Cholesterol Biosynthesis (EVERYTHING YOU NEED TO KNOW BIOCHEMISTRY MCAT)

[@jeremysperling6128]

Awesome presentation. First video on KZbin specific for cholesterol biosynthesis for the MCAT!

[@sciencesimplified3890]

Thanks Jeremy! Those are the exact type of comments that motivate me to make more videos!

[@jeremysperling6128]

On thing I really find that helps is the visual diagrams which you did well! My favorite goto channel is AK lectures. The thing that separates him from others is the way he explains a concept multiple times before moving on. Similar to what you did alot here, it really helps. keep it up!

[@rohamhadidchi1196]

Amazing explanation of the carbonyl organic chemistry, molecular biology, and biochemistry. It is clear you have put a lot of effort into getting good at this.

[@surfergirl22330]

this was perfectly helpful and concise, thank you so much!

[@faylouise8169]

I just wanted to make a simple clarification that vitamin D cholecalciferol is made not from cholesterol, but a cholesterol precursor in the KR pathway, called 7DHC, 7 dehydrocholesterol. This is a very important distinction because all further metabolites of this steroidal-compound 'vitamin D' umbrella term- are dependent on that preprohormone cholecalciferol and not on cholesterol. Many cells make 7DHC, but only in epidermal cells is there the ability for UVB + heat to mechanically change the configuration to cholecalciferol (no enzyme required) So, that does leave vitamin D as a nutrient status, (and indeed that is the correct term), it is not just a cholesterol-based compound for further metabolite conversions. 'Vitamin D' umbrella term- and all its further metabolites are not made from cholesterol, rather they are substrate-dependent, that parent compound being cholecalciferol, so one can easily become deficient.

[@sciencesimplified3890]

I believe cholesterol is a precursor to 7dhc, which then is a precursor to vit d derivatives…? So technically cholesterol is still a precursor just not directly?

[@faylouise8169]

@@sciencesimplified3890 in the mevalonate pathway, you'll see the KR (kandutsch-Russell) pathway and Bloch pathways to cholesterol, in the KR you'll see 7DHC 7-dehydrocholesterol.

[@faylouise8169]

@@sciencesimplified3890 I think the confusion is in the term cholesterol and steroid, Vitamin D3 is grouped into the steroidal family, but it itself is not synthesized from cholesterol, but its active hormone calcitriol is considered a steroidal hormone. 7DHC is a precursor to cholesterol in the KR pathway. (all cells that use the mevalonate pathway are able to synthesize cholesterol for themselves and their own use, some have more preferential use of the Bloch pathway, or the KR pathway) Endogenous cholesterol synthesis. Only in skin cells specifically, where there is interaction with the suns rays, the 7DHC can convert to cholecalciferol not enzyme-dependent, but rather mechanical in nature. In those same cells though, 7DHC can also be converted to cholesterol by an enzyme. As far as I know epidermal cell do not have LDR receptors, they do have HDL recptors. which may play in with cholesterol exchange, or reverse transport, and /or may be immune modulatory. Epidermis cells have no direct blood supply, that is located in the dermis. A good question though is, Do statins affect epidermal cells? if they do, then in fact statins will decrease that mevalonate cholesterol synthesis, and by doing so also decrease the ability to synthesize vitamin D3 cholecalciferol. If they don't, as some researchers say then that is good.

[@Eric-sq4hd]

so can cholesterol be synthesized in both SER and mitochondrial membrane?