Biochem Enzymes, Coenzymes, And Vitamins

Front 1

What are the 6 classes of enzymes?

Back 1

1) Oxidoreductases
2) Transferases
3) Hydrolases
4) Lyases
5) Isomerases
6) Ligases

Front 2

Oxidoreductases

Back 2

-redox rxns
-frequently use coenzymes NAD+, FAD, NADP+, or O2 as electron acceptors
(i.e. dehydrogenase, oxidase, reductase)

Front 3

Transferases

Back 3

-transfer of chemical group from donor to acceptor
-groups transferred include amino, carboxyl, acyl, glycosyl, phosphoryl
(i.e. transaminase, kinase)

Front 4

Hydrolases

Back 4

-cleavage of a bond between carbon and some other atom by the addition of water
(i.e. protease, phosphatase, amylase)

Front 5

Lyases

Back 5

-nonhydrolytic cleavage of C-C, C-S, and some C-N bonds
(i.e. aldolase, decarboxylase, dehydratase)

Front 6

Isomerases

Back 6

-interconversion of isomers
(i.e. epimerase, mutase)

Front 7

Ligases

Back 7

-formation of bonds between C and O, N, or S in rxns that require energy
(i.e. carboxylase, thiokinase)

Front 8

What are the 4 factors affecting rate of enzyme-catalyzed reactions?

Back 8

1) Substrate concentration (straight up, then flattens out as enzyme reactive sites become occupied)
2) Temperature (bell-shaped)
3) Enzyme concentration (straight up)
4) pH (bell-shaped)
"STEP up the reaction rate"

Front 9

Michaelis-Menten equation

Back 9

v = Vmax[S] / Km + [S]

Vmax = maximum velocity (the rate obtained when all of the enzymes are present as E-S complexes). Theoretical rate when all the enzymes are working.

Km = substrate concentration required to achieve exactly half of the maximum velocity. Where V = 1/2 Vmax

Front 10

Lineweaver-Burk plot

Back 10

Obtained by taking the reciprocal of the Michaelis-Menten equation:

1/v = (Km/Vmax)1/S + 1/Vmax

Front 11

Vmax increases as?

Back 11

The concentration of enzyme increases.

Front 12

What are the types of reversible inhibitors?

Back 12

Competitive, Noncompetitive, Uncompetitive

Front 13

Competitive inhibition

Back 13

Compete with substrate for binding to the active site. Can only be overcome by increasing [S].
-Km increases
-Vmax unchanged
-Slope (L-B plot) increases
-y-intercept unchanged
-x-intercept shifts to right

Front 14

Noncompetitive inhibition
(allosteric inhibitor)

Back 14

Inhibitor binds to site other than active site and are not structural analogs of substrate. Increasing [S] won't change anything.
-Km unchanged
-Vmax decreases
-Slope increases
-y-intercept shifts upward
-x-intercept unchanged

Front 15

Uncompetitive inhibition

Back 15

Bind directly to E-S complex, but NOT to free enzyme. Causes conformational change at active site that renders enzyme inactive.
-Km unchanged
-Vmax unchanged
-slope remains the same
-x-intercept shifts to left
-y-intercept shifts upward

Front 16

Irreversible inhibitors

Back 16

Bind covalently to the enzyme, resulting in permanent inactivation. The effect on kinetics is identical to that of the noncompetitive inhibitor.

Front 17

What are the 4 major mechanisms for regulating the activity of enzymes?

Back 17

1) Allosteric regulation
2) Covalent modification
3) Isoenzymes
4) Induction and repression of enzyme synthesis

Front 18

Allosteric regulation

Back 18

Involves effector molecules that bind to sites other than active site. Effectors can be either positive (activators) or negative (inhibitors).
Activators = decrease Km, increase Vmax
Inhibitors = opposite

Common effectors include end products of pathwaysor molecules that reflect the energy state of the cell (ATP, ADP, AMP, NADH, NAD+, acetyl-CoA)
Sigmoidal substrate saturation curve.

Front 19

Covalent modification

Back 19

Involves phosphorylation / dephosphorylation of serine, threonine, tyrosine side chains --> by kinases and phosphatases in response to hormonal stimulation of cells.

Front 20

Isoenzymes

Back 20

Isoenzymes are different proteins that catalyze the same reactions but have different properties and differ in organ/tissue specificity. The appearance of tissue-specific isoenzymes in plasma is of diagnostic value in identifying sites of tissue damage.

Front 21

Induction and repression of enzyme synthesis

Back 21

Generally mediated by thyroid or steroid hormones that act in the nucleus to increase or decrease the rate of transcription or protein synthesis.

Front 22

Coenzymes

Back 22

Enzyme intermediates that carry specific functional groups. Usually involved in redox and transfer reactions. Small, organic. More stabl than proteins. Derived from vitamins.

Front 23

Vitamins

Back 23

Must come from diet. Cannot be synthesized in body. Can be fat or water-soluble. All of the water-soluble vitamins and some of the fat-soluble vitamins serve as precursors for coenzymes.

Front 24

Water-soluble vitamins

Back 24

Thiamine (B1)
Riboflavin (B2)
Niacin (B3)
Pyroxidine (B6)
Pantothenic acid
Biotin
Folic acid
Vitamin C
Cobalamin (B12)

Front 25

Thiamine (B1)

Back 25

Function:
-metabolism of carbohydrates and AA's
-decarboxylation of alpha-ketoacids
Deficiency:
-Beriberi (peripheral nerve damage)
-Wernicke-Korsakoff syndrome (CNS damage)
Other facts:
-deficiency associated with alcoholism and malnutrition

Front 26

Riboflavin (B2)

Back 26

Function:
-component of FAD and FMN
Deficiency:
-cheilosis
-dermatitis
-photosensitivity
-glossitis
Other facts:
-synthesized by intestinal bacteria

Front 27

Niacin (B3)

Back 27

Function:
-component of NAD and NADP
Deficiency:
-Pellagra
Other facts:
-formed from Tryptophan

Front 28

Pantothenic acid (B5)

Back 28

Function:
-component of Coenzyme A
-FA synthesis
Deficiency:
-dermatitis
-fatigue
-sleep impairment
-diarrhea

Front 29

Pyridoxine (B6)

Back 29

Function:
-precursor or pyridoxal phosphate (a coenzyme in transamination rxns)
Deficiency:
-fatigue
-depression
-impaired growth
-convulsions
Other facts:
-formed from pyridine; deficiency associated with oral contraceptive use

Front 30

Cobalamin (B12)

Back 30

Function:
-formation of methionine
-converts methylmalonyl CoA --> succinyl CoA
-intrinsic factor required for GI absorption
Deficiency:
-pernicious anemia
-glossitis
Other facts:
-not found in plant foods (only animal sources)
-synthesized by intestinal bacteria

Front 31

Folic acid

Back 31

Function:
-synthesis of purines (A & G) and thymidine (required for DNA formation)
Deficiency:
-megaloblastic anemia
-glossitis
Other facts:
-most common vitamin deficiency in the US
-inhibited by antimetabolites (i.e. methotrexate)

Front 32

Biotin

Back 32

Function:
-protein and AA synthesis
-converts acetyl CoA --> malonyl CoA in FA synthesis
Deficiency:
-fatigue
-depression
-muscle pain
-hair loss
-dermatitis
Other facts:
-inactivated by avidin (protein in egg whites)
-synthesized by intestinal bacteria

Front 33

Vitamin C

Back 33

Function:
-coenzyme for the hydroxylation of proline and lysine (in collagen synthesis)
Deficiency:
-Scurvy (delayed wound healing, poor bone matrix formation, increased permeability of oral mucosa, capillary fragility
Other facts:
-deficiency associated with gingival dz

Front 34

Fat soluble vitamins

Back 34

ADEK

Front 35

Vit. A (Retinol)

Back 35

Function:
-epithelial development and maintenance
-growth and remodeling of bone
Deficiency:
-night blindness
-xerophthalmia (ocular tissue keratinization)
-dry skin
-enamel irregularities
Other facts:
-constituent of the visual pigments rhodopsin (rods) and iodopsin (cones)

Front 36

Vit. D (Calciferol)

Back 36

Function:
-growth and mineralization of bone and teeth
-Ca++ and PO4 metabolism
Deficiency:
-rickets (children)
-osteomalacia (adults)
Other facts:
-most toxic of fat-soluble vitamins

Front 37

Vit. E (Tocopherol)

Back 37

Function:
-antioxidant
Deficiency:
-neurologic dysfunction (premature infants)
Oher facts:
-least toxic of fat-soluble vitamins

Front 38

Vit. K
(Phylloquinone)
(Menaquinones)
(Menadione)

Back 38

Function:
-activation of prothrombin and vit. K dependent clotting factors (II, VII, IX, X)
-synthesis of gamma-carboxyglutamate (chelates Ca++)
Deficiency:
-diminished blood clotting
-increased PT and INR (extrinsic clotting pathway)
Other facts:
-Warfarin (Coumadin) blocks hepatic synthesis of vit. K dependent clotting factors
-synthesized by intestinal bacteria