Lipid: Perbedaan antara revisi
Konten dihapus Konten ditambahkan
Tag: Suntingan perangkat seluler Suntingan peramban seluler |
|||
Baris 253:
=== Degradasi ===
[[Oksidasi beta]] adalah proses metabolisme di mana asam lemak dipecah di dalam [[mitokondria]] dan/atau [[peroksisom]] untuk menghasilkan [[asetil-KoA]]. Untuk sebagian besar, asam lemak dioksidasi oleh suatu mekanisme yang mirip, tapi tidak identik dengan, kebalikan dari proses sintesis asam lemak. Artinya, fragmen dua karbon dikeluarkan secara berurutan dari ujung karboksil asam setelah langkah [[dehidrogenasi]], [[hidrasi]], dan [[oksidasi]] untuk membentuk [[asam beta-keto]], yang dipecah melalui [[tiolisis]]. Asetil-KoA kemudian diubah menjadi [[Adenosina trifosfat|ATP]], {{Chem2|CO|2}}, dan {{Chem2|H|2|O}} menggunakan [[siklus asam sitrat]] dan [[rantai transpor elektron]]. Oleh karena itu siklus asam sitrat dapat mulai dari asetil-KoA ketika lemak dipecah untuk energi jika glukosa yang tersedia hanya sedikit atau tidak ada sama sekali. Energi yang dihasilkan dari oksidasi lengkap asam lemak palmitat adalah ATP 106.<ref>[[Lipid|Stryer ''et al.'']], pp. 625–626.</ref> Asam lemak tak jenuh dan berantai ganjil membutuhkan langkah-langkah enzimatik tambahan untuk degradasi.
<!-- ==Nutrisi dan kesehatan==
Sebagian besar lemak yang ditemukan dalam makanan berada dalam bentuk trigliserida, kolesterol, dan fosfolipid. Beberapa lemak diet diperlukan untuk memudahkan penyerapan vitamin yang larut dalam lemak ([[retinol|A]], [[kalsiferol|D]], [[tokoferol|E]], dan [[filokuinon|K]]) serta [[karotenoid]].<ref>[[#Bhagavan|Bhagavan]], p. 903.</ref> Humans and other mammals have a dietary requirement for certain essential fatty acids, such as [[linoleic acid]] (an [[omega-6 fatty acid]]) and [[alpha-linolenic acid]] (an omega-3 fatty acid) because they cannot be synthesized from simple precursors in the diet.<ref name="Stryer et al., p. 643"/> Both of these fatty acids are 18-carbon [[polyunsaturated fat|polyunsaturated fatty acids]] differing in the number and position of the double bonds. Most [[vegetable oil]]s are rich in linoleic acid ([[Safflower oil|safflower]], [[sunflower oil|sunflower]], and [[Corn oil|corn]] oils). Alpha-linolenic acid is found in the green leaves of plants, and in selected seeds, nuts, and legumes (in particular [[linseed oil|flax]], [[rapeseed]], [[walnut]], and [[soy]]).<ref name="Russo 2009"/> [[Fish oil]]s are particularly rich in the longer-chain omega-3 fatty acids [[eicosapentaenoic acid]] (EPA) and [[docosahexaenoic acid]] (DHA).<ref>[[#Bhagavan|Bhagavan]], p. 388.</ref> A large number of studies have shown positive health benefits associated with consumption of omega-3 fatty acids on infant development, cancer, cardiovascular diseases, and various mental illnesses, such as depression, attention-deficit hyperactivity disorder, and dementia.<ref name="Riediger 2009"/><ref name="Galli 2009"/> In contrast, it is now well-established that consumption of [[trans fat]]s, such as those present in [[Partially hydrogenated vegetable oil#In the food industry|partially hydrogenated vegetable oil]]s, are a risk factor for [[cardiovascular disease]].<ref name="Micha 2008"/><ref name="Dalainas 2008"/><ref name="Mozaffarian 2007"/>
A few studies have suggested that total dietary fat intake is linked to an increased risk of obesity<ref name="Astrup 2008"/><ref name="Astrup 2005"/> and diabetes.<ref name="Astrup 2008b"/> However, a number of very large studies, including the Women's Health Initiative Dietary Modification Trial, an eight-year study of 49,000 women, the Nurses' Health Study and the Health Professionals Follow-up Study, revealed no such links.<ref name="Beresford 2005"/><ref name="Howard 2006"/> None of these studies suggested any connection between percentage of calories from fat and risk of cancer, heart disease, or weight gain. The Nutrition Source, a website maintained by the Department of Nutrition at the [[Harvard School of Public Health]], summarizes the current evidence on the impact of dietary fat: "Detailed research—much of it done at Harvard—shows that the total amount of fat in the diet isn't really linked with weight or disease."<ref name="urlFats"/>-->
== Lihat pula ==
| |||