module 6 Flashcards
(100 cards)
what does life depend on?
-the ability to efficiently and selectively catalyze chemical reactions
-many biomolecules are very stable with rates if uncatalyzed transformations that are too slow to permit life
what is the introduction of enzymes?
-provide a mechanism for acceleration, regulation and coordination of these reactions
-side reactions leading to useless or dangerous molecules must be avoided
-some enzymes are information sensors as well as catalysts
what is the most striking feature about enzymes?
-their catalytic power and specificity (can’t screw up)
what is vitalism?
-originally, biochemical molecules were believed to be inseparable from life
-vitalism is the belief that living things are fundamentally different from non-living things; that they contain some non-physical element and are governed by different principles than inanimate objects
-has famous supporter such as louis pasteur
what did Edward Buchner demonstrate?
-that dead yeast still convert sugars into alcohol, indicating reactions of life were separate from life
-there was a factor in yeast catalyzing the reaction; the term enzyme if from the greek word “in yeast”
-this work won him a nobel prize, ten years before he was killed in WWI
proteins are well suited to form ____________
-a variety of complex three-dimensional structures that enable binding of a variety of substrates
do all enzymes need co-factors or co-enzymes?
-for some enzymes, the protein component alone is fully active
-other do require them for activity
what are co-enzymes, co-factors and prosthetic groups?
-co-factors= inorganic ion (Mg, Fe, etc) (pick up and put down hammer)
-co-enzymes=complex organic molecules (vitamins) (pick up hammer)
-a co-enzyme or co-factor that is tightly associated with the enzyme is called a prosthetic group (the different is the degree of association)(glue hammer to hand)
what is an example of an enzyme with a co-enzyme?
what are catalysts?
-lower the amount of energy required for a reaction to proceed
-sped up attainment of equilibrium but do not change equilibrium
-are unchanged by the reaction; recycled to participate in another reaction
(can’t hammer 1 nail, must hammer for years)
enzymes offer incredible __________ in the rate enhancement they provide
-CATALYTIC POWER
enzymes vs. chemical catalysts
- speed: enzymes are often much faster than chemical catalysts, some approaching catalytic perfection
- conditions: many chemical catalysts that require extremes of temperature, pressure and pII while enzymes function under physiological conditions
- specificity: enzymes have a higher degree of specificity (including stereospecificity) than most chemical catalysts. This includes specificity for what they act upon and what they produce
- regulation: unlike chemical catalysts, many enzymes are responsiveness to the dynamic need of the cell and organism (how much product to produce, respond to changes)
what is the Circe effect?
-enzymes rates of catalysis can approach the physical limit of rates of diffusion of molecules in solution
-some enzymes have rate-determining steps that are roughly as fast as the binding of substrates to the enzymes
-some enzymes are able to catalyze reaction faster than predicted by diffusion-control limits
-this is called the Circe effect, named after a figure in green mythology who was renowned for her ability to draw her enemies to her, then transform them into animals
Enzymes catalyze the interconversion of substrate and product formula?
-substrate (S): the molecule acted upon the enzyme
-product (P): the molecule produced by the enzyme
-active site: the portion of enzyme (E) responsible for binding the substrate to formation of an enzyme-substrate (ES) complex
what are the active sites of enzymes?
BINDING SITE
1. is a 3D cleft formed from different parts of the polypeptide chain
2.represents just a small part of the enzyme
3. are unique microenvironments
4.substrates are bound to enzymes by multiple weak interactions
5. the specificity of substrate binding depends on the precisely defined arrangement of atom in the active site. Enzymes and their active sites can be quite flexible. Substrate binding can caused “induced fit” or “conformation selection”
what is the lock and key vs key in glove of enzyme specificity?
what does change in G depend on?
-G of a reaction depends only on the free energy of the product minus the free energy of the reactants.
-G of a reaction is independent of the steps of the transformation
what does G provide information for?
-no information about the rate of a reaction
-a negative G indicates that a reaction can take place spontaneously but does not signify whether it will proceed at a perceptible rate
what happen when +G, -G or G=0?
-+G= reaction cannot take place spontaneously, an input of free energy is required (endergonic)
–G= reaction is spontaneous, will proceed without input of energy and the reaction releases energy (exergonic)
-G=0: system at equilibrium, there is no net change in the concentrations of the products and reactants
what determines the rate at which equilibrium is reached?
-activation energy, G between S and P (difference of free energy)
what is the relationship between the rate of a reaction and the activation energy?
-is inverse and exponential
what does no influence the equilibrium?
-enzymes do not influence the difference in free energy between S and P and therefore do not influence the equilibrium
enzymes provide ______________________, lowering ____
what increases the rate of reactions? and what do they no affect?
-enzymes provide a lower-energy pathway between the substrate and product, decreasing the activation energy of the transition state and increasing the rate of reaction
-enzymes do not affect the different in free energy between the substrate and product and therefore do not influence the equilibrium of a reaction