0:00 Humans need vitamins and minerals because they help with many enzymatic 0:11 reactions in 0:11 our body to help keep our bodies healthy and functioning, including our eyes 0:16 and our bones. 0:18 Vitamin B12, also known as cobalamin, is an important vitamin to keep our red 0:24 blood cells 0:25 healthy as well as our neurons, the nerves of our body. Deficiency of vitamin B 0:30 12 is 0:31 associated with megaloblastic anemia, large red blood cells as well as 0:36 neurological psychiatric 0:38 symptoms. We will focus on vitamin B12 metabolism and absorption. 0:47 Human cells cannot make vitamin B12 or folate. Vitamin B12 is present in many 0:53 animal products, 0:54 including meats, dairy products, eggs and now they are also included in cereal 1:00 products. 1:01 Vitamin B12 in foods are usually protein bound. So we masticate, we chew the 1:09 food and then 1:10 it enters the stomach. The vitamin B12 and protein complex is then exposed to 1:16 the acidic 1:17 environment of the stomach and then peps in which is an enzyme will disass 1:22 ociate vitamin 1:23 B12 from the protein. During the same time when vitamin B12 is eaten, the saliv 1:31 ary glands 1:32 produces another protein called the R-binder, also known as haptocorin, which 1:37 will enter 1:38 the stomach and then bind to the released vitamin B12, forming the vitamin B12 1:45 R-binder complex. 1:50 The stomach contains many special cells called parietal cells, which are the 1:55 ones that produce 1:56 the acid, hydrochloric acid, as well as another important substance, intrinsic 2:02 factor. Intrinsic 2:03 factor here in green enters the small intestine together with the R-binder 2:10 vitamin B12 complex. 2:13 The complex is exposed to pancreatic proteases secreted into the higher pH of 2:20 the duodenum. 2:22 The pancreatic proteases cleave off the R-binders, allowing the vitamin B12 to 2:29 now bind to intrinsic 2:30 factor. Now you form what's called the vitamin B12 intrinsic factor complex. So 2:40 a word from 2:40 responses. Look, I discovered a very interesting channel with short explainers. 2:47 It's called 2:48 geekly edu. Geekly edu have lots of different video playlists covering topics 2:54 right across 2:55 math, statistics, biology, physics, chemistry and economics. If you're studying 3:03 biology, 3:04 you should definitely subscribe. Check them out. The link to geekly edu is in 3:08 the description 3:09 and I'll put a link up at the end of this video. 3:25 The vitamin B12 intrinsic factor complex travels along the small intestine to 3:29 the end 3:30 called the islam, where it is taken up by mucosal receptors. These receptors 3:37 allow for take 3:39 up of vitamin B12 intrinsic factor complex. The intrinsic factor is degraded in 3:50 the cell. 3:52 The vitamin B12 is absorbed into circulation and then binds to another 3:57 transport protein, 3:59 a family known as trans-cobalamin. Vitamin B12 bound to trans-cobalamin is 4:06 taken up by other 4:07 cells throughout the body by receptor-mediated endocytosis. So for example, 4:14 here, the vitamin 4:15 B12 is taken up by the liver cells. The liver cell is an important organ 4:21 because it actually 4:22 stores your vitamin B12 for up to 3 to 5 years worth. If someone completely 4:29 stops absorbing 4:30 vitamin B12, signs of deficiency do not typically show up until 2 to 3 years 4:40 later. 4:41 Continuing on our journey, now that vitamin B12 is absorbed into the cells 4:46 around the 4:47 body, what does it actually do? Vitamin B12 and folate both play a critical 4:54 role in DNA 4:54 and RNA synthesis. Vitamin B12 and folate is involved in the folate and methion 5:01 ine cycle. 5:04 Vitamin B12 is a co-factor with methionine synthase, which helps drive some of 5:09 the reactions 5:10 within these two cycles. The folate cycle is important for DNA and RNA 5:16 synthesis as they 5:17 donate methyl groups to form nucleotides, adenine and guinine, as well as drive 5:23 a reaction 5:24 to synthesize a nucleotide thymidine. Vitamin B12 specifically is a co-factor 5:33 in the conversion 5:34 of methylmalenylcoA to succinylcoA, a reaction that occurs in the mitochondria 5:42 of the cell. 5:43 And this reaction is catalyzed by methylmalenylcoA mutase. 5:53 EthylmalenylcoA or MMA and homocysteine will be elevated if someone has vitamin 6:02 B12 deficiency 6:05 because they are unable to drive both these enzymatic reactions. The synthesis 6:12 of nucleotides 6:13 adenine, guinine and thymidine are reduced or are insufficient in vitamin B12 6:20 deficiency. 6:20 And because of this, vitamin B12 deficiency will cause problems in rapidly 6:25 dividing cells, 6:27 such as your red blood cells and your white blood cells in the bone marrow. 6:32 Classically 6:33 in vitamin B12 deficiency, what you see as a result are megaloblastic macrocy 6:39 tic red 6:39 blood cells, as well as hypersegmental neutrophils. You also see ineffective 6:46 erythropoasis, also 6:47 known as intramadullary hemolysis, due to premature death of these myeloid 6:54 cells. 6:55 Finally, importantly, vitamin B12 deficiency causes urinal problems, 7:03 specifically demyelination, 7:05 which results in many neurological signs and symptoms, including cognitive and 7:09 psychiatric 7:10 symptoms as well. So in summary, vitamin B12 is a very important 7:17 vitamin for a number of reasons, mainly for proper mature red blood cells, as 7:23 well as 7:24 proper functioning neurons. Deficiency of vitamin B12 results in anemia, 7:31 specifically 7:31 megaloblastic anemia, as well as neurological symptoms and conditions, 7:36 including parastasia 7:38 and peripheral neuropathy. Thank you for watching.
