Ch 4 Flashcards
Enzymes Definition
A class of proteins (exception – ribozymes are made of RNA) that serve as biological catalysts
What do enzymes do?
- Increase the rate of a reaction
- Are not changed by the reaction (so can be used again)
- Do not change the nature of the reaction – the reaction could have occurred without the enzyme, just much slower
- Lowers the activation energy of the reaction
What is activation energy?
the energy required for reactants to engage in a reaction (energy barrier we have to overcome)
• Most molecules lack the activation energy for a reaction.
- -> Adding heat increases the likelihood of are action occurring. This increases the rate of reactions, however, heat has some negative effects on cells.
- -> Catalysts help the reaction occur at lower temperatures.
Enzyme Activity
- structure dictates function
- characteristic 3D shape w/active sites
- reactants: substrates
- Measured by the rate at which substrate is converted to product
What are substrates?
fit into the active site like a key to a lock (“lock-and-key model”)
Induced-Fit Model
Sometimes the initial fit is not exact but will change as the substrate moves into the active site
Enzyme Nomenclature
- suffix: -ase
- first part of the name apply to the function
Phosphatases
remove phosphate groups
Synthetases/synthases
catalyze dehydration synthesis
Hydrolases
promote hydrolysis
Dehydrogenases
remove hydrogen atoms
Kinases
add phosphate groups
Isomerases
rearrange the atoms
Isoenzymes
-same name for enzymes w/same function in diff locations
molecules may be slightly different (in areas outside the active site) = isoenzyme
Enzyme activity influenced by….
- Temperature
- pH
- Cofactors and coenzymes
- Enzyme activation
- Substrate concentration
- Possible stimulatory or inhibitory effects of products on enzyme function
Enzymes and pH
- exhibit peak activity within a narrow pH range
- changes will result in enzyme conformational changes (like temp)
- Optimum pH reflects the pH of the fluid the enzyme is found in (ex. stomach vs. saliva vs. small intestine)
Coenzymes
organic molecules derived from water-soluble vitamins
- transport H/small molecules between enzymes
- larger
- required
Cofactors
help form the active site through a conformational change of the enzyme or help in enzyme-substrate binding
- Cofactors are metal ions such as, Ca2+, Mg2+, Mn2+,Cu2+, Zn2+
- smaller, help form active site
Enzyme Activation
zymogen: inactive form of enzyme that is activated when needed (stored so don’t have to make again –> pepsinogen to pepsin)
-often requires additional enzymes to phosphorylate or
dephosphorylate the molecule
-inhibition can be controlled through turnover, by which enzymes are degraded
Substrate Concentration
- as substrate concentration increases, so will rate of enzyme saturation
- Adding more substrate will NOT increase the rate of the reaction
saturated
every enzyme in the solution is being used
Reversible Reactions
-enzyme can drive reaction in two different directions depending of concentration of substrate/product
the law of mass action
one side gets higher, the other reaction reverses
Metabolic Pathways
-reactions linked together in chains
-begin with an initial substrate and end with a final product,
–> w/many steps along the way
BRANCHED: where several products can be produced
End Product Inhibition
- Branch points are often inhibited by a form of negative feedback in which one of the final products inhibits the branch point enzyme
- allosteric inhibition
- keeps final product from accumulating
allosteric inhibition
the product binds to the enzyme at a location away from the active site and changes the 3D conformation of the enzyme
Endergonic Reactions
Chemical reactions that require an INPUT of energy
- products contain more free energy than the reactants
ex. glucose -> glycogen (synthesis reaction) - STORED energy
Exergonic Reactions
Chemical reactions that produce energy
- products will have less free energy than the reactants
- -> ex. breaking glucose down into carbon dioxide and water produces energy
- -> Energy is used to make ATP for use in other endergonic reactions in the body
Coupled Reactions
Energy from the environment (food) is broken down in exergonic reactions to drive the endergonic reactions in our bodies
- energy must be stored in a usable form = ATP
- -> production of ATP is actually an endergonic reaction that is coupled to an exergonic reaction to drive it
- -> ATP molecule stores energy in its bonds to be used elsewhere
how is ATP made?
adenosine diphosphate (ADP) + inorganic phosphate = adenosine triphosphate (ATP)
