Titov: Lecture 1

Question 1

which vitamins are water vs lipid soluble

Answer 1

water soluble: B, C
lipid soluble: K, A, D, E,

Question 2

vitamin functions

Answer 2

(1) enzyme cofactors/coenzymes

• part of an enzyme, always protein bound, regenerated after cycle (vit A/retinol, B1/thiamine, B2/riboflavin (FAD, FMN), B4/pyridoxal, B7/biotin, B12/cobalamin)
• modified during cycle; more like enzyme substrates/products (B3/niacin (NAD(P)), B5/panthothenate (CoASH))

(2) Hormones
- vit A/retinol
- vit D/cholecalciferol

Question 3

vitamin B6 (pyridoxine)

Answer 3

• deficiency: anemia, electroencephalographic abnormalities, dermatitis, swollen tongue
• aldehyde group pyridoxal phosphate (PLP) is unique
• cofactor in amino acid metabolism
• required for neurotransmitters, heme, sphingolipids, & degradation/transamination of AA
• several enzymes figured out how to form ketone/aldehyde groups from side chains of AA to catalyze similar reactions as B6

Question 3

vitamin B1 (thiamine)

Answer 3

• deficiency: BERIBERI (fatal if untreated)
• loss of appetite, weakness, limb pain, shortness of breath, swollen feet/legs
• enzyme cofactor for 5 enzymes in humans; allows for a-keto acid decarboxylation (CO2 removed)
• most cells depend on atleast 1 of the 5 rxns for ATP prod

Question 3

vitamin B7 (biotin)

Answer 3

• deficiency: hair loss (alopecia) and skin inflammation (dermatitis)
• identified in egg whites
• AVINID is a biotin binding protein with the strongest binding of protein to small molecule
• enzyme cofactor for carboxylation (add CO2)
• usually bound to biotin carboxylase carrier protein (BCCP) domain
• biotin containing enzymes contain biotin carboxylase (BC) and carboxyl transferase (CT)

Question 4

vitamin B2 (riboflavin)
vitamin B3 (niacin)
iron

Answer 4

all of these are redox reaction cofactors
- B3 deficiency: PELLAGRA (diarrhea, dermatitis, amnesia, delirium; fatal untreated)
- B2 deficiency: milder symptoms (rarely fatal)

*Fe does 1 electron transfer rxns
*FADH2 does both 1, 2 electron transfer rxns
- unstable with O2
- reacts quick (2 unpaired O2 electrons)
*NADH does 2 electron transfers
- stable with O2
- reacts slower

Question 5

vitamin B5 (pantothenate)

Answer 5

• deficiency is rare (fatigue, insomnia, depression, irritability, vomiting, stomach pain, burning feet, upper respiratory infections)
• COENZYME A (CoASH) is the important part of the molecule (a remnant of a cystine AA)
• acetyl coA is another kinetically stable & thermodynamically activated cofactor
• CoASH participates in many metabolic rxns and acetyl-CoA is used for the acetylation of proteins

Question 6

vitamin A (retinol)

Answer 6

• deficiency causes night blindness, corneal ulceration, and eventually blindness
• acts as a cofactor for rhodopsin in rode cells (night vision) & photopsin in code cells (color vision)
• retinal isomerization leads to plasma membrane polarization via cGMP signaling & plasma membrane polarization is used by neurons (transports signals to brain)
• retinoic acid also acts as hormone by binding to retinoic acid receptor (RAR and RXR) in many cells and effect expression of many genes

Question 7

vitamin K

Answer 7

• deficiency can lead to blood clotting defects
• clots blood via many proteases which allow for amplification; also contain Gla residues allowing for overall coagulation cascade
• unusual rxn: vit K attaches CO2 to make Gla residue and vit K gets oxidized (and recycled)
• blood thinning drug WARFARIN works by inhibiting vit K recycling (minimizes blood clots, stroke, & heart attack risk)