Lecture 5 Energy and Enzymes Flashcards
Metabolism
total of all chemical reactions in the body
Catabolic reactions
break down large molecules into smaller ones ex: glycogen -> glucose
Anabolic reactions
Build up larger molecules from smaller ones amino acids -> proteins
Exergonic reactions
release energy
endergonic reactions
require energy
Name the types of metabolic reactions
Hydrolysis & Dehydration Phophorylation & Dephosphorylation Oxidation-Reduction Reactions
Hydrolysis
Add H20 to break bonds between monomer units
catabolic
A-B + H20 -> A-OH + H-B
e.g. surcose + H20 -> glucose + fructose
Dehydration
Remove H20 to join monomers
anabolic
A-OH + H-B -> A-B +H20
e.g. peptide bond formation
Phosphorylation
addition of a phosphate group (Pi)
C+Pi -> C-P+H20
e.g. ATP synthesis
Transfer of phosphate from ATP
catalyzed by kinase enzyme
C+ATP -> C -P +ADP
Dephosphorylation
removal of a phosphate group
C-P + H20 -> C + Pi
e.g. ATP hydrolysis
Oxidation-Reducation (redox) Reactions
Electron transfer reactions: Oxidation is loss, Reduction is gain of electrons
major energy source of cells: Oxidation of sugars, fatty acids, and amino acids
Redox reactions
are coupled: one molecule is oxidized another is reduced
in cells usually involve transfer of H atoms (not H+ ions)
e.g. reduction of pyruvate to lactate
Coenzymes in redox reactions
role in cellular respiration
act as temporary carriers of H atoms and their electrons
NAD+ + 2 H (oxidized) -> NADH + H+(reduced)
FAD + 2H (oxidized) -> FADH2 (reduced)
oxygen is the final electron acceptor in cellular respiration 1/2 O2 + 2H -> H20
Energy Metabolism
cells use chemical energy to do biological work: movement, synthesis, transport
energy is released in exergonic reactions that convert high-energy to lower-energy molecules
e.g. oxidation of glucose
ATP energy currency of cells
role in energy metabolism
(production of ATP)
energy captured from oxidation of substrates is used to produce ATP
energy released from ATP hydrolysis powers energy-required processes
Enzymes
are biochemical catalyst - speed up chemical reactions
most enzymes are proteins
increase reaction rate by lowering activation energy or providing an alternative chemical pathway for the reaction
Name the 4 functional properites of enzymes
Substrate specificity
Sensitivity to temp and pH
Saturation kinetics
Regulation
Substrate Specificity
substrate (reactant) binds reversibly to active site of the enzyme
specific fit between substrate and active site (shape and charge polarity)
induced fit: enzyme pulls on chemical bonds of substrates
Sensitivity to temp and pH
effects on tertiary structure of proteins
Saturation Kinetics
low and high [s] what happens
limited by?
reaction rate depends on substrate concentration (non-linear)
at low [s] reaction rate increases w/ increasin [s]
at high [s] reaction rate reaches maximum level
at the saturation point, all active sites are occupied
maximum rate is limited by number of available enzymes
Regulation
Covalent Regulation
Involves?
regulation of enzyme via covalent binding of a chemical group
usually involves addition of phosphate group which activates the enzyme
E (inactive enzyme) + ATP -> E-P (acitve enzyme) + ADP
Allosteric Regulation
regulation by non-covalent binding of a modulator to a regulatory site on the enzyme
can be either allosteric activation or allosteric inhibition
reaction rate depends on concentration of the modulator as well as substrate
Feedback inhibition
product of a reaction pathway can act as a modulator which inhibits an enzyme in an earlier step (via allosteric inhibiton)
regulates formation of products
Example of enzymes
Catalase
2 H202 -> 2 H20 + 02
Carbonic anhydrase
H20 + C02 -><- H2C03 -><- H+ + HCO3-
Hexokinase
glucose + ATP -> glucose-6-phosphate + ADP
Clinical applications
abnormal enzyme levels may be associated with disease (e.g. liver enzyme tests)
Genetic deficiency in an enzyme -> inborn errors of metabolism (e.g. PKU)
Kinase
protein kinase enzymes catalyze phosphorylation of other enzymes; important in cell signaling
