Nutrition 3: Fat soluble : Vit D and A Flashcards
What is the sources of vitamin A in the diet
Carotenoids: b-carotene in plants.
Esterified retinol from animal sources (orginally sourced from carotenoids)
What is b-carotene function in plants
It acts as an accessory chlorophyll pigment which absorbs light which is convert into chemical energy
What does b-carotene get converted to the two active forms of Vit A and what are these
B-carotene is split in half when it enters the body to become 2x all-trans- retinal molecules.
This is converted to all-trans-retinol which is transported around the body.
In the cells this is taken up and can be made to two active forms
- All-trans-retinoic acid (hormonelike)
- 11 cis retinal (vision)
What is the function of All trans retinoic acid
It binds to RAR- retinoic acid receptors which regulate gene expression which relate to development, immune function and reproduction
How is Vit A transported from the intestine to be stored
The retinol is converted into retinyl ester and this is transported by Chylomicrons which are lipid vesicles
What form is excess Vit A not used by peripheral cells stored and where is it stored
It is stored in the liver as retinyl esters.
How is Vit A transported when it is released from stores in the blood
It converts Retinyl ester to Retinol (still hydrophobic). This is carried around the body by a protein: Retinol binding protein (RBP) which keep it in a hydrophobic pocket in the centre.
How does Vit A get released from RBP at the target cell
The RBP binds to the receptor STRetinoicAcid6 on the surface of the cell membrane. This receptor is a pore. The vit A is allowed to through this protein and sit in the hydrophobic membrane where it will be bind to other carrier molecules to get to the hydrophillic parts of the cell
What are the ways the body regulates how active substances like vitamins are in the body
- Regulation of peripheral levels in the blood
- Regulate release by signal (change in environment/metabolic state)
- Regulate transport
- Receptor - Tissue specificity
Therefore regulating toxicity
What is the role of retinal in rhodopsin in
Retinal as 11 cis retinal is the Rhodo component which binds to the protein Opsin through binding to lysine residue. It captures light energy to make an electrical signal
What is the effect of Vit A consumption and which state of vit A does it occur with
Occurs with ingestion of preformed state not carotenoids (b-carotene).
Causes acute abdominal pain, nausea, vomiting, dizziness
Chronic: bone abnormalities, joint pain, visual disturbances
Where does Vit D come from
Dietary sources are fish liver oils and fortified foods but humans can make Vit D using UV sunlight in the skin
How is Vit D prepared in the skin from dehydrocholesterol to active form
Vit D is made from a precursor of cholesterol pathway which is chopped by UV into a precursor Vit D3 which spontaneously converts in Vit D3.
It then undergoes more reactions (first reaction in the liver, 2nd in the kidney) to form active form: Calcitrol
How is Vit D precursors transported in the blood to the liver and kidney for two reactions to form active form
VitDBindingProtein
What are the effects of Vit D in the target cell and how does it target the cell
Targets the cell through Vit D receptor.
Effects
- increases bone mineralisation in bone
- increases absorption of Ca2+ and P+ in intestine
- Induces differentiation of immune cells
