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Lecture 13

BIOCHEM 4M03 Lecture Notes - Lecture 13: Prostaglandin, Nutrient, Chromosome


Department
Biochemistry
Course Code
BIOCHEM 4M03
Professor
Deborah Sloboda
Lecture
13

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Biochem 4M03 Lecture 13 “AVitamin & Fat Metabolism
Each Lecture is a Story
- Outcome is not always disease but focus on disease often
Goals
- An example of how a micronutrient alters metabolism
- Vitamin A
o Types, absorption, metabolism
- Retinal
o Vision
- Retinoic Acid
o Nuclear receptors: RAR, RXR, PPAR
o Gene transcription
Vitamin A & Carotenoids
- Vitamin A
o Preformed vitamin A (comes from animal sources)
o Ingest preformed vitamin A from:
Foods of animal origin: liver, dairy, eggs, fish, fish oils
Some foods may be fortified
- Preformed types of vitamin A: retinol, retinal (retinaldehyde) and retinoic acid
- Retinoid: Animal source
- Carotenoid: Plant source
- Biological processing of carotenoids
o Need to process preformed sources of vitamin A to get sources you find from
animals or in us
o Arrows are interchangeable
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Plants: Carotenoids
- Carotenoids
o >600 types: Yellow/orange/red fruits & vegetables
o α-, -, - carotene function as Provitamin A
o Provitamin A: Retinol Activity Equivalents
o You get less from plants (because of conversion from plants)
o -carotene: Greatest (plant) potential
o -carotene 15, 15’-dioxygenase cleaves it in the intestine
o Overall: <10% provitamin A can be converted in to retinol
- 1 unit of retinol (from animals)
o Need 12 times the amount of -carotene
o -carotene supplements can be more potent (2 times the amount)
How Vitamin A gets in the Gut
- 1) Eat meat, fat, carrots (preformed vitamin A)
- 2) Goes into lumen of the gut
- 3) Strip away the protein
- 4) Remove lipid
- 5) Repackaged so that we can absorb it
- 6) Have types of vitamin A can have effects or be stored
- 7) Beta-carotene can be processed to from retinal
- 8) Can be processed to retinoic acid important for metabolism
o Retinoic acid can directly enter the blood, where it attaches to albumin to
transport to the liver
Vitamin A & Carotenoids
- Digestion & absorption (highlights)
o Carotenoids & retinoids metabolized in gut enterocytes to some extent
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Retinol-binding proteins facilitate them moving around
o Retinol esterified & incorporated into chylomicrons for transport
o Chylomicrons carry retinol to liver
o Additional metabolism in liver
Where is it stored and used? The Liver
- 1) Chylomicron coming from gut with micronutrients
- 2) Enter liver by stripped away lipid, giving retinol or retinal in hepatocyte
- 3) Body decides what to do with it
- 4) Store in different cell type
- 5) Convert to retinoic acid in liver
- 6) Excrete in bile bile acid metabolism or transport to other parts of body
- 7) Even when transported out, it can still come back and impact the liver
Liver: Vitamin A
- Liver Metabolism (highlights)
o Retinol that is esterified may be stored in the liver
o Converted to retinoic acid: acts on liver
o Transported in blood via proteins complex
Retinol-binding protein (RBP)
o Excreted in bile
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