Chapter 4 Energy & Cellular Metabolism Flashcards
For a chemical reaction to take place what must occur? What is needed to usually start a reaction?
Most biological reactions require enzymes to make the rxn occur due to most chemical reactions are energetically unfavorable.
What is the term for the type of energy needed to start the reaction and for it to proceed>
Activation Energy- the hump that needs to be over come for the rxn to take place
What is the role of enzymes in biological rxns?
Enzymes reduce the activation energy
They serve as protein catalysts
Increase the likelihood that the rxn will occur and will also increase the rate of rxn
What happens after the enzyme binds with a substrate and the reaction proceeds
Enzymes are not consumed and left unchanged when the reaction is complete
Do enzymes work for every substrate? And what are the conditions that an enzyme favorably operates at
Enzymes are substrate specific
Most but not all enzymes work best at physiological neutral conditions (pH = 7.4) and a temp of 37 degrees C.
E.g. Of an enzyme that operates at a pH different than 7.4 is enzymes that are located with in the stomach (Pepsin) pH = 2.0
Enzymes sometimes require additional help to either make a rxn proceed or facilitate the binding to a specific substrate? What is the additional help and what is the function of this help?
Some enzymes require co-factors which can be metal ions such as Mg2+, Ca2+, Mn2+, Cu2+, Zn2+ and selenium.
Co-enzymes are derived from vitamins
Co-factors allow the enzyme to work more efficiently and they can change the conformation of the binding site to allow for tighter binding affinity
Co-enzymes can change the conformation of the binding site, but what else can it do in regards to the binging site?
They may serve as carriers for the reactants’ functional group. They do not alter the binding site.
Enzymatic activity is very well regulated. What are some of the mechanisms?
I.e. Storage, modification, or modulation etc..
Many enzymes (but not all) are produced and stored as an inactive form -precursor or zymogen, which are activated proteolytically (small part removed) when needed
-They can be covalently modified by phosphorylation or dephosphorylation
(In many but not all instances adding a -P activates it)
-enzymes activity may be modulated by second messengers.
Ca2+, IP3, cAMP
What is Turnover in regards to enzymes?
Refers to the rate of enzyme destruction or inactivation
Some enzymes are created in several related forms and these are referred to as?
What are their properties and functions?
Isozymes
The related forms means they exhibit slight differences in structure
However, they tend to catalyze the same reactions
Often found in different tissues
Even though isozymes have different structures they don’t all share the same properties. What are some of the differences?
They don’t share the same properties, reaction rates, conditions of reactions
Ex. Different pH
What is the definition of Reaction rate?
We can monitor the appearance of the product or the disappearance of the reactants for a given reaction.
How fast an enzyme works is the reaction rate
What does it mean when it says the reaction has reached saturation?
I means at saturation, all enzymes are bound by substrate
Once the reactant concentration is saturated, any further increase reactant level does not affect the reaction rate.
In non reversible rxn’s the rate goes in what direction?
In reversible rxn’s the rate goes in what direction
Non-reversible rxn’s goes in the direction the rxn defines most of the time forward!
In reversible rxn’s the reaction tens to go toward a state of equilibrium, whether towards the left or the right.
Describe the law of mass action in regards to the direction of the rxn and its rate!
Disturbing the reaction by adding components to either the left or right side of the reaction will drive the reaction to the right or left (respectively) until equilibrium is achieved
