Vitamins

4 categories of macronutrients

1. proteins

2. carbohydrates

3. lipids

4. nucleic acids

3 categories of micronutrients

1. vitamins

2. minerals

3. trace elements

which lipids are micronutrients

omega 3 and 6

3 essential functions of vitamins

1. coenzymes/cosubstrates

2. ligands for protein receptors

3. antioxidants

vitamins are able to function as coenzymes and cosubstrates because of…

their special functional groups not found in the 20 proteinogenic amino acids

the special functional groups of vitamins which allow them to act as coenzymes/cosubstrates are involved directly in the … … or chemistry of the enzyme

catalytic mechanism

vitamins act as coenzymes usually by lowering … (3 words)

reaction energy barriers

which vitamins act as coenzymes? (mnemonic)

BACK

do all B vitamins have coenzyme roles or only some?

all

vitamins which function as ligands for protein receptors act functionally as …

hormones

example of a vitamin which acts as a ligand for a protein receptor and influences gene expression (full name including positions of hydroxyl groups)

1,25 dihydroxy vitamin D

calcitriol (1,25-dihydroxy vitamin D3) acts as a ligand to what kind of protein receptor?

nuclear

name of the nuclear protein receptor calcitriol binds to? - not the official gene symbol

vitamin D receptor (VDR)

what is the official gene symbol of the nuclear protein receptor calcitriol (vit D3) binds to?

NR1I1

outline the 3 steps in which vitamin D3 acts as a ligand for a protein receptor and influences gene expression

1. calcitriol binds to VDR

2. the ligand activated VDR complex binds to VDREs

3. this binding recruits either coactivators or corepressors either increasing or decreasing gene expression

what are the components of the ligand activated VDR complex?

1. calcitriol bound VDR

2. RXR (RXR-VDR heterodimer)

3. coregulator proteins (coactivators or corepressors)

complex of … + … + … binds to the vitamin D response elements (VDREs), with additional … proteins determining whether transcirption is increased or decreased

calcitriol + VDR + RXR, coregulator

what does RXR stand for?

retinoid X receptor

because … is expressed in many cell types the regulatory effects of vitamin D are widespread and present in many systems of the body (skeletal, muscular, immune, gastrointestinal, renal, parathyroid etc)

VDR

vitamin D regulates the expression of genes involved in which processes?

1. calcium absorption

2. bone and mineral metabolism

3. hormone regulation

what does VDREs stand for?

vitamin D response elements

example fo a vitamin which acts as a very important coenzyme?

vitamin B3 (niacin)

outline the mechanism of how niacin (B3) acts as a coenzyme

1. niacin is converted to NAD+

2. NAD+ binds to dehydrogenase enzymes

3. in the reaction NAD+ accepts a hydride ion to form NADH

4. the enzyme itself cannot carry out the redox reaction

niacin (via NAD+) acts as a coenzyme that carries … between reactions

electrons

vitamins which function as antioxidants function as electron … (donors/acceptors)

donors

which form of vitamin E acts as an antioxidant?

alpha tocopherol

alpha tocopherol breaks lipid … … reactions (write all 4 words)

lipid peroxidation chain reactions

alpha tocopherol is embedded where?

lipid bilayer

reaction between lipid peroxyl radicals (LOO*) and alpha tocopherol (TOH)

… + … → … + …

LOO* + TOH → LOOH + TO*

the lipid peroxidation chain reaction is stopped once the lipid peroxyl radical is converted to … (3 words)

nonradical lipid hydroperoxide

TO* is converted back to TOH by other antioxidants such as …

vitamin C

ROS attack what type of FAs?

polyunsaturated

lipid radicals (L*) reacts with oxygen to form … (LOO*)

lipid peroxyl radicals

after lipid peroxyl radicals (LOO*) are formed, they attack other lipids, propagating a damaging chain reaction

copy this cus its important

after lipid peroxyl radicals are formed they attack other lipids propagating a damaging chain reaction

vitamin C works as a cosubstrate by donating … to the metal center of certain enzymes (Fe³⁺ → Fe²⁺ and Cu²⁺ → Cu⁺)

electrons

three types of aqueous free radicals that vitamin C reduces?

r*, ro* and roo*

vitamin C (ascorbate) acts as a cosubstrate to which 2 types of enzymes by keeping their metal centers reduced?

oxidases and oxygenases

why is ascorbate said to act as a cosubstrate for some oxidases and oxygenases and not a coenzyme?

it is consumed in the reaction

after ascorbate donates an electron to either iron or copper containing metal centers of some oxidases and oxygenases, it forms which molecule?

dehydroascorbate

ascorbate → … + e^-

dehydroascorbate

example of iron dependent oxygenases which add OH groups to proline and lysine residues in collagen and which depend on ascorbate to keep their metal groups reduced?

collagen prolyl/lysyl hydroxylases

hydroxyproline and hydroxylysine are cruicial for … the collagen triple helix

stabilising

chain of reactions which lead from vitamin C deficiency to scurvy?

vit C deficiency → … → … → scurvy

poor hydroxylation → weak collagen

how many human vitamins are there?

13

which B vitamins are there?

1,2,3,5,6,7,9,12

what are the common names of vitamins B1, B2, B3, B5, B6, B7, B9 and B12 respectively? (TRN PP BF C)

thiamin, riboflavin, niacin, pantothenic acid, pyridoxal phosphate, biotin, folic acid and cobalamin

what is the common name of vitamin A?

retinol

what is the common name of vitamin E?

alpha tocopherol

what are the common names of vitamins K1, K2 and K3?

phylloquinone, menaquinone and menadione

general name for vitamin D? (chole and ergo forms)

calciferol

what disease forms as a consequence of vitamin B1 (thiamine) deficiency?

beri beri

which is the synthetic form of vitamin K?

menadione (K3)

vitamin K1 primarily functions in … while K2 has a broader role, supporting … and … health by helping direct calcium to the … away from …

coagulation, bone, heart, bones, arteries

4 common symptoms of scurvy

1. swollen gums

2. loss of teeth

3. joint pain

4. poor wound healing

all symptoms of scurvy can be linked to a disruption in the … matrix and … tissue

extracellular, connective

collagen fibers are formed from a … helix

triple

the basic structural unit of collagen, consisting of three polypeptide chains twisted into a triple helix

tropocollagen

the enzymes which respectively add a hydroxyl group to the 3rd and 4th position of a proline residue in collagen

prolyl 3 and prolyl 4 hydroxylases

hydroxyproline is cruicial for … of the triple helix while hydroxylysine is especially important in … linking and …

stabilising, cross, glycosylation

what is glycosylation?

addition of sugar chains to proteins or lipids

cells which produce collagen

fibroblasts

hydroxylation of proline by proyly 4 hydroxylase

… + … + … + … → … + … + …

proline + vitamin c + oxygen + alpha ketoglutarate → 4 hydroxyproline + succinate + co2

is 4 hydroxyproline or 3 hydroxyproline prevalent?

4 hydroxyproline

hydroxylation of proline creates a distinct … (bent shape) that favour the … conformation of collagen

pucker, helical

vitamin A and vision

1. … + … → …

2. … → … + … (exposure to light)

1. 11 cis retinal + opsin → rhodopsin

2. rhodopsin → all trans retinal and opsin

11-cis-retinal is regenerated from all-trans-retinal through the … cycle

visual cycle

in the visual cycle all-trans-retinal travels from the photoreceptor cells to the … … epithelium and … cells where it is converted to 11-cis-retinal and can return to photoreceptor cells

retinal pigment, muller

1. in the photoreceptor cells all-trans-retinal → … which is then exported to retinal pigment epithelium (RPE) and Muller cells.

2. in RPE … → … → 11-cis-retinal (which returns to photoreceptors)

3. in Muller cells … → … (which is then exported to photoreceptors)

4. in photoreceptors the … from Muller cells is converted back to 11-cis-retinal

include even the already written out intermediates

1. all trans retinal → all trans retinol

2. all trans retinol → 11 cis retinol → 11 cis retinal

3. all trans retinol → 11 cis retinol

4. 11 cis retinol → 11 cis retinal

do Muller cells mainly serve rods or cones?

cones

deficiency of which two B vitamins is associated with anemia?

B9 and B12

outline the cycle through which folic acid is used in the synthesis of dTMP (deoxythymidine monophosphate)

1. … → … (…)

2. modified … is used to convert … → …

3. in that reaction the modified … → …

4. … → … (by DHFR)

1. folic acid → THF (tetrahydrofolate)

2. modified THF is used to convert dUMP → dTMP

3. in that reaction the modified THF → DHF

4. DHF → THF (by DHFR)

what is the enzyme which converts DHF → THF

dihydrofolate reductase (DHFR)

which vitamins are lipid soluble? (mnemonic)

DEKA

which is the only completely protein independent vitamin?

E

are the water soluble vitamins stored in large quantities?

no

which vitamin undergoes multiple transformations to form Coenzyme A?

vitamin B5 (pantothenate)

which vitamins are not processed at all?

ECK