Post on 27-Jan-2016
transcript
Lecture 5
Fall 2015 BSC203/BIO132
By
M. Jawad Khan, PhD
Course Outline
• General chemistry including atomic nature of matter, molecules, principles of chemical reactions, stochiometry, acids and bases, oxidation-reduction, water as a solvent, pH, and buffers.
• Structure and function of biomolecules, including structure and function of proteins (amino acids, peptides and, enzymes including classification and how it works), protein conjugates, carbohydrates and glycol-conjugates, nucleosides, nucleotides and nucleic acids, lipids (triglycerols, phospholipids, waxes, sphingolipids, glycolipids, steroids) and nature of biological membranes (lipid bilayers), prostaglandins, leukotrienes, vitamins, hormones, co-enzymes, co-factors.
•
Holoenzyme and Apoenzyme
• Holoenzyme – Complex of protein and prosthetic groups
– Catalytically active
• Apoenzyme – The enzyme without the prosthetic groups
– Catalytically inactive
Types of cofactors
• Some enzymes require cofactors for activity
(1) Essential ions (mostly metal ions)
(2) Coenzymes (organic compounds)
Types of cofactors
inactive) (
active) (
)protein only(
Holoenzyme
+ Cofactor Apoenzyme
Cofactors and Coenzymes Cosubstrates:
- Altered in reaction and regenerated to original structure in subsequent reaction
- Disassociated from active site
- Shuttle chemical groups among different enzyme reactions.
Prosthetic groups:
- Remains bound to enzyme
- Must return to original form
Both cosubstrates and prosthetic groups supply reactive groups not present on amino acid side chains
Cofactors and Coenzymes Examples:
1) Metabolite coenzymes – synthesized from common metabolites
2) Nucleoside triphosphates – (ATP) can donate phosphates, pyrophosphates, adenosyl grroups
3) S-adenosylmethionine (SAM) – donates methyl groups
4) Nucleotide sugars (uridine diphosphate glucose = UDP-glucose) - transfer sugars in carbohydrate metabolism
Cofactors and Coenzymes • Many Enzymes Require Inorganic Cations
• Enzymes requiring metal ions for full activity:
(1) Metal-activated enzymes
(2) Metalloenzymes
Example: Carbonic anhydrase
• A metalloenzyme
• Zinc ion promotes the ionization of bound H2O.
Resulting OH- attacks carbon of CO2
Vitamin-Derived Coenzymes
• Animals rely on plants and microorganisms for vitamin sources (meat supplies vitamins also)
•Must be obtained from diet
•Synthesized by microorganisms and plants
• Most vitamins must be enzymatically transformed to the coenzyme
• Vitamin deficiencies lead to disease state
Vitamin-Derived Coenzymes Vitamin Coenzyme Ascorbic acid (C) not a coenzyme
Niacin (B3) NAD(P)+/NAD(P)H
Riboflavin (B2) FMN & FAD
Thiamin (B1) Thiamin-pyrophosphate
Pyridoxal (B6) Pyridoxal phosphate
Biotin (B7) Biotin
Folate (B9) Tetrahydrafolate
Cobalamin (B12) adenosyl-and methylcobalamin
Vitamin A Retinal Vitamin K Vitamin K
Pantothenate (B5) Coenzyme A
Vitamins: Definition • Organic compound found in foods
• Required in small amounts
• Required in the diet (dietary essential)
• Proven to be required for health, growth, and reproduction
– Deficiency syndrome identified
Vitamin Nomenclature
• Fat soluble “A” & Water soluble “B”
• “Vital amines”
– vitamines = vitamins
• Vitamin B “complex” – Collection of water soluble vitamins that function as enzyme
cofactors
• Vitamin C
• Vitamins D and E
• Mistaken Vitamins
Fat and Water Soluble Vitamins
Fat Soluble Vitamins (A, D, E, K) • Soluble in lipids and
solvents • Excess stored and not
excreted • Excess may be toxic • Deficiency slow to
develop
Fat and Water Soluble Vitamins
Water Soluble Vitamins
• B vitamins, C
• Soluble in water
• Excess excreted in urine, little stored
• Generally less toxic
• Deficiency develops quickly
General Functions of Vitamins
Hormones
–Vitamin D • Calcium homeostasis
–Vitamin A • Cell division and development
General Functions of Vitamins
Non-specific chemical reactions
• Vitamin E –Antioxidant
• Vitamin C –Chemical reducing agent
General Functions of Vitamins
Coenzymes or Cofactors
– Chemicals that assist enzymes to function as catalysts • B vitamins
• Vitamin C, A, K