indeb\u00e6rer intensiv elektrontransport og kan danne reaktive oxygenforbindelser.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Ascorbat hj\u00e6lper planten med at kontrollere disse.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det har ogs\u00e5 funktioner i:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>enzymreaktioner<\/li>\n\n\n\n<li>cellev\u00e6kst<\/li>\n\n\n\n<li>fotosyntese<\/li>\n\n\n\n<li>regulering af oxidativt stress<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">12. Det interessante ved mennesket og vitamin C<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">De fleste pattedyr kan faktisk <strong>selv fremstille vitamin C<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det sker blandt andet fra glucose.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Men mennesker og andre h\u00f8jere primater kan ikke.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Vi har stadig n\u00e6sten hele syntesevejen, men genet for enzymet:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>L-gulonolactonoxidase<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">er blevet inaktiveret gennem evolutionen.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Derfor stopper vores syntesevej f\u00f8r vitamin C.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det er et meget godt eksempel p\u00e5, hvad et vitamin egentlig er:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">Et stof kan v\u00e6re et vitamin for \u00e9n art, men ikke for en anden.<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">For en hund er vitamin C derfor normalt ikke et vitamin i ern\u00e6ringsm\u00e6ssig forstand, fordi hunden selv kan fremstille det.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For mennesket er det.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">13. Vitamin A kommer ofte oprindeligt fra planter<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Planter laver ikke n\u00f8dvendigvis retinol, som vi kalder vitamin A.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">De fremstiller blandt andet <strong>carotenoider<\/strong>, fx:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>\u03b2-caroten<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Carotenoider har flere funktioner i planten.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">De indg\u00e5r blandt andet i fotosynteseapparatet og beskytter det mod oxidativ skade.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">N\u00e5r vi spiser \u03b2-caroten, kan vi spalte det:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>\u03b2-caroten \u2192 retinal \u2192 retinol<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Dermed fremstiller kroppen vitamin A fra et plantestof.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">14. Vitamin D er anderledes<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Vitamin D kan mennesket selv fremstille.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Udgangspunktet er et kolesterolbesl\u00e6gtet molekyle i huden:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>7-dehydrocholesterol<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">UVB-lys rammer molekylet:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>7-dehydrocholesterol + UVB \u2192 previtamin D\u2083 \u2192 vitamin D\u2083<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Derefter sker yderligere omdannelse:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>hud<\/strong><br>\u2192 vitamin D\u2083<br>\u2193<br><strong>lever<\/strong><br>\u2192 25-hydroxy-vitamin D<br>\u2193<br><strong>nyre<\/strong><br>\u2192 aktivt calcitriol<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Den aktive form fungerer n\u00e6rmest som et <strong>steroidhormon<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Derfor er vitamin D p\u00e5 mange m\u00e5der mere et hormon end et klassisk vitamin.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">15. Vitamin E kommer hovedsageligt fra planter<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Vitamin E, tocopheroler, dannes is\u00e6r af:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>planter<\/li>\n\n\n\n<li>visse fotosyntetiske organismer<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Det findes blandt andet i plantecellernes membraner.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Her fungerer det som en <strong>fedtopl\u00f8selig antioxidant<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det beskytter is\u00e6r um\u00e6ttede fedtsyrer i membranerne mod k\u00e6dereaktioner med frie radikaler.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Vi overtager alts\u00e5 grundl\u00e6ggende den samme antioxidant, som planten selv bruger til at beskytte sine membraner.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">16. Vitamin K har to v\u00e6sentlige biologiske kilder<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Der findes flere K-vitaminer.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">K1 \u2013 phylloquinon<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Produceres is\u00e6r af planter.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det indg\u00e5r i plantens <strong>fotosyntetiske elektrontransport<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det har alts\u00e5 en helt anden prim\u00e6r funktion i planten end den funktion, vi bruger det til.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">K2 \u2013 menaquinoner<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Produceres af bakterier.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Hos bakterier fungerer menaquinon ogs\u00e5 som elektrontransport\u00f8r i energistofskiftet.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Hos mennesket bruger vi vitamin K til kemisk modificering af bestemte proteiner, blandt andet koagulationsproteiner.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">17. Samme molekyle \u2013 forskellig anvendelse<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Det er et vigtigt biologisk princip.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Et molekyle kan v\u00e6re udviklet og anvendt til \u00e9n funktion i \u00e9n organisme og f\u00e5 en anden funktion i en anden.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Eksempel:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Vitamin K1 i en plante<\/strong><br>\u2192 elektrontransport ved fotosyntese<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">men:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Vitamin K i mennesket<\/strong><br>\u2192 aktivering af koagulationsproteiner.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Molekylets kemiske egenskaber g\u00f8r begge funktioner mulige.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">18. Hvorfor har vi mistet evnen til at fremstille nogle vitaminer?<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Evolution\u00e6rt er der ingen fordel ved at opretholde en dyr biosyntesevej, hvis stoffet n\u00e6sten altid findes i f\u00f8den.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Hvis en forfader regelm\u00e6ssigt fik fx vitamin C gennem frugt, kunne en mutation, der \u00f8delagde vitamin-C-syntesen, v\u00e6re n\u00e6sten neutral.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Der var derfor ikke st\u00e6rk selektion mod mutationen.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Over tid kunne synteseevnen forsvinde.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det samme princip findes mange steder i evolutionen:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Hvis omgivelserne leverer stoffet stabilt \u2192 egen syntese kan blive overfl\u00f8dig \u2192 gener kan g\u00e5 tabt.<\/strong><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">19. Derfor er &#8220;vitamin&#8221; et menneskecentreret begreb<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Kemisk set findes der ikke en naturlig kategori af molekyler, der hedder vitaminer.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">De er vidt forskellige:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>steroider<\/li>\n\n\n\n<li>quinoner<\/li>\n\n\n\n<li>alkoholer<\/li>\n\n\n\n<li>organiske syrer<\/li>\n\n\n\n<li>komplekse ringstrukturer<\/li>\n\n\n\n<li>koboltholdige molekyler<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Det, der g\u00f8r dem til vitaminer, er relationen mellem <strong>molekylet og organismen<\/strong>:<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><strong>Organismen har brug for stoffet<\/strong><br>+<br><strong>kan ikke selv fremstille tilstr\u00e6kkeligt<\/strong><br>+<br><strong>skal derfor have det udefra<\/strong><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>vitamin<\/strong><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Samlet set<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Man kan derfor f\u00f8lge vitaminerne s\u00e5dan:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>planter \/ bakterier \/ svampe<\/strong><br>\u2193<br>fremstiller molekyler til deres eget stofskifte<br>\u2193<br>molekylerne fungerer fx som coenzymer, elektrontransport\u00f8rer eller antioxidanter<br>\u2193<br>dyr spiser planterne og mikroorganismerne<br>\u2193<br>molekylerne f\u00f8res gennem f\u00f8dek\u00e6den<br>\u2193<br><strong>mennesket bruger de samme molekyler i sit eget stofskifte<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Det mest interessante er derfor, at vitaminer i h\u00f8j grad er <strong>gamle biokemiske v\u00e6rkt\u00f8jer<\/strong>, som forskellige organismer deler. Vi har blot mistet evnen til selv at fremstille nogle af v\u00e6rkt\u00f8jerne og er derfor blevet afh\u00e6ngige af at f\u00e5 dem fra andre organismer.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I naturen dannes vitaminer ikke for at v\u00e6re vitaminer for os. De er molekyler, som planter, svampe og mikroorganismer producerer til deres eget stofskifte. For os bliver de til vitaminer, fordi vi under evolutionen har mistet evnen til at fremstille nogle af dem, men stadig har brug for dem. De fleste vitaminer dannes biologisk af: [&hellip;]<\/p>\n","protected":false},"featured_media":0,"menu_order":0,"template":"","meta":[],"categories":[],"tags":[],"aktivitetstype":[],"elementrolle":[],"fag":[],"fagomraade":[],"produkt":[],"class_list":["post-2338","aktivitet","type-aktivitet","status-publish","hentry"],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=\/wp\/v2\/aktivitet\/2338","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=\/wp\/v2\/aktivitet"}],"about":[{"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=\/wp\/v2\/types\/aktivitet"}],"wp:attachment":[{"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2338"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2338"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2338"},{"taxonomy":"aktivitetstype","embeddable":true,"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=%2Fwp%2Fv2%2Faktivitetstype&post=2338"},{"taxonomy":"elementrolle","embeddable":true,"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=%2Fwp%2Fv2%2Felementrolle&post=2338"},{"taxonomy":"fag","embeddable":true,"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=%2Fwp%2Fv2%2Ffag&post=2338"},{"taxonomy":"fagomraade","embeddable":true,"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=%2Fwp%2Fv2%2Ffagomraade&post=2338"},{"taxonomy":"produkt","embeddable":true,"href":"https:\/\/www.jrebsen.dk\/index.php?rest_route=%2Fwp%2Fv2%2Fprodukt&post=2338"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}